Family PTYCHODERIDAE

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Family PTYCHODERIDAE

Compiler and date details

C. Burdon-Jones, Queensland Museum, Brisbane, Queensland, Australia

Introduction

Worms of the Ptychoderidae Spengel, 1893 vary in length from a few centimetres to over two metres. Externally they are markedly different from harrimaniids and spengelids. They have a short ovoid or broadly pyriform proboscis. The collar is as long or longer than the proboscis, has a deep vestibular region, and a flared, often indented, anterior margin. When relaxed, it envelops the proximal half of the proboscis, giving the appearance of an acorn in its cup. The branchial region is partially or completely encased by broad flattened genital wings which may or may not overlap the prominent external sacculation of the anterior hepatic region. The proboscis skeleton differs markedly from that of the Harrimaniidae. It has a much shorter, thicker shaft and shorter, widely splayed crura, which are mostly confined to the anterior third of the collar. The branchial skeletons have synapticulae. Peripharyngeal cavities are present in all ptychoderids but oesophageal pores are absent. Lateral septa are present in the trunk coelom, and the circular musculature is external to the longitudinal musculature. Other distinguishing features include one or more dorsal nerve links between the neurocord and the epidermal nerve plexus of the collar, the absence of oesophageal pores, the presence of longitudinal parabranchial (hypobranchial) ridges separating the dorsal branchial pharynx from the ventral food conducting region and they also have paired or single ridges and ciliary tracts on the inner dorso-lateral walls of the hepatic and post-hepatic intestine.

Ptychoderids are widespread throughout Mediterranean and Red Seas, and the Indo-Pacific and Atlantic waters (Van der Horst 1939). Worldwide they are the most common enteropneust, especially in the tropical and sub-tropical intertidal regions, often on coral reefs, and frequently in association with mangrove and seagrass areas.

The family comprises three genera, Balanoglossus Delle Chiaje, Glossobalanus Spengel, and Ptychodera Eschscholtz, and 36 species worldwide. Two species of Balanoglossus, and one each of Glossobalanus and Ptychodera have been described from Australia. One species may be endemic to the Australasian Region (Hill 1897; Dakin 1916; Trewavas 1931; Morton 1950; Morton & Millar 1968), but the conspecificity of the Australian Balanoglossus australiensis (Hill, l895) and the New Zealand B. australiensis (Morton 1950) has been queried (see Packard 1968). Thus the endemism of the species remains undetermined pending further comparative study of specimens from both populations by the author.

Collections made by the author along the tropical coast of Queensland include specimens of Glossobalanus and Balanoglossus which may prove to be new endemic species.

The life histories of several ptychoderids have been studied by Morgan (1891, 1894); Heider (1909); Stiasny (1913, 1914a, 1914b, 1941); Stiasny-Wijnhoff & Stiasny (1926, 1927); Payne (1937); Björnberg (1953, 1955, 1959); Rao (1954); Hadfield (1975, 1978); Hadfield & Young (1983). Tornaria larvae are common in Australian waters (Trewavas 1931), and have been allocated specific names pending further studies to determine parentage. Several of these are listed here under Species Incertae Sedis. Others remain unidentified. Some have been described by Trewavas (1931: 60–62, 65–66) and are among those held by the Natural History Museum, London U.K., Reg. nos. 1931.3.20.51, 62, 63, 74, 44, 78, 83 from Stns 19, 20, 34, 37 and 40. For further discussion and comment on the possible synonymy of some tornaria larvae, and their distribution and correlation with adult distributions, see see Van der Horst (1939: 281–321); Björnberg (1959: 26–31), Damas & Stiasny (1961), and the section on Species Incertae Sedis, p. 26.