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Title: Phylogeny and evolution of Basal living chitons (mollysca , polyplacophora, lepidopleurida)
Author: Sigwart , J. D.
ISNI:       0000 0001 3409 4568
Awarding Body: Queens University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2008
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The Lepidopleurida is the earliest-derived living group ofpolyplacophoran molluscs (chitons). This group includes 130 living species, distributed worldwide and primarily found in the deep sea; they are small and superficially homogenous in their external morphology. This thesis addresses seven aspects of the biology of these plesiomorphic chitons: (1) Chitons endemic to sunken wood in the South Pacific comprise the most speciose lepidopleuran local fauna. Distribution patterns and faunal composition are examined and five new species are described; (2) The type species ofLeptochiton (and oforder Lepidopieurida) - L. asellus - is examined through histological sections and dissection to identify potential morphological characters for phylogenetic inference; (3) Placement of gonopores and nephridiopores in the pallial cavity are examined across species and their positional homology and phylogenetic informativeness is discussed; (4) Morphology...,.... shell anatomy, girdle armature, and gills - is described encompassing 69 new characters and is analysed using parsimony to assess existing dubordinal divisions; (5) Morphological phylogenetic hypotheses are tested by analysis ofmolecular sequences (complete 18S rRNA, complete 28S rRNA and COl); (6) Two new polyplacophoran ectoparasites are described, from separate populations of lepidopleurans; a parasitic foraminifera (North Atlantic) and an epibiotic bryozoan (South Pacific). Populations infested with these epibionts are investigated for host s~lectivity and distribution; (7) Analysis of fossil and recent basal molluscs-is used to assess placement ofLepidopleurida in molluscan evolution. This thesis shows that Lepidopleurida is not monophyletic, but an assemblage of species that retain plesiomorphic characters. The earliest-derived members are seen in sunken wood; shallower water members of the Lepidopleurida Vll Supplied by The British Library - 'The world's knowledge' are derived from deep sea, wood-living ancestors. Both the deep sea habitat and morphological uniformity ofLepidopleurida obscure efforts at describing phylogenetic patterns within the 'order'. These studies of biology and phylogeny substantially advance the state of knowledge of the group.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available