Benthomodiolus geikotsucola Okutani & Miyazaki, 2007

Oliver, P. Graham, 2015, Description and morphology of the " Juan de Fuca vent mussel ", Benthomodioluserebus sp. n. (Bivalvia, Mytilidae, Bathymodiolinae): " Phylogenetically basal but morphologically advanced ", Zoosystematics and Evolution 91 (2), pp. 151-165 : 156-158

Taxon classification Animalia Mytiloida Mytilidae

Benthomodiolus geikotsucola Okutani & Miyazaki, 2007

Benthomodiolus geikotsucola Okutani & Miyazaki, 2007: 49-55, figs 2-3.

Material examined.

Holotype. 1 shell, NSMT-Mo-76703, Summit of Torishima Seamount, 30°55'N 141°49'E, 4020m. Not examined, image courtesy of NSMT.

Paratype. 1 specimen, NSMT Mo-76704j as holotype.

Shell.

The holotype (Fig. 6a) is slightly larger than any of the shells of Benthomodiolus erebus reaching 42.5 mm. The paratype dissected here (Fig. 6 b–d) was 28.1 mm in length. The shell is umbonate, narrowly arcuate in outline and medially sulcate; in these there is strong similarity to Benthomodiolus erebus . The beaks are rather distant from the anterior margin, more so than in B. erebus with a total length /anterior length of 0.28 compared with a value of 0.24 for Benthomodiolus erebus . As in Benthomodiolus erebus the periostracum is smooth and devoid of hairs.

Pedal byssus musculature.

The arrangement of the pedal and adductor muscles (Fig. 7 b–c) is almost identical to that in Benthomodiolus erebus in that the byssal retractors (pbr2 and pbr1) are widely separated with pbr2 attached in the rear of the umbonal cavity. Both the anterior pedal retractor (apr) and posterior byssal retractor (pbr1) are slender. The posterior protractor muscle (ppr) in Benthomodiolus geikotsucola is very slender and simple and lacking the secondary muscles (sppr) seen in Benthomodiolus erebus .

Ctenidium and labial palps.

The ctenidium consists of both demibranchs and as in Benthomodiolus erebus the filaments are relatively short (Fig. 7a, 4f). The ascending and descending arms of the filaments are fused for over half their lengths and the abfrontal surface is extending creating a triangular laminar form to each filament (Fig. 4g). The filaments have a single row of ciliary junctions on the ascending and descending arms (Fig. 4 g–h). The abfrontal surface is composed of polygonal cushions of microvilli.

Mantle edge and apertures.

The mantle edge is free for most of its length and fused only posteriorly to separate the ventral gape for the exhalant aperture. The entire length of the ventral gape the middle fold is thrown into a dense series of folds (Fig. 7a, mef) and in this unlike the almost lack of folding seen in Benthomodiolus erebus .

Alimentary system.

The stomach was not dissected. The gut follows a similar path to that in Benthomodiolus erebus but the hindgut loop is distinct with a short reversed portion (Fig. 7b, hgl).