Schizoproctus tripartitus Kim & Boxshall 2021, sp. nov.
Creators: name: Kim, Il-Hoi
name: Boxshall, Geoff A.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Cyclopoida
Ascidicolidae
Schizoproctus
Schizoproctus tripartitus

description: Schizoproctus tripartitus sp. nov.   
(Figs. 71, 72)  
 Type material. Holotype ♀ (MNHN-IU-2018-1979) and 1 ♀ paratype (MNHN-IU-2014-17378, dissected) from Araneum sẚgma Monniot C. & Monniot F., 1973 (syntypes: MNHN-IT-2008-821, MNHN-IT-2008-826); NE Atlantic, BIACORES cruise, RV “Jean Charcot”, Stns DS 126, CHG245, CHG-F249, depth 3360-4690 m, Boury-Esnault coll., October-November 1971.   
 Etymology. The name of the new species refers to the 3-segmented abdomen of the female.   
 Description of female. Body (Fig. 71A) slightly dorsoventrally depressed, with thin exoskeleton; body length 0.98 mm; width 0.35 mm across cephalosome. Anterior part of body gradually narrowing posteriorly, consisting of cephalosome and 4 indistinctly separated metasomites; fourth metasomite consisting of completely fused fourth and fifth pedigerous somites. Posterior part of body (Fig. 71B) consisting of genital somite and 3-segmented abdomen. Genital somite about 2.1 times wider than long (82×170 μm), distinctly wider than abdomen; genital apertures large, located dorsally. Abdomen with parallel lateral margins; first to third abdominal somites 73×118, 65×120, and 110×120 μm, respectively. Caudal rami divergent; each ramus (Fig. 71C) about 1.7 times longer than wide (60×36 μm), with shorter outer and longer inner margins; armed with 5 straight claws and 1 seta; inner dorsal claw 12 μm long, accompanied by several spinules near base; lengths of 4 distal claws 27, 37, 28, and 10 μm.   
Rostrum (Fig. 71D) strongly tapering towards blunt apex; with rows of fine spinules ventrally along lateral margins. Antennule (Fig. 71E) 5-segmented; first segment extremely inflated; armature formula 11, 5, 3, 4, and 7+aesthetasc. Antenna (Fig. 71F) consisting of coxa, basis, and 2-segmented endopod; coxa and first endopodal segment unarmed; basis unarmed, but ornamented with 2 rows of fine spinules on inner distal surface; second endopodal segment about 3.2 times longer than wide (77×24 μm) and ornamented with 4 rows of fine spinules; armed with 8 spines (spines on inner margin shorter than width of segment), including 2 outer spines on distal margin longer than segment width, 38 (outer) and 41 μm long (inner).  
Labrum (Fig. 71G) weak, flexible, semicircular. Mandible (Fig. 71H) with 4 major teeth on coxal gnathobase; palp with large tubercle near middle and 8 setae arranged as 3, 1, 2, and 2. Maxillule (Fig. 48I) consisting of precoxa and palp; precoxa with 8 unequal setae on arthrite, 2 distal setae rudimentary; palp consisting of coxa, basis, and endopod; armed with 1 vestigial seta on coxal epipodite, 2 medial and 3 outer setae on basis, and 3 setae on endopod; digitiform lobe present distally on basis. Maxilla (Fig. 71J) indistinctly 3-segmented, with 2, 3, and 4 setae on first to third segments, respectively. Maxilliped (Fig. 72A) 4-segmented; syncoxa and basis each with 2 small setae; first endopodal segment short and unarmed; second endopodal segment with 2 small setae subdistally; terminal claw shorter than second endopodal segment, with 1 small denticle proximally on inner margin.  
Legs 1-4 biramous with 1-segmented rami (Fig. 72 B-D); coxa unarmed; basis with outer seta and ornamented with patch of spinules on inner side of anterior surface, this patch of spinules becoming smaller from legs 1 to 4. Distalmost seta on endopod of leg 1 small and spiniform. Distal spines on endopods of legs 2-4 small. Leg 4 similar to leg 3, but endopod bearing only 1 spine and 1 seta. Inner subdistal seta on exopod of legs 1-4 rudimentary. Distal spines on endopod of legs 2 and 3 small. Armature formula for legs 1-4 as follows:  
     Coxa  Basis  Exopod  Endopod      Leg 1  0-0  1-0  V, 1  6      Leg 2  0-0  1-0  IV, 1  II+ 3      Leg 3  0-0  1-0  IV, 1  II+ 1      Leg 4  0-0  1-0  IV, 1  I+ 1      
Leg 5 (Fig. 72E) arising on posterodorsal surface of double metasomite (comprising fused fourth and fifth pedigerous somites); roughly quadrate, lamellate, longer than wide (159×130 μm,); armed with 4 setae, 1 distinctly larger than other 3. Leg 6 represented by 2 small spinules on genital operculum.  
 Male. Unknown.   
 Remarks. The setal combination on the endopods of legs 1-4 (6-5-3-2) of SK trẚpartẚtus sp. nov. is unique within the genus (see Table 3) and this allows the new species to be distinguished from all of its congeners. The 3-segmented abdomen of S. trẚpartẚtus sp. nov. is a feature shared with S. vestẚtus (Sars, 1921) and S. mçllẚs sp. nov. described below. These two species are easy to distinguish from S. trẚpartẚtus sp. nov. by the setation of endopods of legs 1-4 (the combination on the endopods of legs 1-4 is 3-2-?- 6 in S. vestẚtus (the setation of the endopod of leg 3 is unknown in S. vestẚtus) and 7-6-4- 3 in S. mçllẚs sp. nov.). In addition there are two other significant differences, as follows: (1) the body length is 1.80 mm in S. vestẚtus according to Sars (1921), and 1.94 mm in S. mçllẚs sp. nov., in contrast to 0.98 mm in S. trẚpartẚtus sp. nov., and (2) the exopods of legs 1-4 of S. vestẚtus and S. mçllẚs sp. nov. are armed with 6 spines each, in contrast to 5 spines plus 1 seta in leg 1 and 4 spines plus 1 seta in legs 2-4 of S. trẚpartẚtus sp. nov.
description: 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 112-115, DOI: 10.11646/zootaxa.4978.1.1, http://zenodo.org/record/4820443