Argestigens celibis, Gómez, 2018

Gómez, Samuel, 2018, Two new deep-sea species of Argestidae and Ameiridae (Copepoda: Harpacticoida) from the Eastern Mexican Pacific and Gulf of California, with proposal of a new genus of the family Argestidae, Journal of Natural History 52 (41 - 42), pp. 2613-2638 : 2626-2630

Argestigens celibis sp. n.

( Figures 7 – 11 )

Material examined

Dissected male holotype mounted onto nine slides (ICML-EMUCOP-110207-02); Talud X cruise; 11 February 2007; coll. S. Gómez.

Type locality

Southern Trough of Guaymas Basin , Gulf of California, México, between Isla San Pedro Nolasco and Isla Tortuga (27°42 ʹ N, 111°38 ʹ W), 1570 m depth .

Diagnosis (based on the male only)

Body subcylindrical. Surface of cephalothorax and prosomites and P5-bearing somite smooth, with few sensilla along posterior margin; hyaline frill of cephalothorax and P2 – P4-bearing somites plain. Posterior hyaline frill of genital somite and fourth to fifth urosomites finely serrated. Anal somite slightly shorter than two preceding somites combined, quadrate from dorsal view, posterior margin deeply cleft medially, anal operculum situated in the middle of somite. Caudal rami short, 1.2 times as long as wide, with six setae. Antennule eight-segmented, haplocer.

Description of male

Body. Total body length, 387 µm measured from anterior margin of rostrum to posterior margin of caudal rami, subcylindrical, tapering slightly posteriorly, without clear demarcation between prosome and urosome ( Figure 7 (a)). Rostrum ( Figure 7 (a)) fused to cephalothorax, the latter 0.3 times as long as entire body length; without surface ornamentation except for few sensilla along posterior margin; posterior hyaline frill smooth.

P2–P5-bearing somites ( Figure 7 (a)). Without surface ornamentation except for sensilla close to posterior margin; posterior hyaline frill smooth; P2 – P4-bearing somites with, P5- bearing somite without medial pore. Second urosomite (P6-bearing somite) seemingly without surface pores, without surface ornamentation except for posterior continuous spinular row dorsally and some sensilla close to posterior margin, posterior hyaline frill finely serrated ( Figure 7 (a – c)). Third and fourth urosomites with paired pores dorsally; third urosomite with one, fourth urosomite with two pores ventrally; both urosomites with continuous row of spinules of moderate sized dorsally ( Figure 7 (a)) and laterally ( Figure 7 (c)), ventrally ( Figure 7 (b)) with spinular pattern consisting of sets of larger spinules alternating with sets of smaller ones, posterior hyaline frill finely serrated. Fifth urosomite with paired pores dorsally, without any other surface ornamentation dorsally and laterally ( Figure 7 (a,c)); ventrally ( Figure 7 (b)) with medial row of spinules consisting of two sets of lager spinules flanked by sets of smaller ones, hyaline frill finely serrated.

Anal somite ( Figure 7 (a–c)). Quadrate, slightly longer that preceding somite, posterior margin deeply cleft medially, without surface ornamentation dorsally except for two sensilla associated to anal operculum, the latter shifted anteriorly and with row of minute spinules close to posterior margin; ventrally ( Figure 7 (b)) with two anterior sets of spinules, each consisting of two sets of larger spinules flanked by smaller ones, and with some sets of spinules close to caudal rami as shown; with lateral spinules anteriorly and close to joint with caudal rami ( Figure 7 (c)).

Caudal rami ( Figure. 7 (a–c)). Cylindrical, short, 1.2 times as long as wide (width measured at the widest medial part), without surface ornamentation except for few spinules close to posterior margin, with six setae, all issuing from distal fifth, as follows: seta I lost; homologation of setae II and III difficult, both visible from lateral view, probably seta II dorsal to seta III, both setae subequal in length; setae IV and V longest; seta VI issuing at inner distal corner; dorsal seta VII issuing subdistally, tri-articulated.

Antennule ( Figure 8 (a)). Eight-segmented, haplocer, with three segments distal to geniculation; first segment with few spinules proximally, other segments without surface ornamentation. Armature formula as follows: 1-[1se], 2-[1se], 3-[7se], 4-[5se], 5-[4se+ 3 sp + ae], 6[2se+ 1sp], 7-[3se], 8-[2se+ 5art+ acro].

Antenna, mandible, maxillule, and maxilliped. Lost during dissection.

Maxilla ( Figure 8 (b)). Syncoxa with outer spinules, seemingly without any other surface ornamentation; with two endites; proximal (praecoxal) endite small, rounded, with apical row of spinules, with two setae; distal (coxal) endite elongated, with one strong spinulose element fused to endite, and one bare seta. Allobasis seemingly without spinules, drawn out into strong, un-ornamented claw, and accompanied by one seta. Endopod represented by two setae.

P1 ( Figure 9 (a,b)). Basis with inner and outer strong spinulose spines, inner one modified; with strong spinules medially, between rami and at base of inner spine. Exopod threesegmented; exopodal segments subequal in length, with spinules as depicted; EXP1 without, EXP2 with inner seta, EXP3 with five elements. Endopod three-segmented, longer than exopod; ENP1 and ENP2 with inner seta; ENP3 with three elements, outermost a spine.

P2–P4 ( Figures 9 (c), 10(a,b)). Praecoxa as in P2 and P4 (see Figures 9 (c), 10(b)), small, triangular, with a transverse row of spinules close to joint with coxa, the latter with some spinules close to distal outer corner. Basis with spinules between rami and at base of outer seta, and with slender, long spinules (setules?) at distal inner corner. Outer basal seta of P2 lost during dissection, of P3 and P4 slender, naked. Exopod three-segmented, longer than endopod, with spinular ornamentation as shown; EXP1 and EXP2 with inner seta; P2 EXP2 ( Figure 9 (c)) with two inner setae, two apical elements (innermost setiform, outermost spine-like), and three outer spines; P3 – P4 EXP3 ( Figure 10 (a,b)) with three inner setae (all setae of P3 bipinnate and slender, medial seta of P4 strong and spinulose), two apical elements (innermost setiform, outermost spine-like) and three outer spines. Endopod three-segmented, with spinular ornamentation as shown; P2 – P4 ENP1 and ENP2 ( Figures 9 (c), 10(a,b)) with one inner seta; P2 ENP3 ( Figure 9 (c)) and P4 ENP3 ( Figure 10 (b)) with two inner and two apical setae, and one outer spine; P3 ENP3 ( Figure 10 (a)) with three inner and two apical setae, and one outer spine.

P5 ( Figure 11 (a)). Seemingly without spinules on baseoendopod and on baseoendopodal setophore. Endopodal lobe poorly developed, with three setae of which outermost and medial element close to each other (outermost smallest), innermost separated from the former two elements by wide gap. Exopod distinct, oval, two times as long as

wide (maximum width at medial part); only one small spinule was observed on medial outer margin; with three outer, one apical and two inner setae.

Figures

Figure 7. Argestigens celibis sp. n., male holotype. (a) habitus, dorsal; (b) urosome, ventral, P5- bearing somite omitted; (c) urosome, lateral.

Figure 8. Argestigens celibis sp. n., male holotype. (a) antennule; (b) maxilla.

Figure 9. Argestigens celibis sp. n., male holotype. (a) left P1, anterior, with aberrant EXP3; (b) right P1 EXP3, anterior; (c) P2, anterior.

Figure 10. Argestigens celibis sp. n., male holotype. (a) P3, anterior; (b) P4, anterior.

Figure 11. Argestigens celibis sp. n., male holotype. (a) P5, anterior; (b) P6.