Enteropsis tasmanica Kim & Boxshall 2021, sp. nov.

Enteropsis tasmanica sp. nov.

(Figs. 183)

Type material. Holotype ♀ (MNHN-IU-2014-21588, dissected and mounted on a slide) from Styela pçlypes Monniot C., Monniot F. & Millar, 1976; Tasman Sea, RV “Galathea” Expedition, Stn 601 (45°51’S, 164°32’E), depth 4400 m, 14 January 1952.

Etymology. The name of the new species is derived from its type locality, the Tasman Sea,

Description of female. Body (Fig. 183A) fusiform, smooth, straight, unsegmented. Body length 3.15 mm; maximum width 0.89 mm (at anterior third). Cephalosome indistinctly defined from trunk by faint lateral wrinkles; posterior third of body tapering posteriorly; leg 4 positioned at 77% of body length. Abdomen (Fig. 183B, C) about 160×220 μm, discernible from trunk by weak constriction. Genital areas (Fig. 183B, C) located laterodistally on trunk, anterior to abdomen.Anal prominence weak, bilobed. Caudal rami narrow, widely separated from each other; each ramus (Fig. 183D) about 2.6 times longer than wide (94×36 μm), shorter than abdomen, tipped with 1 naked spine (42 μm long).

Rostrum (Fig. 183E) semicircular, bearing 8 sensilla (4 proximal, 2 middle, and 2 subdistal). Antennule (Fig. 183F) broad, tapering, unsegmented, about 110×73 μm, and ornamented with 3 setules; armed with 10 unequal setae (4 larger and 6 small, setule-like), 2 of larger setae articulating with swollen base. Antenna (Fig. 183G) unsegmented, about 2.3 times longer than wide (132×58 μm), with tapering proximal two-thirds and narrow distal third, spinulose in distal half; armed with 1 subdistal and 1 distal, sparsely spinulose spines; lengths of subdistal and distal spines 42 and 55 μm, respectively.

Labrum (Fig. 183H) broad, spinulose on ventral surface and along convex posterior margin; armed with 6 broad, medially curved, spinulose setiform processes, medial 2 longer and broader than lateral 4. Mandible absent. Maxillule (Fig. 183I) distally bilobed; inner lobe longer but narrower than outer lobe, tipped with 2 spinulose spines, 38 and 27 μm long; outer lobe spinulose, armed with 3 equal spines 28 μm long (2 on distal margin and 1 on medial margin). Maxilla (Fig. 183J) 2-segmented; proximal segment broad with 1 small tubercle on medial margin; distal segment terminating in strong claw, with 1 small seta proximally on lateral margin. Maxilliped absent.

Leg 1 (Fig. 183K) 2-segmented, both segments much wider than long; distal segment bearing rudimentary exopod and endopod; exopod sclerotized inside; endopod fleshy, shorter than exopod. Legs 2-4 same as leg 1. Leg 5 absent. Leg 6 probably represented by 2 minute spinules in genital area (Fig. 183C).

Male. Unknown.

Remarks. The labrum of bK tasmanẚca sp. nov. is armed with 6 setiform processes. Five other species of bnterçpsẚs (b. capẚtulata, b. fusẚfçrmẚs, b. geçrgẚana, b. rçscçffensẚs, and b. arctẚca) also have 6 (or 5 or 6) processes on the labrum, like b. tasmanẚca sp. nov. The first four of these can be readily distinguished from the new species by the following characters: b. capẚtulata has rudimentary caudal rami and a distinctly 2-segmented antenna; b. fusẚfçrmẚs lacks caudal rami and has a claw-like distal segment of the antenna; b. geçrgẚana has a longer, 4-segmented genitoabdomen and a 2-segmented antennule (Illg & Dudley, 1980); and b. rçscçffensẚs has a claw-like distal part of the antenna and lacks a rostrum (Ooishi, 2008b).

The remaining species, b. arctẚca, is associated with several species of solitary ascidians in the White Sea (Marchenkov, 1994), and appears to be closely related to b. tasmanẚca sp. nov. However, in b. arctẚca, the body is cylindrical (cf. fusiform in the new species), the caudal rami are vestigial with its terminal element not articulated from the ramus (cf. 2.6 times longer than wide), the antenna is 2-segmented (cf. unsegmented), the outer lobe of the maxillule is armed with 3 processes (cf. spines), and the 6 setiform processes on the labrum are small and subequal in length (cf. large, with median pair distinctly longer than lateral 4). These differences are sufficient to differentiate b. tasmanẚca sp. nov. from b. arctẚca.

Genus Mychophilus Hesse, 1865

Diagnosis. Female: Body vermiform, unsegmented. Anus positioned dorsally, anterior to genital apertures. Caudal rami rudimentary, tipped with 1 small seta. Rostrum weakly developed or absent. Antennule small, 1- or 2-segment- ed, armed with few setae. Antenna 1- to 3-segmented; terminal segment usually claw-like. Labrum bearing 3 to 6 setiform processes (lacking processes in M. capẚllatus Kim I.H. & Moon, 2011; labrum unknown in M. fallax Stock, 1967). Mandible absent. Maxillule bilobed, with 0 or 2 setiform processes on inner lobe and 2 or 3 processes on outer lobe. Maxilla lobate, 1- or 2-segmented, tipped with 1 seta; if 2-segmented, distal segment very small (maxilla of M. capẚllatus unusual, bnterçpsẚs - type). Legs 1-4 similar to those of bnterçpsẚs. Legs 5 and 6 absent.

Male (of M. rçseus): Body cyclopiform, with clear prosome-urosome division. Prosome consisting of cephalosome and first to fourth pedigerous somites. Urosome 6-segmented, including fifth pedigerous somite. Caudal rami armed with 6 setae. Rostrum well-developed. Antennule 6-segmented; armature formula 13, 2, 2, 2, 1, 6+2 aesthetascs. Antenna 3-segmented; first segment with 1 seta; terminal segment spiniform. Labrum rudimentary. Mandible absent. Maxillule small, 2-segmented, with unarmed proximal and 3 setae-bearing distal segment. Maxilla as in female. Maxilliped absent. Legs 1-4 biramous with 2-segmented protopod; coxae unarmed; basis with outer seta. Leg 1 exopod 2-segmented; other rami of legs 1-4 all 3-segmented. First endopodal segment of leg 1 unarmed. Second endopodal segment of leg 4 with 2 medial setae. Armature formula for legs 1-4 as follows:

[table omitted]

Leg 5 represented by 2 separated setae on surface of fifth pedigerous somite. Leg 6 absent.

Type species. Mychçphẚlus rçseus Hesse, 1866 by original monotypy.

Remarks. Ooishi (2008c) redescribed both sexes of the type species of Mychçphẚlus, M. rçseus Hesse and M. palmatus López-González & Conradi, 1996. Subsequently Kim I.H. and Moon (2011) added a fourth species, M. capẚllatus Kim I.H. & Moon, 2011. Mychçphẚlus has been characterized by the dorsally displaced anus positioned close to the level of genital apertures and by the lobate, unsegmented maxilla (Illg & Dudley, 1980; Boxshall & Halsey, 2004). Mychçphẚlus is closely related to bnterçpsẚs. Both genera share the same structure of the swimming legs and MK capẚllatus exhibits a Mychçphẚlus - type position of the anus combined with an bnterçpsẚs - type of maxilla, which is 2-segmented and bears a strong claw on the distal segment. Mychçphẚlus capẚllatus was tentatively included in Mychçphẚlus but its placement in this genus may need to be reviewed. Re-analysing of the relationships between these two genera will be facilitated by the discovery of the male of bnterçpsẚs, which is currently unknown.