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Studies on Opisthobranchia. / Helen Caroline Marshall

Swansea University Author: Helen Caroline Marshall

Abstract

Several species of nudibranch mollusc considered rare can be found at Mumbles, Swansea, UK. Collections were made during every spring low tide, weather permitting, for three years. During the course of this investigation several aspects of nudibranch ecology were investigated. Oogenesis and spermato...

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Published: 2006
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42671
Abstract: Several species of nudibranch mollusc considered rare can be found at Mumbles, Swansea, UK. Collections were made during every spring low tide, weather permitting, for three years. During the course of this investigation several aspects of nudibranch ecology were investigated. Oogenesis and spermatogenesis were studied using light microscopy in Thecacera pennigera (Montagu), Ancula gibbosa (Risso), Facelina auriculata (Muller) and Valio notbus (Johnston). Significant differences were found in oocyte length in relation to animal size, and nucleolus diameter in relation to the oocyte stage of development. It was concluded that oogenesis in all four species occurs in discrete waves; this is probably attributable to the lack of space within the female follicles once vitellogenesis has occurred. Spermatogenesis was uniform among T. pennigera, F. auriculata and A. gibbosa. However, a difference in the orientation of the developing spermatids was observed in P. nothus. Data presented in this chapter for P. nothus contradict previous studies investigating other Palio spp. Veliger development was investigated using T. pennigera, P. nothus, Onchidoris bilamellata (L.), A. gibbosa, and Cuthonagymnota Couthouy. No veliger development or shell growth were observed in A., gibbosa or C. gymnota. Shell growth was observed in P. nothus, but the veligers did not structurally develop further towards metamorphic competency. O. bilamellata and T, pennigera showed significant development; both exhibited shell growth and developed eye spots. The latter species also developed a larval heart and underwent mantle fold retraction. However, when introduced to Bugula plumosa (Pallas) T. pennigera failed to undergo metamorphosis. The population genetics of T. pennigera was investigated using mtDNA techniques. Three populations were sampled from South Wales; all three showed genetic homogeneity which was attributed to the long-term planktonic stage, and the extensive flushing which occurs within the Bristol Channel. Light microscopy was used to investigate the internal morphology and histology of A. gibbosa. Many feamres were similar to that reported for other members of the Goniodorididae. However, A. gibbosa was discovered to have a diaulic reproductive system, suggesting that Ancula may be a primitive member of this family. Several of the A. gibbosa sectioned were parasitized with Splanchnotrophus willemi Canu. The effects of this parasite on A. gibbosa varied from no internal damage to complete disintegration of the visceral mass. Despite infection, all animals had copulated at least once as evidenced by the presence of allosperm within their receptaculum seminis. It was considered that the individuals suffering severe internal damage due to parasitism would have been unlikely to produce viable spawn. S. willemi was implemented as the cause for its sporadic occurrence. The lecithotrophic anaspidean Akera bullata (Muller) was reared through metamorphosis on a variety of algal substrata, biofilm, and a control. Metamorphosis could be initiated within 24 hours of hatching, and was promoted by the presence of Chondrus.
Keywords: Biological oceanography.
College: Faculty of Science and Engineering

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