Policordia hispida, Safonova, Lyudmila A. & Barwick, Kelvin L., 2016

Safonova, Lyudmila A. & Barwick, Kelvin L., 2016, A new species of the genus Policordia (Bivalvia, Verticordioidea, Lyonsiellidae) from off the coast of southern California, ZooKeys 622, pp. 37-46 : 39-43

Taxon classification Animalia Anomalodesmata Lyonsiellidae

Policordia hispida sp. n.

Type locality.

USA, California, Orange County; 33.3688°N; 117.6899°W; 411 m (OCSD B13-9137; 30 July 2013).

Type material.

Holotype: LACM 3322, valves separated, with soft parts in 70% ethanol, length 4.8 mm, height 4.3 mm, width 1.8 mm. Paratype: SBMNH 462739, USA, California, San Diego County; 32.7993°N; 117.4055°W; 449 m (CSD-EMTS 8338, 23 July 2014); valves separated, with soft parts in 70% ethanol, length 3.8 mm, height 3.4 mm, width 1.4 mm.

Diagnosis.

Shell subquadrate, longer than high with broadly rounded posterodorsal margin; 30-32 radial periostracal lamellae present; umbones prominent. Each mantle margin with approximately 30 mantle glands lacking long cylindrical portion. Inhalant siphon with 18-19 papillated tentacles and 2 pairs of smooth tentacles. Exhalant siphon with 5 conical tentacles. Byssal thread present.

Description.

Shell. The translucent fragile shell is subquadrate (Figs 1, 3) with the length greater than the height (Table 1); inequivalve, with the right valve overlapping the left. The beaks are prosogyrate, delimited from the posterior angle by compressions. The posterodorsal margin is straight and is directed obliquely downwards from umbo; the posteroventral margin is slightly rounded and forms extended and slightly compressed angle with the posterodorsal margin. The anteroventral margin is rounded on the left valve and nearly straight on the right valve. Shell with irregular fine commarginal growth checks, covered with a colorless periostracum, which in turn forms a series of regularly spaced, radial lamellae (30-32) extending from the umbo, of the total, 13-14 are secondary (incomplete). Adhering to some radial lamellae are bunches of fine fibers giving the shell a slightly hirsute appearance externally. Shell nearly completely covered with fragile thick-silt coating (not shown, removed prior to examination). Hinge margin thin, edentate, with relatively large lithodesma inserted posterior to umbo along posterodorsal margin. Lithodesma has small posterior sinus, about ¼ of length, right posterior branch less than the left (Fig. 1).

Anatomy. Mantle of the holotype has about 30 flask-shaped mantle glands located along the mantle edge. Mantle glands consist of short ducts formed by a few cells and oval structure above them, similar to glands of Policordia atlantica ( Allen and Turner 1974). There is one row of papillated tentacles surrounding the inhalant siphon, 10 tentacles on the right side and 9 on the left (Figs 2, 3). Each tentacle carries 6-8 short papillated extensions (Figs 2, 4). Additionally, slightly outside the row of papillated tentacles, there are two, left and right, pairs of simple conical tentacles (Fig. 4). The first pair (counting from anterior to posterior) is between the fifth and sixth papillated tentacles; the second pair is between the seventh and eighth papillated tentacles. The exhalant siphon is surrounded by a total of five conical tentacles, one located dorsally and two pairs laterally (Figs 2, 3).

The foot has a heel; byssus present (Figs 2, 3).

Gills comparably wide, elongated, longer than base of foot. They consist of inner and outer demibranchs (Fig. 5); attached by outer demibranch margin laterally to mantle wall and posteriorly to junction between siphons. Outer demibranch without inter-filamentary junctions, inner demibranch with a single inter-filamentary connection.

Mouth is wide, funnel-liked, followed by a rigid oesophagus. Stomach covered with digestive diverticula; hindgut passes through pericardium (Fig. 2).

The holotype is a hermaphrodite with both testes covering anterior upper quarter of digestive diverticula and the ovaries located posteriorly (Figs 2, 3).

Variation.

The shell of the paratype is slightly smaller in absolute dimensions but retains the same ratios of width to length and height to length (Table 1). Like the holotype, the translucent fragile shell is subquadrate; inequivalved with the right valve overlapping the left. In keeping with its smaller size ( Allen and Turner 1974), the shell surface has both fewer radial periostracal lamellae (27-29) and secondary lamellae (8-10). The hinge margin is thin and edentate, with a lithodesma that matches the holotype in size and proportions. No silt covering observed.

The mantle of the paratype, as with that of the holotype, has flask-shaped mantle glands. The inhalant siphon is surrounded by 17 papillated tentacles. As in the holotype, there are two left and right pairs of conical tentacles located slightly outside of the row of papillated tentacles. The first pair is located between the second and third papillated tentacles; the second pair is between fifth and sixth (counting from anterior to posterior). The exhalant siphon is surrounded by a total of five conical tentacles; one dorsal and two pairs of laterals. As in the holotype, the foot has a single byssal thread attached.

Etymology.

The new species name is derived from the Latin adjective hispida due to the somewhat ‘shaggy’ appearance of the shell.

Distribution.

Known only from the type material: Eastern Pacific, southern California, 411-449 m.

Habitat.

Type specimens found in silt and fine sand.