Studies on the systematics and biogeography of terrestrial flatworms (Platyhelminthes: Tricladida: Terricola) of the Australian region

Winsor, Leigh (2003) Studies on the systematics and biogeography of terrestrial flatworms (Platyhelminthes: Tricladida: Terricola) of the Australian region. PhD thesis, James Cook University.

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Abstract

This study contributes to knowledge of the systematics and biogeography of terrestrial flatworms (Platyhelminthes: Tricladida: Terricola) of the Australian region. Terrestrial flatworms are carnivorous soil animals some of which are important commercially as biological control agents for the Giant African snail, or as introduced pest species preying upon earthworms in Europe.

The total Australian terrestrial flatworm fauna is estimated to be in excess of 300 species. At present only 137 species are named of which three-quarters have been described solely from external features. Taxonomy of the Terricola is based on a combination of external features and internal anatomical characters and remains in a state of flux. Recent molecular studies of the Tricladida have cast doubt on the monophyly of the Terricola. The austral fauna is poorly known anatomically, and taxonomy of the group further hampered by the existence of numerous species complexes which are poorly understood.

The objectives of this study are to locate and examine type and supplementary specimens, review the functional anatomy of austral terrestrial flatworms, identify reliable taxonomic characters and states, revise certain taxa, and develop identification keys. Furthermore, efforts have been made to determine the distribution of terricolan taxa of the region, identify the biogeographical components of the austral terricolan fauna and to identify the occurrence of introduced, threatening and vagrant terrestrial flatworms. Cladistic and molecular analyses of the taxa have not been undertaken.

Fixation and parasite-induced artifacts can cause mis-interpretation of anatomical characters. A suite of taxonomic characters and states is used to provide standardized diagnoses for genera. Included in the characters assessed for their application in taxonomy are colour and pattern of markings, pharyngeal musculature, configuration of the nephridial ducts, dorsoventral distribution of testes, penis type, resorptive organs, and musculoglandular organs (adenodactyls). Seven types of the hitherto enigmatic adenodactyls are identified, some of which function to secrete sclerotins which form the cocoon wall. The mechanism of cocoon formation in the Terricola involves the deposition of sclerotins, derived from antral secretions or adenodactyls, on the outer pre-cocoon membrane. This mechanism differs from the generally accepted Triclad model based upon the Paludicola, in which the cocoon is formed from within the pre-cocoon membrane by shell-globule components of the vitellocytes.

Representatives of all three terricolan families are present in the Australian region. A new subfamily is erected in the Geoplanidae, and of the twenty-seven genera considered in the study, ten are new. The problematic Australoplana complex is resolved into five genera and two sub-genera. Field keys are provided for the Terricola genera of the Australian region. This study supports the view that the Terricola are polyphyletic. Anatomical data suggest a possible phylogenetic relationship between some austral caenoplaninid and maricolan taxa.

The Australian flatworms mostly occur within hyper-humid to sub-humid moisture regions, and are assigned to two principal families. In the Rhynchodemidae: Rhynchodeminae 45 species are accommodated within Cotyloplana, Digonopyla, Dolichoplana, Platydemus, Rhynchodemus and in new genera not considered in this study. In the Geoplanidae: Caenoplaninae, 80 species are assigned to Artioposthia, Australoplana, Caenoplana, Fletchamia, Lenkunya, Parakontikia, Reomkago, Tasmanoplana and additional new genera considered here. Four species are assigned to two new genera in a new subfamily of the Geoplanidae. Eight introduced species are identified, none of which at present poses an ecological or commercial threat in the Australian region.

Two major flatworm faunal units are recognized in Australia. A northern element dominated by rhynchodemid genera including taxa which also occur in Papua-New Guinea - Irian Jaya and Indonesia. The southern element is dominated by geoplanid genera including some with currently poorly-defined Gondwanan affinities. These flatworm faunal units broadly accord with the Torresian (northern) and with the Tasmanian, South-western, and Bassian or Kosciuskan (southern) zoogeographic subregions.

Item ID: 24134
Item Type: Thesis (PhD)
Keywords: Australia; classification; geographical distribution; Tricladida
Date Deposited: 13 Dec 2012 01:25
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060301 Animal Systematics and Taxonomy @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060208 Terrestrial Ecology @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 100%
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