Order GADILIDA

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Order GADILIDA

Compiler and date details

Kevin L. Lamprell, Queensland Museum, Brisbane, Australia John M. Healy, Center for Marine Studies, University of Queensland, Brisbane, Australia

Introduction

The order Gadilida Starobogatov, 1974 (=Siphonodentalida Palmer, 1974) is distinguished from the Dentaliida by the vermiform foot often with a terminal disc, rachidian tooth of the radula either higher than wide or height equal to width, and by the generally smaller, polished, usually unsculptured shells (exceptions: strong ribs in Entalinidae; certain Gadilidae with striations) which often have contracted apertures (Palmer 1974; Boss 1982; Steiner 1992; Scarabino 1995; Lamprell & Healy 1998; Steiner & Palmer 1998). In addition, several features of internal anatomy separate the Gadilida from Dentaliida including body and captacular musculature, mantle and midgut gland morphology and nerve ganglia positioning (Steiner 1992).

Some 28 gadilidan species, principally from the family Gadilidae, have been recorded from the Australian region. Five Australian fossil species are known from the Miocene and Pliocene of South Australia and Victoria (Ludbrook 1956, 1959, 1960, 1984).

Superficially, the external shelly tubes of certain polychaete worms (for example Ditrupa) may resemble shells of the Gadilidae (see General Introduction and also ten Hove & Smith 1990).

Two suborders are recognised: Entalinimorpha, with one family, the Entalinidae, and Gadilinimorpha, with the families Gadilidae and Pulsellidae represented in Australia. The Entalinimorpha was erected by Steiner (1992) to accommodate all Gadilida with strongly ribbed shells which are polygonal or laterally compressed in cross section (i.e. the Entalinidae). Details of radular, pedal muscle and captacular morphology were also cited by Steiner as defining features of the suborder.

The Gadilinimorpha was introduced for those Gadilida which have smooth to polished shells lacking longitudinal sculpture save for occasional fine striae. Steiner (1992) pointed out features of the radula (rachidian tooth with one or more cusps, laterals 3, marginals keeled) and soft anatomy (musculature, presence of mucoid epithelium on the terminal disk of the foot) which further characterise the group.