Maxacteon cf. kawamurai (Habe, 1952)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 606-607

Maxacteon cf. kawamurai (Habe, 1952)

Figs 8C-E, 9

Acteon kawamurai Habe, 1952 a: 70, 76, text fig. 1.

TYPE MATERIAL. — Holotype NSMT Mo 38613.

TYPE LOCALITY. — Sagami Bay , central Honshu, Japan .

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10: stn DW 18°19’S, 178°05’E, 234-361 m, 2 dd (Fig. 8C) .

1365, S of Viti Levu, 18°13’S, 178°32’E, 295-302 m, 1 dd (Figs Tonga. BORDAU 2: stn DW 1536, 21°45’S, 175°21’W, 320- 8D, E); stn DW 1374, 18°19’S, 178°06’E, 259-348 m, 3 dd; stn 323 m, 1 dd.

DW 1384, 18°19’S, 178°06’E, 260-305 m, 3 dd; stn CP 1390,

DISTRIBUTION. — Known from several localities in Japan, in 93-200 m (Hori 2000a). Material herein collected from Fiji and Tonga (Fig. 9), in 302-320 m.

DESCRIPTION. — Shell morphology. Length 15 mm, width 8 mm (largest specimen examined). Shell solid, elongate, with convex sides (Fig. 8C). Body whorl large, about 4/5 of the shell length. Spire elongate, conical, with 3-4 whorls. Suture channeled. Protoconch globose, eroded in all specimens examined (Fig. 8D); about 1 whorl and approximately 400 Μm in diameter. Umbilicus very narrow, almost completely covered by an extension of the columellar margin. Aperture short and narrow, wider anteriorly, about 3/4 of the body whorl length. The anterior end of the aperture is expanded into a lip that is more conspicuous near the middle of the shell. Columellar margin thickened, oblique, with a conspicuous fold. Sculpture of a number of punctuated spiral grooves (Fig. 8E). The punctuations are large, oval, almost rectangular, partially fused to the next one within each groove. The grooves are separated by gaps that are normally narrower but occasionally as wide as the grooves. Colour uniform pale grey to brownish.

Anatomy. Unknown. All shells collected lacked soft parts.

REMARKS. — The specimens here examined from Fiji and Tonga resemble the illustration of Punctacteon kawamurai of Hori (2000a). However, the sculpture of the Japanese specimens differs from the material here examined in having wider gaps between the spiral grooves. A positive identification of this material is not possible until more specimens become available for study, so I prefer to leave them provisionally under P. kawamurai . Punctacteon kawamurai is here transferred to Maxacteon , while realizing that this placement may be revised in the light of future study.

Maxacteon cf. kawamurai is similar to Maxacteon fabreanus (Crosse, 1874) but it is distinguishable on the basis of several conchological differences that include its narrower umbilicus and the less marked columellar tooth. Maxacteon cf. kawamurai is also similar to Japonacteon sieboldii but differs from this species in having a distinct umbilicus. Another similar species is “ Acteon ” sp. 9 (see below), which also lacks an umbilicus and has larger punctuations in the sculpture.

FIG. 8. Shell morphology and anatomy of species of Japonacteon Taki, 1956 and Maxacteon Rudman, 1971 . A, Japonacteon sieboldii (Reeve, 1842) , radula, Tonga, BORDAU 2 stn DW 1586, scale bar = 100 Μm. B, Japonacteon longissimus n. sp., radula of paratype MNHN 20266, Philippines, MUSORSTOM 3 stn CP 106, scale bar = 200 Μm. C, Maxacteon cf. kawamurai (Habe, 1952) , (15 mm), ventral view, Fiji, MUSORSTOM 10 stn CP 1390; D, protoconch, Fiji, MUSORSTOM 10 stn DW 1365, scale bar = 300 Μm; E, sculpture of shell, Fiji, MUSORSTOM 10 stn DW 1365, scale bar = 200 Μm. F, Maxacteon sagamiensis (Kuroda & Habe, 1971) , (5.5 mm), ventral view, Philippines, MUSORSTOM 2 stn DR 33; G, same shell, protoconch, scale bar = 500 Μm; H, sculpture of shell, Philippines, MUSORSTOM 2 stn DR 33, scale bar = 100 Μm.