ASPECTS OF THE REPRODUCTIVE BIOLOGY AND ANATOMY OF THREE DENDROCHIROTE SEA CUCUMBERS BELONGING TO THE GENERA PHYLLOPHORUS AND PENTACTA

Abstract

Three local species of dendrochirote sea cucumbers - Phyllophorus parvipedes (C1ark, 1938), Pentacta sp. aff. quadrangularis (Lesson, 1883) and Pentacta anceps (Quoy and Gaimard, 1833) are studied in this project. The gonad maturation cycle of Phyllophorus parvipedes was followed using gonad index estimations and histological examination. Monthly samples were taken from the east coast of Singapore from June to November 1990, a period of six months. All male and female individuals sampled possessed spawning stage gonads. A likely explanation is that asynchronous spawning is practised, where the eggs and sperm are discharged as and when they are ready to be spawned. Freshly stripped oocytes of Phyllophorus parvipedes show no response to maturation inducing substances (MIS) - DTT (Dithiothreitol) and 1-methyladenine. Injection of live animals with the two MIS and the human chorionic hormone, gonadotropin did not produce any spawning during a 24 hours period. Treatment of ovarian fragments with DTT and 1-methyladenine did not result in contraction of the fragments nor did it result in the shedding of eggs. It may be concluded that DTT is ineffective as an artificial MIS for Phyllphorus parvipedes. In addition, the results may be used as evidence against 1-methyladenine being the natural MIS. Eggs and sperm were stripped from their respective gonads and placed together into the seawater media in petri dishes, to facilitate in-vitro fertilization. However, there had been no success wi th the above mentioned technique in inducing artificial fertilization of Phyllophorus parvipedes. The spicules of Phyllophorus parvipedes, Pentacta sp. aff. quadrangularis and Pentacta anceps are isolated and characterised. The tentacles of Phyllophorus parvipedes are characterised by complex dichotomously branched rods and clubs (another type of rod), while the body wall is characterised by perforated plates, simple rods and low-spired tables. Clubs are absent in the body wall. The tentacles and tube feet of P. sp. aff. quadrangularis are characterised by clubs, baskets and perforated plates with toothed edges. Likewise, the body wall and paillae lacks clubs. Except for this, the skeleton of the body wall and papillae is similar to that of the tube feet and tentacles. For P. anceps, clubs and dichotomously branched rods characterise the tentacles. Different types of spicules are present in the body wall. They are baskets (which can be subdivided into two types), perforated plates with tubercles and large perforated plates with bridges. In the three species described, clubs are present in the tentacles but absent in the body wall. This brings up the question of a relation between body structure and spicule type. The variation in spiculation during growth in Pentacta anceps was studied. Spicules of very young individuals were isolated, characterised and compared with that of the adults. The length of clubs from the tentacles and tube feet of the young are significantly greater than that of the adults. That is also the case for perforated plates with tubercles and baskets with smooth edges. However, the length of complex dichotomously branched rods and of baskets with toothed edges of the young are not significantly greater than that of the adult. This suggests varying patterns of growth in different spicules. The gross anatomy and histology of some organs of Phyllophorus parvipedes and Pentacta sp. aff. quadrangularis were examined. and described. A complete account of the external morphology of the two species and Pentacta anceps is given. An attempt was made to provide a more complete and accurate description of Phyllophorus parvipedes, through the author's examination of collected specimen's and in comparison with past literature.