Reproductive biology of the brooding Antarctic lamellibranch Kidderia subquadratum Pelseneer

• Main Author: Shabica, Stephen V.
• Other Authors: Hedgpeth, Joel Walker, School of Oceanography, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Bivalvia; Antarc*; Antarctic; Antarctic Peninsula; Antarctica
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kk91fn76b

The reproductive biology of Kidderia (Kidderia) subquadratum (Pelseneer, 1903) was studied from collections which were made at Palmer Station, Antarctica during 1970 and 1971. Kidderia subquadratum is a small lamellibranch (the largest observed was 6.8 mm long) found on rocky substrates in the intertidal and subtidal zones of the Antarctic Peninsula. The sexes are separate and the females comprised 54.1% of the population studied. The differential in the sex ratio is neither size nor age related. The females are ovoviviparous and retain their embryos in brood pouches of the demibranchs. The brood pouch is a modification of the form and function of the ancestral, molluscan ctenidia and allows the retention of embryos by the female. The eggs are large and rich in yolk. Embryogenesis is without traces of the typical marine, molluscan larvae, the trochophore and the veliger. Development of the embryo follows the normal indirect, marine lamellibranch pattern until gastrulation. This includes unequal cleavage, formation of a stereoblastula with a reduced blastocoel, and gastrulation by epiboly with slight invagination. Following gastrulation development is considerably modified and follows the normal freshwater lamellibranch pattern of direct development. This is partially attributed to the large amounts of yolk that the egg contains, to the absence of the free living trochophore and veliger larvae, and to the incidence of brood protection. No structures analogous to the trochophore and veliger larvae occur. The reproductive system is described and includes the male and female systems, and the ctenidial and siphonal systems. The female gonad is unusual in that unilaminar ovarian follicles are present. The follicles consist of simple squamous follicle epithelia and either developing oögonia or oöcytes. Oögenesis takes 15 to 19 months. Egg formation consists of the rounding-off of a single germ cell which includes a nucleolus, nucleus, and cytoplasm complex. This complex, called an oögonium, grows out from the germinal ...