Cassidula

About: Cassidula is a research topic. Over the lifetime, 7 publications have been published within this topic receiving 113 citations.

The evolution of the Ellobiidae with a discussion on the origin of the Pulmonata.

Abstract: SUMMARY. The primitive phonate family, the Ellobiidae, is discussed with reference to the structure, ecology and relationships of the following genera—Pythia, Ophicardelus, Cassidula, Ovatella, Leucophytia, Ellobium, Pedipes, Leuconopsis, Marinula, Rangitotoa, Melampus and Carychium. Ecologically, the family is shown to fall into four sections, a more primitive estuarine section, and sections containing marine intertidal, coastal terrestrial and inland terrestrial genera of rather more specialized character. In relation with detailed descriptions about to be published of the functional morphology of British ellobiids, a wider comparative account is now given of the digestive system and the genital ducts, and their evolution throughout the family. Further trends, chiefly concerning the adult and embryonic shell, are dealt with, in a discussion of the evolutionary pattern of the Ellobiidae. The frequent occurrence of parallel evolution, and the relative absence of adaptive radiation, or characters of obvious selective value, are noted. A scheme is proposed for the classification of ellobiid genera into subfamilies, which in some points departs from that of Thiele, based on radular studies by Odhner. A wider review is then given of the evolutionary significance of the Ellobiidae, with reference both to the evolution of pulmonates from prosobranchs, and to their relationships with primitive tectibranchs. Finally, the relationships of the Basommatophora and the Stylommatophora are discussed, and the significance of the Ellobiidae is pointed out, with reference to the origins of both groups. The Basommatophora are held to be a phylogenetically unnatural group. The Ellobiidae is the only family of this group that could have provided possible ancestors for Stylommatophora, and these are unlikely to have occurred among known genera. Reference is made to the geological evidence in support of the view of gastropod evolution presented from this study.

Fluctuations in the reproductive condition of Cassidula auris‐felis, a Malayan mangrove ellobiid snail (Pulmonata: Gastropoda)

Abstract: Cassidula auris-felis Brug, occurs abundantly on flat, mangrove mud on the west coast of Malaya at a level within three feet of the highest spring tides. Ovotestesof only very few snails lacked developing male gametes but oocytes were often very uncommon, becoming abundant at irregular intervals. Abundant oocytes were found in large proportions of the population after periods of more than eight days without tidal wetting. Abundant oocytes were not found after periods when the mud was left exposed for periods of seven days or less. Statistically, proportions of “predominantly female” snails are shown to be correlated with the number of days without tidal wetting in a complete period of continuous exposure prior to collection. In addition, rather more snails bore abundant oocytes in the lunar “weeks” following new and full moon than in “weeks” following half moons. Conditions leading to abundant oocytes also appear to promote copulation in adults and commencement of gametogenesis in young snails.

Ophicardelus (Mollusca, Pulmonata) in eastern Australia: how many taxa?

Abstract: The common south-eastern Australian estuarine ellobiid snails belonging to Ophicardelus have been considered to be one variable taxon by some authors, and three largely sympatric species by others. This study was undertaken to determine the number of taxa present. Different types of data collected included shell shape, allozyme electrophoresis, shell and radular morphology, anatomy and geographic range. These data sets were then examined for consistent discontinuities, and the results showed that the nominal species could be distinguished by a combination of shell shape and sculpture. Individuals from each nominal species also grouped together using allozyme data, although one taxon (Ophicardelus quoyi) is sometimes paraphyletic based on these data. There are several differences in the anatomy and radular morphology that separate the three taxa. These included marked differences in the penial complex, vagina, and presence or absence of a pallial gland. The three taxa also have different geographic ranges,...

Taxonomic assessments of some Cyprinotinae Bronstein, 1947 species (Crustacea: Ostracoda) from Japanese and Korean rice fields, including (re-) descriptions of six species and a review of the type species of the subfamily.

Abstract: Rice is the staple food crop for approximately half the world's population, but some common and abundant taxa inhabiting rice fields, such as ostracods, are poorly studied. For many ostracod species only brief, initial descriptions are available, hindering reliable identifications, and so their ecological roles in rice fields remain obscure. This study partially addresses this problem by assessing the taxonomic validity of six species of Cyprinotinae ostracods reported from rice fields in Japan and South Korea: Cyprinotus uenoi Brehm, 1936, Hemicypris megalops Sars, 1903, Hemicypris ovata Sars, 1903, Hemicypris vulgaris Okubo, 1990, Heterocypris rotundata (Bronstein, 1928), and Hemicypris kawagaensis Okubo, 2004 nomen nudum. Type material of C. uenoi was not designated and Brehm's ostracod collection is missing, but Japanese and Korean records of C. uenoi differ significantly from Brehm's original description. The Japanese and Korean species is described and named herein as Cyprinotus cassidula sp. nov. Japanese specimens reported to be Hemicypris megalops are probably misidentified, but details of the carapace of Hemicypris megalops are obscure due to poor preservation of type material. Examination of topotype material of Hemicypris posterotruncata Bate, 1970, a sub-fossil from near Lake Turkana in Kenya, demonstrates that this species is extant in Asian rice fields. Investigation of type material of Hemicypris kliei (Lindroth, 1953) has revealed that it is not a senior synonym of Hemicypris posterotruncata, contrary to previous studies. Size and morphological data indicates that Hemicypris vulgaris is a large form of Hemicypris posterotruncata and the two species are treated as synonyms herein. Examination of paralectotypes of Hemicypris ovata indicates that it is very similar to Hemicypris posterotruncata, especially the larger morphotypes, but as these two species can be distinguished by morphological features they are both retained as separate species. However, Japanese records of Hemicypris ovata are considered misidentifications of the larger forms of Hemicypris posterotruncata. Hemicypris kawagaensis, which has only been reported once from East Asia, is herein regarded as a junior synonym of Hemicypris barbadensis Broodbakker, 1983, and is likely an alien species in Asia. Asian specimens previously identified as Heterocypris rotundata show sufficient differences to European specimens to determine that they are not conspecific. This species is described as Heterocypris savatenalintonae sp. nov. Taxonomic descriptions of Hemicypris ovata, Hemicypris posterotruncata, Hemicypris megalops, Hemicypris kliei, Heterocypris savatenalintonae sp. nov., and Cyprinotus cassidula sp. nov. are presented. Finally, it is noted that past redescriptions of Cyprinotus cingalensis Brady, 1886, the type species of the genus and the subfamily Cyprinotinae Bronstein 1947, are based partly on other species.

Chromosomes of Some Archaeopulmonata (Mollusca: Basommatophora)

Abstract: This paper presents the chromosome numbers of 7 species of primitive basommatophoran snails and discusses these numbers in relation to systematics and to those numbers reliably reported for the Archaeopulmonata by other authors.1. Sixteen bivalents were observed in cells of the first division of meiosis in the 4 species of Siphonariidae studied, Siphonaria alternata, S. guamensis, S. laciniosa and S. pectinata.2. Several different chromosome numbers were observed in the two species of Ellobiidae studied. Seventeen bivalents were observed in Cassidula vespertilionis and 19 pairs of chromosomes were found in Melampus coffeus and in a population (of hybrids?) resembling this species but differing slightly on shell morphology. One specimen in this latter population was a tetraploid individual with 38 bivalents.3. The one species of Chilinidae examined, Chilina fluviatilis, had 18 pairs of chromosomes.4. The caryotype of Melampus bidentatus lineatus consists of 7 pairs of metacentric chromosomes and 11 pairs of submetacentric chromosomes. This is the first accurate report of the caryotype of an ellobiid snail.