Taxonomic account
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Order Decapoda Latreille, 1802
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Infraorder Anomura MacLeay, 1838
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Family Chirostylidae Ortmann, 1892
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Genus Chirostylus Ortmann, 1892
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Chirostylus dolichopus Ortmann, 1892
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Figs. 1 & 2
Synonymy
Chirostylus dolichopus Ortmann, 1892: 246, figs. 2, 2b, c, e, i, o, z [type locality: Kadsiyama (= Katsuyama), Boso Peninsula, Japan, shallow water]; Miyake, 1960: 97, pl. 48, fig. 8; Miyake & Baba, 1968: 381, figs. 1a, b, 2; Takeda, 1982: 49, fig. 147; Baba, 2005: 16 (part, see discussion), fig. 2; Baba et al., 2008: 14 (part, see discussion; not fig. 1A).
Material examined
CMNH-ZC 02495, 1 female (CL 5.5 mm), Uki-shima Islet, Katsuyama, Kyonan, Boso Peninsula (east side of Tokyo Bay), Honshu, Japan, 35°06.7′N, 139°48.8′E, 30 m, SCUBA, 14 July 2015, coll. J. Okuno.
Distinguishing characters
Rostral lobe rounded, unarmed (Fig. 1a). Gastric and cardiac regions unarmed. Branchial regions armed each with 1 spine near anterior extremity of each cervical groove (Fig. 1a). Third thoracic sternite with surface concave; anterior margin transverse, armed with 6 small spines (Fig. 1b). Abdominal somites with smooth dorsal surface. Ocular peduncle with feebly dilated cornea (Fig. 1a). Dactyli of second to fourth pereopods each with 6 (except for 7 in left fourth pereopod) corneous spines on flexor margin, penultimate spine distinctly stouter than ultimate spine (Fig. 1c).
Colouration
Ground colour of body and pereopods overall bright yellow (Fig. 2a, b). Dorsal surface of carapace (Fig. 2c) pale orange, with 3 main concentric U- to V-shaped markings: outermost U-shaped, red with clear inner and outer margins, approximately following carapace outline; next white with narrow, clear margins, apex tightly rounded, approximately enclosing protogastric region; innermost white-clear with red margins, acutely triangular, anterior apex slightly exceeding cervical groove. Pterygostomian flap with alternating white and orange-red longitudinal lines. Abdominal tergites (Fig. 2c) transparent; anterior margin and midline each with orange line. Ocular peduncles each with thick red line dorsomesially. Cheliped (first pereopod) (Fig. 2a, b) with white and red longitudinal lines dorsolaterally. Second to fourth pereopods (Fig. 2a, b) each with red longitudinal line dorsally except for distal part of propodus, this part brighter yellow than others; all meri each with white and red spots (red spot larger) near disto-extensor end, meri of both second pereopods and right fourth pereopod each with additional 1 or 2 red small spots on distal one third of extensor margin.
Habitat
The present specimen was associated with an unidentified alcyonarian octocoral attached to a small rock on the sandy slope at a depth of 30 m (Fig. 2a). The steep slope is situated at eastern margin of the Tokyo Submarine Canyon, and reaches about 200 m depth over narrow horizontal distance (about 3 km) (see Yano et al., 2007). At the diving sites around Uki-shima Islet, divers have observed nine other individuals referable to C. dolichopus during June to August of 2015, some living on colonies of fan-like gorgonaceans (Jiro Uochi, personal communication).
Distribution
Type locality: Kadsiyama (= Katsuyama), west coast of Boso Peninsula (east side of Tokyo Bay), Honshu, Japan (Ortmann, 1892). Also known from Sagami Bay (Miyake & Baba, 1968). Other records of C. dolichopus from outside of Japan (cf. Baba et al., 2008) should be confirmed (see discussion). Known from the depths ranging 22 to 70 m (Miyake & Baba, 1968; present study).
