Schizoproctus fusiformis Kim & Boxshall 2021, sp. nov.

Schizoproctus fusiformis sp. nov.

(Figs. 69, 70)

Type material. Holotype ♀ (MNHN-IU-2018-1978, dissected and mounted on a slide) from mçlycarpa fẚbrçsa (Stimpson, 1852); off Tromsø, Norway, NORBI Cruise, RV “Jean Charcot”, Stn CP 11 trawl, (69°52’N, 17°08’E), depth 250-300 m, Bouchet & Warén coll., 01 July 1975.

Etymology. The specific name refers to the fusiform anterior part of body of the new species.

Description of female. Body (Fig. 69A) straight, with fusiform anterior part and narrower posterior part; body length 1.40 mm. Anterior part 800×440 μm, not segmented, but cephalosome and 4 metasomal somites discernible by weak cephalic shield and 4 dorsal tergites. Fifth pedigerous somite not defined from fourth pedigerous somite. Posterior part of body consisting of genital somite and 4-segmented abdomen. Genital somite 250×220 μm, gradu- ally narrowing posteriorly; genital apertures positioned dorsally. Four abdominal somites 82×131, 90×118, 77×105, and 122×98 μm, respectively. Caudal ramus (Fig. 69B) wider than long, armed with 4 spines and 1 seta; outer distal spine very small, nipple-shaped, not articulated from ramus.

Rostrum absent. Antennule (Fig. 69C) short, 5-segmented; first segment broad; distal segments gradually narrowing; armature formula 12, 5, 3, 4, and 7+aesthetasc. Antenna (Fig. 69D) 4-segmented; coxa, basis, and first endopodal segment unarmed; second endopodal segment about 4 times longer than wide (95×24 μm), with partial subdivision on inner side at distal third; armed with 8 spines (4 on inner margin and 4 on distal margin); spines on inner margin shorter than width of segment; longest second outer spine on distal margin 65 μm long, twice as long as second longest adjacent spine.

Labrum (Fig. 69E) weak, thin-walled, strongly tapering towards rounded distal margin. Mandible (Fig. 69F) with 3 teeth on coxal gnathobase; palp with 9 setae and 1 large medial swelling; 3 outer proximal setae pinnate, but remaining distal setae naked. Maxillule (Fig. 69G) consisting of precoxa and palp; precoxa with 7 setae on arthrite, proximalmost seta bluntly tipped; palp consisting of coxa, basis, and endopod; coxa with vestigial seta on epipodite; basis with 2 setae on medial margin, 3 setae on outer margin (proximal seta naked, others pinnate), and bilobed distal tubercle; endopod distinctly articulated from basis, with 3 setae on distal margin. Maxilla (Fig. 69H) indistinctly 3-segmented with 9 setae (1 distal seta minute). Maxilliped (Fig. 69I) 4-segmented, but second endopodal segment and terminal claw completely fused; syncoxa much broader than long, with 2 setae on inner margin; basis with 2 widely isolated setae; first endopodal segment short and unarmed; terminal segment (fused second endopodal segment and terminal claw) strongly curved, with 2 small setae proximally and 1 small subterminal denticle.

Legs 1 and 2 (Fig. 70A, B) biramous with 1-segmented rami; endopods much smaller than exopods. Legs 3 and 4 uniramous with 1-segmented exopod; endopod lacking; third outer spine rudimentary. Armature formula for legs 1-4 as follows:

[table omitted]

Leg 5 (Fig. 70D, E) 1-segmented, subrectangular: left leg 5 (Fig. 70D) 2.93 times longer than wide (123×42 μm) with 1 proximal and 4 distal setae: right leg 5 (Fig. 70E) 2.96 times longer than wide (142×48 μm), with 1 proximal and 3 distal setae; right leg 5 accompanied by 1 tubercle on fifth pedigerous somite near base of leg segment. Leg 6 not discernible.

Male. Unknown.

Remarks. All known species of Schẚzçprçctus have biramous legs 1-4. Therefore, the possession of uniramous legs 3 and 4, lacking an endopod, in S. fusẚfçrmẚs sp. nov. serves to distinguish the new species from all congeners. The armature patterns of legs 1 and 2 also are unique within the genus (Table 3). The fusion of the second endopodal segment with the terminal claw in the maxilliped of S. fusẚfçrmẚs sp. nov. is a notable feature shared with the type species, S. ẚnflatus, and with S. frẚgẚdus sp. nov. described below. Other morphological features of these two species also differ from those of S. fusẚfçrmẚs sp. nov., such as the broad circular shape of their leg 5.