Botryllophilus pentachaetus Kim & Boxshall 2021, sp. nov.

Botryllophilus pentachaetus sp. nov. (Figs. 51-53) Type material. Holotype ♀ (MNHN-IU-2009-5057), 2 ♀♀ paratypes (intact, MNHN-IU-2018-1970) and ♀ para- type (dissected, MNHN-IU-2014-17374) from budẚstçma vẚrẚde Tokioka, 1955 (MNHN-IT-2008-4294 = MNHN A3 / EUD/344); Danau A Gam lake mangrove (marine lake), Raja Ampat, West Papua, Indonesia, Stn DAG 043 (00º26.518’N, 130º41.134’E), depth 0.5 m, F. Monniot coll., 23 November 2007. Etymology. The name of the new species is derived from the Greek pent (=five) and chaet (=a bristle), referring to the presence of five setae on the antenna. Description of female. Body (Fig. 51A, B) slightly asymmetrical, consisting of moderately swollen anterior part and narrower, cylindrical posterior part: body length 1.48 mm in dissected largest specimen and 1.30 mm in smallest specimen. Anterior part of body nearly elliptical, 860×468 μm, roundly expanded dorsally, unsegmented, without any constriction or trace of suture; dorsal cephalic shield distinct. Posterior part of body occupying 43% of total body length, consisting of genital somite and 4 abdominal somites. Genital somite 154×231 μm; genital apertures positioned dorsally. Four abdominal somites 115×173, 119×148, 104×135, and 135×115 μm, respectively. Caudal ramus (Fig. 51C) armed with 4 claws and 1 seta (lacking inner seta); 1 of outer distal claws blunt. Rostrum absent. Antennule (Fig. 51D) 4-segmented; armature formula 13, 2+aesthetasc, 4, and 7+aesthetasc; first segment subdivided by incomplete suture line on one surface; setae on first segment comprising 5 large and 8 small ones. Right antenna (Fig. 51E) 4-segmented, including obscure coxa; proximal 3 segments unarmed; second endopodal segment 3.6 times longer than wide (69×19 μm), characteristically armed with 5 setae, 1 on inner margin and 4 on distal margin. Left antenna different from right antenna in having shorter second endopodal segment and longer outer distal setae. Labrum with broad posteromedian lobe. Mandible (Fig. 51F) with coxal gnathobase (Fig. 51G) bearing 3 teeth, distal tooth bifurcate; palp with 9 setae arranged as 3, 2, and 4. Maxillule (Fig. 51H) consisting of precoxa and unsegmented palp; precoxal arthrite bearing 6 distinct setae; palp bearing 2 medial and 3 outer setae on basis region; endopod completely fused with basis, armed with 3 setae. Maxilla (Fig. 51I) indistinctly 3-segmented with 3 setae on each segment. Maxilliped (Fig. 51J) 4-segmented; broad syncoxa unarmed; basis with 2 small setae; first endopodal segment unarmed; second segment with 1 small seta and 1 tooth-like process on inner margin; terminal claw simple, slightly shorter than second endopodal segment. Legs 1-4 (Figs. 52 A-F, 53A, B) biramous, asymmetrical; with unsegmented exopods and 2-segmented endopods; coxa unarmed; basis with outer seta. Basis of leg 2-4 with patch of spinules at inner distal corner. First endopodal segment of right and left leg 1 bearing setulose tubercle on anterior surface (arrowed in Figs. 52A and B). One of setae on second endopodal segment of right and left leg 1 markedly smaller than other setae on same segment; second endopodal segment of right legs 2-4 with 1 spine in addition to setae. Outer subdistal seta on second endopodal segment of left legs 1-4 small, setule-like. Setal formula for right and left legs 1-4 as follows: Leg 5 (Fig. 52G) very small, lobate, slightly wider than long (54×60 μm), armed with 4 small setae (1 proximal and 3 distal) of subequal lengths. Leg 6 (Fig. 52H) represented by 1 spinule and 1 spiniform process on genital operculum. Male. Unknown. Remarks. The most conspicuous diagnostic feature of B. pentachaetus sp. nov. is the presence of only 5 setae on the antenna, this feature is shared only with B. nçrvegẚcus within the genus. Bçtryllçphẚlus nçrvegẚcus cannot be confused with B. pentachaetus sp. nov. or any other species of Bçtryllçphẚlus as it displays unique features such as the extremely swollen metasome and the strongly curved leg 5. Another conspicuous feature of B. pentachaetus sp. nov. is the small size of its leg 5, which is wider than long and comparable only with the smallest known leg 5, in B. kçzlçffẚ, which is 1.33 times longer than wide (Ooishi, 2014c). The combination of the numbers of armature elements on the rami of legs 1-4 of B. pentachaetus sp. nov. also is unique within the genus.Published as part of Kim, Il-Hoi & Boxshall, Geoff A., 2021, Copepods (Cyclopoida) associated with ascidian hosts: Ascidicolidae, Buproridae, Botryllophilidae, and Enteropsidae, with descriptions of 84 new species, pp. 1-286 in Zootaxa 1 on pages 84-87, DOI: 10.11646/zootaxa.4978.1.1, http://zenodo.org/record/482044