POTAMOPYRGUS ANTIPODARUM--A MOLLUSCAN COLONISER OF EUROPE AND AUSTRALIA

The hydrobiid gastropod genus Potamopyrgus is shown to be representedin Australia by the New Zealand species P. antipodarum (Gray).It is widely distributed in south eastern Australia and Tasmaniafollowing its introduction about the middle of the last century.The Australian populations of Potamopyrgus were known, incorrectly,as P. niger, because of a misinterpretation of Paludina nigraQuoy & Gai-mard, 1835. Paludina nigra, here placed in thegenus Fluvidona, is redescribed and a neotype designated. Potamopyrgusantipodarum has also been introduced to Europe, where it isknown as P. jenkinsi (Smith) (Received 19 August 1987; accepted 16 December 1987)     

INFERIOR OVARY AND GENERIC AFFINITIES OF GARRYA

Characters of the inflorescence and flower distinguish 2 sections in Garrya. Female flowers of sect. Garrya bear 2 small epigynous appendages, usually considered a rudimentary perianth. In sect. Fadyenia, female flowers are nude, but occasionally 2 more or less foliaceous bracts are partially adnate to the ovary, sometimes simulating the appearance of appendages in sect. Garrya. Authors who have observed this infer that the adnate bracts are homologous to epigynous appendages in sect. Garrya and that the ovary, therefore, cannot be considered inferior. This inference, if valid, would weigh against a close relationship between Garrya and Cornaceae. Clearing and sectioning show, however, that the vascular pattern in flowers of sect. Garrya is similar to the pattern in many Cornaceae. Perianth bundles are united with ventral carpellaries for most of their length, whereas bundles of the adnate bracts in sect. Fadyenia are associated with dorsal carpellary strands; therefore, the 2 kinds of appendages are not homologous. In gynoecial characters Garrya most closely resembles Griselinia and, to a lesser extent, A ucuba. These 3 genera probably had a common origin within the Cornaceae.     

INTERACTIONS BETWEEN SOIL BACTERIA AND THE MOLLUSCAN ALIMENTARY TRACT

The alimentary tract is a major site of interaction betweenan animal's ecosystem and its physiology. It may be intermittentlyor permanently populated by microorganisms from its environmentthat could be beneficial or pathogenic in their influence. Thebacterial populations of the snail (H. aspersa) and the woodlouse(O. asellus) have therefore been estimated in terms of colonyforming units. gm body weight^–1. The bacteria in the snailappear to be similar to those found in soil and show wide resistanceto antibiotics. The main types are gram negative rods tentativelyidentified as belonging to Pseudomonas, Xanthomonas, Acinobacter,Vibrio and Enterobacteriaceae. Some gram positive and endosporeforming bacteria of Bacillus, Staphylococcus and Micrococcusspp were also present. The numbers of bacteria increase towardsthe posterior of the alimentary tract although the numbers inthe digestive gland are more constant. An artificial diet is described that can be used to feed snailsand study the effects of known amounts of additives. When starvedor kept under clean conditions the bacterial population of thesnail gut falls and the thickness of the alimentary tract decreases.All the indications are that the bacteria in the alimentarytract of the snail are indiscriminately accumulated from thenatural environment and are transient populations. (Received 7 June 1989; accepted 24 July 1989)     

THE USE OF MOLLUSCAN SHELL GROWTH PATTERNS IN ECOLOGY AND PALEOECOLOGY

The influence of substratum, depth of water, turbidity, and temperature on daily growth patterns has been studied by transplanting juvenile Mercenaria mercenaria (Linnaeus) from the laboratory to intertidal and subtidal environments.
The study of seasonal growth variations in a population of Gemma gemma Totten from Long Island Sound shows that shell growth patterns may be used to determine the season of death and age of dead shells.
Deep-water species (e.g. Nucula cancellata Jeffreys, Malletia sp., and Calyptogena ponderosa Boss) exhibit growth increments that are more uniform in thickness and less sharply defined than those in shallow-water species.     

THE MOLLUSCAN RHOGOCYTE (PORE-CELL, BLASENZELLE, CELLULE NUCALE), AND ITS SIGNIFICANCE FOR IDEAS ON NEPHRIDIAL EVOLUTION

The rhogocyte (Leydig's cell, cellule nucale, Blasen-zelle,pore cell) is a specific molluscan cell type that occurs throughoutthe animal's primary body cavity, i.e free in the haemocoelor embedded in connective tissue. Rhogocytes closely resemblecyrtocytes and podocytes jn having slit-Uke diaphragms withan encoating extracellular matrix at their surface which probablyacts as a molecular sieve However, rhogocytes are solitary cells,whereas cyrtocytes and podocytes form epitheha Occurrence, variability,naming, and possible functions of the rhogocyte among the MoUuscaare reviewed and discussed. In general, rhogocytes play an importantrole in metal ion metabolism of molluscs, they are possiblyinvolved in the recycling of respiratory pigments and may alsoact in detoxification. Up to now direct homologues of the molluscan rhogocyte havenot been described in any other bi-laterian phylum, so-called‘pore cells’ of other phyla show entirely differentfine-structures However, at least partial (serial) homologycan be accepted between rhogocytes (free cells), arthropod nephro-cytes(cell aggregates or solitary cells) and podocytes (true epithelialcells), and there is also a cytological and functional continuumof both rhogocytes and podocytes to protonephndial cyrto- respectivelysolenocytes. Implications of this postulated ‘cell-family’with slit-diaphragms and their respective ultrafiltration systemsfor theories on the evolution of filtration nephndia are discussed. (Received 10 February 1995; accepted 10 October 1995)     

TEMPERATURE AND INHIBITOR EFFECTS ON FAST AXONAL TRANSPORT IN A MOLLUSCAN NERVE

—The cerebro-visceral connective of Anodonta cygnea has been shown to provide a convenient system for experiments on fast axonal transport. The transport mechanism is directional, independent of the cell bodies, inhibited by cyanide, dinitrophenol and colchicine but is resistant to anoxia. Although the rate of transport increases with temperature above 15°C it is more or less temperature-independent from 4 to 15°C, i.e. over the normal temperature range of this pond-dwelling mollusc.     

A COMPARISON OF THE MOLLUSCAN COMMUNITIES ON INTERTIDAL SAND FLATS IN OYSTER HARBOUR AND PEEL INLET, WESTERN AUSTRALIA

Intertidal molluscs on sandflats in Oyster Harbour and PeelInlet, Western Australia, were compared using transects. Twenty-fourspecies of molluscs were recorded in Oyster Harbour and only7 in Peel Inlet. Two groupings were foundin Oyster Harbour:a midlittoral component and infralittoral fringe. There wasno vertical community structure in Peel Inlet. Molluscs retainedon a 1 mm sieve had about the same mean density and biomassin the two areas but molluscs retained on a 2 mm sieve had amean density of 203/m² and a biomass of 132 g/m² in Oyster Harbourand were absent in Peel Inlet. Several possible reasons forthe absence of large molluscs in Peel Inlet are discussed. PeelInlet is on the west coast in a faunal overlap zone where thenumber of species is reduced. The mean temperature in Peel Inletis 2-3°C higher than in Oyster Harbour and salinity variationsare much more pronounced. (Received 20 November 1979;     

THE DISPERSAL BARRIER IN THE TROPICAL PACIFIC: IMPLICATIONS FOR MOLLUSCAN SPECIATION AND EXTINCTION

Stretches of deep ocean constitute barriers to the dispersal of many shallow-water marine species in the tropical Pacific. The purpose of this study was to assess the selectivity of these barriers with respect to the habitat characteristics, adult size, and predation-related shell architecture of gastropods, and to explore the implications of this selectivity for macroevolutionary patterns of extinction and speciation. The dispersal barrier between continental islands (represented in my collections by species from eastern Indonesia, the southern Philippines, and the north coast of New Guinea) and the nearby oceanic Palau Islands was studied by evaluating the percentage of each architectural and habitat category that is present on the continental islands but missing in Palau. The barrier is significantly more effective against sand-dwelling species than against rock-dwellers, and among rock-dwellers it is most effective against aperturally unarmored taxa. Barriers between Palau and Guam, Guam and the Hawaiian Islands, and the Line Islands and the tropical Eastern Pacific are generally unselective with respect to substratum type and architecture. The fact that narrow-apertured species are less affected by the barrier between the continental islands and Palau than are other rock-dwelling gastropods is consistent with the interpretation that this group has been unusually resistant to extinction and highly susceptible to founder speciation when oceanic circulation is altered. These patterns of susceptibility and geographical distribution may explain why armored gastropods have increased in numbers relative to unarmored ones in the tropical Pacific during the Cenozoic.     

GENERIC RELATIONSHIPS OF DECASCHISTIA (MALVACEAE) AND THE DESCRIPTION OF A NEW TRIBE,DECASCHISTIEAE

The Asiatic genus Decaschistia has traditionally been placed in the tribe Hibisceae, but it is shown that this genus has a combination of characters that does not permit it to be accommodated either in the Hibisceae or in any other tribe of the Malvaceae. A new tribe, the Decaschistieae Fryx., is therefore described and distinguished from the other four tribes currently accepted in the Malvaceae.     

ON THE STATUS OF THE GENERIC NAMES OF THE NUDIBRANCH GENERA CATRIONA, CRATENA, HERVIA, RIZZOLIA AND TRINCHESIA

The genus Catriona Winckworth (1941) is synonymous with TrinchesiaPruvot-Fol (1951) but not with Trinchesia von Jhering (1879). It has priority over Trinchesia Pruvot-Fol. The genus Cratena Bergh (1864) is valid and synonymous withRizzolia Trinchese (1877) but not with Hervia Bergh (1871). The genus Hervia Bergh (1871) is synonymous with Facelina Alderand Hancock (1855), but not all species of Hervia can be includedin the latter genus, and these should, therefore, be distributedamong other genera, some of which are listed. (Received 8 October 1954;