Ascidicola antarctica, Kim & Boxshall, 2021

Kim, Il-Hoi & Boxshall, Geoff A., 2021, Copepods (Cyclopoida) associated with ascidian hosts: Ascidicolidae, Buproridae, Botryllophilidae, and Enteropsidae, with descriptions of 84 new species, Zootaxa 1, pp. 1-286 : 15-18

Ascidicola antarctica sp. nov.

( Figs. 6 , 7 )

Type material. Holotype ♀ (MNHN-IU-2018-1942, dissected and mounted on a slide) from Cçrella antarctẚca Sluiter, 1905; Antarctic Ocean, Eltanin cruise 12, Stn 1078 (61°26´S, 41°55.4´W), depth 604 m, 12 April 1964.

Etymology. The name of the new species refers to its distribution in the Antarctic Ocean.

Description of female. Body ( Fig. 6A, B ) elongate, cylindrical, segmented as in congeners. Body length 2.56 mm. Prosome slightly depressed; maximum width 560 μm across fourth pedigerous somite. Prosome 1.08 mm long, occupying 41% of body length, gradually broadening distally; cephalosome 351×425 μm; first to fourth pedigerous somites 68×431, 154×480, 203×505, and 283×560 μm, respectively. Urosome 5-segmented; fifth pedigerous somite about 220×440 μm, genital somite ( Fig. 6C ) 1.40 times longer than wide (578×412 μm); small copulatory pore visible on proximal ventral surface. Three abdominal somites 265×302, 154×252, and 185×197 μm, respectively; ventral spinose pad absent between last 2 abdominal somites. Caudal ramus ( Fig. 6D ) 2.53 times longer than wide (81×32 μm), 0.44 times as long as anal somite, with slightly convex inner margin: armed with 6 small setae (1 lateral and 5 distal); lateral seta positioned at 47% of ramus length; largest of distal setae 47 μm long, 0.58 times as long as caudal ramus, all other setae shorter than width of ramus at base.

Rostrum absent. Antennule ( Fig. 6E ) short, 5-segmented; all segments wider than long; armature formula 5, 8, 5, 5+aesthetasc, and 12+3 aesthetascs; all setae naked; shorter setae usually broadened; aesthetascs small. Antenna ( Fig. 6F ) 3-segmented, consisting of coxobasis and 2-segmented endopod; basis slightly longer than wide (50×47 μm) armed with 1 large spine (45 μm long) distally and ornamented with several scattered rows of spinules; first endopodal segment about 1.6 times longer than wide (38×24 μm), armed with 1 element (only insertion scar was observed) and 2 rows of spinules; second endopodal segment 3.5 times longer than wide (77×22 μm), terminating in slender claw; armed with 1 stout spiniform seta near middle and 4 unequal setae distally (1 much smaller than other 3), and ornamented with several rows of spinules; terminal claw 38 μm long, half as long as second endopodal segment.

Labrum ( Fig. 6G ) with concave posterior margin and bearing pair of teeth at each posterolateral corner. Mandible ( Fig. 6H ) consisting of coxa and palp: coxa with well-developed gnathobase bearing 4 teeth on medial margin; distal 3 teeth bearing 1-4 subsidiary denticles and proximal tooth setiform, weakly pinnate; palp 1-segmented, articulated from broad, pedestal-like extension of coxa; as long as wide, armed with spiniform elements (only 2 spines confirmed; other elements missing). Maxillule ( Fig. 6I ) consisting of precoxa and unsegmented palp; precoxa bearing 7 spines and 1 proximal seta on arthrite and 2 rows of minute spinules on outer side; palp bearing 7 spiniform elements and 1 minute seta along oblique outer and distal margins, and ornamented with 2 rows of minute spinules subdistally; 2 proximal elements on palp distinctly longer than others. Maxilla ( Fig. 7A ) consisting of syncoxa and allobasis; syncoxa broad, bearing 1 endite tipped with 1 seta and 1 spine (spine not articulated at base); allobasis drawn out into claw-like process, armed with 7 spiniform setae (grouped as 4, 2, and 1) along outer margin and 1 setiform process on inner margin. Maxilliped ( Fig. 7B ) 2.4 times longer than wide (58×24 μm), unsegmented, digitiform, ornamented with several rows of fine spinules; armed with 1 apical and 2 medial spinulose setae; apical seta not articulated at base.

Legs 1-4 ( Fig. 7 C-F) biramous with 2-segmented rami and narrow intercoxal sclerites; coxa lacking inner seta. Leg 1 with inner distal spine on basis 19 μm long, as long as first endopodal segment. Spines on second exopodal segment of legs 1-4 increasingly longer from outer proximal to inner distal, but fifth spine markedly smaller than other spines. Inner setae on endopods elongate and stiff, as usual for genus. First endopodal segment of legs 3 and 4 bearing inner seta, but this seta absent in legs 1 and 2. Armature formula for legs 1-4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-I	I-0; III, I, III	0-0; I II, 1
Leg 2	0-0	1-0	I-0; III, I, III	0-0; I, III, 3
Leg 3	0-0	1-0	I-0; III, I, III	0-1; I, III, 3
Leg 4	0-0	1-0	I-0; III, I, II	0-1; 0, II, 2

Leg 5 ( Fig. 6C ) lamellate, covering fifth pedigerous and genital somites, not extending to posterior margin of genital somite, bearing 3 minute vestigial setae (2 ventro-proximal and 1 ventro-distal); left and right legs separate from each other on dorsal side, but fused proximally on ventral side. Leg 6 ( Fig. 7G ) represented by bifurcate process bearing 2 small setae on genital operculum.

Male. Unknown.

Remarks. The leg armature of Ascẚdẚcçla antarctẚca sp. nov. is similar to that of A. rçsea except for the second endopodal segment of leg 4, which is armed with 2 spines and 2 setae (compared to 3 spines and 2 setae in A. rçsea). In the second exopodal segment of legs 1-4 of A. antarctẚca sp. nov. the fifth spine is the smallest, but in legs 3 and 4 of A. rçsea the fourth is the smallest. Ascẚdẚcçla antarctẚca sp. nov. differs from A. rçsea and A. secunda in the dimension of the caudal ramus which is 2.53 times longer than wide, while it is 3.93 times (present study) or about 4 times ( Ooishi, 2007a) longer than wide in A. rçsea and 2.82 times (present study) or 4.60 times (Kim I.H. & Moon, 2011) longer than wide in A. secunda .

Ascẚdẚcçla antarctẚca sp. nov. has a similar shape caudal ramus to A. phẚlẚppẚnensẚs sp. nov. and both new species possess the same number of setae (3) on the maxilliped. However, they are easy to distinguish because the setal armature of legs 1-4 is very different.

Figures

FIG. 6. Ascẚdẚcçla antarctẚca sp. nov., female. A, habitus, dorsal; B, habitus, right; C, anterior part of urosome, ventral; D, left caudal ramus, ventral; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars:A-C, 0.2 mm; D, G, 0.05 mm; E, F, H, I, 0.02 mm.

FIG. 7. Ascẚdẚcçla antarctẚca sp. nov., female.A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, genital aperture. Scale bars: A, C-F, 0.05 mm; B, G, 0.02 mm.