Botryllophilus stenurosus, 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 : 76-80

Botryllophilus stenurosus sp. nov.

( Figs. 45-47 )

Type material. Holotype ♀ (MNHN-IU-2018-1967), 3 ♀♀ paratypes (intact, MNHN-IU-2018-1968), and 2 ♀♀ paratypes (dissected, MNHN-IU-2014-17372) from bxçstçma ẚanthẚnum (Sluiter, 1909); Papua New Guinea, south coast near bootless inlet, South Motupore reef, OCDN 1643-I (09°31.81’S, 147°17.05’E), depth 3 m, CRRF coll., 29 October 1992.

Additional material. 1 ♀ (MNHN-IU-2014-17373, dissected) from b. ẚanthẚnum, Papua New Guinea, CRRF coll .

Etymology. The specific name is derived from the Greek sten (=narrow) and urç (=tail), referring to the slender abdomen of the new species.

Description of female. Body ( Fig. 45A ) narrow, slightly asymmetrical, arched ventrally; body length 1.50 mm. Anterior part of body gradually broadening posteriorly, unsegmented, but divisible into 5 parts by indistinct cephalic shield and 3 weak dorsolateral constrictions; fourth and fifth pedigerous somites not defined from each other. Leg 5 positioned dorsolaterally. Posterior part of body ( Fig. 45B ) slender, occupying 45% of body length, consisting of genital somite and abdomen of 4 somites. Genital somite 152×242 μm, narrowing posteriorly; genital apertures positioned dorsally.Abdominal somites 121×167, 133×152, 127×145, and 172×123 μm, respectively. Caudal ramus ( Fig. 45C ) armed with 4 claws and 2 setae; larger inner distal claws longer than ramus; 1 inner distal claw blunt with membranous tip. Egg sac ( Fig. 45D ) oval, 640×455 μm; each egg about 160 μm in diameter.

Rostrum absent. Antennule ( Fig. 45E ) short, 4-segmented; armature formula 8, 5, 1+aesthetasc, and 10+aesthetasc; 2 larger setae on first, 2 on second, and 1 on third segments. Left antenna ( Fig. 45F ) slender, 4-segmented; proximal 3 segments unarmed; second endopodal segment about 3.4 times longer than wide (79×23 μm), distinctly shorter than basis, armed with 7 bluntly tipped, slender setae, longest outer distal seta 128 μm. Second endopodal segment of right antenna ( Fig. 45G ) about 4 times longer than wide (91×23 μm), longer than that of left antenna, but with shorter setae, longest second outer distal seta 83 μm.

Labrum ( Fig. 45H ) with thickened lateral borders and linguiform posteromedian lobe bearing small lobe on ventral surface and minute setules on distal margin. Mandible ( Fig. 45I ) bearing bifurcate distal tooth and 3 smaller teeth on coxal gnathobase; palp with 9 setae arranged as 3, 2 (including 1 minute seta), 2, and 2; distal 2 of 3 outer proximal setae broadened. Maxillule ( Fig. 45J ) with 6 distinct setae on precoxal arthrite; coxobasis with 1 vestigial seta on epipodite, 2 medial and 3 outer setae on basis region; setulose distal lobe present on basis; endopod distinctly articulated from basis, armed with 3 setae. Maxilla ( Fig. 45K ) indistinctly 3-segmented with 3, 4, and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 46A ) relatively narrow, 4-segmented; syncoxa as long as wide, with 2 small setae proximally and row of several spinules near middle of outer surface; basis with 2 small setae; small first endopodal segment unarmed; second segment twice as long as wide, with 1 small seta on inner margin and produced inner distal corner; terminal claw small, shorter than second endopodal segment.

Legs 1-4 ( Figs. 46 B-E, 47A-D) biramous, asymmetrical; coxa obscure, lacking inner seta; basis with small outer seta, ornamented with patch of spinules at inner distal corner. Exopods of all swimming legs unsegmented, but all endopods distinctly 2-segmented. Second endopodal segment of right legs 2-4 bearing spines in addition to setae. Numbers of spines (Roman numerals) and setae (Arabic numerals) on right and left legs 1-4 as follows:

Leg 5 ( Fig. 47E ) elongate, extending beyond posterior margin of genital somite ( Fig. 45A ), 2.5 times longer than wide (380×150 μm); armed with 4 setae (3 thin, setule-like); largest distal seta 110 μm long, but shorter than proximal width of leg 5. Leg 6 represented by 1 small spinule and 1 spinule-like process on genital operculum.

Male. Unknown.

Remarks. Leg 5 is generally large in members of the Bçtryllçphẚlus type B species group but small in members of the type A species group. Bçtryllçphẚlus stenurçsus sp. nov. belongs to the type A group, but possesses a large leg 5 which seems to be the most salient diagnostic feature of the new species. Within the type A group, B. abbçttẚ Ooishi & Illg, 1989 and B. banyulensẚs Brément, 1909 carry a fairly large leg 5, but they differ from B. stenurçsus sp. nov. in having different combinations of armature elements on the swimming legs. For example, B. abbçttẚ and B. banyulensẚs each have 6 spines (cf. 7 spines in B. stenurçsus sp. nov.) on the exopod of right leg 1, and 7 setae (cf. 8 setae in B. stenurçsus sp. nov.) on the endopod of right leg 2.

The combination of setal numbers (8-7-6-6) on the endopods of left legs 1-4 of B. stenurçsus sp. nov. is unique within the genus and this feature alone serves to differentiate B. stenurçsus sp. nov. from all of its congeners.

Figures

FIG. 45. Bçtryllçphẚlus stenurçsus sp. nov., female. A, habitus, right; B, posterior part of body, dorsal; C, caudal ramus; D, egg sac; E, antennule; F, left antenna; G, distal part of right antenna; H, labrum; I, mandible; J, maxillule; K, maxilla. Scale bars: A, D, 0.2 mm; B, 0.1 mm; C, H-K, 0.02 mm; E, F, G, 0.05 mm.

FIG. 46. Bçtryllçphẚlus stenurçsus sp. nov., female.A, maxilliped; B, right leg 1; B, left leg 1; D, right leg 2; E, left leg 2. Scale bars: 0.02 mm.

FIG. 47. Bçtryllçphẚlus stenurçsus sp. nov., female.A, right leg 3; B, left leg 3; C, right leg 4; D, left leg 4; E, leg 5. Scale bars: A-D, 0.05 mm; E, 0.1 mm.