Punctulum flavum

Punctulum flavum (Okutani, 1964)

(Fig. 2 G–I)

Microstelma flava Okutani, 1964: 389–390, pl. 6, fig. 5 (see Hasegawa [2014] for more detailed synonymy).

Material examined. SoJsBio A 2-10, MIBM 14270 (Fig. 2 G–H); SoJsBio A 3-10, MIBM 39344; SoJsBio A 3-11, MIBM 39335; SoJaBio A 6-7, MIBM 39334 (Fig. 2 I–J); SoJaBio A6-8, MIBM 14412; SoJaBio B 6-6, MIBM 39346; SoJaBio B 6-7, MIBM 14492; SoJaBio B 7-6, MIBM 39345; SoJaBio B 7-7, MIBM 39341 [depth range: 470–2555 m].

Additional material examined (cited from Hasegawa, 2014). IORAN, non-registered, R/ V Vityaz st. 6649, Peter the Great Bay, 42°37.4’N, 134°19.2’E –42°37.8’N, 134°18.5’E, 1186– 1130 m.

Distribution. Off the Primorsky Krai coast on the northern slope, and from off Rebun Island to the southernmost part of the southeastern slope in the Sea of Japan; the western Okhotsk Sea and Pacific coast of the Japanese archipelago south to Kyushu. Depth range in the Sea of Japan is 200–2027 m.

Remarks. On both the northern and southeastern slopes of the Sea of Japan, two distinct phenotypes have been recognized in this species that are distinguished by the depth of their habitat [Hasegawa, 2014]. Down to ca. 1,000 m, specimens possess a low conical shell, with strong axial and spiral sculpture (the “shallow-water form”; Fig. 2G, H), while those from deeper stations possess a more inflated shell with very much weaker sculpture (the “deep-water form”; Fig. 2I, J). Furthermore, there is a correlation between the size of the protoconch and depth, with the “deep-water form” tending to have a larger protoconch. These two forms are still considered conspecific here because of the presence of intermediate forms at around 1,000 m. However, Criscione et al. [2019] indicated the presence of two genetically slightly distinct specimens identified as P. flavus and P. cf. flavus in their analysis and if the latter corresponds to the “deep-water form”, the two may be separable as distinct species.