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Title: Systematics, ecology, and evolution of hydrothermal vent endemic peltospirids (Mollusca: Gastropoda) from the Indian and Southern oceans
Author: Chen, Chong
ISNI:       0000 0004 5346 2751
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2015
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This thesis centres around two genera of large peltospirid gastropods (Mollusca: Neomphalina: Peltospiridae) endemic to hydrothermal vent ecosystems. One is the 'scaly-foot gastropod', an emblematic species of the Indian Ocean vents with unique dermal sclerites covering the foot like roof tiles. The other was recently discovered from expeditions to the Southern and Indian oceans, lacks sclerites and possesses large opercula. As both genera and their assigned species remained undescribed, they were formally described herein which forms a basis to understanding their biology. The 'scaly-foot gastropod' from both the Central Indian Ridge (CIR) and the Southwest Indian Ridge (SWIR) were confirmed to represent a single species and is formally named as Chrysomallon squamiferum. Through molecular genetic analyses using the COI gene, genetic differentiation between SWIR and CIR populations was detected for the 'scaly-foot gastropod'. In contrast, the peltospirids with large opercula from the East Scotia Ridge (ESR) and the SWIR proved to be two distinct species within an undescribed genus. The ESR species was formally described as Gigantopelta chessoia and the SWIR species as G. aegis. The molecular genetic analyses of the COI gene, confirmed the genetic isolation of the two and consolidated their status as separate species. A 3D tomographic model of Chrysomallon squamiferum was generated to characterise the soft anatomy and morphology as well as to understand its internal anatomy and adaptation which remained little-studied. Further to the enlarged esophageal gland already known to house chemosynthetic endosymbionts, C. squamiferum was discovered to have a hypertrophied circulatory system with a gigantic, muscular heart and large ctenidium to adapt to life in a hypoxic environment and to supply the endosymbionts with necessary chemicals. Histological examinations of the sclerites and operculum showed that it was unlikely that the sclerites originated from operculum duplication. Comparisons with polyplacophoran scales revealed starkly different secretion mechanisms despite the superficial similarity, which has implications on the placement of sclerite-bearing Cambrian taxa. Overall, the results from this thesis ascertained the systematic positions of these large-sized, enigmatic peltospirids, and led to improved understanding of their ecology and evolution. The important role of larval dispersal in maintaining metapopulations across the distribution of a vent-endemic taxa is highlighted. The adaptations of vent-endemic taxa remains little-known even in well-studied species, warranting future studies on these and other species.
Supervisor: Rogers, Alex D.; Copley, Jonathan T.; Linse, Katrin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ecology (zoology) ; Evolution (zoology) ; Zoological sciences ; Biodiversity ; Biology ; Life Sciences ; hydrothermal vent ; gastropod ; mollusc ; evolution ; systematics ; taxonomy