Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 94-100). Also available via the Internet.

Thesis (Ph. D.)--Oregon State University, 1977. / Includes bibliographical references (leaves 165-175). Also available on the World Wide Web.

The keyhole limpet, Fissurella barbadensis (Gmelin), is a diotocardian prosobranch gastropod belonging to the most primitive group, the Zeugobranchia. It is closely related to such genera as Diodora, Puncturella and Lucapinella. F. barbadensis ranges from S.E. Florida and Bermuda to the West Indies and from Mexico to British Guiana (Farfante 1943). [...]

No description available.

Helcion pruinosus, the rayed limpet, is found in the midshore region of the intertidal zone, (i.e. the Balanoid zone) of rocky shores, from Saldanha Bay to Sodwana Bay along the coast of South Africa. At Gonubie (32°57'S/25°01'E) this species of limpet was found under boulders, (when not feeding), and could reach average densities of 85/ m². The limpets prefer smooth boulders, avoiding those encrusted by coralline algae or boulders with a rough texture. There was no habitat segregation between adult and juvenile H. pruinosus, i.e. there was no sign of up-shore migration by larger individuals. Males out-numbered females by, on average 1.4 : 1, which was a similar sex ratio to that of the congeneric species, H. pectunculus (Gray, 996). Unlike H. pectunculus, there were no differences in shell lengths between males and females (p = 0.946 at Gonubie, south-east coast and p = 0.961 at Kommetjie, south-west coast; t-test). Shell height could also not be used as a criterion to differentiate between the sexes. The average maximum shell length of H. pruinosus at Gonubie and Kommetjie was 25 mm, but the maximum shell lengths found were 30 mm, (one individual in each case), on both the southeast coast and west coast. Growth occurred most rapidly in the first year of life, with individuals reaching 15 mm after 1 year. In the second year limpet growth slowed to only 7 mm. Sexual maturity was reached at a shell length of between 11 to 14 mm (at an age of 8 months to 1 year). The life-span of H. pruinosus was determined at 2.55 years on the south-east coast and 2.9 years on the south-west coast. Micro-growth bands were produced tidally. Growth occurred allometrically, i.e. shell length increased at a faster rate than shell height. The limpets foraged during low tide, at night, presumably feeding on epilithic algae on the boulders. A second smaller peak of limpet activity was often recorded during the day, when low tide coincided with dawn). More limpets (up to ten times more) were active at spring tides compared to neap tides. Limpet activity was greatest during the spring tides of autumn. During all seasons limpet activity peaked 30 minutes before low water, after which numbers decreased rapidly. All limpets had retreated beneath the boulders before being covered by the flooding tide. It was concluded that the limpets were responding to both endogenous and exogenous cues, but the actual stimulus for retreat could not be determined. The limpets did not return to a fixed scar nor did they return rigidly to a home site. H. pruinosus was found to be gonochoristic. Sexes could be separated, on dissection, according to the colour of their gonads (males had white gonads, whilst that of the females was olive-green). Gonads were present throughout the year in most individuals, i.e. totally spent animals were never observed. Reproductive seasonality was similar in west coast and south-east coast animals. The gonad indices of the west coast limpets were higher, (maximum of 35%), compared to that on the southeast coast, (25%). The animals were probably trickle spawners, with some individuals liberating gametes throughout the year. There was however synchrony in gametogenesis between male and female limpets on both the west coast and south-east coast lines. Gonad indices peaked in the summer months (October to December) with a second minor peak in April/May. These peaks occurred before the release of the gametes in spawning events. The gonad index was lowest in winter, (July). The ovaries were full of mature eggs (oocytes having a diameter of 200 to 250 ~) prior to spawning. The acinal wall thickness had been decreasing prior to spawning. After spawning there was an increase in previtellogenic eggs « 100 μm) in females, and an increase in the acinal wall thickness to indicate spermatogenesis. The two populations are subjected to different environmental conditions and the actual cue for stimulating the release of gametes could not be determined. Finally, a table of differences between H pruinosus and its sister species, H pectunculus was created to show the life-style of H pruinosus.

Id30/2/2727The neakshore prosobranch gastropod epifauna of Signy Island, South Orkney Islands. Picken,-.G.B.The prosobranch gastropod epifauna associated with a mature algal community on a rocky substrate in the depth range 2-12 m was studied at Signy Island, South Orkney Islands, Antarctica (60°S.43°W). Quantitative samples were collected by divers at monthly intervals from April 1975 to March 1977, using an air-lift suction sampler. Thirty-one prosobranch species were found in a total sample of about 138,000 animals; 7 species were undescribed, and 10 were new to the South Orkney Islands. Small, cryptic "Rissoids" such as Eatoniella kerguelenensis, E.caliginosa and Ovirissoa adarensis were numerically dominant, but the limpet Nacelle (Patinigera) concinna was dominant in terms of biomass. Mean prosobranch density was 4,591 individuals 1r2. and mean biomass 17.1 g dry tissue m2. Diversity was high throughout most of the depth range and the assemblage was both complex and stable. Ten species developed non-pelagically by means of large yolky eggs laid on algal fronds or stones in the sub-littoral. Spawning periods were prolonged and largely aseasonal, and development times were long. Recruitment of juveniles was also aseasonal, though a peak of recruitment was observed in one species during the Austral spring. Laevilacunaria antarctica shows several characteristics of 'K-selection'; it develops non-pelagically, grows slowly and lives for more than one year. Other weed-dwelling prosobranchs at Signy Island which develop non-pelagically probably also tend towards 'K-selection'. The limpet Nacella develops pelagically after adults congregate briefly in summer to form spawning "stacks" of 3-6 individuals. Nonetheless, the species shows several 'K-selection' traits, particularly very slow growth and deferred maturity, and tends towards 'K-selection'.Collections from other sites to 80 m depth off Signy Island yielded 20 more species; 13 of these were undescribed and 5 were new to the South Orkney Islands. The study has shown that the prosobranch fauna of the South Orkney Islands was incompletely known, and that a greater understanding of the distribution, endemism and origins of the Antarctic prosobranch fauna will not be possible until more key sites are investigated in greater detail.

The chloride ion concentration of blood, urine, and foot muscle, blood and muscle water content, and blood and urine osmotic pressure, were measured in summer and winter adapted populations of the prosobranch limpet Collisella persona, over a range of salinities from 25% to 125% SW (100% SW = 480 mEq Cl⁻/L). Blood, urine, and foot muscle Cl⁻ were not regulated in all salinities tested. Blood Cl⁻ was generally hypoionic and urine isoionic to the experimental sea water concentrations. Muscle Cl⁻ did not reach a level greater than one-half of equivalent blood or sea water values in all salinities tested. However, muscle and blood values were similar, if muscle Cl⁻ were expressed in terms of extracellular water. Extracellular volume remained relatively unchanged and showed only a 7% increase in salinities ranging from 50% to 125% SW. Seasonal differences were apparent in muscle Cl⁻, with winter values higher than summer values by 20-25 mEq/kg tissue, in salinities ranging from 75% to 125% SW. However, this could be accounted for by the slightly larger (4-8%) extracellular space recorded from winter animals. Summer and winter adapted limpets were osmoconformers in salinities ranging from 25% to 125% SW. Summer animals had blood hyperosmotic, and urine isosmotic to the experimental sea water concentrations. Winter limpets had blood hyperosmotic to 75% SW, and isosmotic in 25% and 125% SW. Urine was hyposmotic to 25% and 75% SW, and isosmotic in 125% SW. Summer blood was hyperosmotic to winter blood, although summer and winter urine remained isosmotic. In addition, for both summer and winter animals, blood was hyperosmotic to urine. The foot muscle water content of winter adapted limpets returned to the control value in 50% to 125% SW, between 48 hours and 1 week. Over the same time period, summer animals only regulated muscle water in 50% and 75% SW. Blood water content remained relatively unchanged for both summer and winter adapted limpets, and showed a 4% decrease over a salinity range from 25% to 125% SW. There were no significant seasonal differences in blood water content. Seasonal differences recorded during the present study, in particular the comparatively large variation in measurements from summer animals, were attributed to seasonal changes in salt and water permeability, or metabolic rate. In addition, an attempt was made to relate the physiological responses recorded from limpets in the laboratory, to the survival of limpets in the field. / Science, Faculty of / Zoology, Department of / Graduate

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Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 215-251).

Scheltema (1971, 1978) and others have proposed that extensive larval dispersal allows marine invertebrate species to establish great geographic ranges; several studies along a single margin of an ocean basin have supported this proposal (Shuto, 1975; Hansen, 1978). This study makes use of the fossil record to examine larval dispersal patterns on a larger geographic scale: across an entire ocean basin. Sixteen genera/subgenera of marine prosobranch gastropods were selected as the data base for the study. Eight of the genera were widely distributed (have fossil representatives on both the eastern and western margins of the North Atlantic Ocean) during the Neogene, and eight genera were narrowly distributed (fossil representatives were restricted to either the eastern or the western margin of the North Atlantic) during the Neogene. The larval forms of fossil species within each genus were inferred by examination of protoconch morphologies, according to guidelines established by modern biologists (Robertson, 1974; Shuto, 1975). The two groups were compared using statistical methods to test a null hypothesis of no relationship between geographic distribution and larval form. The results of the study reject the null hypothesis, and support the conclusion that Neogene marine prosobranch genera that are widely distributed across the North Atlantic Ocean basin are much more likely to exhibit planktotrophic larval development than are prosobranch genera that are geographically limited to a single margin of the ocean basin. / Master of Science