Benthomodiolus lignocola Dell, 1987

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 : 158-160

Taxon classification Animalia Mytiloida Mytilidae

Benthomodiolus lignocola Dell, 1987

Benthomodiolus lignocola Dell, 1987: 33-34, figs. 44, 45, 48, 49, 52, and 53.

Material examined.

Holotype. 1 shell, NW of Orete Point, White Island, 37°23.7'S 177°39.5'E, 1075-1100m, 23/Nov/1981; Museum of New Zealand Te Papa Tongarewa M.075023. Not examined, image courtesy of NMNZ.

Paratype. 5 specimens, NE of Chatham Islands, 42°47.10' 175°45.60'W, 1174-1180m, 22/Aug/1984; NMNZ M– 075248/1.

Shell.

The shells have a maximum length of 18.1 mm (Holotype, Fig. 8 a–b) and the dissected specimen was 17.4 mm in length (Fig. 8 c–d). The shell is umbonate, weakly arcuate with the posterior distinctly deeper than anterior in outline and medially sulcate. The beaks are rather distant from the anterior margin with a total length /anterior length of 0.23. The sculpture is weak of commarginal lines only except over the sulcate zone where faint fine irregular radial creases are present. Fine periostracal hairs are present but worn off in the larger specimens.

Pedal byssus musculature.

The byssal retractors (Fig. 8f, g pbr2 and pbr1) are widely separated with pbr2 attached in the rear of the umbonal cavity. The angle between the byssal retractors is acute. The anterior pedal retractor (apr) is more slender than the posterior byssal retractor (pbr1). The posterior protractor muscle (ppr) is slender with secondary muscles (sppr).

Ctenidium and labial palps.

The ctenidium consists of both demibranchs with relatively short strap-like filaments and has a flimsy appearance with weak inter-filamentar junctions (Fig. 10a). The ascending and descending arms of the filaments are fused for only a short distance (Fig. 10b, d). The filaments have a single row of ciliary junctions on the ascending and descending arms (Fig. 10c). The frontal cilia are present but the abfrontal surfaces are largely devoid of epithelium, probably a consequence of poor fixation. Where present a weak polygonal pattern can be seen (Fig. 10e).

Mantle edge and apertures.

The mantle edge (Fig. 8e) is free for most of its length and fused only posteriorly to separate the ventral gape for the exhalant aperture. The mantle edge along the ventral gape is smooth.

Alimentary system.

The stomach was not dissected. The gut follows a similar path to that in Benthomodiolus erebus but the hind gut loop is distinct with a short reversed portion.