LIFE HISTORY AND POPULATION DYNAMICS OF COCHLICELLA ACUTA (MuLLER) (GASTROPODA: HELICIDAE) IN A PASTURECEREAL ROTATION

The conical snail Cochlicella acuta was sampled over a 3-yearperiod in a pasture-cereal rotation and a nearby roadside wastelandat Hardwicke Bay, South Australia. The life cycle of C. acuta was primarily biennial in the agriculturalfields, with offspring being produced in large numbers in thepasture phase but not the cereal phase of the rotation. Thebreeding season lasted from autumn to spring. Snails were mostabundant in spring and summer, especially near the edges offields. During summer, snails aggregated on robust weeds suchas Reseda lutea. Many snails were killed by burning pasturesin autumn, prior to sowing crops. Snails were more abundantand smaller in size in the roadside wasteland than in the agriculturalfields. Strategies for the control of C. acuta in pasture-cereal rotationsare discussed. (Received 9 April 1990; accepted 10 August 1990)     

EFFECT OF CONTROLLED TEMPERATURES ON GAMETOGENESIS IN THE GASTROPODS PHYSA ACUTA (PHYSIDAE) AND BULINUS TROPICUS (PLANORBIDAE)

The effects of a range of constant temperatures on gametogenesiswere investigated in two freshwater snail species which occursympatrically in the Umsin-dusi River, Natal, South Africa,Physa acuta (invasive) and Bulinus tropicus (endemic). Bothwere shown to be simultaneous hermaphrodites with slight protandry.An increase in temperature accelerated the process of gametogenesisbut P. acuta responded more rapidly to these changes than B.tropicus. This, coupled with the greater fecundity and shorterincubation period of P. acuta, gives it a reproductive advantageover the endemic species, providing a possible explanation forthe invasive's success in rapidly repopulating disturbed riverinehabitats. (Received 16 November 1990; accepted 1 May 1991)     

FURTHER STUDIES ON THE TAXONOMY AND BIOLOGY OF THE OCTOCORAL-FEEDING GENUS PHYLLODESMIUM EHRENBERG, 1831 (NUDIBRANCHIA: AEOLIDOIDEA)

The aeolid nudibranch genus Phyllodesmium (Mollusca: Gastropoda)is reviewed, three new species are described and further informationon the biology, anatomy and distribution on the eight previouslyknown species is reported. The genus Ennoia Bergh, 1896 is considereda synonym of Phyllodesmium and the type species Ennoia briareusredescribed. The genus Phyllodesmium is unique amongst the aeolidsin feeding on octocoral cnidarians. This has led to the evolutionof nudibranch- zooxanthellae symbioses, zooanthellae being obtainedfrom the octocoral prey. The adaptations developed throughoutthe genus are described and possible relationships between thespecies proposed. (Received 6 January 1990; accepted 20 May 1990)     

MORPHOLOGY, ANATOMY AND HISTOLOGY OF FLABELLINA AFFINIS (GMELIN, 1791) (NUDIBRANCHIA, AEOLIDOIDEA, FLABELLINIDAE) AND ITS RELATION TO OTHER MEDITERRANEAN FLABELLINA SPECIES

The Atlantic and Mediterranean flabellinid Flabellina affinis(Gmelin, 1791) (Opisthobranchia, Nudi-branchia, Aeolidoidea)is examined morphologically, anatomically and histologicallywith special emphasis on characters which have been widely neglectedin recent literature (e.g. the histological structure of theoral glands, typhlosole). The study provides detailed data aboutall organ systems which are compared to existing data of otherauthors. The species described as Flabellina affinis by Bergh(1875; 1886) is considered not to be conspecific with the Flabellinaaffinis examined in this and other studies. Furthermore, Flabellinaaffinis is compared to other Mediterranean species, especiallyF. ischitana (Hirano & Thompson, 1990). F. ischitana differsfrom F. affinis mainly by the structure of the genital system.The phylogenetic trees presented for the genus by Gosliner &Kuzirian (1990) and Gosliner & Willan (1991) are discussed. (Received 5 August 1996; accepted 9 June 1997)     

A novel spermatozoan ultrastructure in the shrimp Hippolyte obliquimanus Dana, 1852 (Decapoda: Caridea: Hippolytidae)

The aim of this study was to describe and illustrate the morphology of the spermatozoon of the Western Atlantic shrimp, Hippolyte obliquimanus. Individuals were sampled from Itaguá Beach (Ubatuba, southern Brazil). The male reproductive system was dissected and morphological analysis was undertaken using a stereomicroscope, a light microscope, and transmission electron and scanning electron microscopes. When viewed from the nuclear or acrosomal poles, each spermatozoon has many translucent radiating arms (about 20) from a denser cell body, while laterally the cell body and arms resemble a “cnidarian medusa”, with all the arms projecting away from the bell-like cell body. This sperm morphology is distinct from the “thumbtack”-shaped spermatozoa observed in the majority of carideans but has similarities to the spermatozoa of Rhynchocinetes spp. The morphology of sperm of several species of the genus Hippolyte resembles the spermatozoon of H. obliquimanus with the presence of posterior nuclear arms, but it is necessary to study other Hippolyte species to place these arms in the context of the genus.     

Larval development of Hexapanopeus caribbaeus (Stimpson, 1871) (Crustacea, Decapoda, Xanthoidea, Panopeidae) reared under laboratory conditions

The genus Hexapanopeus Rathbun, 1898 contains eight species,of which three are found in the Brazilian coast. The larvaldevelopment of two of these species has already been studiedin the laboratory. This article describes in detail the morphologyof the complete larval stages of Hexapanopeus caribbaeus rearedunder laboratory conditions, and the morphology is comparedwith that of the larvae of the other species of the same genus.     

DESCRIPTION OF A NEW GENUS AND SPECIES BELONGING TO THE FAMILY PHYLLIDIIDAE (NUDIBRANCHIA: DORIDOIDEA)

A new genus of phyllidiid nudibranch, Reticulidia, is described.Distinguishing features are the reticulate pattern of smoothridges on the dorsum and the radially arranged, glandular discswhich make up the pharyngeal bulb. Additional features of theforegut are described and compared with other genera. The importanceof the alimentary system for the separation of genera withinthe Phyllidiidae is supported and its validity reinforced bythis new genus. One species, Reticulidia halgerda, is describedas new and differentiated from a second, sympatric species.Reticulidia is presently known from the eastern Indian Ocean,South China Sea and western Pacific Ocean. ^*Present address: Australian Biological and Environmental Survey,Australian National Parks and Wildlife Service. GPO Box 1383,Canberra. ACT 2601. Australia. (Received 15 August 1989; accepted 8 January 1990)     

SPERM ULTRASTRUCTURE IN THE AUSTRALIAN OYSTER SACCOSTREA COMMERCIALIS (IREDALE & ROUGHLEY) (BIVALVIA: OSTREOIDEA)

Sperm ultrastructurc is investigated in the economically importantAustralian oyster Saccostrea commercialis (Iredale & Roughley).Mature spermatozoa consist of a broad, cap-shaped acrosomalvesicle, sub-acrosomal material (axial rod embedded in a granularmatrix), a round nucleus (deeply invaginated anteriorly), twotriplet substructure centrioles surrounded by four sphericalmitochondria, and a flagellum anchored via satellite fibresto the distal centriole and plasma membrane. Spermatozoa ofS. commercialis closely resemble those of other investigatedostreids, with the exception that the anterior region of theacrosomal vesicle is transversely banded. Differences in acrosomalsubstructure correlate with the known inability of Saccostreaand Crassostrea gametes to interact. Potential exists for useof sperm morphology in the resolution of taxonomic problemswithin the Ostreoidea. (Received 23 April 1990; accepted 28 June 1990)     

THE ANATOMY AND RELATIONSHIPS OF A MARINE VALVATOIDEAN (GASTROPODA: HETEROBRANCHIA)

The anatomy of Cornirostra (new genus) pellucida (Laseron),a marine Indo-West Pacific gastropod, is described and is shownto be similar to that of the northern hemisphere, freshwaterValvatidae. There are, however, several differences betweenCornirostra and valvatids, notably in details of the anatomyof the reproductive system, the morphology of the head-foot,the spawn and in radular characters that warrant family-levelseparation for Cornirostra. Tomura bicaudata (Pilsbry and McGinty) from Florida is alsoa member of the family. (Received 9 September 1989; accepted 30 December 1989)     

COMPARATIVE SPERMATOLOGY OF FOUR SYMPATRIC SPECIES OF SIPHONARIA (PULMONATA: BASOMMATOPHORA)

The fine structure of the modified sperm and spermatogenesisof four sympatric species of Siphonaria is described. The morphologyof the sperm of all species is very similar. The head, whichis about 6 µm long, is composed of a nucleus with fibrouschromatin capped by an acrosome (about 1 µm long) comprisedof an acrosomal pedestal and apical vesicle. The midpiece hasa mitochondrial derivative which surrounds a single glycogenhelix, posterior to which is a glycogen piece. Although differencesbetween each species exist, the value of sperm morphology forpurposes of taxonomy in this genus is questioned. Comparisonwith other basommatophorans however suggests that sperm morphologymay be of value at a higher taxo-nomic level. The morphologicalchanges that occur during spermatogenesis are similar to thosedescribed for other molluscs with modified sperm, except thatduring early spermiogenesis the Golgi body and smooth endoplasmicreticulum become highly developed. This proliferation of theSER and Golgi occurs at the same time as elongation of the spermatid.Throughout spermatogenesis, the germ cells are closely associatedwith a somatic cell which, because of structural similaritieswith the somatic cell of mammalian seminiferous epithelium,has been termed a Sertoli cell. After the spermatids have beenreleased from the Sertoli cells of the testis, maturation continuesin the hermaphrodite duct where the acrosome reaches its finalsize and glycogen accumulates in the glycogen compartment ofthe mid-piece. (Received 25 April 1990; accepted 1 September 1990)     

ULTRASTRUCTURE OF THE MATURE SPERMATOZOA OF THE LAND SNAIL EPIPHRAGMOPHORA TUCUMANENSIS (DOERING, 1874) (GASTROPODA: HELICOIDEA)

The ultrastructure of the sperm of Epiphragmophora tucumanensis(Doering), a pulmonate land snail belonging to the family Xanthonychidae,was examined. The results showed that this spermatozoon presents a similarmorphology to the other advanced stylommatophoran sperm described.The most peculiar characteristic is the form of the nucleus,which is straight instead of helically coiled. An acrosome ispresent, composed of an apical vesicle and an acrosomal pedestal.The connecting piece or neck region is formed by a basal bodyplus a centriolar derivative. It is also the point of originof coarse fibres that accompany the axoneme. Thus, the axonemalcomplex exhibits a 9+9+2 pattern. The midpiece is an elongatedregion composed of paracrystalline and matrix materials (collectively,the mitochondrial derivative) enclosing a single glycogen helixand the axoneme. The mitochondrial derivative extends to theposterior tip of the spermatozoon. As observed in other stylommatophorans,both an annulus and a glycogen piece are absent. (Received 25 October 1993; accepted 4 February 1994)     

THE OCCURRENCE OF ANOPAEA (BIVALVIA : INOCERAMIDAE) IN THE ANTARCTIC PENINSULA

The genus Anopaea represents a small but distinctive group ofinoceramid bivalves that apparently remained functionally endobyssate.The somewhat unusual morphology (for an inoceramid) probablyresults from structural modifications tofacilitate sedimentpenetration at a high angle and anchorage by an antero-ventralbyssus. Although never as common as thecontemporary genera Retroceramusand Inoceramus, Anopaea is now known from temperate bivalveassemblages in both the Northern and Southern Hemispheres. Itpersisted from the Late Jurassic (Tithonian) to the Early Cretaceous(Neocomian), and possibly even later. (Received 26 June 1980;     

REVIEW OF THE GENUS DENDRODORIS EHRENBERG, 1831 (GASTROPODA: NUDIBRANCHIA) IN THE ATLANTIC OCEAN

Six valid species of the nudibranch genus Dendrodons Ehrenberg,1831 inhabit the Atlantic Ocean, including the Mediterraneanand Caribbean Seas. Dendrodons lumbata (Cuvier, 1804), Dendrodonsgrandiflora (Rapp, 1827), Dendrodons nigra (Stimpson, 1855)(immigrant from the Red Sea), Dendrodons krebsu (Mörch,1863), Dendrodoru senegalensis Bouchet, 1975 and Dendrodonswarta Marcus & Gallagher, 1976. Additional data about thebiology and geographical distribution of these species are presented.New evidence suggests that other species assigned to the genusDendrodons, Dendrodons racemosa Pruvot-Fol, 1951 and Dendrodonsminima Pruvot-Fol, 1951, must be included in the genus DoriopsillaBergh, 1880. Three new species of Dendrodoris are describedfrom the Northeastern Atlantic and West Africa;Dendrodons angolensis,Dendrodoris guineana and Dendrodons herytra. The variable external morphology makes species recognition difficult.Instead, the diagnostic characters utilised to separate speciesare the shape of the male cirrus hooks, the structure of thereproductive system and features of the egg-mass. (Received 25 April 1995; accepted 1 August 1995)     

AN ULTRASTRUCTURAL STUDY OF SPERMATOZOA OF HELIX ASPERSA AND HELIX POMATIA (GASTROPODA, PULMONATA)

Spermatozoa of the pulmonates Helix aspersa Müller andH. pomatia Linnaeus are examined in detail using transmissionelectron microscopy (TEM). Important features such as the acrosome,perinuclear sheath, nucleus and terminal region of the midpieceare described for the first time. Also presented are the firstultrastructural observations on spermatozoa from spermatophoresin any pulmonate gastropod (H. aspersa). No morphological differencescould be found between sperm taken from spermatophores and thosewithin the hermaphrodite duct in H. aspersa. Spermatozoa ofH. aspersa and H. pomatia snow all the characteristics of euthyneuranspermatozoa, namely: a helically-keeled nucleus; distinctivearrangement of acrosomal components (apical vesicle, acrosomalpedestal), and extremely elongate midpiece (axoneme and glycogenhelix enclosed by matrix and paracrystalline layers). The spermnucleus of both species is short, and the midpiece also formsthe terminal portion of the spermatozoon (glycogen piece absent).The extraordinary positioning of the acrosome in H. aspersa—reflectedbackwards from the nuclear apex—is not observed in H.pomatia, though a perinuclear sheath (possibly another acrosomalcomponent) is present in sperm of both species. Helix spermatozoaare compared with other euthyneuran sperm and briefly discussedfrom the systematic viewpoint. Present address: Department of Zoology, St. Lucia, 4067, Brisbane,OLD, Australia (Received 23 May 1988; accepted 17 August 1988)     

ANATOMY AND SYSTEMATIC PLACEMENT OF SAYELLA LAEVIGATA (GASTROPODA: PYRAMIDELLIDAE: SAYELLINAE)

The ectoparasitic snail Sayella laevigata was first describedby Orbigny (1842) and first placed in the genus Sayella by Odé (1994) without discussion. This study provides justificationfor this assignment to the genus Sayella Dall, 1885 and to the subfamilySayellinae Wise, 1996. Sayella laevigata possesses an elongatepenis, with subapical swelling tapering to a short terminalnipple, that is characteristic of the genus.     

Autoecology and some life history stages of Dinophysis acuta Ehrenberg

A persistent and unusual bloom of Dinophysic acuta Ehrenbergin the RIas Bajas (Northwest Spain) from early July to mid-November1989, was associated with a diarshetic shellfish poisoning (DSP)outbreak that prevented mussel extraction in some areas fromearly August to mid-December. Integrated samples (0–5,5–10 and 10–15 m) were taken once or twice a weekat six stations. Maximum numbers of D.acuta (up to 2.3 10⁴intheintegratedsamples)andpercentageofobserveddMdingcells(upto3l%),appearedin August, and formed a maximum in the thermodine. Cellnumbers were minimal when upwelling caused a breakdown of stratification.Fligh numbers of D.acuta (up to 1.8 10⁴ cells 1^–1 appearedagain when persistent south winds in late October caused a reversalof the circulation. Thus, the two cell maxima occurred duringtwo distinct hydrographic regimes, but in both cases at temperaturesof 15–17C. Numerous cells with one typical D.acuta valve,but the other valve reduced in size, were seen during the bloom,as well as Dinophysts dens Pavillard cells that might be a lifecycle stage of D.acuta. Other observations include double- walled,unwinged forms that are perhaps some kind of cyst, and a hypothetical‘fertilizing tube’ emerging from the larger cellof a D.acuta/D.dens couplet. It is suggested that the maximaduring stratification and during downwelling episodes couldcorrespond to periods with a predominance of in situ growthand physical accumulation, respectively, and that the exceptionalmeteorological conditions during 1989 provided the optimum scenariofor the unusual occurrence of D.acuta.