Rhynchoplax messor Stimpson, 1858

Poore, Gary C. B., Guinot, Danièle, Komai, Tomoyuki & Naruse, Tohru, 2016, Reappraisal of species attributed to Halicarcinus White, 1846 (Crustacea: Decapoda: Brachyura: Hymenosomatidae) with diagnosis of four new genera and one new species from New Ireland, Papua New Guinea, Zootaxa 4093 (4), pp. 480-514 : 491-493

Rhynchoplax messor Stimpson, 1858

( Fig. 3 )

Rhynchoplax messor — Stimpson, 1858: 109.— Stimpson 1907: 148. — Tesch 1918: 18. — Sakai 1934: 289, fig. 5a. — Sakai 1935: 70, fig. 27. — Sakai 1938: 197 –198, fig. 1, pl. 20 fig. 2. — Sakai 1965: 63, fig. 9, pl. 25 fig. 2. –– Sakai 1976: 147 –148, textfig. 76c (English text), pl. 46 fig. 2, 92 (Japanese text). –– Miyake 1983: 192, pl. 64 fig. 6.

Halicarcinus messor— Lucas 1980: 163, fig. 9A. — Dai & Yang 1991: 116 –117, fig. 59. — Kim 1992: 257. –– Ng et al. 1999: 88– 89, fig. 4.

Not Rhynchoplax messor — Yokoya 1928: 761 –762, fig. 1 [= Stimpsoplax setirostris ( Stimpson, 1858) ].

Material examined. Japan. Chiba Prefecture, Ubara, Katsuura, intertidal, 3 June 1996, coll. E. Nishi, CBM-ZC 3507 (1 male, 4.8 mm). Hasama, Tateyama, intertidal, 22 July 2001, coll. T. Komai, CBM-ZC 6024 (1 ovigerous female, 4.3 mm). [Shizuoka Prefecture], S[h]imoda, AM P.10497 (3 males, largest 3.3 mm; 3 females, largest 3.0 mm, 1 ovigerous female, 3.0 mm). Wakayama Prefecture. Kushimoto, Shionomisaki, Naminoura, 9 m, 16 May 1978, SCUBA diving, coll. S. Yamaguchi, CBM-ZC 4163 (1 ovigerous female, 4.0 mm).

Diagnosis. Carapace 1.1 times as wide as long; subhepatic region inflated, forming low elevation visible in dorsal view, with 2 conspicuous tubercles inferior to subhepatic elevation (not visible in dorsal view); anterolateral margin with minute tubercles (sometimes greatly reduced); epibranchial spine present, sharp; dorsum with gastrocardiac groove, cardiac median ridge. Male rostrum about 0.3 as long as carapace, spatulate with slightly convex lateral margins, with pair of small but sharp supraocular spines proximally; apex without long setae. Female rostrum narrower, tapered, length similar to that of male. Supraocular eave poorly developed; postocular margin with small acute spine. Supraocular spines small, at base of rostrum just mesial to base of eyestalk. Eyestalks compact, with small protuberance on anterior surface ventrally. Maxilliped 3 merus rounded distolaterally. Cheliped in male at most twice carapace length, with fairly swollen propodus, fixed finger with denticulate cutting edge; dactylus with simple proximal tooth, excavate in middle third; gape obscured by dense mat of setae; carpus short, cup-like; merus widened distally, with blunt dorsodistal tubercle. Pereopods 2–5 meri each with prominent dorsodistal tubercle; pereopod 2 dactylus weakly arcuate, not falcate, dactyli of pereopods 3–5 falcate. Male gonopore with prominent penial process. Gonopod 1 with swollen base, almost straight section, strongly curved tip terminating in fine apex. Gonopod 2 small, strongly flattened, terminating in short, non-tapered, terminally truncate tube-like process; lateral margin expanded into angular lobe, mesial margin gently concave.

Distribution. East Asian endemic: Japan, Korea and China, intertidal to 9 m.

Remarks. This species has been mentioned in literature often and the dorsal habitus illustrated several times. Sakai ( 1934, 1935, 1976) and Lucas (1980) figured the gonopod 1. Sakai (1938) figured the dactylus of pereopod 4 and the male pleomeres 3 and 4 erroneously as free. Sakai (1965: fig. 9) figured the maxilliped 3 and the male pleon, and again stated that ‘the male abdomen is composed of six distinct segments.’ Ng et al. (1999) illustrated variation of the male rostrum. Re-examination of material from the type locality and elsewhere confirmed characters in earlier figures.

Figures

FIGURE 3. Rhynchoplax messor Stimpson, 1858. Male, cl 3.3 mm, AM P. 10497: a, rostrum and eyestalks; b, anterior carapace and rostrum, right side; c, buccal region, ventral; d, thoracic sternum (penial process shown); e, pleon; f, left cheliped, lateral face; g, pereopod (uncertain); h, gonopod 1; i, gonopod 2; Female, cl 3.0 mm, AM P. 10497: j, left lateral view, pleon slightly open; k, right thoracic sternites 7, 8, lateral margins of pleomeres 1, 2 (branchiosternal canal aperture shown). Upper scale bar = 1 mm; lower scale bar = 0. 5 mm.