Hosekia symmetrinuda ( Edmondson, 1951 ), 2024

Ng, Peter K. L., Ahyong, & Shane T., 2024, Redefining Lophoplax Tesch, 1918: recognising Myopilumnus Deb, 1989, and the establishment of three new genera, Hosekia, Takedaplax, and Striacoeloma (Crustacea: Brachyura: Pilumnidae), Raffles Bulletin of Zoology 72, pp. 335-355 : 344-347

Hosekia symmetrinuda ( Edmondson, 1951) , new combination

( Figs. 6 , 7 )

Pseudocryptocoeloma symmetrinudus Edmondson, 1951: 233 , fig. 34; Serène, 1968: 86; Ng, 1987: 79, 97; Ng et al., 2008: 144; Marumura & Takeda, 2012: 192, figs. 2A, 3, 4; Maenosono, 2019: 32, figs. 8B, 10, 13B, 14K, L.

Lophoplax symmetrinudus — Takeda & Kurata, 1984: 201; Takeda & Marumura, 1995: 90; Poore & Ahyong, 2023: 680; Ng & Rahayu, 2023: 444, fig. 12.

Material examined. Holotype: BPBM 5109 , male (6.5 × 5.0 mm), Siufaga, Tau, Samoa, low tide, table reef, coll. W. Harris, 1937. Others: RUMF-ZC-5199, 1 male (7.6 × 4.2 mm), Bise, Motobu, Okinawa, Ryukyus, Japan, coll. T. Maenosono, 10 February 2016; RUMF-ZC-7536, 1 female (9.7 × 6.9 mm), Odo Beach, Itoman, Okinawa, Ryukyus , Japan, coll. T. Maenosono , 7 April 2020.

Diagnosis. As for genus.

Description. Carapace transversely ovate-subhexagonal; frontal and anterolateral margins with scattered tufts of short and long setae, not brush-like, not concealing margins; regions well demarcated with areoles smooth, prominent: epigastric areoles distinct; protogastric areole well developed, extending obliquely to branchial region, approximately separated by median constriction; cardio-branchial areole transversely ovate, well-developed; gastro-cardiac region depressed, with grooves barely visible ( Figs. 6A, B , 7A, C, D ); intestino-branchial areoles prominent, transversely ovate, one on each side of low intestinal region; posterior carapace margin cristate, adjacent to prominent intestino-branchial areole, forming narrow channel extending to beginning of sub-branchial region; no ridges on sub-branchial region ( Figs. 6A, B , 7A, C, D ). Subhepatic and suborbital regions slightly rugose to almost smooth; pterygostomial region with numerous closely packed small granules ( Fig. 6C–E ). Frontal margin bilobed, gently convex, with narrow, small median notch, without lateral lobe ( Figs. 6A–D , 7C, D ). Supraorbital margin short, sinuous, with low lobe on posterior half (formed by anterior margin of hepatic areole), without fissure or cleft ( Figs. 6A , 7C, D ). Orbit dorsal, supraorbital margin appears confluent with general carapace outline, eyes clearly visible in dorsal view; eyes mobile, ocular peduncle short, filling orbit ( Fig. 6B–D ). Anterolateral margin with 3 distinct teeth (including external orbital tooth), first 2 broadly triangular with cristate margin, last tooth lower, more rounded; distinct groove visible adjacent to margin, formed with outer margin of hepatic lobe ( Figs. 6A , 7C, D ). Posterolateral margin gently convex, smooth, unarmed; margins distinctly converging towards posterior carapace margin ( Figs. 6A , 7C, D ). Antennules rectangular, relatively large; antennules folding laterally ( Fig. 6C, D ). Basal antennal article subquadrate; flagellum enters orbital hiatus ( Fig. 6C, D ). Epistome with biconcave posterior margin, median lobe triangular with very short median fissue ( Fig. 6C, D ). Endostome distinct, sloping gradually posteriorly into buccal cavern, endostomial ridges, short, low ( Fig. 6C, D ).

Third maxilliped with ischium relatively short, subquadrate, length 1.2× width; merus quadrate, anterolateral angle gently auriculiform. Exopod relatively stout, tip reaching to just before distal edge of merus ( Figs. 6D, E , 7B ).

Male thoracic sternum surface relatively smooth; sternites 1 and 2 completely fused, lateral margins gently concave; sternites 3 and 4 fused with only very shallow median groove and lateral notches visible; suture between sternites 2 and 3 gently concave towards buccal cavity ( Figs. 6D, E , 7E ). Tubercle of male pleonal locking mechanism on anterior third of somite 5 ( Fig. 6E ).

Adult male chelipeds symmetrical, stout ( Fig. 7A ). Basis-ischium fused but suture visible, flexor margin with low granules ( Fig. 7E ). Merus short, surface slightly rugose; flexor and extensor margins with small granules; inner distal angle sharp visible but not with subdistal angle not elongate ( Fig. 7E ). Carpus surface granulate; inner distal angle with low sharp tooth ( Fig. 7A ). Chela with dorsal surface densely covered with granules; inner surface almost smooth; margins of chela with scattered long and short setae, not dense or brush-like; fingers relatively slender, shorter than palm, pigmented brown along distal ⅔; occlusal margins with low teeth, forming small gape when closed ( Fig. 6F ).

Ambulatory legs short, P4 longest, about 1.2× carapace width; P4 merus length about 2.2–2.4× height, less than half carapace width; outer surface slightly rugose to almost smooth; coxa rounded; merus short, extensor margin not cristate, surface of P2–5 gently convex, without ridge; P2–5 carpus smooth, with low submarginal ridge, lowest in P5; propodus laterally flattened, unarmed, relatively short in P2–4, shortest in P5; P2–4 dactylus falciform, unarmed, P5 dactylus shorter, tip slightly upturned; dactylo-propodal lock distinct ( Fig. 7A ).

Male pleon triangular, all somites and telson free; somite 1 broadly rectangular, reaching base of P5 coxae; somite 2 transversely narrower than somite 1, trapezoidal; somites 3–6 trapezoidal, gradually decreasing in width. Telson wider than long, rounded-subtriangular, lateral margins weakly convex, longer than somite 6 ( Fig. 7E ).

G1 strongly sinuous, distally gently curved outwards, tip mucronate; with short row of setae subdistally. G2 sigmoid, about ¼ length of G1.

Female pleon longitudinally ovate; with 6 somites and telson, all free; not completely covering thoracic sternum; somite 1 broadly subrectangular, just reaching base of P5 coxae; somite 2 transversely narrower than somite 1, trapezoidal; somite 3 widest, somite 4 as wide as somite 2; somites 3–6 trapezoidal, gradually decreasing in width; telson triangular with convex lateral margins, longer than somite 6.

Sternopleonal cavity shallow ( Fig. 7F ; vulva large, obliquely ovate, covering anterior ⅔ on sternite 6, without vulvar projections ( Fig. 7F ).

Remarks. Hosekia symmetrinuda is a reef species currently known only from Samoa and southern Japan. The specimens from both locations are nearly identical and we are confident they are conspecific. Nothing else is known about its biology except that it occurs in the intertidal zone ( Maenosono, 2019).

Figures

Fig. 6. Hosekia symmetrinuda (Edmondson, 1951), new combination, holotype male (6.5 × 5.0 mm) (BPBM 5109), Samoa. A, dorsal view of carapace (right side denuded); B, subfrontal view of cephalothorax (right side denuded); C, frontal view of cephalothorax (right side denuded); D, frontal view showing buccal cavity; E, buccal cavity, anterior thoracic sternum and sternopleonal cavity; F, left chela.

Fig. 7. Hosekia symmetrinuda (Edmondson, 1951), new combination. A–C, E, male (7.6 × 4.2 mm) (RUMF-ZC-5199), Japan; D, E, female (9.7 × 6.9 mm) (RUMF-ZC-7536), Japan. A, dorsal habitus (right side denuded); B, right third maxilliped; C, dorsal view of carapace (right side denuded); D, dorsal view of carapace (not denuded); E, male buccal cavity, anterior thoracic sternum and pleon; F, female sternopleonal cavity and vulvae.