Opisthogastric earthworms (Megascolecidae: Oligochaeta) and allied forms in north-western Tasmania

Author: Blakemore R.J.   Kingston T.J.  

Publisher: Taylor & Francis Ltd

ISSN: 1464-5262

Source: Journal of Natural History, Vol.31, Iss.11, 1997-11, pp. : 1683-1708

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Abstract

A new genus Nexogaster is established for a Tasmanian megascolecid earthworm, Nexogaster sexies sp. nov., that has an oesophageal gizzard and intestinal gizzards, the opisthogastric condition, that in this species are moniliform. The only previously known opisthogastric species from Australia, Hickmaniella opisthogaster , is also from Tasmania but has a single intestinal gizzard; this species is redescribed. A new species, Hickmaniella gogi , is bithecal but otherwise similar to the type-species. Nexogaster differs from Hickmaniella in being lumbricine and having prostates that are racemose, rather than tubuloracemose (although both forms are an apomorphy of tubular prostates). Sympatric species are newly described that have close morphological similarities: one, Anisochaeta simpsonorum , is comparable with Hickmaniella , and two others, Notoscolex pilus and Megascolides maestus , not only resemble one another but are also similar to Nexogaster . A major morphological difference is that M. maestus has tubular prostates; this combined with its other primitive character states, such as lumbricine setae, give an indication of a possible precursor to the other species. Extensive generic reviews and redefinitions have been required to accommodate the new species.