THE GROWTH AND BREEDING CYCLE OF LITTORINA OBTUSATA (GASTROPODA : PROSOBRANCHIATA) FROM CARDIGAN BAY

The population structure of Littorina obtusata was for mostof the year bimodal, with a stable adult component and an activelygrowing juvenile component. Growth rate of the juvenile componentwas similar at different beach levels and there was a retardationof growth as the snails approached sexual maturity. There was little variation in the histology and external appearanceof the reproductive organs throughout the year and the breedingcycle has been characterized by the amount of spawn laid andthe presence of mature eggs in the oviduct of the female. ^*Present address: Portway School, Penpole Lane, Shirehampton,Bristol. (Received 7 September 1977;     

A NEW GENUS AND SPECIES OF PLANORBIDAE (GASTROPODA: HETEROBRANCHIA: PULMONATA) FROM NORTHERN AUSTRALIA

A new genus and species of Planorbidae, Kessneria papillosa n.gen.and sp. from the Northern Territory, Australia, are described.The new genus is morphologically most similar to Leichhardtia,another genus restricted to Northern Australia, from which itdiffers in a number of important shell and anatomical characters.The shell of the new genus differs from all other planorbidsin having a raised, papillate protoconch, and is also uniqueamongst Australian high-spired genera in being umbilicate and inhaving a sinuate outer lip. (Received 12 May 2000; accepted 25 September 2000)     

REVISION OF THE GENUS ACAVUS FROM SRI LANKA (GASTROPODA: ACAVIDAE)

The genus Acavus from Sri Lanka includes three species, Acavushaemastoma (Linnaeus), Acavus superbus (L. Pfeiffer) and Acavusphoenix (L. Pfeiffer) with two subspecies, Acavus phoenix phoenix(L. Pfeiffer) and Acavus phoenix castaneus new subspecies.The conchological and anatomical differences between these species,as well as their intraspecific variation are described. Theirdistribution is shown on maps and all locality records are listed.The presence of extensive intraspecific polymorphism, the developmentof geographical subspecies and the presumable hybridizationbetween some species show that the Acavus species are not isolatedrelict species, but that speciation is in progress and thatthe radiation of the Acavus species is probably much youngerthan the radiation of the acavid genera. The three Acavus speciesare not acutely endangered at present. In contrast to manyother land snails, there is no risk of a rapid decline of theAcavus species due to deforestation, because these species alsooccur in synanthropic habitats. (Received 22 December 1998; accepted 2 October 1999)     

THE ANATOMY OF PACHYDERMIA LAEVIS (ARCHAEOGASTROPODA: 'PELTOSPIRIDAE')

The anatomy of Pachydermia laevis Warén & Bouchet,1989 is investigated. It is a deep-sea gastropod and restrictedto hydrothermal vents of the East Pacific Rise. Its anatomyresembles that of Melanodrymia aurantiaca Hickman, 1984 (Melanodrymiidae)in most respects, except that its gonopericardial duct opensinto the renopericardial duct, not into the peri-cardial chamber,and that it lacks a copulatory organ. Examination of M. aurantiacamain confirms earlier work. The two species have a cerebralbuccal connective fused with the cerebral ganglion (not freefrom it), a synapomorphy that has not been described for anyother archaeogastropod. The investigation suggests that Melanodrymiaand Pachydermia are closely related and together with Cyathermiidaeand Neomphalidae form a monophyletic group within the Neomphalina.No evidence was found to support earlier speculations aboutclose relations of Neomphalina to Viviparoidea. (Received 10 January 1996; accepted 3 April 1997)     

A NEW SPECIES OF ABYSSOCHRYSOS (GASTROPODA: LOXONEMATOIDEA) FROM THE OMAN MARGIN

A new species of Abyssochrysos, A. xouthos n. sp. isdescribedfrom south-west Oman in the northern Arabian Sea at a depthof3150 metres. This represents the first record of this genusfromthe northern Indian Ocean. Of the five previously describedextantspecies of Abyssochrysos A. xouthos is most similar toA.melanioides from which it differs in radular and shellcharacters. (Received 22 February 1999; accepted 20 May 1999)     

THE ANATOMY AND RELATIONSHIPS OF ELACHISINA DALL (GASTROPODA: RISSOACEA)

Species of Elachisina are marine and extend from the Caribbeanand western North and Central America to the Philippines, Hawaiiand New Zealand. The anatomy and other morphological featuresof Elachisina ( = Microdocluis) floridana (Rehder) from theFlorida Keys are described and compared with rissoacean familiesjudged to be most closely allied. This species has a uniquecombination of characters which do not correspond to those character-setsused to define any known rissoacean family. Important featuresinclude a metapodial as well as pallial tentacles, a wide ctenidiumwith low, triangular filaments, an osphradium which is shortrelative to the ctenidium, an S-shaped loop of the intestinewhich extends into the pallial roof, long dorsal folds in themidoesophagus, a rather loosely organised nervous system, anopen prostate gland from which the pallial vas deferens exitsat its anterior extremity, glandular lobes on the penis, a non-glandularfold on the right side of the ventral channel of the capsulegland and a fold on the left side in the posterior end of thechannel, a pair of seminal receptacles lying between the albumenand capsule glands, a bursa which lies alongside the capsulegland and opens posteriorly to the ventral channel and a U-shaped,expanded section of the oviduct proximal to the albumen glandand seminal receptacles. This combination of characters is consideredto be sufficiently distinct to arrant the erection of a newfamily-level taxon to accommodate the small group of speciesjudged to be congeneric with E. floridana. The Elachisinidaeappears to be most closely related to the Rissoidae, Iravadiidaeand Hydrobiidae. (Received 19 October 1983;     

ANATOMY AND RELATIONSHIPS OF THE BONE-FEEDING LIMPETS, COCCULINELLA MINUTISSIMA (SMITH) AND OSTEOPELTA MIRABILIS MARSHALL (ARCHAEOGASTROPODA)

The anatomy of Cocculinella minutissima (Smith, 1904) and Osteopeltamirabilis Marshall, 1987 is described. Both species belong tothe Lepetelloidea and are closely related to Addisonia Dall,1882, the anatomy of which has been recently described by theauthor. Commonly derived (symapomorphic) characters of all threegenera are found especially in the genital system (hermaphrodites,tcstis and ovary separated, with separated ducts, open seminalgroove to the unmodified right cephalic tentacle), and in thealimentary tract (paired oesophageal glands). Distinct similaritiesin genital and excretory system (large right kidney isolated;hermaphrodites, separated gonads) with the Pseudococculinidae,Pyropeltidae and Lepetellidae justify a uniting superfamilyLepetelloidea, the anatomy of which is quite different fromthat of the Cocculinoidea (Cocculinidae and Bathy-sciadiidae) Osteopelta has retained certain primitive characters (rhipidoglossateradula, true stomach), but is specialized in having a snout-likehead, a concentrated cerebropedal ring, and secondary gill leaflets(vestigial gill in Cocculinella, distinct gill leaflets in Addisonia).Cocculinella and Addisonia share additional synapomorphic featuresof the posterior alimentary tract (reduction of stomach, intestineforms a large sac, midgut gland contains dark granules). Severalaut-apomorphies of each genus justify their status as distinctfamilies. Relationships to the (coiled) Choristellidae, whichfeed on empty egg-cases of sharks or skates (as do addisoniids)and have a cocculinellid-like radula type, are discussed ^*Present address: Insitut fr Zoologie der Universitat, Technikerstr.25; A-6020 Innsubruck, Auttria (Received 10 March 1987;     

ON TWO NEW SPECIES OF THE GENUS TRIGULA FROM CHINA (GASTROPODA: POMATIOPSIDAE)

Among the materials of minute freshwater snails collected from Guangxi and Huana Provinces, two species are considered to be new to science. Holotype and paratypes are kept in the Laboratory of Medical Malacology, Department of Parasitology, Hubei Medical College.     

中国沟颈螺属一新种记述(腹足纲:柄眼目:艾纳螺科)

记述中国沟颈螺属１１种,其中包括１新种,即芒康沟颈螺Ｈｏｌｃａｕｃｈｅｎ ｍａｒｋａｍｅｒｓｉｓ Ｃｈｅｎ ｅｔ Ｚｈａｎｇ,ｓｐ．ｎｏｖ．,编制了分种检索表,对新种进行了描述,并与近似种进行了比较。     

海南水域玉蟹科六新种记述(甲壳动物:十足目:短尾次目)

海南水域蟹类区系十分丰富,仅玉蟹科就有54种,本文报道了其中发现6新种。     

GENITAL DUCTS OF THE CERITHIACEA (GASTROPODA: MESOGASTROPODA) FROM THE GULF OF CALIFORNIA

In the Cerithiacea the pallial genital duct exhibits varyingdegrees of closure. In addition, two anatomical groupings occurwithin their genital systems. These groups are based on differencesin the location of the accessory sperm sacs, albumen gland andthe presence or absence of a distal sperm collecting groovein the female. Criteria in the male include the nature of (thevas deferens and the existence of spermatozeugmata. (Received 13 February 1984;     

COPULATORY ACTIVITY AND SPERM PRODUCTION IN BULINUS (PHYSOPSIS) GLOBOSUS (GASTROPODA: PLANORBIDAE)

Young Bulinus (Physopsis) globosus performed male copulatoryactivity and cross-fertilized other snails before their femalereproductive tracts were mature. The two most immature snailsshowed preputial eversion when secretion was present only inthe muciparous gland and at the carrefour region of the oviduct.Sixteen snails showed preputial eversion and four snails cross-fertilizedother snails when their oothecal glands and/or major portionof the oviducts contained either no secretion or only scantyamounts. When paired with a partner snail for 12 or 20 consecutive days,adult snails copulated as males on approximately 60% of thedays paired and up to 8 consecutive days. Virgin snails raisedin isolation copulated as male at the same rate as non-virgin,community-raised snails. Ability to copulate as male was notdependent upon previous experience as male or female. Aftera single copulation as male after 7 days isolation, the hermaphroditicducts of maleacting snails contained 87 000 sperm. Sperm productionoccurred at approximately 50 000 sperm.d-¹, until at 10 dayspost-copulation, snails contained 639 000 sperm. (Received 25 May 1982;