Botryllophilus antarcticus, 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 : 60-63

Botryllophilus antarcticus sp. nov.

( Figs. 33- 35 )

Type material. Holotype ♀ (MNHN-IU-2018-1958, dissected and mounted on a slide) from Aplẚdẚum falklandẚcum Millar, 1960 (MNHN-IT-2008-386 = MNHN A1 / APL.B/532); Antarctic, Terre Adélie, CEAMARC cruise, RV “Aurore Australis”, Stn 18EV479 (66º10’S, 139º41’E), depth 402-437 m, IPEV-AAD-MNHN coll., 15 January 2008.

Etymology. The name of the new species is based on its type locality, the Antarctic.

Description of female. Body ( Fig. 33A ) fleshy with thin exoskeleton; length 1.58 mm. Anterior part of body unsegmented; cephalosome recognizable from metasome only by faint dorsal constriction. Narrower posterior part ( Fig. 33B ) comprising genital somite and abdomen consisting of 5 indistinct annulations. Genital somite 170×250 μm, obscurely defined from fifth pedigerous somite; genital apertures positioned dorsolaterally. Abdomen gradu- ally narrowing posteriorly; first to fourth abdominal annulations subequal in length; fifth (anal somite) 77×115 μm, distinctly wider than long. Caudal rami divergent; each ramus ( Fig. 33C ) about 1.4 times longer than wide (54×38 μm), armed with 4 claws and 2 setae; all caudal claws pointed at tip, longest claw straight, 48 μm long, as long as caudal ramus.

Rostrum absent. Antennule ( Fig. 33D ) stout, 195 μm long, 4-segmented, but terminal segment subdivided by incomplete suture on one surface; first and second segments expanded, incompletely articulated from each other; armature formula 9, 5, 2, and 11+aesthetasc; all setae naked. Antenna ( Fig. 33E, F ) 4-segmented; coxa, basis, and first endopodal segment unarmed; second endopodal segment 4.7 times longer than wide, armed with 3 spines on inner margin and 5 setae on distal margin. No difference recognizable between right and left antennae.

Labrum ( Fig. 33G ) simple, nearly semicircular. Mandible ( Fig. 33H ) with 3 teeth on coxal gnathobase; palp with 9 setae, grouped as 3, 2, 2, and 2. Maxillule ( Fig. 33I ) consisting of precoxa and palp; precoxa with 6 setae on arthrite, minute second distal seta lobate and tipped with setule; palp with 2 setae on medial margin, 3 setae on outer margin, and 1 minute naked seta at outer proximal corner (representing epipodite); endopod not articulated at base, armed with 3 setae on distal margin. Maxilla ( Fig. 33J ) obscurely segmented, armed with 10 setae (4 small and naked). Maxilliped ( Fig. 33K ) stout, 4-segmented; syncoxa (first segment) unarmed but with 3 transverse rows of fine spinules; basis (second segment) with 2 unequal setae and 1 transverse row of fine spinules subdistally; first endopodal segment short and unarmed; second endopodal segment about twice as long as wide, armed with 2 small setae subdistally and 1 denticle at inner distal corner; terminal claw about 0.65 times as long as second endopodal segment, bearing 1 denticle subdistally on concave margin.

Legs 1-4 ( Figs. 34 A-F, 35A, B) biramous, asymmetrical in setation between left and right legs; coxa unarmed: basis with outer seta and 2 or 3 rows of minute spinules on inner side of anterior surface. Exopods of legs 1 and 2 unsegmented, but other rami of swimming legs 2-segmented. Exopods of left legs 1 and 2 ( Fig. 34B, D ) characteristically with mixture of spines and setae (as figured). Second endopodal segment of right leg 2 ( Fig. 34C ) and left leg 3 ( Fig. 34F ) bearing 1 small spine in addition to setae. One seta on second exopodal and endopodal segments of left leg 4 ( Fig. 35B ) remarkably reduced in size. Almost all setae on legs 1-4 naked. Numbers of spines (Roman numerals) and setae (Arabic numerals) on rami of right and left legs 1-4 as follows:

Leg 5 ( Fig. 34G ) evenly tapering, about 1.5 times longer than wide (163×108 μm); armed with 4 setae. Leg 6

( Fig. 34H ) represented by 2 spinules and 1 prominent spiniform process on genital operculum.

Male. Unknown

Remarks. In legs 1-4 of Bçtryllçphẚlus species the exopods of the right legs are typically armed only with spines whereas the exopods of the left legs are typically armed only with setae. One exception to this generalisation is B. macrçpus, in which the right and left legs are symmetrical and the exopods of both right and left legs 1 and 2 are armed with mixture of spines and setae. Bçtryllçphẚlus antarctẚcus sp. nov. is another species bearing a mixture of spines and setae on the exopods of legs 1 and 2, although it differs from B. macrçpus in the precise armature formula for the swimming legs and in other respects. Other unique features of B. antarctẚcus sp. nov. include the abdomen consisting of 5 annulations, and the combination of the armature on the exopods and endopods of right legs 1-4 which are 6-5-6-6 and 8-9-6-5, respectively. These unique features clearly differentiate B. antarctẚcus sp. nov. from its congeners, and support the establishment of the new species.

Figures

FIG. 33. Bçtryllçphẚlus antarctẚcus sp. nov., female.A, habitus, right; B, posterior part of body, ventral; C, caudal ramus; D, antennule; E, left antenna; F, second endopodal segment of right antenna; G, labrum; H, mandible; I, maxillule, with inset showing modified seta on precoxa; J, maxilla; K, maxilliped. Scale bars: A, 0.2 mm; B, 0.1 mm; C, G, I-K, 0.02 mm; D-F, H, 0.05 mm.

FIG. 34. Bçtryllçphẚlus antarctẚcus sp. nov., female. A, right leg 1; B, left leg 1; C, right leg 2; D, left leg 2; E, right leg 3; F, left leg 3; G, leg 5; H, leg 6. Scale bars: A-F, H, 0.02 mm; G, 0.1 mm.

FIG. 35. Bçtryllçphẚlus antarctẚcus sp. nov., female. A, right leg 4; B, left leg 4. Scale bars: 0.02 mm.