THE FUNCTIONAL-ANATOMY OF SPHENIA-ANTILLENSIS DALL AND SIMPSON, 1901 (BIVALVIA, MYIDAE)

Sphenia antillensis Dall & Simpson, 1901 is a small bivalve living in the southern Brazilian littoral zone. It lives attached by byssus thre ads on substrata that provide shelter and protection against the direc t wave action. The bivalve lives where there is some disturbance of th e bottom deposits and the water contains a small amount of suspended m aterial. The mantle edges and periostracal grooves are fused along the median ventral line, except for a small anterior pedal aperture and t he two siphonal orifices. The siphons are short, united, and belong to type C of Yonge (1948, 1982). They do not diverge terminally and are light sensitive. The foot is short and it is concerned mostly with the direction of the byssus threads. The ctenidia are smooth, homorhabdic and classified as Atkin's (1937) type C (1), with minor differences i n the ciliary currents on the outer demibranch. The oesophagus enters dorsally into the anterior part of the stomach. The style-sac and midg ut open separately into the ventral region of the stomach which belong s to Type V as defined by Purchon (1960). It has much the same structu re and functions as that of a typical suspension-feeding eulamellibran ch. A comparison is made with other myoidean bivalves.