Pseudanthessius excertus Kim 2014, n. sp.

Pseudanthessius excertus n. sp. (Figs. 9, 10)

Material examined. Six from polychaetes (mainly Hydroides ezoensis Okuda) epizoic on shells of the oyster Crassostrea gigas (Thunberg) attached to the wharf in Gangneung Port (37 46′15′′N, 128 57′08′′E), depth about 50 cm, 21 November 2012. Holotype (, NIBRIV 0000286631) and paratypes (3

32) have been deposited in the National Institute of Biological Resources (NIBR), Incheon. Dissected paratypes (2

Female. Body (Fig. 9A) rather small. Body length 945 Μm in dissected and figured paratype (in other 2 measured specimens 868 and 968 Μm). Prosome 584 Μm long. Cephalothorax 403 Μm, nearly globular, as dorsoventrally deep as wide, with weak dorsal suture delimiting cephalosome and first pedigerous somite. Second pedigerous somite broad, with prominent, tapering lateral projection on both side. Third and fourth pedigerous somite much narrower and shorter than second pedigerous somite, 240 and 154 Μm wide, respectively, with round lateral margins. Urosome (Fig. 9B) 5-segmented. Fifth pedigerous somite 117 Μm wide. Genital double-somite 140 132 Μm, slightly longer than wide, with broad lateral expansion, widest at 0.4 region of somite length and gradually narrowing posteriorly from widest region; genital aperture large and locating dorsally. Three free abdominal somites 37 72, 26 60, and 51 60 Μm, respectively. Anal somite twice as long as penultimate abdominal somite, with large anal region. Caudal ramus (Fig. 9C) 71 26 Μm (ratio 2.73: 1), slightly narrowing distally, with 6 setae; outer lateral seta (seta II) locating at 0.6 region of ramus length.

[table omitted]

Rostrum (Fig. 9D) stout, as long as wide; proximal half with parallel lateral margins and distal half strongly tapering, with rounded posterior apex. Antennule (Fig. 9E) 183 Μm long and 7-segmented; armature formula: 4, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna (Fig. 9F) 4-segmented; last segment 33 Μm (ratio 1.65: 1); armature formula: 1, 1, 2+claw, and 3+4 claws; claws slender; outermost one of 4 terminal claws distinctly longer than other 3.

Labrum (Fig. 9G) with elongate posterior lobes bearing hemi-circular notch on medial margin and membranous flange along posterior margin and distal part of medial margin. Mandible (Fig. 9H) curved in a right angle, with 1 broad, transparent scale on convex outer corner at base of blade; medial margin of blade with about 10 spines near middle of margin and fine spinules distally; outer margin of blade smooth, only with delicate striations; distal part of blade blunt, with small point, without lash. Paragnath as small digitiform process (indicated by dotted line in Fig. 9G). Maxillule (Fig. 9I) lobate, with 1 lateral and 3 distal setae; 2 larger ones of latters unilaterally spinulose in distal half. Maxilla (Fig. 10A) 2-segmented; proximal segment expanded but unarmed; distal segment armed with 3 setae: medial margin seta (seta I) large, almost extending to distal end of distal lash of segment; anterior seta (seta II) stout, spiniform, and spinulose along medial margin; proximal seta (seta III) small and blunt at tip; distal lash of second segment relatively short, armed with 2 rows of thick teeth on convex side and with setules along distal region. Maxilliped (Fig. 10B) 3-segmented; first segment unarmed; middle segment slightly longer than wide, with 1 massive spine bearing 4 teeth, 1 small seta, and 1 longitudinal row of minute spinules; distal segment terminating in spiniform process bearing 4 or 5 teeth, with 1 stout spine bearing 5 teeth.

Legs 1 (Fig. 10C), 2, and 3 (Fig. 10D) with 3-segmented rami. Leg 4 (Fig. 10E) with 3-segmented exopod and 1-segmented endopod. Third exopodal segment of leg 3 characteristically armed with 3 spines and 5 setae. Leg 4 with minute inner seta on coxa; endopod 46 15 Μm, about 3 times as long as wide, with several setules on outer margin but lacking notch or process on outer margin. Armature formula of legs 1-4 as follows:

Leg 5 represented by a lobe bearing 1 dorsal seta proximally and 1 spine and 1 seta distally (Fig. 10F). Leg 6 represented 2 small setae (distal one of them proximally thick and distally thin) and 1 dentiform process on genital operculum (Fig. 10F)

Male. Unknown.

Etymology. The specific name extcertus is a Latin meaning “projecting” which alludes to the prominent lateral projections on the second pedigerous somite of the new species.

Remarks. Two extraordinary morphological features of Pseudanthessius excertus n. sp. may typify this species: the third exopodal segment of leg 3 is armed with 3 spines and 5 setae (armature formula II, I, 5), and the second pedigerous somite has a prominent lateral process on both sides. The second feature allows the new species to be readily identified without dissection, because no similar process on the second pedigerous somite has been reported in Pseudanthessius. Within the genus an example of the first feature is known in P. asper Kim, 2009 which was described as an associate of a sponge in Madagascar (Kim, 2009). Otherwise, P. asper, which has a peculiar body form, is not related to P. excertus n. sp.