SHELL AND PALLET MORPHOLOGY OF EARLY DEVELOPMENTAL STAGES OF BANKIA-GOULDI (BARTSCH, 1908) (BIVALVIA, TEREDINIDAE)

The margin of the larval shell of Bankia gouldi (Bartsch) undergoes a progressive change in shape during ontogeny from an initial D-shape, t o nearly circular, and then to elliptical just prior to metamorphosis. The length of the hinge is 37.9 +/- 2.3 mum, n = 30 (range: 34.0-43.0 mum). The D-stage larval shell is inequilateral with the anterior end broader than the posterior end. The provinculum, composed of two card inal teeth and three sockets in the left valve, and three cardinal tee th and two sockets in the right valve, is well developed in shells as small as 75 mum. The length of the central tooth in the right valve ra nges from 12 to 19 mum. The other teeth are one-half to one-third of t he length of the central tooth. A lateral hinge system, consisting of two lateral flanges on the left valve that interlock with two lateral grooves on the right valve, is present in specimens as small as 75 mum . This hinge system persists until metamorphosis. Metamorphosis, first seen in the development of a ligament pit, occurred in larvae with sh ells as small as 197 mum in height; and leads to the development of th e chondrophore, apophysis, anterior and posterior slopes, disc, umbona l-ventral ridge, dorsal condyle, ventral condyle, denticulated ridges and pallets. Asymmetrical growth results in the formation of the chara cteristic form of the teredinid postlarval shell with a new axis of ar ticulation oriented dorsoventrally along the condyles. Each pallet con sists of a proximal stalk and a distal blade with one to several segme nts. Pallets with one segment were first observed in early postlarval shells at 0.4 mm in length.