Scabies songkramensis Kongim & Panha

Kongim, Bangon, Sutcharit, Chirasak & Panha, Somsak, 2015, Cytotaxonomy of unionid freshwater mussels (Unionoida, Unionidae) from northeastern Thailand with description of a new species, ZooKeys 514, pp. 93-110 : 97-98

Taxon classification Animalia Unionoida Unionidae

Scabies songkramensis Kongim & Panha sp. n. Fig. 5A, B, F; Table 3

Type material.

Holotype ZMMSU 00500 (length 30 mm, height 18 mm, width 7.5 mm) Paratypes: ZMMSU 00501 (20 shells; length 29-33 mm, height 17-19 mm, width 7-8 mm); CUMZ (five shells).

Type locality.

Houy Plahang stream in Songkram River Basin, Ban Klang Charern, Pangkon, Sakon Nakorn, Thailand - 17°24'22"N, 103°50'1"E. Type locality indicated in Fig. 1, locality 4).

Etymology.

The specific name songkramensis refers to the Songkram River, type locality of this new species. Authorship of this new species is to be credited to Kongim and Panha in Kongim, Sutcharit and Panha.

Description.

Shell of medium size (length 29-33 mm), ovate in outline, H/L ratio = 0.59, anterior portion rounded, umbonal area elevated and sloping downwards posteriorly. Underlying shell colour brown. Shell sculptured with a series of coarse, v-shaped ribs radiating outwards from umbo; v-line arrangement loose, with 4-fold number on 10 mm; posterior slope with coarse and distinct ridges. Sculpture reduced to nearly obsolete near ventral and posterior shell margin. Periostracum brown, tending towards dark green where ribs are worn. Hinge plate well-developed; pseudocardinal tooth (pt) forming a thickened plate and raised lamelliform on right valve, but thinner and also raised lamelliform on left valve. Two well-developed posterior lateral teeth (lt) present in each valve, long and sharp. Anterior adductor muscle scar (aa) prominent and deeply impressed; posterior adductor muscle scar (pa) shallow; pallial line (pl) faintly impressed. Nacre bluish-white with little iridescence.

Remarks.

The new species differs from the closely related Scabies crispata (Gould) and Scabies phaselus (Lea) by having a smaller, harder, thicker, ovate shell that is brown in colour, with dark brown v-line sculpture. The two other species have larger, more elongate shells that are yellowish brown in colour, combined with greenish v-line sculpturing in Scabies crispata and a nearly smooth shell surface in Scabies phaselus . Scabies songkramensis sp. n. differs from Scabies nucleus (Lea) in having a larger shell and v-line sculpture, compared with w-line sculpture in Scabies nucleus .

Habitat.

Scabies songkramensis sp. n. occurs in a small tributary of the Songkhram River. It lives in shallow water in a sandy-gravel substrate, or less frequently in sandy-mud. This new species is currently known only from the type locality, approximately 100 km from the main stem of the Songkhram River (Fig. 1, locality 4), in slow moving water at depths that ranged from 0.5 to 2 m in the wet season (i.e. from June to October).