Botryllophilus angustus, 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 : 88-91

Botryllophilus angustus sp. nov.

( Figs. 54-56 )

Type material. Holotype ♀ (MNHN-IU-2018-1971) and paratype ♀ (dissected, MNHN-IU-2014-17375) from budẚstçma sp.; Mabul , Malaysia, OPHG 1067 -S (04º14.51’N, 118º37.32’E), depth 5-20 m, CRRF coll., 16 January 2004.

Etymology. The name of the new species is derived from the Latin angust (=narrow), indicating the narrow body.

Description of female. Body ( Fig. 54A, B ) narrow, consisting of broader anterior and narrower posterior parts; body length 1.45 mm, width 0.33 mm. Cephalosome longer than wide. Anterior part of body gradually broadening posteriorly, unsegmented, but with 4 dorsal traces of articulations. Posterior part of body ( Fig. 54C ) not articulated from anterior part, consisting of genital and 4 abdominal somites. Genital somite much wider than long, with complicated, densely sclerotized sculpture on ventral surface; genital apertures positioned dorsally. Four abdominal somites clearly defined, 112×154, 127×140, 119×127, and 135×110 μm, respectively. Caudal ramus ( Fig. 54D ) armed with 4 claws and 1 seta; 1 of 2 outer distal claws massive and blunt, other outer claw not articulated from ramus.

Rostrum absent. Antennule ( Fig. 54E ) 120 μm long, 4-segmented; first and second segments broadened; ar- mature formula 9 (3 large + 6 small), 4 (2 large + 2 small), 2 (1 large + 1 small), and 12. Left antenna ( Fig. 54F ) 4-segmented; proximal 3 segments unarmed; terminal segment (second endopodal segment) about 2.7 times longer than wide (59×22 μm), armed with 7 bluntly tipped setae. Terminal segment of right antenna ( Fig. 54G ) about 3.3 times longer than wide (69×21 μm), longer than that of left antenna; all setae distally capped with finely serrate membrane, 3 outer setae on distal margin shorter than those of left antenna.

Labrum weak, easily destroyed. Mandible ( Fig. 54H ) consisting of coxa and palp; coxal gnathobase with 4 teeth including 2 distal acutely-pointed, longer teeth; palp with 9 setae arranged as 3, 2, 2, and 2. Maxillule ( Fig. 54I ) consisting of precoxa and palp; precoxa with 6 distinct setae on arthrite; palp divisible into coxa, basis, and endopod; coxa with 1 vestigial seta on epipodite; basis with 2 setae on medial margin, 3 setae on outer margin, and setulose lobe distally; endopod articulated from basis, distinctly wider than long, armed with 3 setae. Maxilla ( Fig. 55A ) indistinctly 3-segmented, armed with 3, 4 and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 55B ) 4-segmented; syncoxa with 2 small setae on inner margin; basis with 1 rudimentary seta on inner margin; first endopodal segment unarmed; second endopodal segment with 1 rudimentary seta on inner margin and 1 minute denticle at inner distal corner; terminal claw small, bearing minute subdistal denticle.

Legs 1-4 ( Figs. 55 C-F, 56A-D) biramous, asymmetrical, with unsegmented exopods and 2-segmented endopods; coxa unarmed; basis with outer seta and row of spinules at inner distal corner. Second endopodal segment of right legs 2-4 with mix of spines and setae. Numbers of spines (Roman numerals) and setae (Arabic numerals) on right and left legs 1-4 as follows:

Leg 5 ( Fig. 56E, F ) small, about 1.4 times longer than wide (86×60 μm), strongly tapering, armed with 4 setae (1 proximal and 3 distal), distal longest seta 114 μm, distinctly longer than segment. Leg 6 ( Fig. 55G ) represented by 1 spinule and 1 spiniform process on genital operculum; several dentiform elements on surface immediately adjacent to leg 6.

Male. Unknown.

Remarks. The exopods of right legs 1-4 of B. angustus sp. nov. are armed with 7, 6, 6, and 6 armature elements, respectively (the combination 7-6-6-6). This combination is common in members of the type B group (species with 5 or more annulations in the abdomen), but is very rare in members of the type A group, because the exopod of right leg 4 in type A usually bears 4 or 5 spines. In the type A group only two species, B. nçrvegẚcus and B. angustus sp. nov., deviate from this pattern, although in the former species the combination may be either 7-6-6-6 or 7-6-6-7. Bçtryllçphẚlus nçrvegẚcus does not require detailed comparison with B. angustus sp. nov., because it carries distinctive features, such as the swollen metasome and the elongate and curved leg 5.

In BK angustus sp. nov. the antenna is armed with 7 setae and leg 5 is very small. Both of these features are shared with three congeners, B. dẚstẚnctus, B. mẚllarẚ Ooishi, 2014, and B. tuberculatus sp. nov. However, all three of these species bear 5 setae on the second endopodal segment of right leg 4, and differ from B. angustus sp. nov. which has 2 spines and 3 setae on that segment of right leg 4.

Figures

FIG. 54. Bçtryllçphẚlus angustus sp. nov., female. A, habitus, left; B, habitus, dorsal; C, posterior part of body, ventral; D, caudal ramus; E, antennule; F, left antenna; G, distal part of right antenna; H, mandible; I, maxillule. Scale bars: A, B, 0.2 mm; C, 0.1 mm; D-I, 0.02 mm.

FIG. 55. Bçtryllçphẚlus angustus sp. nov., female. A, maxilla; B, maxilliped; C, right leg 1; D, left leg 1; E, right leg 2; F, left leg 2; G, genital aperture. Scale bars: 0.02 mm.

FIG. 56. Bçtryllçphẚlus angustus sp. nov., female.A, right leg 3; B, left leg 3; C, right leg 4; D, left leg 4; E, F, leg 5. Scale bars: A-D, 0.02 mm; E, F, 0.05 mm.