Acritozosime spinesco, Kim & Lee, 2021

Kim, Jong Guk & Lee, Jimin, 2021, Proposal of two new genera of the family Zosimeidae Seifried (Copepoda: Harpacticoida): Heterozosime gen. nov. and Acritozosime gen. nov., European Journal of Taxonomy 760, pp. 32-60 : 48-56

Acritozosime spinesco gen. et sp. nov.

urn:lsid:zoobank.org:act:838FDBD8-4A20-4696-B885-6486ABD1B732

Figs 9–12

Etymology

The species epithet is derived from the Latin intransitive verb ‘ spinesco ’ (‘grow spiny’), alluding to the spinulose ornamentation on the urosome.

Material examined

Holotype

NORTHWESTERN PACIFIC • ♀; East Mariana Basin ; 18º17′26.64″ N, 149º50′14.88″ E; stn WP1908; depth 5317 m; 3 Oct. 2019; J.G. Kim leg.; MABIK CR00247790 (preserved in 80% ethanol).

Paratypes

NORTHWESTERN PACIFIC • 1 ♀; same collection data as for holotype; MABIK CR00247791 (on 11 slides) • 1 ♀; same collection data as for holotype; MABIK CR00247792 (preserved in 80% ethanol) .

Other material

NORTHWESTERN PACIFIC • 1 ♀; East Mariana Basin ; 18º51′56.22″ N, 149º51′40.20″ E; stn WP1909; depth 5416 m; 4 Oct. 2019; J.G. Kim leg.; MInRB-Hr61-L001 (preserved in 80% ethanol) • 1 ♀; East Mariana Basin ; 19º19′45.78″ N, 150º19′19.26″ E; stn WP1910; depth 5078 m; 5 Oct. 2019; J.G. Kim leg.; MInRB-Hr61-S001 (on four slides) • 1 ♀; same collection data as for preceding; MInRB-Hr61-L002 (preserved in 80% ethanol) • 1 copepodid; East Mariana Basin ; 19º01′26.4″ N, 151º08′49.56″ E; stn WP1912; depth 5550 m; 17 Oct. 2019; J.G. Kim leg.; MInRB-Hr61-L003 (preserved in 80% ethanol) • 1 ♀; Philippine Basin of the Philippine Sea; 19º59′37.14″ N, 128°21′49.13″ E; stn WP1802; depth 5642 m; 19 Oct. 2018; J. Lee leg.; MInRB-Hr61-L004 (preserved at 80% ethanol) • 1 ♀; Philippine Basin of the Philippine Sea; 18º51′30.05″ N, 129º10′44.22″ E; stn WP1803; depth 5578 m; 20 Oct. 2018; J. Lee leg.; MInRB-Hr61-L005 (preserved at 80% ethanol) • 1 ♀; Philippine Basin of the Philippine Sea; 17º28′40.73″ N, 131º11′01.68″ E; stn WP1804; depth 5856 m; 22 Oct. 2018; J. Lee leg.; MInRB-Hr 61-L006 (preserved at 80% ethanol) .

Description

Female (based on the paratype MABIK CR00247791)

MEASUREMENTS. Body length about 406–535 μm (mean 479 μm, n = 10; holotype 437 μm) measured from anterior tip of rostrum to posterior end of caudal rami in lateral aspect.

HABITUS ( Fig. 9A–B ). Semi-cylindrical, slightly depressed dorsoventrally, tapering posteriorly; with distinct constriction between prosome and urosome. Rostrum ( Fig. 9A ) large, broad, triangular, reaching to mid-length of third antennular segment, fused to cephalothorax basally; anterior tip with a pair of sensilla. Cephalothorax slightly longer than wide, with almost parallel lateral margins in dorsal aspect. First pedigerous somite completely incorporated into cephalothorax. Second to fourth free pedigerous somites slightly tapering posteriorly. Urosome ( Figs 9A–B , 10A ) composed of P5 bearing-somite, genital double-somite and 3 abdominal somites, about 0.8 times as long as prosome. Genital double-somite formed by dorsal and ventral fusion of genital and first abdominal somites; mark of original division remains internally on both lateral sides; gonopores ( Fig. 10C ) fused medially forming single genital slit covered by single broad plate bearing 1 stout spinulose seta and 2 small spines, representing P6, on both sides distally; copulatory pore large, located in midventral surface posterior to genital slit, connected to pair of internal seminal receptacles. Penultimate somite ( Figs 9A–B , 10A–B ) with pseudoperculum bearing 4 weak protuberances (two of them damaged and represented by a dotted line in Fig. 10B ). Anal somite ( Figs 9A–B , 10A–B ) small, with small operculum bearing distal setules; dorsal surface with 1 pair of sensilla; anal opening wide, armed with 2 diagonal rows of setules.

BODY ORNAMENTATIONS. Integument of cephalothorax ornamented with paired pores and sensilla and other somites except penultimate and anal somites ornamented with paired sensilla posteriorly ( Fig. 9A–B ). Hyaline frills of all somites weak; genital double-somite, second and third abdominal somites irregular dorsally. Urosomites armed with posterior spinules laterally in all somites and dorsally in first urosomite and first abdominal somite.

CAUDAL RAMI ( Figs 9A–B , 10A–B ). Slightly longer than anal somite, about 1.8 times as long as greatest width; inner margin convex proximally, ornamented with setules; with 7 setae: ventrolateral seta I smallest, inserted at mid-length of outer margin; dorsolateral seta II about 1.1 times as long as caudal ramus, inserted at same level as seta I; seta III arising from ventral surface subdistally, about twice as long as caudal ramus; setae II and III accompanied by few spinules at their bases; principal setae IV and V well-developed, tri-spinulose, with internal fracture plane proximally; seta IV about ⅓ of seta V length; seta V very long, about 4/5 of body length; seta VI inserted at inner distal corner ventrally, as long as caudal ramus; seta VII tri-articulate basally, located dorsally in mid-length of inner margin.

ANTENNULE ( Fig. 10D ). Short, robust, 7-segmented. First segment ornamented with inner spinules and with 1 pinnate seta bearing a few spinules near base. Second segment largest, partially with cuticular ridge indicating original segmentation; with 7 pinnate setae, 5 spinulose setae, 5 tri-spinulose setae, of which one is bi-articulated basally, and 1 ae. Third segment small, with 1 small spinulose seta and 1 stout tri-spinulose seta. Fourth segment small, with 2 spinulose setae. Fifth segment small with 1 bare bi-articulate seta, 1 spinulose seta and 1 stout tri-spinulose seta. Sixth segment smallest, with 1 spinulose seta and 1 bare bi-articulate seta. Seventh segment small, with 1 small spinulose, 1 stout tri-spinulose, 1 spinulose and 2 bare bi-articulate setae and 1 ae. Each ae on second and distal segments fused basally with adjacent spinulose seta. Setal armature formula as: 1-[1], 2-[16 + (1 + ae)], 3-[2], 4-[2], 5-[3], 6-[2], 7-[4 + (1 + ae)].

ANTENNA ( Fig. 11A ). Coxa small, unornamented. Basis small, with 2 short rows of setules and 1 small spinulose abexopodal seta. Exopod large, 3-segmented; proximal segment with 1 short bare seta proximally and 1 spinulose seta distally; middle segment smallest, unarmed; distal segment as long as two preceding segments combined, with 1 spinulose lateral and 3 spinulose distal setae. Endopod 2-segmented; proximal segment small, unarmed; distal segment about twice as long as preceding one, ornamented with 2 rows of spinules on lateral margin proximally and 1 row of spinules on distal margin; lateral armature comprising 3 stout spinulose setae; distal armature composed of 2 spinulose rigid setae, 2 uni-spinulose setae, of which longest fused to adjacent spinulose rigid seta basally, and 3 spinulose geniculate setae.

MANDIBLE ( Fig. 11B ). Coxa with bulge medially; gnathobase armed with several multicuspidate teeth and 1 dorsal unipinnate spine. Palp comprising basis, exopod and endopod; basis elongate, with 2 plumose setae subdistally; exopod 1-segmented, with 4 spinulose setae; endopod 1-segmented, with 1 uniplumose seta laterally and 4 spinulose setae distally.

MAXILLULE ( Fig. 11C ). Praecoxa ornamented with 1 row of spinules near outer margin; arthrite developed, with 2 parallel setae and 2 rows of spinules on anterior surface, 1 row of spinules on posterior surface and 7 stout spines, 1 small bare seta and 1 unipinnate seta along distal margin. Coxa small, without epipodite; endite with 1 pinnate and 2 plumose setae. Basis ornamented with 2 rows of dorsal spinules, with 3 bare and 4 pinnate setae apically and subapically. Exopod smaller than endopod, with 2 plumose setae distally. Endopod transversely elongate, with 1 bare and 2 pinnate setae distally and 1 pinnate and 1 plumose seta subdistally.

MAXILLA ( Fig. 11D ). Syncoxa ornamented with 1 row of setules on outer margin; two praecoxal endites fused basally, proximal one ornamented with rows of spinules on lateral margin and anterior surface, respectively, with 2 spinulose spines distally and distal one with 1 spinulose seta, 1 bare seta and 1 unispinulose spine; both coxal endites elongate, with 1 bare and 2 spinulose setae, respectively. Allobasis with 2 stout uniserrate spines and 1 bare seta. Endopod small, 2-segmented; proximal with 2 bare setae; distal one with 3 uniplumose setae distally and 1 bare seta subdistally.

MAXILLIPED ( Fig. 11E ). Comprising syncoxa, basis and endopod, forming right angle between syncoxa and basis. Syncoxa ornamented with 3 short rows of spinules; with 1 spinulose seta subdistally and 1 long tri-spinulose seta proximally, which is about 3 times as long as syncoxa. Basis with 1 spinulose seta distally; inner margin extended distally, bearing 1 row of long spinules. Endopod small, with 2 stout spinulose setae distally and 2 bare setae laterally.

P1 ( Fig. 11F ). Praecoxa large, unornamented. Both coxae connected by pentagonal intercoxal sclerite. Coxa wide, with 2 rows of long outer spinules and 1 row of minute distal spinules on anterior surface. Basis wide, with 1 spinulose outer spine and 1 spinulose inner spine, ornamented with 2 groups of spinules on anterior surface, 1 row of long setules along inner margin, 1 row of spinules near distal margin and 1 row of spinules near base of outer and inner spines; inner spine displaced onto anterior surface. Exopod 2-segmented, as long as endopod; exp-1 with 1 unispinulose outer spine; ornamented with 3 groups of outer spinules, 3 rows of anterior spinules and 1 row of inner setules; exp-2 slightly larger than exp-1, ornamented with 4 groups of spinules near base of spines, with 3 unispinulose outer spines, 2 spinulose distal spines, of which inner one armed with inner setules, and 1 small plumose inner seta; all outer spines with gradually increasing outer spinules toward distal tip. Endopod 2-segmented; enp-1 subrectangular, unarmed, ornamented with rows of spinules along outer margin and 2 rows of anterior spinules near outer distal corner; enp-2 with 1 small spinulose spine and 1 long spinulose seta (inner seta about 3 times as long as outer spine) on distal margin, ornamented with rows of spinules along outer and inner margins and 1 row of anterior spinules near distal margin ( Table 2 ).

P2–P4 ( Fig. 12A–C ). Praecoxae short but wide, with 1 row of distal spinules near outer margin. Both coxae connected by pentagonal intercoxal sclerite bearing concave posterior margin. Coxae large, wide, with 1 row of anterior spinules near outer margin. Bases wide, ornamented with 1 group of long setules along inner margin, 1 row of distal spinules on pedestal of inner ramus and 1 group of anterior spinules near base of outer setophore; outer seta arising from setophore, stout and spinulose. Exopods longer than endopods, 3-segmented; exp-1 elongate, largest, with 1 spinulose outer spine, ornamented with 3 groups of spinules along outer margin, 1 row of setules on inner margin, 1 row of minute spinules on distal margin and 1 row of anterior spinules near base of outer spine; exp-2 smallest, with 1 spinulose outer spine and 1 plumose inner seta, ornamented with 1 row of spinules on outer margin, few setules on inner margin and 1 group of anterior spinules near base of outer spine; exp-3 elongate, with 2 spinulose outer spines, 1 (outer) distal spine, which is armed with inner setules and outer spinules, 1 plumose (inner) distal seta and 1 (in P2) or 2 (in P3–P4) plumose inner setae; ornamented with 1 row of spinules on outer margin and 3 groups of spinules near base of outer spines. Endopods slightly exceeding end of exp-2 (in P2 and P4) or reaching to distal fourth of exp-2 (in P3), 2-segmented; enp-1 armed with outer and inner setules/spinules; P2 enp-1 ornamented with anterior spinules near distal margin; P2–P3 enp-1 unarmed and P4 enp-1 with 1 plumose inner seta; enp-2 elongate, ornamented with outer, inner and distal (absent in P2) setules/spinules; P2 enp-2 with 1 short spinulose outer spine and 1 long plumose distal seta; P3–P4 enp-2 with 2 long plumose setae on distal margin and 1 plumose seta on inner margin ( Table 2 ).

P5 ( Figs 10A , 11G ). Baseoendopod wide, with outer setophore bearing 1 weakly pinnate seta; endopodal lobe weakly pronounced, reaching to mid-length of exopod; with 3 setae distally, outermost one small, weakly pinnate, of which 2 inner ones plumose proximally and spinulose distally. Exopod small, with 3 setae; outermost one armed with long spinules and 2 inner ones spinulose distally.

Male

Unknown.

Variability

A paratype female specimen (MABIK CR00247791) exhibits two abnormal conditions in the P4 enp-1 and P5 exopod. The right leg of the P4 lacks an inner seta on the proximal endopodal segment ( Fig. 12D , arrowhead) and the left leg of the P5 has four setae on the exopod ( Fig. 10A , arrowhead). These setal abnormalities were not detected in other examined specimens.

Remarks

Interestingly, this new species exhibits several characteristics intermediate between those of the families Idyanthidae and Zosimeidae . Detailed morphological examination revealed that certain characteristics of the antenna and maxilliped resemble those of idyanthid copepods. The antenna of Acritozosime spinesco gen. et sp. nov. shares the presence of two elements on the proximal exopodal segment with the idyanthid genera Idyanthe Sars, 1909 , Idyella Sars, 1905 , Idyellopsis Lang, 1948 , Nematovorax Bröhldick, 2005 and Tachidiella Sars, 1909 (all known zosimeid copepods have only one seta); and the distal endopodal segment bears seven elements as in members of the Idyanthidae (zosimeid species have at most six setae). The maxilliped of A. spinesco gen. et sp. nov. resembles those of idyanthid copepods in the presence of a joint between the syncoxa and basis and the presence of two setae on the syncoxa (members of the Zosimeidae have no setae on that segment, except for Zosime eliasi Pointner, 2017 having one seta). However, this new taxon also seems to have a close affinity with the family Zosimeidae as shown by the following features: (1) the female antennules are short, robust and armed with stout tri-spinulose setae; this is not the case in the Idyanthidae other than Tachidiella ; (2) the distal endopodal segment of the antenna has a lateral armature composed of three elements (vs four setae in the Idyanthidae ); (3) the mandibular endopod has only one lateral seta (vs 2–3 setae as in Idyanthe , Idyella and Tachidiella of the Idyanthidae ); (4) the mandibular exopod is one-segmented, with four setae (vs two-segmented, with four setae on proximal segment and two setae on the distal one as in Styracothorax and Tachidiella of the Idyanthidae ); (5) the maxillular exopod is smaller than the endopod (vs longer than the endopod as in Idyellopsis of the Idyanthidae ); (6) all endites on the maxillary syncoxa are displaced toward the anterior half (vs the praecoxal endite is displaced toward the proximal half as in Idyella of the Idyanthidae ); (7) the maxilliped has a small and almost square endopod bearing four non-geniculate elements (vs with geniculate setae or strong claws as in Idyanthe , Idyella , Meteorina and Styracothorax of the Idyanthidae ); (8) the P1 enp-1 is almost square (vs elongate and broadened at the level of the inner element in the Idyanthidae ); and (9) the shape of the female P5 is similar to that of Zosime bathybia Bodin, 1968 , although the number of setae on the exopod differs.

Seifried (2003) listed four significant autapomorphies of the Idyanthidae : (1) the mandibular exopod has a long proximal segment bearing four setae and a small distal segment bearing two setae; (2) the maxillulary exopod is elongate; (3) the P1 enp-1 is elongated and broadened at the level of the inner seta; and (4) the proximal outer seta on the female P5 exopod is inserted near the basis. Acritozosime spinesco gen. et sp. nov. does not share these characteristics. Instead, this new species exhibits several autapomorphies of the Zosimeidae in the antennary endopod, mandibular both rami, maxillulary exopod, maxillary syncoxa, maxillipedal endopod and P1 endopod as mentioned above (characters 2–8 in the previous paragraph). Therefore, we suggest that an allocation of A. spinesco gen. et sp. nov. to the Zosimeidae is more reasonable; the organism retains certain plesiomorphic conditions (at least in the antenna and maxilliped) of Idyanthidimorpha, as noted above. Within the Idyanthidimorpha, the sexual dimorphism of the male P2 is a clue to the taxonomic position of the harpacticoids (Moura & Martínez Arbizu 2004; Bröhldick 2005). Unfortunately, we could not confirm this character state because we lacked males of the new species.

Within the Zosimeidae , the most conspicuous characters of A. spinesco gen. et sp. nov. are the reduced segmentation and setal armature of the thoracic legs. The new species shares the two-segmented endopod in the thoracic legs with Pseudozosime , but differs from it by the reduced setal armature; the inner element of the proximal endopodal segment is lost in P1–P3; the distal exopodal segment in P2–P4 has two outer spines instead of three. All zosimeid copepods have one or two inner setae on the distal endopodal segment of P1, while these are lacking in A. spinesco gen. et sp. nov.

This new species is also characterized by the following unambiguous features: (1) the loss of abexopodal elements on the proximal endopodal segment of the antenna (present in other zosimeid genera); (2) the lack of an epipodal element on the coxa of the maxillule (present in other zosimeid genera); and (3) the caudal seta V is notably elongated, being at least 80% of the total body length.

Figures

Fig. 9. Acritozosime spinesco gen. et sp. nov. Paratype, ♀ (MABIK CR00247791). A. Habitus, dorsal view. B. Habitus, lateral view.

Fig. 10. Acritozosime spinesco gen. et sp. nov. Paratype, ♀ (MABIK CR00247791). A. Urosome, ventral view; arrowhead indicates an abnormal condition of the P5 exopod. B. Posterior end of penultimate somite, anal somite, and caudal rami, dorsal view. C. Genital field, ventral view. D. Antennule. D’. Antennule without ornamentation.

Fig. 11. Acritozosime spinesco gen. et sp. nov. Paratype, ♀ (MABIK CR00247791). A. Antenna. B. Mandible. C. Maxillule. D. Maxilla. E. Maxilliped. F. P1. G. P5.

Fig. 12. Acritozosime spinesco gen. et sp. nov. Paratype, ♀ (MABIK CR00247791). A. P2. B. P3. C. P4. D. Abnormal condition of P4 endopod lacking an inner seta on the proximal segment.