taxonID	type	description	language	source
039387F17B1D3E47261E7F54FC11276E.taxon	description	Genus Pseudomesochra Scott T., 1902. Type species: Pseudomesochra longifurcata Scott T., 1902. Other species: Pseudomesochra aberrans Bodin, 1968; P. abyssalis Becker and Schriever, 1979; P. affinis (Sars G. O., 1920 a); P. axa sp. nov.; P. bathyalis sp. nov.; P. bathyhabitatrix sp. nov., P. bathysicola sp. nov.; P. beckeri Becker and Schriever, 1979; P. brucei (Scott T. and Scott A., 1901); P. crispata (Brady, 1910); P. divaricata (Sars G. O., 1906 a); P. gemina Coull, 1973 a; P. gertwilleni Willen, 1996; P. laptevensis Willen, 1996; P. latifurca (Sars G. O., 1911); P. media (Sars G. O., 1911); P. meridianensis Willen, 1996; P. minor Becker, 1974; P. perplexa Bodin, 1968; P. scheibeli Schriever, 1982; P. similis Lang, 1936 b; P. tatianae Drzycimski, 1968. 3.1.1.1. Pseudomesochra bathyalis sp. nov. urn: lsid: zoobank. org: act: 74 D 93084 - 20 DD- 469 A-A 155 - DE 1 D 8879667 A Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP- 170616 - 02); June 17, 2016; Ivonne Martínez-Mendoza leg. Type locality. Xiximi 5 cruise; stn A 5, Gulf of Mexico, northern Sigsbee Deep (25.1168 ◦ N, 92.0002 ◦ W); 3513 m depth; clay 16 %, silt 66 %, sand 18 %. Etymology. The specific epithet comes from the ancient Greek Вαθύς (bathús, deep), and the Latin suffix - alis. It is an adjective in the nominative singular, gender feminine. Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 390 μm. Habitus (Fig. 2 A) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum (Figs. 2 A and 4 A) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown. Prosome (Fig. 2 A) composed of cephalothorax, and P 2 – P 4 - bearing somites, widest at the middle of cephalothorax; urosome (Figs. 2 B and 3 A) composed of P 5 - bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P 5 - bearing somite without spinular ornamentation; genital double-somite formed by the complete fusion of genital and third urosomites, without spinular ornamentation; genital complex (Fig. 3 A) medially on proximal half, with single copulatory duct and copulatory pore posterior to P 6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P 6; fourth urosomite with short lateral row of spinules; fifth urosomite with dorsal posterior frill extended medially forming pseudoperculum, with lateral spinules smaller than in preceding somite and with stronger and larger lateroventral spinules close to posterior margin; anal somite cleft medially, dorsally with one medial sensilla and an oblique row of small setules on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami. The latter cylindrical, slightly twice as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II, III, and VI, and with large pore between setae III and IV; with six setae as follows: lateral seta II slender, arising at distal third of ramus; seta III slender, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like and furnished with minute pinules; seta VI issuing at distal inner corner; dorsal seta VII triarticulate at base, located on distal third of ramus close to inner margin. Antennule (Fig. 4 B) six-segmented; surface of segments smooth except first segment; relative length of segments as shown, sixth segment longest; all setae smooth except for the seta on first segment, one seta on fourth, and three setae on sixth segment. Armature formula as follows: 1 (1), 2 (10), 3 (9), 4 (4 + ae), 5 (2), 6 (12 + ae). Antenna (Fig. 4 C and D) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with transverse row of small spinules subdistally, with two lateral and two distal setae as shown. Free endopodal segment with proximal longitudinal row of small spinules and with curved row of longer ornaments subdistally; lateral armature consisting of one proximal slender seta and two median spiniform elements; distal armature consisting of six setae of which five rat-tail-like and outermost longest fused basally to slender short normal seta. Mandible (Fig. 5 A – C) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with two spines and one unipinnate seta. Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and five distal setae; exopod with six setae in all. Maxillule (Fig. 5 D) with well-developed praecoxa; arthrite of praecoxa with two surface setae, and eight spines and one ventral seta as depicted. Coxal endite with four setae of which three slender and bare, one spiniform and spinulose. Basis with few subdistal spinules, with four slender apical elements and one slender lateral seta. Rami one segmented; endopod elongate, with three distal setae; exopod shorter than endopod, with three elements. Maxilla (Fig. 6 A) with large syncoxa ornamented with few strong outer spinules subdistally, with three elongate subequal endites armed with three setae each. Basis drawn out into strong claw accompanied by strong spine and one anterior and one posterior seta. Endopod incorporated into allobasis, represented by three slender setae. Maxilliped (Fig. 6 B) robust. Syncoxa nearly as long as basis, unornamented, with one inner subdistal seta. Basis with few inner strong spinules as shown, with one subdistal seta. Endopod one-segmented, with distal spinulose claw. P 1 (Fig. 7 A) with transversely elongate intercoxal sclerite. Coxa subrectangular, with few outer and some inner subdistal spinules. Basis with spinules at base of inner spiniform element, between rami, and at base of outer seta. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown, EXP 1 with inner setules and few distal minute spinules; EXP 1 without, EXP 2 with inner seta; EXP 3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP 1 slightly shorter than ENP 2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP 2 with longitudinal row of outer spinules and some ornaments subdistally, with one inner seta, two distal elements of which innermost rat-tail-like and medial spiniform, and one outer spine. P 2 (Fig. 7 B) with trapezoidal intercoxal sclerite ornamented with strong spinules distally on rounded distal tines. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular, with few outer short spinules. Basis with one proximal outer and one medial pore, with spinules at base of outer seta and between rami. Exopod inserted at a lower level than but reaching tip of endopod, three-segmented; EXP 1 and EXP 3 longest; EXP 1 and EXP 2 with outer spinules as shown; EXP 1 without, EXP 2 with subdistal outer pore; EXP 1 and EXP 2 with outer spine of which outer spine of EXP 2 visibly longer; EXP 1 without, EXP 2 with inner seta; EXP 3 with outer spinules at the base of outer and distal armature elements and with subdistal medial pore, with three outer spines, two distal spiniform elements, and two inner slender setae. Endopod three-segmented; segments with outer spinules as shown; ENP 1 widest, with medial subdistal pore, with outer distal corner moderately produced, inner distal margin with produced pointed projection, inner element strong, spiniform, strongly spinulose; ENP 2 largely as ENP 1 but visibly narrower, with outer distal corner drawn out into long pointed outgrowth; ENP 3 longest and narrowest, with medial pore, with two inner slender setae, two distal elements of which outer spiniform and inner setiform (rat-tail-like condition of the latter not evident), and one outer spine. P 3 (Fig. 8 A) with intercoxal sclerite similar to that of P 2 but with less-developed distal rounded outgrowths ornamented with comparatively shorter outer spinules, and with pointed distal outer tines slightly larger. Praecoxa (not shown), coxa and basis as in P 2. Exopod largely as in P 2 but EXP 3 without pore, and with three inner setae. Endopod as in P 2 but ENP 2 with less-developed distal outer outgrowth, and inner armature of ENP 1 and ENP 2 comparatively longer. P 4 (Fig. 8 B) with intercoxal sclerite ornamented with few distal outer spinules, without distal rounded outgrowths, but with outer distal pointed tines well-developed. Praecoxa as in P 2. Coxa and basis as in P 2 and P 3. Exopod as in P 3, but medial inner seta on EXP 3 visibly longer. Endopod largely as in P 3, but with one inner long seta. Pair of P 5 (Figs. 2 B and 3 B) not fused medially; baseoendopod and exopod fused; baseoendopodal and exopodal lobes subequal in length; baseoendopod with outer basal seta, endopodal lobe with two inner and two distal setae of which distal inner element longest. Exopodal lobe with one subdistal outer and one distal seta. P 6 (Fig. 3 A) represented by two setae. Male. Unknown. Variability. The exopodal lobe of the left P 5 (Fig. 3 B) bears the typical long apical and the shorter outer seta, and an additional outer proximal small seta. 3.1.1.2. Pseudomesochra axa sp. nov. urn: lsid: zoobank. org: act: A 40 FA 660 - 2803 - 401 A-B 1 D 6 - 48112 C 8 B 5 F 21 Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP- 210817 - 01); August 21, 2017; Ivonne Martínez-Mendoza leg. Type locality. Xiximi 5 cruise; stn B 18, Gulf of Mexico, Campeche Escarpment (24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 %. Etymology. The species is dedicated to Dr Axay´acatl Rocha-Olivares (Centro de Investigacion´Científica y de Educaci´on Superior de Ensenada, Baja California, Mexico) for providing us with the biological material from the Xiximi 5 cruises in the Gulf of Mexico). The speciesgroup name is to be treated as indeclinable and need not agree in gender with the genus name. Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 335 μm. Habitus (Fig. 9 A) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum (Figs. 9 A and 11 A) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown. Prosome (Fig. 9 A) composed of cephalothorax, and P 2 – P 4 - bearing somites, widest at the middle of cephalothorax; urosome (Figs. 9 A and B, 10 A) composed of P 5 - bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P 5 - bearing somite without spinular ornamentation; genital double-somite formed by the fusion of genital and third urosomites, with internal cuticular rib indicating former division between somites, without spinular ornamentation; genital complex (Fig. 10 A) medially on proximal half, with single copulatory duct and copulatory pore slightly posterior to unarmed P 6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P 6; fourth urosomite without spinular ornamentation; fifth urosomite seemingly without pseudoperculum, with lateral spinules; anal somite cleft medially, dorsally with one medial sensilla on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami. The latter cylindrical, slightly twice as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II, III, and VII, and with large pore between setae III and IV; with six setae as follows: lateral seta II slender, arising at distal third of ramus; seta III slender, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like and furnished with minute pinules; seta VI issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin. Antennule (Fig. 11 B) six-segmented; surface of segments smooth except for first segment; relative length of segments as shown, sixth segment longest; all setae seemingly smooth except for one seta on sixth segment. Armature formula as follows: 1 (1), 2 (10), 3 (8), 4 (4 + ae), 5 (2), 6 (12 + ae). Antenna (Fig. 11 C) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with subtle notch midway outer margin aligned with insertion site of proximal seta (arrowed in figure), with transverse row of small spinules subdistally, with two lateral and two distal setae. Free endopodal segment with proximal longitudinal row of small spinules and with subdistal spinular ornaments; lateral armature consisting of one proximal slender seta and two median elements of which one spiniform and one setiform; distal armature consisting of six setae of which five rat-tail-like and outermost longest fused basally to slender short normal seta. Mandible (Fig. 12 A) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with three spines and one unipinnate seta (the latter missing in figure). Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and five distal setae; exopod with six setae as shown. Maxillule (not shown) lost during dissection. Maxilla (Fig. 12 B) with large syncoxa ornamented with two outer spinular patches as shown, with three endites of which proximal thicker, middle and distal endites elongate and subequal in length; proximal and middle endites with three, distal endite with two setae. Basis drawn out into strong claw accompanied by strong spine and one seta. Endopod seemingly one-segmented (?), with three setae. Maxilliped (Fig. 12 C) robust. Syncoxa visibly shorter than basis, unornamented, with one inner seta. Basis with hump-like inner protrusion proximally, ornamented with inner spinules as shown and with subdistal outer spinular ornaments, with one subdistal seta. Endopod one-segmented, with distal spinulose claw. P 1 (Fig. 13 A) with transversely elongate intercoxal sclerite. Coxa rectangular, with few outer spinules close to outer distal corner. Basis with spinules at base of inner spiniform element and between rami, with outer pore close to outer basal seta. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown, EXP 1 and EXP 2 with somewhat elongate outer spines, without inner armature; EXP 3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP 1 slightly shorter than ENP 2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP 2 with longitudinal row of outer spinules, with two distal elements of which innermost rat-tail-like and medial spiniform, and one outer spine. P 2 (Fig. 13 B) with trapezoidal intercoxal sclerite ornamented with spinules distally. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular, with few short spinules close to outer distal corner. Basis with small spinules between rami, with one outer pore, and short outer seta. Exopod inserted at a lower level than and not reaching tip of endopod, three-segmented; EXP 1 and EXP 3 longest; EXP 1 and EXP 2 with outer spinules as shown, with outer spines of which outer spine of EXP 2 visibly longer; EXP 1 without, EXP 2 with inner seta; EXP 3 with outer spinules at the base of outer armature elements and with subdistal medial pore, with three outer spines, and two distal spiniform elements. Endopod three-segmented; segments with outer spinules as shown; ENP 1 widest, with outer distal corner moderately produced, inner distal margin with produced pointed projection, inner element strong, spiniform, spinulose; ENP 2 largely as ENP 1 but visibly narrower, with outer distal corner drawn out into pointed outgrowth; ENP 3 longest and narrowest, with medial pore, with one inner slender seta, two distal elements of which innermost setiform (rat-tail-like condition of the latter not evident) and outer spiniform, and one outer spine. P 3 (Fig. 14 A) with intercoxal sclerite similar to that of P 2 but with larger distal tines, unornamented. Praecoxa transversely elongate, triangular, with transverse spinular row distally. Coxa and basis as in P 2 except for spinular ornamentation of basis. Exopod largely as in P 2. Endopod as in P 2 but inner armature of ENP 1 and ENP 2 comparatively longer. P 4 (Fig. 14 B) with unornamented intercoxal sclerite of which outer distal pointed tines well-developed. Praecoxa, coxa and basis as in P 3. Exopod as in P 3 except for outer spine of EXP 2 not as elongate as in P 3 EXP 2. Endopod largely as in P 3, but with inner elements comparatively longer. Pair of P 5 (Fig. 10 B) not fused medially; baseoendopod and exopod completely fused making difficult to discern between endopodal and exopodal lobes; with six setae in all of which outermost basal. P 6 (Fig. 10 A) seemingly unarmed. Male. Unknown. 3.1.1.3. Pseudomesochra bathysicola sp. nov. urn: lsid: zoobank. org: act: 9 CB 31 E 90 - 7120 - 41 A 7 - 87 FD-E 498 C 204 BDD 8 Type material. Female holotype dissected and mounted on six slides (ICML-EMUCOP- 210817 - 02); August 21, 2017; Ivonne Martínez-Mendoza leg. Type locality. Xiximi 5 cruise; stn B 18, Gulf of Mexico, Campeche Escarpment (24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 %. Etymology. The specific epithet comes from the ancient Greek Вαθύς (Bathús, deep), and the Latin suffix - cola (from colo ¯, - ere, dwell). It is a noun in the nominative singular, gender feminine. Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 326 μm. Habitus (Fig. 15 A) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum (Figs. 15 A and 16 A) large, broad, subrectangular, with two lateral sensilla subdistally and pores as shown, tip slightly bilobate. Prosome (Fig. 15 A) composed of cephalothorax, and P 2 – P 4 - bearing somites, widest at the middle of cephalothorax; urosome (Fig. 15 A and B) composed of P 5 - bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Prosomites with sensilla as shown, with smooth posterior fills. Urosomites with sensilla and pores as shown; P 5 - bearing somite without spinular ornamentation; genital double-somite formed by the fusion of genital and third urosomites, with internal lateral cuticular rib indicating former division between somites, with two medial rows of tiny spinules dorsally; genital complex (Fig. 15 C) medially on proximal half, with single copulatory duct and copulatory pore slightly posterior to P 6 medially, single dumpbell-shaped seminal receptacle slightly anterior to P 6; fourth urosomite without spinular ornamentation; fifth urosomite seemingly without pseudoperculum, with posterior ventrolateral spinules as shown; anal somite cleft medially, dorsally with one medial sensilla on each side, laterally and ventrally with transverse row of small spinules close to insertion of caudal rami, with two ventral pores. Caudal rami (Fig. 15 A – C) cylindrical, about three times as long as wide, divergent; with small spinules medially on lateroventral surface, and at bases of setae II and VII, and with large pore between setae III and IV; with six setae as follows: lateral seta II short and slender, arising at distal fourth of ramus; seta III slender about three times as long as seta II, issuing subdistally close to outer distal corner; setae IV and V well-developed, the former shorter, both setae with fracture planes, distal half rat-tail-like; seta VI shorter than seta III, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin. Antennule (Fig. 16 A) six-segmented; surface of segments seemingly smooth; relative length of segments as shown, sixth segment longest; all setae seemingly smooth. Armature formula as follows: 1 (1), 2 (9), 3 (7), 4 (3 + ae), 5 (2), 6 (10 + ae). Antenna (Fig. 16 B) with allobasis, the latter as long as free endopodal segment, with few proximal spinules and one long slender abexopodal seta. Exopod two-segmented; first segment visibly shorter than second, unornamented, with two setae; second segment elongate, with transverse row of small spinules subdistally, with two lateral and two distal setae. Free endopodal segment with proximal longitudinal row of small spinules and with subdistal spinular ornaments; lateral armature consisting of one proximal slender small seta and two median setiform elements of which one spiniform, the other setiform; distal armature consisting of five rat-tail-like setae of which outermost longest and fused basally to slender short seta. Mandible (Fig. 17 A) with well-developed coxa; gnathobase with bicuspidate teeth as depicted, with two spines and one unipinnate seta. Palp biramous; basis large, with three setae; rami one-segmented; endopod with two inner and six distal setae; exopod with six setae as shown. Maxillule (Fig. 17 B) with well-developed praecoxa ornamented with few spinules as shown; praecoxal arthrite armed with two surface setae, eight spines as shown, and one ventral seta. Coxal endite with four setae. Basis elongate, with one lateral and three distal setae. Exopod and endopod one-segmented, with three setae each. Maxilla (Fig. 17 C) with large syncoxa ornamented with outer spinular rows as shown, with three endites of which proximal thicker, middle endite shortest, distal endite elongate, each with three setae. Basis drawn out into strong claw accompanied by strong spine and two setae. Endopod represented by three setae. Maxilliped (Fig. 17 D) robust. Syncoxa visibly shorter than basis, unornamented, seemingly unarmed. Basis with hump-like inner protrusion proximally, ornamented with spinules as shown, with one subdistal seta. Endopod one-segmented, with distal spinulose claw. P 1 (Fig. 18 A) with transversely elongate intercoxal sclerite. Coxa rectangular, with few distal spinules close to inner distal corner. Basis with spinules at base of inner spiniform element and between rami. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP 1 and EXP 2 with outer spine, EXP 1 without EXP 2 with inner small seta; EXP 3 with two outer spines and two distal elements of which distal outer spiniform, distal inner setiform and rat-tail-like. Endopod two-segmented, longer than exopod; ENP 1 shorter than ENP 2, with inner, subdistal, and outer spinules as depicted, unarmed; ENP 2 with longitudinal row of outer spinules, with one inner element (the latter missing in figure), two distal elements of which distal inner setiform and rat-tail-like and distal outer spiniform, and one outer spine. P 2 (Fig. 18 B) with trapezoidal intercoxal sclerite ornamented with subdistal spinules on distal pointed tines. Praecoxa triangular, transversely elongate, with transverse row of distal spinules. Coxa subrectangular. Basis with small spinules between rami, with one outer pore, and short outer seta. Exopod inserted at a lower level than and not reaching tip of endopod, three-segmented; EXP 1 and EXP 3 longest; EXP 1 and EXP 2 with outer spinules as shown, with outer spines of which outer spine of EXP 2 visibly longer; EXP 1 without, EXP 2 with inner seta; EXP 3 with outer spinules at the base of outer armature elements and with subdistal medial pore, with three outer spines, two distal spiniform elements, and two inner slender setae. Endopod three-segmented; segments with outer spinules as shown; ENP 1 widest, with outer distal corner moderately produced, inner distal margin with produced pointed projection, with outer pore, unarmed; ENP 2 largely as ENP 1 but visibly narrower, with outer distal corner drawn out into pointed outgrowth, with outer pore and inner short element; ENP 3 longest and narrowest, with outer spinules as shown, with medial pore, with one (or two?) inner slender seta, two distal elements of which outer spiniform and inner setiform (rat-tail-like condition of the latter not evident), and one outer spine. P 3 (Fig. 19 A) with intercoxal sclerite similar to that of P 2 but broader and with larger distal tines, unornamented. Coxa and basis largely as in P 2. Exopod largely as in P 2, but EXP 3 with three inner slender setae. Endopod largely as in P 2 but ENP 1 and ENP 2 without outer pore, ENP 1 with strong inner element, and inner element of ENP 2 visibly stronger; ENP 3 as in P 2 but with one inner seta only. P 4 (Fig. 19 B) with unornamented intercoxal sclerite with outer distal pointed tines well-developed. Praecoxa, coxa and basis as in P 3. Exopod largely as in P 3. Endopod largely as in P 3, but barely reaching tip of EXP, ENP 1 narrower and unarmed, ENP 2 with insertion site of inner element separated from segment by deep groove; ENP 3 largely as in P 2, with one inner seta. Pair of P 5 (Fig. 19 C) not fused medially; baseoendopod and exopod completely fused; with three setae in all of which outermost basal. P 6 (Fig. 15 C) with one small seta. Male. Unknown. Variability. Left P 4 malformed (not shown), with basis bearing one inner element, endopodal segments abnormally thin, ENP 2 without inner armature, ENP 3 with two posterior setae. 3.1.1.4. Pseudomesochra bathyhabitatrix sp. nov. urn: lsid: zoobank. org: act: A 8590 E 63 - 31 CD- 43 B 0 - A 9 BE- 8 C 235 D 28 F 6 F 1 Type material. Male holotype dissected and mounted on eight slides (ICML-EMUCOP- 230800 - 03); August 23, 2000; Samuel Gomez´leg. Type locality. Talud IV cruise; stn 5, Eastern Tropical Pacific, off Nayarit state, north-western Mexico (22.0172 ◦ N, 106.6672 ◦ W); 1540 m depth. Etymology. The specific epithet comes from the ancient Greek Вαθύς (Bathús, deep), and Latin habit ¯ atr ¯ ıx, dweller. It is a noun in the nominative singular, gender feminine. Description. Male. Total body length measured from tip of rostrum to posterior margin of caudal rami 324 μm. Habitus (Fig. 20 A) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum (Figs. 20 A and 21 A) large, broad, triangular, with two lateral sensilla subdistally. Prosome (Fig. 20 A) composed of cephalothorax, and P 2 – P 4 - bearing somites, widest at the posterior margin of cephalothorax; urosome (Fig. 20 A – C) composed of P 5 - bearing somite, genital somite, three free urosomites, and anal somite with caudal rami. Cephalothorax with pores and sensilla as shown; P 2 – P 4 - bearing somites with smooth posterior hyaline frill, with sensilla and pores as depicted; P 2 and P 3 - bearing somites without, P 4 - bearing somite with medially interrupted row of small spinules close to posterior margin; P 5 - bearing somite and genital somite as P 4 - bearing somite dorsally, laterally with row of comparatively stronger spinules close to P 5 and P 6, ventrally without spinular ornamentation; first and second free urosomites as previous somite dorsally, with ventral row of strong spinules; penultimate somite as preceding somite but without sensilla; anal somite cleft medially, with two dorsal pores, anal operculum not detected, with strong lateral spinules and comparatively smaller ornaments ventrally. Caudal rami (Fig. 20 A – C) cylindrical, about three times as long as wide, slightly divergent; with small spinules medially on lateral surface, and at base of setae II and V; with six setae as follows: lateral setae II and III arising (sub) distally, seta III longer and ventral to seta II; setae IV and V broken off; seta VI very short, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin. Antennule (Fig. 21 A) subchirocer, eight-segmented; surface of segments smooth except for few spinules on first and sixth segments; fifth segment shortest, sixth segment longest; all setae seemingly smooth; with exceedingly long aesthetasc on segments six and eight. Armature formula as follows: 1 (1), 2 (1), 3 (8), 4 (6), 5 (1), 6 (10 + ae), 7 (0), 8 (5 + ae). Antenna (Fig. 21 B) with allobasis, the latter as long as free endopodal segment, unornamented, unarmed. Without exopod. Free endopodal segment with two sets of long spinules proximally and medially; lateral armature consisting of two spiniform elements; distal armature consisting of five setae as shown of which two outermost rat-tail-like, medial and two inner spiniform (rat-tail-like condition of the three latter not conclusive). Mandible (Fig. 21 C) very reduced with non-functional gnathobase. Palp biramous; basis large, unornamented; rami one-segmented, elongate, each with two setae. Maxillule and maxilla not observed, most probably very reduced. Maxilliped (Fig. 21 D) very reduced, non-functional; syncoxa and basis subquadrate, slightly wider than long, unarmed and unornamented; endopod globose, seemingly fused to vestigial endopodal claw. P 1 (Fig. 22 A) with basis ornamented with spinules between rami, and with inner spiniform, and outer setiform element. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP 1 and EXP 2 with outer spine, that of EXP 1 visibly longer, EXP 1 without EXP 2 with inner seta; EXP 3 with two outer spines and two distal setae seemingly rat-tail-like. Endopod two-segmented, longer than exopod; ENP 1 shorter than ENP 2, with outer and subdistal spinules, unarmed; ENP 2 with longitudinal row of outer spinules, with one inner seta and three distal elements of which inner setiform and rat-tail-like, medial spiniform, and outer a bipinnate spine. P 2 (Fig. 22 B) with triangular unornamented praecoxa. Coxa rectangular, with short row of small spinules close to outer distal corner. Basis with spinules between rami, with spiniform outer element. Exopod three-segmented, inserted at a lower level than and barely reaching tip of ENP 3; EXP 1 and EXP 2 shortest, with outer spinules as shown, outer spines not elongate; EXP 1 without, EXP 2 with inner seta and outer pore; EXP 3 with outer spinules as depicted, with three outer spines, two distal setae (rat-tail-like condition of the innermost not evident), and two inner elements. Endopod three-segmented; segments with outer and inner spinular ornamentation and pores as shown; ENP 1 widest and shortest, ENP 3 longest; ENP 1 and ENP 2 with inner short setae; ENP 3 with two inner setae, and one seta and one recurved apophysis distally. P 3 (Fig. 23 A) with coxa and basis largely as in P 2, but with outer slender seta. Exopod largely as in P 2 but longer than endopod, and with three inner setae. Endopod three-segmented, barely reaching middle of EXP 3; ENP 1 shortest, largely as in P 2; ENP 2 with outer and inner distal corners expanded, the former with pointed tip, the latter rounded, with one inner seta; ENP 3 longest, with two inner, two distal setae of which distal inner visibly shorter and not rat-tail-like, and one outer spine. P 4 (Fig. 23 B) with coxa and basis as in P 3 but basis without spinular ornamentation and with large outer pore. Exopod as in P 3. Endopod three-segmented, barely reaching proximal third of EXP 3, segments with outer spinules as shown; ENP 1 shortest, ENP 3 longest; ENP 1 and ENP 2 with inner seta; ENP 3 with one inner seta, two distal elements of which distal inner shorter and not rat-tail-like, and one outer spiniform element. Pair of P 5 (Fig. 20 B and C) not fused medially; baseoendopod and exopod completely fused, unornamented; baseoendopod with outer basal seta, without endopodal lobe. Exopod represented by two setae. P 6 (Fig. 20 B and C) with one small seta. Female. Unknown. 3.1.2. Subfamily Danielsseniinae Huys and Gee, in Huys, Gee, Moore and Hamond, 1996 3.1.2.1. Genus Nuriaella gen. nov. urn: lsid: zoobank. org: act: AFF 9 DA 3 D- C 4 B 9 - 401 C-AF 68 - 028 DFB 2855 DF Type species: Nuriaella mendezae gen. et sp. nov., by monotypy Diagnosis (based on the female of N. mendezae gen. et sp. nov.). Pseudotachidiidae: Danielsseniinae. Habitus semicylindrical. Rostrum not fused to cephalothorax, large, broad, subrectangular. Pro- and urosomites with large cup-shaped pores, except for P 5 - bearing somite. Second (genital) and third urosomites completely fused dorsally forming genital double-somite, with lateroventral internal cuticular rib. Fifth Etymology. The genus name comes from the combination of the Basque proper noun Nuria and the Latin diminutive suffix - ella. It is in the nominative singular, gender feminine. The genus is dedicated to the fond memory of our friend and colleague María Nuria Mendez-Ubach´† (Instituto de Ciencias del Mar y Limnología, UNAM). 3.1.2.1.1. Nuriaella mendezae gen. et sp. nov. urn: lsid: zoobank. org: act: 34 E 93 BC 5 - AA 3 B- 41 F 1 - 8239 - 226 FFD 1 BD 1 AA Type material. Female holotype dissected and mounted on seven slides (ICML-EMUCOP- 210817 - 03); August 21, 2017; Ivonne Martínez-Mendoza leg. Type locality. Xiximi 5 cruise; stn B 18, Gulf of Mexico, Campeche Escarpment (24.0501 ◦ N, 86.8835 ◦ W); 1150 m depth; clay 7.4 %, silt 55.8 %, sand 36.8 %. Etymology. The specific name comes from the family name of Dr María Nuria M´endez-Ubach. It is a noun in the genitive case. It is dedicated to the late Dr María Nuria Mendez-Ubach´† (Instituto de Ciencias del Mar y Limnología, UNAM). Description. Female. Total body length measured from tip of rostrum to posterior margin of caudal rami 293 μm. Habitus (Fig. 24 A and B) semicylindrical, tapering posteriad, with clear division between pro- and urosome. Rostrum (Figs. 24 A and B, 26 A) large, broad, subrectangular, with two lateral sensilla subdistally, tip slightly bilobate. Prosome (Fig. 24 A and B) composed of cephalothorax, and P 2 – P 4 - bearing somites, widest at the posterior margin of cephalothorax; urosome (Figs. 24 A and B, 25 A) composed of P 5 - bearing somite, genital double-somite, two free urosomites, and anal somite with caudal rami. Cephalothorax with cup-shaped pores and few posterior sensilla dorsally urosomite with posterior hyaline frill expanded dorsally forming pseudoperculum. Caudal rami cylindrical, about two times as long as wide, divergent, with six setae of which seta IV (and most probably seta V) well-developed, with fracture plane, distal part not rat-tail-like. Antennule six-segmented. Antenna with allobasis, the latter with long slender abexopodal seta; exopod three-segmented, with armature formula 1,1,120; free endopodal segment with three lateral setae of which one geniculate, and distal armature consisting of four geniculate setae of which outermost spinulose and fused basally to short slender seta, and one spinulose spine and one subdistal smooth seta. Mandibular basis with two setae; endopod one-segmented with three lateral inner and five distal setae; exopod two segmented, slightly longer than endopod, ENP 1 with one medial and one subdistal seta, ENP 2 with three distal elements. Maxillule with four coxal setae; basis with four setae; rami one-segmented, exopod with two, endopod with three setae. Maxilla with three endites of which proximal with two, middle and distal endites with three setae each; endopod one-segmented, with four setae. Maxilliped subchelate, slender; syncoxa with one seta; basis with one seta. Outer spines of P 1 – P 4 EXP elongate and thin. Armature of swimming legs as in Table 1. Table 1. Armature formula of swimming legs of Nuriaella gen. et sp. nov. (based on the female of its only and type species, N. mendezae sp. nov.). P 1 P 2 P 3 P 4 EXP 0,1,022 0,1,123 0,1,122 0,1,222 ENP 1111 1,1,121 1,1,121 1,0,121 Both P 5 not fused medially; EXP and BENP separate; EXP small, with five setae; endopodal lobe well-developed, with five setae. and laterally as shown; P 2 – P 4 - bearing somites with smooth posterior hyaline frill, and with dorsal and lateral cup-shaped pores and sensilla as depicted; P 5 - bearing somite with smooth posterior hyaline frill, without cup-shaped pores, with two dorsolateral surface pores and posterior sensilla as shown, and with posterolateral row of small spinules interrupted medially; genital double-somite with finely serrated hyaline frill, anterior (second urosomite) and posterior (third urosomite) halves completely fused dorsally, with lateroventral internal cuticular rib, with dorsal and lateral cup-shaped pores as shown, with one median and one posterior dorsolateral row of small spinules interrupted medially; genital complex (Fig. 25 A) ventrally on the middle of anterior half of composite somite, with single copulatory duct and copulatory pore slightly posterior to P 6 medially, anterior part of genital double-somite damaged during dissection and seminal receptacle not discernible; fourth urosomite largely as posterior half of genital double-somite dorsally, with finely serrated posterior hyaline frill, ventrally with one cup-shaped pore on each side, and with four short crescentic spinular rows and few sensilla; fifth urosomite with posterior hyaline frill finely serrated and expanded dorsally forming pseudoperculum, with one dorsal and one lateral cup-shaped pore dorsally, ventrally as preceding somite; anal somite cleft medially, with two dorsal and two ventral cup-shaped pores, with lateroventral row of small spinules close to caudal rami, ventrally with pair of surface pores as depicted. Caudal rami (Figs. 24 A and B, 25 A) cylindrical, about two times as long as wide, divergent; with small spinules medially on lateral surface, and at base of setae II and V, dorsally with medial pore, ventrally with inner proximal surface pore and median cup-shaped pore; with six setae as follows: lateral setae II and III arising distally, seta III longer and ventral to seta II; setae IV well-developed, with fracture plane, distal part seemingly not rat-tail-like; seta V broken, presumably with fracture plane and longer than seta IV; seta VI very shorter, issuing at distal inner corner; dorsal seta VII triarticulate at base, located in the middle of the ramus close to inner margin. Antennule (Fig. 26 B and C) six-segmented; surface of segments smooth except for few spinules on first segment; first and second segments nearly subequal in length, third segment longest, fourth, fifth and sixth segments combined as long as third segment; all setae seemingly smooth except for one seta on third, two on fifth and one seta on sixth segments. Armature formula as follows: 1 (1), 2 (9), 3 (11 + ae), 4 (5), 5 (3), 6 (6 + ae). Antenna (Fig. 26 D) with allobasis, the latter as long as free endopodal segment, seemingly unornamented, with long slender abexopodal seta. Exopod with three distinct segments of which third segment longest, middle segment shortest, all segments seemingly unornamented; first and second segments with one seta each; third segment with one lateral and two distal elements. Free endopodal segment with two sets of long spinules medially and subdistally; lateral armature consisting of three setae of which one geniculate; distal armature consisting of four geniculate setae of which outermost spinulose and fused basally to short slender seta, and one spinulose spine and one subdistal smooth seta. Mandible (Fig. 27 A) with well-developed coxa; gnathobase with elongate bicuspidate teeth as depicted, with one spine and one unipinnate seta. Palp biramous; basis elongate, with row of slender spinules medially, with two setae; endopod one-segmented, elongate, with three lateral inner and five distal setae; exopod two segmented, slightly longer than endopod, ENP 1 with one medial and one subdistal seta, ENP 2 with three distal elements. Maxillule (Fig. 27 B) with well-developed praecoxa ornamented with few spinules as shown; praecoxal arthrite armed with two surface setae, eight spines, and one ventral seta. Coxal endite with four setae. Basis with four setae. Exopod and endopod one-segmented, the former with two the latter with three setae. Maxilla (Fig. 27 C) with large seemingly unornamented syncoxa, with three endites of which proximal thicker with two, middle and distal endites elongate with three setae each. Basis drawn out into strong claw accompanied by spine and two setae. Endopod one-segmented, with four setae. Maxilliped (Fig. 27 D) rather slender. Syncoxa visibly shorter than basis, with few spinules as shown, with one subdistal seta. Basis with inner and outer spinules as shown, with one seta. Endopod with distal spinulose claw. P 1 (Fig. 28 A) with rectangular coxa ornamented with outer spinules, with subdistal inner pore. Basis with spinules at base of inner spiniform element and at base of endopod, with outer pinnate element. Exopod three-segmented, inserted at a lower level than endopod; segments with outer and subdistal spinules as shown; EXP 1 and EXP 2 with outer spine, that of EXP 1 visibly longer, EXP 1 without EXP 2 with inner seta; EXP 3 with two outer spines and two distal elements. Endopod two-segmented, longer than exopod; ENP 1 shorter than ENP 2, with outer and subdistal spinules and one medial pore, with one inner seta; ENP 2 with longitudinal row of outer spinules and one medial subdistal pore, with one inner seta and three distal elements of which medial longest and inner shortest. P 2 (Fig. 28 B) with triangular praecoxa ornamented with row of distal spinules. Coxa rectangular, with outer, medial, and inner spinules and one inner pore. Basis with spinules at base of spiniform outer element. Exopod three-segmented, inserted at a lower level than and barely reaching proximal fifth of ENP 3; EXP 1 and EXP 2 shortest; EXP 1 and EXP 2 with outer spinules as shown, with elongate outer spines of which outer spine of EXP 2 visibly longer; EXP 1 without, EXP 2 with inner seta and outer pore; EXP 3 with outer spinules as depicted, with three outer spines, two distal setae, and one inner slender element. Endopod three-segmented; segments with outer and inner spinular ornamentation as shown; ENP 1 widest and as long as ENP 2, ENP 3 longest; ENP 1 and ENP 2 with outer subdistal pore and one inner short seta; ENP 3 with subdistal pore, one inner seta, two distal elements of which distal inner reduced and distal outer very long, and one outer spiniform element. P 3 (Fig. 29 A) with coxa and basis largely as in P 2, but with outer slender seta. Exopod largely as in P 2 but reaching proximal third of ENP 3. Endopod largely as in P 2 but ENP 1 and ENP 2 with comparatively longer inner setae. P 4 (Fig. 29 B) with coxa and basis as in P 3. Exopod three-segmented, visibly longer than ENP, with few outer spinules; EXP 1 and EXP 2 shortest, EXP 3 longest; EXP 1 and EXP 2 with outer spine of which that of EXP 2 visibly longer, EXP 1 without, EXP 2 with inner seta; EXP 3 with two outer spines, two distal setae, and two inner elements of which proximal longest. Endopod relatively shorter than in P 2 and P 3, reaching proximal fourth of EXP 3, segments with few outer spinules as shown; ENP 1 with, ENP 2 without inner armature; ENP 3 with one inner seta, two distal elements of which distal inner shorter, and one outer spiniform element. Pair of P 5 (Fig. 25 B) not fused medially; baseoendopod and exopod separated, ornamented with pores as shown, with long outer seta; endopodal lobe with five setae as figured. Exopod small, reaching about the middle of endopodal lobe, with five setae in all. P 6 (Fig. 25 A) with one small seta. Male. Unknown.	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
039387F17B133E5A252B7AE9FC8E22D9.taxon	description	The species of Pseudomesochra display an amalgam of plesiomorphic and derived character states hampering the assessment of their interspecific relationships. The problematic systematics and taxonomy of this group of copepods is fuelled also by the low number of individuals found in sediment samples which makes the assessment of intraspecific variability difficult, and by the fact that most species are known from the female only. Eight out of 23 species of Pseudomesochra (P. affinis, P. meridianensis, P. gertwilleni, P. divaricata, P. media, P. similis, P. gemina, and P. tatianae) had been described based on more than one female specimen, and the male is known only for P. gemina (one individual), P. perplexa (one individual), and P. bathyhabitatrix sp. nov. (one individual). Bodin (1968) believed that P. perplexa would not belong in Pseudomesochra. Willen (1996) shared Bodin’ s (1968) belief and was of the opinion that P. perplexa does not belong in Pseudomesochra, and suggested that the male CV specimens of P. meridianensis from the Laptev Sea are the only true records of males of Pseudomesochra (see above), but accepted that “ the position of P. meridianensis sp. nov. has to remain open for the moment ” (Willen, 1996: 90). The setation pattern of the rami on the postantennal mouthparts seems to be very variable and it has not been well-documented for several species. Noteworthy, two species, P. laptevensis and P. tatianae possess vestigial maxillipeds. On the other hand, due to its size and ease of observation, the segmentation pattern of the female antennule has been well-documented. The female antennule of Pseudomesochra possesses at most seven segments, with the main aesthetasc on the fourth segment (Willen, 2000; but see also Table S 1). Four species (P. similis, P. gemina, P. laptevensis, and P. tatianae) display the plesiomorphic segmentation of the female antennule with seven segments, and only P. media and P. abyssalis possess five-segmented female antennules; the other species possess six-segmented female antennules (Table S 1). Taking the site of the main aesthetasc as landmark (it is always on the fourth segment), the reduction in the number of segments seems to be the result of fusion of either the sixth and seventh segments (as in the species with six-segmented female antennules) or fifth to seventh segments (as in the species with five-segmented antennules). The segmentation pattern of the female antennule seems to be a potential source of information to better understand the relationships among the species of Pseudomesochra, but this still needs to be evaluated. Species groupings seldom reflect phylogenies, but are still useful for identification purposes. Some groupings of the species of Pseudomesochra are presented below based mainly on the segmentation and armature formula of A 2 EXP, and armature formula of swimming legs. Due to the fact that most species have been described only from the female, and given that the position of the species for which the males have been described still needs to be verified, only the females were considered in these groupings. The position of the males attributed to Pseudomesochra was treated separately. These groupings are useful for species identification but their systematic values still need to be tested. 4.2.1. Group A Only two species (see group A in Table S 1), P. beckeri found off Morocco at 3920 m depth (Becker and Schriever, 1979), and P. brucei from Svalbard archipelago found at 182 – 201 m depth (Scott and Scott, 1901), possess an antennary exopod with three segments — the plesiomorphic condition in Pseudomesochra — of which the first and second segments bear two and one seta, respectively, and the distal segment possesses either one lateral, and one small and three well-developed distal setae (P. beckeri) (Becker and Schriever, 1979), or one lateral, and one small and one well-developed apical element (P. brucei) (Scott and Scott, 1901). Additionally, these two species possess six-segmented female antennules, and P 1 EXP 2 lacks inner armature — similar to what can be observed in species of group C (see below). Pseudotachidids bear a maximum of one lateral, and one reduced and two well-developed apical setae on the third exopodal segment of the antenna (Willen, 2000). The pentasetose distal segment of the antennary exopod (one lateral plus four distal setae) of P. beckeri [Becker and Schriever (1979) believed that the additional distal seta could represent a fourth segment] might be an observational error, and this segment is most probably armed with one lateral, and one small and two well-developed distal setae (the latter reinterpretation was used in Table S 1); the distal segment of the antennary exopod of P. brucei was described with one lateral and two distal setae. The description of P. brucei is incomplete and it is uncertain which leg did Scott and Scott (1901) show in their plate III, Fig. 8. If Becker and Schriever’ s (1979) description of the female P 5 is correct, these two species differ also in the number of setae on the female P 5 baseoendopod (four well-developed and one small outer seta in P. beckeri, but four well-developed setae in P. brucei). 4.2.2. Group B and justification of P. bathyalis sp. nov., P. axa sp. nov., and P. bathysicola sp. nov	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
039387F17B133E5A252B7AE9FC8E22D9.taxon	description	Pseudomesochra axa sp. nov. from the Gulf of Mexico belongs to a group of species with five- or six-segmented female antennules, antennary exopod with two segments of which distal with four (two lateral, two distal) or — rarely — five setae (two lateral, three distal, as in P. gertwilleni), and P 1 EXP 2 without inner armature (group C in Table S 1). To this group of species belong also P. abyssalis from the North-east Atlantic, P. affinis and P. divaricata from Norway, P. meridianensis and P. gertwilleni from the Weddell Sea, P. minor from off Peru, and P. longifurcata from Scotland. Pseudomesochra abyssalis, P. meridianensis and P. minor (group C′ in Table S 1) share the armature formulae of P 1 ENP (1,121, i. e. with one inner seta on ENP 2) and P 2 ENP (1,1,221, i. e. endopod three segmented with two inner setae on third segment), but P. minor and P. meridianensis are morphologically more similar to each other than to P. abyssalis. Pseudomesochra minor and P. meridianensis share the six-segmented female antennule (it is five-segmented in P. abyssalis) and possess three outer spines on P 2 – P 4 EXP 3 (P. abyssalis underwent loss of one outer spine on those segments). Pseudomesochra meridianensis and P. minor share three outer spines on P 3 EXP 3, but the latter is different from the other two species in the loss of one inner seta, i. e. with only two inner setae on P 3 EXP 3. The three-segmented P 3 ENP of P. meridianensis and P. minor displays the maximum number of armature elements on ENP 3 (221); P. abyssalis differs in the loss of one inner seta on P 3 ENP 3, resulting in the armature 121. The armature formula of P 4 EXP 3 of P. abyssalis and P. meridianensis is the same as in P 3, but P. minor displays only one inner seta (which is similar to the condition of P. gertwilleni). The armature formula of P 4 ENP 3 of P. abyssalis, P. meridianensis, and P. minor is different: three elements (armature formula 111) are present in P. abyssalis, four (armature formula 121) in P. meridianensis, and five (armature formula 221) in P. minor. Three baseoendopodal setae are present on the female P 5 of P. abyssalis (as in P. divaricata, P. longifurcata, P. affinis, and P. axa sp. nov.) and four in P. meridianensis and P. minor (as in P. gertwilleni). Four species (P. gertwilleni, P. divaricata, P. longifurcata, and P. affinis; group C ″ in Table S 1) share the loss of the inner armature of P 1 ENP 1 resulting in the armature formula 0,121 (a similar condition is present in most species of group B; see Table S 1). The P 2 ENP and P 4 ENP of P. divaricata has not been described yet. The P 2 ENP of P. longifurcata and P. affinis, P 3 ENP of P. divaricata, P. affinis and P. longifurcata, and P 4 ENP of P. longifurcata and P. affinis have been described as two-segmented, and is the result of fusion of ENP 2 and ENP 3, and occupy an isolated position in group C but also in Pseudomesochra. The second swimming leg is similar in P. longifurcata and P. affinis, but differ in the armature formula of P 2 EXP 3 (with one inner seta in P. longifurcata, but unarmed in P. affinis; P 2 of P. divaricata remains unknown); the armature formula of P 3 EXP / ENP (0,1,023 / 1221) is identical in P. divaricata, P. longifurcata, and P. affinis; the armature formula of P 4 EXP / ENP of P. longifurcata [0,1,023 / 1,1 (2?) 21] and P. affinis is most probably identical, but it is unknown for P. divaricata; P. divaricata, P. longifurcata and P. affinis share also the six-segmented female antennule and the trisetose baseoendopodal part of the female P 5. Pseudomesochra axa sp. nov. occupies an isolated position in group C. In fact, this species is unique in Pseudomesochra in the trisetose P 1 ENP 2 with one inner, one distal, and one outer element. The armature formula of P 2 – P 4 EXP is similar to those of some species of group C’ ’ [P 2 EXP (armature formula 0,1,023) is similar to that of P. affinis; P 3 EXP (armature formula 0,1,023) is similar to that of P. divaricata, P. affinis, and P. longifurcata; P 4 EXP (armature formula 0,1,023) is similar to that of P. longifurcata, and P. affinis]. The endopod of the second swimming leg (armature formula 1,1,121) is similar to that of P. gertwilleni; P 3 and P 4 ENP (armature formulae 1,1,121) is similar to those of P. abyssalis and P. gertwilleni, and P. meridianensis and P. gertwilleni, respectively. The trisetose baseoendopodal part of the female P 5 is shared with P. divaricata, P. longifurcata and P. affinis, and P. abyssalis. The description of P. crispata is very incomplete and the armature formulae of A 2 EXP and swimming legs remain undescribed. Also, Lang (1948: 642) believed that the armature complement of P 2 and P 3 in Brady (1910) might be erroneous. The species is, therefore, regarded here as taxon inquirendum and has been excluded from the analyses above.	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
039387F17B0D3E59252B7F88FF17274D.taxon	description	Huys and Gee, 1993, Fladenia Gee and Huys, 1990, Cylindronannopus, Mucrosenia Gee and Huys, 1994, Danielssenia Boeck, 1873, and Paranannopus can be ruled out given the autapomorphies for the females of these genera:	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
039387F17B0D3E59252B7F88FF17274D.taxon	description	- The genus Fladenia, with its only species, F. robusta (Sars G. O., 1921), was defined by several aspects of the sexual dimorphism of the males [see Gee and Huys (1990): 1566] but also on i) the five-segmented female antennule, ii) the relative length of the mandibular EXP and ENP (endopod twice as long as exopod), iii) the presence of two accessory setae on the endopodal claw of the maxilliped, iv) relative length of the distal outer spine of P 1 EXP 3 (shorter that the middle outer spine), v) insertion site of the inner seta of P 1 ENP 2 (near the base of the segment), vi) transformation of the inner armature of P 2 – P 3 ENP 1 into a spiniform element, vii) shape of the female P 5 EXP and BENP (rami fused), and viii) female P 5 BENP with four setae [see Gee and Huys (1990)]. Gee and Huys (1990) suggested that Fladenia is the link between Paranannopus and the other danielsseniin genera. - With three species, Cylindronannopus primus Coull, 1973 b, C. elongatus (Becker, 1979), and C. bispinosus Schriever, 1985, C ylindronannopus is characterized mainly by its vermiform habitus (Coull, 1973 b), but it also possesses long and densely setulated rostral sensilla, the female P 5 EXP and BENP are fused into a single plate, and P 3 and / or P 2 ENP are three-segmented with reduced number of armature elements on the distal segment [see also Coull (1973 b); Becker (1979); Schriever (1985)]. - The females of Mucrosenia [M. kendalli, and M. kliei (Smirnov, 1946)], have been defined upon a set of autapomorphies: i) presence of a mucroniform process on the female P 2 ENP 2, reaching almost to the end of ENP 3, ii) lack of inner armature on the female P 2 ENP 2, iii) posterior displacement of caudal seta II, iv) presence of bunch of long setules at the distal inner corner of caudal rami, iv) P 2 ENP shorter than EXP, and v) lack of inner armature on P 2 – P 4 EXP 1 (Gee and Huys, 1994: 1035). - At present, the genus Danielssenia is composed of six species, D. quadriseta Gee, 1988, D. reducta Gee, 1988, D. spiridonovi Garlitska and Chertoprud, 2021, D. spitsbergensis Gee and Huys, 1994, D. typica Boeck, 1873, and D. similis Chislenko, 1978 [the latter was regarded as taxon inquirendum by Huys and Gee (1993), but it was redescribed by Garlitska and Chertoprud (2021)]. Danielssenia has been diagnosed by several autapomorphies: i) rostrum ventrally deflected, ii) mandibular gnathobase with blunt teeth, iii) dorsal hyaline frill of P 5 - bearing somite incised, and iv) seminal receptacle with paired anterior, elongate cylindrical chambers reaching the posterior part of the P 5 - bearing somite (Huys and Gee, 1993: 78). - With 22 species, the genus Paranannopus is most probably an amalgam of several genera (Huys et al., 1996; Willen, 2005), and its species are all known from one sex only [see also Gee and Huys (1990: 1568) for the case of P. langi Wells, 1965 and P. triarticulatus Wells, 1965, and P. variabilis Schriever, 1985]. All this makes a sound generic diagnosis difficult. In their diagnosis of the genus, Huys et al. (1996) mentioned the five- or six-segmented antennule in both sexes and only slightly modified in the male, P 2 – P 4 ENP missing or two-segmented, male P 2 ENP 2 with an apophysis, and female and male P 5 EXP and BENP completely fused and indistinguishable, both P 5 not fused medially in the female, but fused in the male. Moreover, except for few danielsseniin species, viz., Paradanielssenia confluenta Kornev and Chertoprud, 2008, P. triseta Kornev and Chertoprud, 2008 (the latter two species with claviform aesthetascs on mouthparts, see below), Cylindronannopus bispinosus, C. primus, Paranannopus longithorax Becker, 1979, P. reductus Becker, 1979, P. uniarticulatus Schriever, 1985, and P. variabilis, all other species possess the full complement of three outer spines on P 1 EXP 3.	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
039387F17B0D3E59252B7F88FF17274D.taxon	description	Huys and Gee (1996 b) recognized two major lineages within Danielsseniinae (former Paranannopidae), the paranannopid branch (Paranannopus, Cylindronannopus, Fladenia, Bathypsammis, and Anapophysia) and the danielsseniid branch (Leptotachidia, Micropsammis, Paradanielssenia, Telopsammis, Peltisenia, Jonesiella, Sentiropsis, Nyxis with aesthetascs on mouthparts which constitute a well-defined group, and Afrosenia, Archisenia, Mucrosenia, Danielssenia, Prionos, and Psammis without aesthetascs on mouthparts), with Fladenia as a link between them. Huys and Gee (1996 b) characterized the paranannopid branch by the shape of the subapical element on the A 2 ENP (modified into a large bi- or multipinnate — apomorphic — spine in the paranannopid branch, but setiform in the danielsseniid branch), but also by the relative length of the outer distal spine of P 1 EXP 3 (at most as long as the median outer spine in the paranannopid branch, but outer spines gradually increasing in size in the danielsseniid branch), and to some extent, by the fused female P 5 EXP and BENP [see Huys and Gee (1996 b: 247)]. Nuriaella mendezae gen. et sp. nov. is placed here in the danielsseniid branch sensu Huys and Gee (1996 b) without aesthetascs on mouthparts by the combination of i) the subapical element on A 2 ENP setiform, ii) the outer spines on P 1 EXP 3 gradually increasing in length, iii) shape of P 1, iv) the three-segmented A 2 EXP, and v) the distinct female P 5 EXP and BENP. Within the genera of the danielsseniid branch without aesthetascs on mouthparts, N. mendezae gen. et sp. nov. seems to be more closely related to Danielssenia by the combination of i) lack of aesthetascs on mouthparts, ii) armature formula of A 2 EXP [1,1,120; also present in the monotypic Afrosenia and Prionos and in M. kendalli, in some taxa of the danielsseniid branch with aesthetascs on mouthparts, viz., Leptotachidia, Paradanielssenia christineae Gee and Huys, 1994, P. kathleenae Gee and Huys, 1994, P. kunzi Soyer, 1970, Telopsammis secunda (Mielke, 1975) and Jonesiella, but also in some species of the paranannopid branch (Paranaannopus kunzi Schriever, 1985 and P. minutus Smirnov, 1946)], iii) armature formula of the two-segmented P 1 ENP (1,121) (present also in all other genera of the danielsseniid branch except for the three-segmented P 1 ENP of Jonesiella eastwardae (Coull, 1971), but also in Fladenia, Anapophysia and Bathypsammis within the paranannopid branch), iv) armature formula of P 2 EXP, 0,1,123 [unique for N. mendezae gen. et sp. nov., Danielssenia reducta and D. spiridonovi; but EXP 1 lacks inner armature also in M. kendalli, Sentiropsis and Nyxis of the danielsseniid branch with aesthetascs on mouthparts, and in C. primus, Paranannopus abyssi (Sars G. O., 1920 b), P. caheti Soyer, 1964, P. longithorax, P. reductus, and P. variabilis], v) P 3 – P 4 EXP 1 without inner armature (but also missing in M. kendalli, in Sentiropsis and Nyxis, and C. primus and some species of Paranannopus — P. abyssi, P. caheti, P. denticulatus Schriever, 1985, P. echinipes Smirnov, 1946, P. longithorax, P. plumosus Schriever, 1983, and P. variabilis), vi) armature formula of P 3 ENP 0,1,121 as in D. quadriseta (but also M. kendalli of the danielsseniid branch without, and P. christineae of the danielsseniid branch with aesthetascs on mouthparts), and vii) female P 5 EXP and BENP separated (this condition is also present in Afrosenia, Archisenia, and M. kendalli, but also in Paradanielssenia, Peltisenia, Jonesiella, Sentiropsis, and Nyxis of the danielsseniid branch with aesthetascs on mouthparts). Only few taxa lack inner armature on the second endopodal segment of the three-segmented P 4 ENP, viz., Leptotachidia and Micropsammis, and Telopsammis galapagoensis (Mielke, 1997) and T. secunda (all these also lack inner armature on P 4 ENP 1) of the danielsseniid branch with aesthetascs on mouthparts, and the armature formula 1,0,121 for P 4 ENP is unique to P. christineae of the danielsseniid branch with aesthetascs on mouthparts, and to N. mendezae gen. et sp. nov. of the danielsseniid branch without aesthetascs on mouthparts. In their study of 1993, Huys and Gee (1993) concluded that Danielssenia was the most advanced genus within the Danielssenia-Psammis - Bathypsammis lineage (Danielssenia and Psammis were the only genera of the, at the time, undiagnosed danielsseniid branch, and Bathypsammis would later be included in the paranannopid branch) by the lack of a seta on the first exopodal segment of the antenna, the mandibular basis, P 2 – P 4 EXP 1, and P 2 ENP 2, and that it was closely related to Psammis. More recent advances show that within the danielsseniid branch (Archisenia, Psammis, Afrosenia, Mucrosenia, Danielssenia, Prionos, and N. mendezae gen. et sp. nov.), Archisenia and Psammis display the plesiomorphic bisetose condition of A 2 EXP 1, and P 2 – P 4 EXP 1 with an inner seta, but Archisenia retained the — plesiomorphic — separate female P 5 EXP and BENP (fused in Psammis), the two-segmented mandibular exopod (one-segmented in Psammis), and nine setae on the mandibular endopod (three or four setae in Psammis). Afrosenia and Prionos underwent reduction in the armature of A 2 EXP 2 from two to one seta, Afrosenia kept the two segmented mandibular exopod (one-segmented in Prionos), and both retained the inner seta on P 2 – P 4 EXP 1, and the separated female P 5 EXP and BENP. Mucrosenia, Danielssenia, and N. mendezae gen. et sp. nov., seem to be more advanced in that they all lack one seta on A 2 EXP 1 and inner armature on P 2 – P 4 EXP 1. Mucrosenia kliei and N. mendezae gen. et sp. nov. are similar in the tetrasetose P 1 EXP 3, and armature formulae of P 2 EXP. Mucrosenia kendalli and N. mendezae gen. et sp. nov. are similar in the P 3 ENP with one, one, and four setae on the first to third segments, respectively, and in the separate female P 5 EXP and BENP. Nuriaella mendezae gen. et sp. nov. is similar to D. quadriseta in the armature formula of P 3 ENP (1,1, 121) and in the separate female P 5 EXP and BENP, but it seems more closely related to D. reducta and D. spiridonovi in the armature formula of P 2 EXP (0,1,123), in the lack of an inner seta on P 3 EXP 3 (armature formula 0,1,123; 0, 1,223 in D. quadriseta, but also in M. kendalli), in the pentasetose female P 5 EXP (with four setae in Mucrosenia and D. quadriseta), and in the separate female P 5 EXP and BENP. Unfortunately, the female of D. spitsbergensis still awaits discovery. Overall, N. mendezae gen. et sp. nov. is unique in the — apomorphic — loss of one outer spine on P 3 – P 4 EXP 3, in the thin and elongate outer spines of P 1 – P 4, the latter similar to Paranannopus and Cylindronannopus but much thinner, and in the large surface pores on pro- and urosomites. Funding This work was supported by the Programa de Apoyo a Proyectos de Investigaci´on e Innovaci´on Tecnol´ogica (PAPIIT) of the Direcci´on General de Asuntos del Personal Acad´emico of the Universidad Nacional Aut´onoma de M´exico (DGAPA-UNAM) (grant number IN 202116) and Consejo Nacional de Ciencia y Tecnología (CONACyT) (grant number 31805 - N), and Ocean Census through the Ocean Census Awards initiative. CRediT authorship contribution statement Samuel Gomez´: Writing – review & editing, Writing – original draft, Methodology, Investigation, Funding acquisition, Conceptualization. Beatriz Ya´nez-Rivera ˜.: Writing – review & editing, Writing – original draft. Leonardo García-V´azquez: Writing – review & editing, Writing – original draft.	en	Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo (2025): Four new species of the genus Pseudomesochra Scott T., 1902 (Copepoda: Harpacticoida: Pseudotachidiidae) from the deep sea of the Gulf of California and Gulf of Mexico, with proposal of a new genus and species of the subfamily Danielsseniinae Huys and Gee, 1996. Zoologischer Anzeiger 316 (8): 53-74, DOI: 10.1016/j.jcz.2025.02.007, URL: https://doi.org/10.1016/j.jcz.2025.02.007
