Trapezionida psylla (Macpherson, 1994)

[New Japanese name: Daidai-chu-koshiori-ebi]

(Figs. 4–6)

Munida psylla Macpherson, 1994: 517, fig. 42 (type locality: New Caledonia, 500 m).— Baba 2005: 271 (compilation).— Baba et al. 2008: 114 (compilation).— Poupin 2010: 56 (list).— Yaldwyn & Webber 2011: 212 (list).—Macpherson et al. 2020: 66.

Trapezionida psylla.— Machordom et al. 2022: 940 (Table 2).

Material examined. JAMSTEC 106858, 1 female (cl 4.4 mm), 1 ovigerous female (cl 4.7 mm; DNA voucher), 1 ovigerous female (cl 5.3 mm), R / V Kaimei, KM20-10 C cruise, KM-ROV dive #133, Nikko Seamount, north of Mariana Arc, 23°04.98’N, 142°19.50’E, 488 m, 9 December 2020; CBM-ZC 16969, 3 males (cl 4.6, 4.6, 6.5 mm) (DNA voucher cl 4.6 mm, see Table 1), TR/ V Seisui-maru, 2018 cruise, stn 6, Kumano Sea, off Shima Peninsula, Mie Prefecture, 34°10’N, 137°10’E, 433 m, dredge, coll. S. Ohtsuka and T. Kimura, 29 November 2018.

Diagnosis. Carapace (Fig. 4A) with few secondary striae; intestinal region without scales; anterolateral spines well developed; frontal margin fairly oblique; branchial margin each with 3 subequal spines; hepatic and branchial dorsal spines present, postcervical spines absent. Thoracic sternum (Fig. 4B) wider than long; sternite 4 with few short arcuate striae; lateral surfaces of thoracic sternites with 6 and 7 with short, distinct carinae. Pleomeres 2 and 3 (Fig. 4A) unarmed, but each with 1 transverse stria on tergite. Eyes (Fig. 4A) moderately large, maximum corneal width about 0.3 times anterior border of carapace between bases of anterolateral spines. Antennular peduncle article 1 (Fig. 4C) with distomesial spine distinctly shorter than distolateral spine. Antennal peduncle (Fig 4D) article 1with distomesial spine reaching distal margin of article 2; article 2 with distomesial spine subequal to article 2, reaching distal margin of article 4. Maxilliped 3 merus (Fig. 4E) unarmed on dorsodistal margin, armed with 2 greatly unequal spines on ventral margin. Cheliped (Figs. 4F, G, 5) not particularly elongate, only with sparse setae; merus distal spines not particularly enlarged; dactylus with proximal and distal spines; fixed finger with 2 subterminal spines. Pereopod 2–4 (Fig. 4A, C, D) relatively slender; dactyli (Fig. 4B) about 0.7 length of propodus, each with row of moderately long, slender accessory spinules on flexor margin over entire length.

Colouration in life. Body and appendages overall orange-red, anterior part of carapace and cheliped fingers darker; tips of cheliped fingers white; meri of ambulatory legs each with 2 whitish bands (Fig. 6).

Distribution. Heretofore known only from South-west Pacific: New Caledonia, Loyalty Islands, Kermadec Islands, and Papua New Guinea, at depths of 287–573 m (Macpherson et al. 2020). The present specimens greatly extend the geographical range of the species to the North-West Pacific.

Remarks. Trapezionida psylla was originally described from waters around New Caledonia (Mac pherso n 1994; as Munida) and since then has been recorded from the South-West Pacific localities, including the Kermadec Islands and Papua New Guinea (Yaldwyn & Webber 2011; Macpherson et al. 2020). Morphologically, the specimens from the Nikko Seamount agree well with T. psylla in diagnostic characters mentioned above (cf. Macpherson 1994). Genetic divergence observed between one of the present three specimens from the Nikko Seamount and one specimen registered in the GenBank as T. psylla are 0.6% for COI gene and 0% for 16S gene, well supporting that these two specimens belong to the same species (cf. Macpherson et al. 2020).

During this study, we have also examined three specimens from the Kumano Sea, central Japan (CBM-ZC 16969), which closely match M. psylla morphologically and genetically. Genetic divergence between one of those three specimens and other specimens mentioned above is 0.6–1.0% for COI gene and 0–0.2% for 16S rRNA gene.