Schizoproctus bisetatus, 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 : 107

Schizoproctus bisetatus sp. nov.

( Figs. 67 , 78 )

Type material. Holotype ♀ (MNHN-IU-2018-1977, dissected and mounted on a slide) from Caenagnesẚa bçckẚ Ärnbäck-Christie-Linde, 1938 (MNHN-IT-2008-1840 = MNHN P3 / CAE/6 ); Weddell Sea, EPOS 3 3 cruise, RV “Polarstern”, Stn MG7 (75°05.5´S, 28°01.0´W), depth 462 m, 01 February 1989.

Etymology. The name is derived from the Latin bẚ (=two) and set (=a bristle), referring to leg 5 of the new species, which is armed with 2 setae.

Description of female. Body ( Fig. 67A ) symmetrical, narrow, 2.90 mm long. Anterior part of body unsegment- ed; cephalosome defined from metasome by dorsal and lateral constrictions; metasome slightly inflated dorsally with convex dorsal margin in lateral view and narrower posterior part. Legs 4 and 5 positioned on same transverse plane. Posterior part of body ( Fig. 67B ) slender, consisting of genital somite and 4-segmented abdomen, but articulation incomplete between last 2 somites. Genital somite 394×406 μm; 4 abdominal somites 187×315, 133×300, 188×255, and 242×182 μm, respectively. Caudal ramus ( Fig. 67C ) as long as wide, ornamented with 2 patches of minute spinules on ventral surface; armed with 5 claws and 1 seta; spine on subdistal inner margin setiform, pale.

Rostrum ( Fig. 67D ) short, strongly tapering towards rounded apex. Antennule ( Fig. 67E ) 5-segmented, forming right angle between first and remaining segments; armature formula 13, 5, 3, 4, and 7+aesthetasc; aesthetasc on last segment very small and similar in appearance to smaller setae. Antenna ( Fig. 67F ) consisting of coxa, basis, and 2-segmented endopod; coxa short and unarmed; basis unarmed but ornamented with 2 patches of minute spinules subdistally; first endopodal segment short and unarmed; second endopodal segment about 3 times longer than wide (121×41 μm), with vestigial suture at distal third: armed with 8 spines (4 on inner margin and 4 on distal margin) and ornamented with 1 patch of minute spinules subdistally; fourth spine on inner margin shortest, and second outer spine on distal margin longest

Labrum ( Fig. 67G ) small, unornamented, with broad posteromedial lobe. Mandible ( Fig. 67H ) consisting of coxa and palp; coxal gnathobase with 3 teeth and finely spinulose proximal part on medial margin; palp with 9 setae arranged as 3, 2, 2, and 2. Maxillule ( Fig. 67I ) consisting of precoxa and palp; precoxa with 8 unequal setae on arthrite (including 2 small distal setae); palp consisting of coxa, basis, and endopod; coxa with 1 minute vestigial seta on epipodite; basis with 2 setae on medial margin, 3 setae on outer margin, and weakly bilobed process distally; endopod incompletely articulated from basis, with 3 setae on distal margin. Maxilla ( Fig. 68A ) obscurely 2-segmented, with 9 setae. Maxilliped ( Fig. 68B ) 4-segmented with 2 setae on syncoxa, 2 on basis, and 1 on second endopodal segment; terminal claw as long as second endopodal segment, with 1 denticle proximally on inner margin.

Legs 1-4 biramous with 1-segmented exopods and endopods ( Fig. 68C, D ), and unarmed coxa. Basis of leg 1 lacking outer seta, but with 2 patches of minute spinules on anterior surface. Basis of leg 2 unornamented, with short, very thin outer seta. Exopods of legs 1-4 armed with 7 spines, but inner subdistal spine rudimentary; ornamented with patch of fine spinules near base of outer and distal spines. Endopod of legs 1 and 2 ornamented with 3 patches of minute spinules on anterior surface. Outer proximal seta on endopod of legs 1 and 2 markedly shorter than other setae. Armature formula for legs 1-4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	0-0	VI, 1	1, 2, 5
Leg 2	0-0	1-0	VI, 1	1, 2, 5
Legs 3 & 4	0-0	1-0	VI, 1	1, 2, 4

Leg 5 ( Fig. 68E ) flattened, sub-rectangular, twice as long as wide (500×245 μm), armed with 2 setae on oblique distal margin. Leg 6 not seen.

Male. Unknown.

Remarks. Schẚzçprçctus bẚsetatus sp. nov. is most similar to S. magnus sp. nov. because they share the same armature formula of legs 1-4, with the exception only of the endopod of leg 2 which bears 8 setae in S. bẚsetatus sp. nov. compared to 9 setae in S. magnus sp. nov. The main differences between these two species are as follows: (1) the abdomen is 4-segmented in S. bẚsetatus sp. nov., but consists of 6 indistinct annulations in S. magnus sp. nov.; (2) the caudal ramus is armed with 5 claws and 1 seta in S. bẚsetatus sp. nov., but with 4 claws and 2 setae in S. magnus sp. nov.; (3) all setae on the antennule of S. bẚsetatus sp. nov. are much shorter than the width of the first segment, whereas some of setae on the antennule of S. magnus sp. nov. are large, as long as the width of the first segment; and (4) leg 5 is sub-rectangular with 2 distinct setae in S. bẚsetatus sp. nov., but elongate and tapering with 4 rudimentary setae in S. magnus sp. nov.

Figures

FIG. 67. Schẚzçprçctus bẚsetatus sp. nov., female.A, habitus, right; B, posterior part of body, ventral; C, caudal ramus; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, 0.5 mm; B, 0.2 mm; C-F, H, I, 0.05 mm; G, 0.02 mm.

FIG. 78. Schẚzçprçctus mçllẚs sp. nov., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4; E, leg 5. Scale bars: A-D, 0.05 mm; E, 0.2 mm.

FIG. 68. Schẚzçprçctus bẚsetatus sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 3; E, leg 5. Scale bars: A-D, 0.05 mm; E, 0.2 mm.