Family MOLGULIDAE

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Family MOLGULIDAE

Compiler and date details

P. Kott, Queensland Museum, Brisbane, Queensland, Australia

Introduction

The Molgulidae Lacaze-Duthiers, 1877 have a thin but often sand-embedded test, branched branchial tentacles and stigmata coiled around cones that project into the branchial folds, or that coil on a flat branchial wall or around cones that project independently into the pharynx. They also have a closed kidney derived from the embryonic epicardial sacs on the parietal wall of the right side of the body and compact folds and pouches (probably glandular) occur in the stomach wall. As in Pyuridae, a single gonad on each side of the body is inside or outside the gut loop or crosses over it. The testis follicles spread out on the body wall around the tubular or sac-like ovary, or parts of it, and do not form a compact covering over the ovary, nor are the gonads subdivided (as usually is the case in Pyuridae). The body muscles are formed into bands and in some species short parallel bands are aligned around the apertures to withdraw them between folds of brittle sand-filled test or to flatten the body (like the sandy phlebobranchs, Ascidia scaevola, Microgastra granosa and certain Agneziidae).

Certain species of the Molgulidae, like some Polycarpa (Styelidae), have viviparous larvae and some develop directly without passing through a tailed larval stage. Berrill (1955) has suggested that these species, characterised by the brittle sand-embedded test and muscles to withdraw apertures and flatten the body, are adapted for life on the open sea floor and have evolved strategies that reduce the time that either gametes or larvae are vulnerable to dispersal.

The family is well represented in Australia by the genus Molgula (12 species), Eugyra (3 species) and a species of Pareugyrioides. In Molgula the left gonad is outside the gut loop. Eugyrioides, with gonads on both sides of the body, is very likely a synonym of Eugyra which has a gonad only on the left (partially or completely enclosed in the gut loop).

The genera not represented in the Australian fauna are known from polar waters or from deeper abyssal waters (see Kott 1985). Around the Australian coast, deeper waters have not yet been explored adequately for these benthic organisms.