Rhythmic egg-release in Littorina littorea (Mollusca: Gastropoda)

Batches of female Littorina littorea from four estuarine sites were kept in aquaria throughout their breeding season (December to July), some permanently submerged in circulating sea-water and others in a regime of simulated semi-diurnal tides of constant small amplitude. Females without the tidal experience released few eggs with little relation to the lunar month. Those in the tidal regime released more than four times the total number of eggs and released far more in periods of new and full moon than in periods of half-moon. Over the whole season, release was 1–5–3–25 times faster (at different sites) during full and new moon but the difference was more accentuated at the height of the season in February to early March and in early May. While individual females differed considerably and there were minor variations between the four sites, it is concluded that a two-weekly rhythm relates egg release to the spring-neap tide cycle and that this rhythm requires a tidal cycle of immersion and emersion for its maintenance. The special significance of such a rhythm for a species with pelagic eggs and larvae in an estuary is discussed.     

On the taxonomy of Littorina africana (Mollusca: Gastropoda)

L. africana and L. knysnaensis are regarded as two morphs of a single species which exhibits a genetic cline along the south-eastern coast of southern Africa. The dark brown morph knysnaensis dominates the western, cooler end of the cline and is replaced by the pale blue morph africana at the warmer end of the cline. These conclusions are based on evidence from the latitudinal distributions, the complete range of intermediate forms regarding shell colour and shell morphology and the lack of differences in redular morphology, penial morphology or habitat.     

The taxonomy of two host-specific, cryptic dendronotoid nudibranch species (Mollusca:Gastropoda) from Australia including a new species description

Two host-specific, extremely cryptic, small dendronotoid nudibranchs from Australia are described and classified, and their phylogenetic position within the superfamily is discussed- Lomanotus vermiformis Eliot, 1908 subsists exclusively on the hydrozoan Lytocarpus philippinus (Kirchenpauer, 1872). Lomanotus stauberi Clark & Goetzfried, 1976 is newly synonymized with L. vermiformis . Marioniopsis platyctenea sp. nov. subsists exclusively on the alcyonacean Parerythropodium hicksoni Utinomi, 1972. Marianina rosea (Pruvot-Fol, 1930) is relocated to the Tritoniidae (wherein it forms a monotypic subfamily, Marianinae) because of possession of palmate rhinophoral clavi, the principal apomorphy of the Tritoniidae. The validity of using the form of the digestive gland as a basis for dividing the Tritoniidae is questioned since it is acknowledged that this organ has progressed from a solid (holohepatic) arrangement to a dispersed (cladohepatic) arrangement in parallel in several major nudibranch lineages; form thus offers merely homoeoplaseous phylogenetic characters. Separation of right and left digestive glands appears to be one of the first steps in the simultaneous and interdependent evolutionary processes of internal detorsion and external 'aeolidization' in nudibranchs.     

Multiple paternity in Littorina obtusata (Gastropoda, Littorinidae) revealed by microsatellite analyses.

Parental identity for juvenile Littorina obtusata was determined from three egg masses by means of microsatellite DNA markers. Results confirm that the attendant adult female in each case was the dam of the offspring and that at least 4-6 males contributed to each brood. This correlates with our behavioral observations that indicated multiple copulations between the female and several males in each experimental aquarium. A significant number of offspring from each brood were sired by non-sampled males (males that had copulated with females before capture) whose sperm had been stored by the female. This is the first direct evidence of multiple paternity in the Littorinidae. Results are discussed in reference to current theories of sperm competition, male precedence, and cryptic female choice.     

Biochemical genetic variation in the genus Littorina (Prosobranchia:Mollusca)

The genus Littorina has been subject to many studies of electrophoretically detectable variation, mostly aimed either at clarifying questions concerned with population structure, or at clarifying difficult taxonomic/systematic problems. This paper reviews many of these studies. Topics covered include Hardy-Weinberg deviations, the extent of genetic differentiation among populations within species, founder effects and the effects of human introductions on genetic variation, the biological significance of allozyme variation, and the uses of allozyme variation in Littorina systematics.     

Hybridisation in the Littorina saxatilis species complex (Prosobranchia : Mollusca)

This paper details attempts to breed members of the L. saxatilis species complex in the laboratory and to construct interspecific hybrids between them. Success in reciprocal crosses between animals from the type localities of the species of Littorina saxatilis (Olivi) and Littorina rudis (Maton) indicates that these two taxa are synonymous. Six of the twelve possible reciprocal hybridisation crosses between the four species (L. saxatilis, L. arcana Hannaford Ellis, L. nigrolineata Gray and L. neglecta Bean) have been attempted, with only one proving successful, that between male L. saxatilis and female L. arcana. This hybrid cross produces viable offspring, although at a lower frequency than either of the parental crosses in the laboratory, while the reciprocal cross has, as yet, proved unsuccessful. Limited work on the F1 hybrids shows them to be inter-fertile and also capable of backcrossing with male L. saxatilis, but not with female L. saxatilis or L. arcana. Details are also given of attempts to find natural hybrids in sympatric populations of the species of the complex, using gel electrophoresis.     

Arion transsylvanus (Mollusca,Pulmonata, Arionidae): rediscovery of a cryptic species

Jordaens, K., Pinceel, J., Van Houtte, N., Breugelmans, K. & Backeljau, T. (2010). Arion transsylvanus (Mollusca, Pulmonata, Arionidae): rediscovery of a cryptic species. —Zoologica Scripta, 39, 343–362. Cryptic species are abundant among invertebrates and are often hard to recognise. Molecular markers are an extremely useful tool to delineate cryptic taxa, although they should be applied with caution because different genes and techniques may yield different outcomes. We illustrate how cross‐validation by molecular and morphological data can be applied to optimise taxonomic interpretations when cryptic species are involved. This is performed for the terrestrial slug Arion subfuscus species complex which represents a historical ‘taxonomic garbage can’. Gonad morphology, allozymes and mtDNA data consistently showed that slugs from Romania and a location in E Poland represent a strongly differentiated taxon within this complex. These slugs are therefore formally redescribed and assigned to A. transsylvanus Simroth 1885 ; a forgotten nominal taxon from Transylvania. Diagnostic characters, including DNA sequences for the mitochondrial 16S rDNA are presented. Animals with the morphology of A. brunneus Lehmann 1862 , a nominal taxon which has also been reported from Romania, have the gonad type, allozyme alleles and 16S rDNA haplotypes of either A. fuscus, A. subfuscus or A. transsylvanus. Therefore, A. brunneus is regarded as a colour morph shared by several species and hence, A. transsylvanus is probably the only A. subfuscus‐like species in the Romanian Carpathians.     

Dimorphic migration,growth, and fecundity in a seasonally split population of Littorina brevicula (Mollusca: Gastropoda) on a boulder shore

Littorina brevicula (Philippi) is an abundant herbivorous gastropod species inhabiting intertidal zones of the north-western Pacific and has internal fertilization with planktonic eggs and a larval stage. A population of L. brevicula on a shore in Amakusa, Japan, splits into an upper and a mid shore sub-population during the mating season in winter, while all individuals occurred in the upper zone in summer. Transplant and recapture experiments have shown that snails from each sub-population have a distinct pattern of seasonal migration, suggesting that the snail population consists of two behavioral morphs. To explore the relationship between migration pattern and life history characteristics in the snails of the two migration morphs, monthly quantitative samplings and a mark-release and recapture survey were carried out for the population of L. brevicula over a 1-year period. In autumn, some of the adults migrated downward to the mid shore and formed the lower sub-population from October to April. Migration between the upper and lower sub-populations was minimal from December to February, when L. brevicula copulate actively. The shell growth rates of the snails in the lower zone were slightly higher than those in the upper zone, but the shell width of females was not a good predictor of the number of mature ova they contained. The number of mature ova was not significantly different between the females of the two migration morphs. In addition, the mortality of marked snails did not differ significantly between the upper and lower zones. Thus, no evidence was obtained to indicate a difference in the reproductive fitness between the two migration morphs.     

Evidence of natural hybridization and introgression between Vasconcellea species (Caricaceae) from southern Ecuador revealed by chloroplast, mitochondrial and nuclear DNA markers

BACKGROUND AND AIMS: Vasconcellea x heilbornii is believed to be of natural hybrid origin between V. cundinamarcensis and V. stipulata, and is often difficult to discriminate from V. stipulata on morphological grounds. The aim of this paper is to examine individuals of these three taxa and of individuals from the closely related species V. parviflora and V. weberbaueri, which all inhabit a hybrid zone in southern Ecuador. METHODS: Molecular data from mitochondrial, chloroplast and nuclear DNA from 61 individuals were analysed. KEY RESULTS: Molecular analysis confirmed occasional contemporary hybridization between V. stipulata, V. cundinamarcensis and V. x heilbornii and suggested the possible involvement of V. weberbaueri in the origin of V. x heilbornii. In addition, the molecular data indicated unidirectional introgression of the V. cundinamarcensis nuclear genome into that of V. stipulata. Several of the individuals examined with morphology similar to that of V. stipulata had genetic traces of hybridization with V. cundinamarcensis, which only seems to act as pollen donor in interspecific hybridization events. Molecular analyses also strongly suggested that most of the V. x heilbornii individuals are not F(1) hybrids but instead are progeny of repeated backcrosses with V. stipulata. CONCLUSIONS: The results of the present study point to the need for re-evaluation of natural populations of V. stipulata and V. x heilbornii. In general, this analysis demonstrates the complex patterns of genetic and morphological diversity found in natural plant hybrid zones.     

Local site differences in survival and parasitism of periwinkles (Littorina sitkana Philippi, 1846)

The periwinkle, Littorina sitkana, is found throughout the intertidal zone, often in isolated subpopulations. The majority of trematode parasites use snails as intermediate hosts, and decreased survivorship is often observed in snails infected with trematodes. Sampling L. sitkana from four sites in Barkley Sound, British Columbia, Canada, we test the effects of parasitic infection on snail survival using maximum likelihood and Bayesian approaches using the software MARK and WinBUGS. We found that survival of periwinkles and trematode community composition differed among sites, but survival and trematode prevalence were uncorrelated. WinBUGS performed better than MARK in two ways: (1) by allowing the use of information on known mortality, thus preventing survival overestimation; and (2) by giving more stable estimates while testing the effect of body size on snail survival. Our results suggest that snail survival depends heavily on local environmental factors that may vary greatly within a small geographical region. These findings are important because the majority of experimental studies on survival are done on snails from a single location.     

Large scale population structure and gene flow in the planktonic developing periwinkle, Littorina striata, in Macaronesia (Mollusca: Gastropoda)

Allozymes were used to investigate the genetic structure of 42 populations of the planktonic developing, Macaronesian periwinkle Littorina striata, throughout its entire geographic range (Azores, Madeira, Canary Islands and Cape Verde Islands). This periwinkle is presumed to have a high dispersal and gene flow potential, because it has a planktonic development. It is therefore expected to show little population genetic differentiation. Indeed, based on Wright's hierarchical F-statistics, no significant genetic differentiation could be detected among populations, at any of the specified hierarchical levels (i.e. population, island, and archipelago). Nevertheless, the Cape Verde Islands seemed genetically more diverse (highest mean number of alleles per locus). The number of loci revealing a significant genetic heterogeneity increased with increasing distance between populations, while private alleles based gene flow (Nm) estimates also revealed a tendency towards a geographical pattern. The distribution of rare and private alleles, might account for these observations which suggested some geographical effect. Because of the low frequency at which these alleles occur, their influence on the genetic population structure is negligible, and not picked up by F-statistics.     

Field observations on the feeding habits of Littorina scutulata Gould and L. sitkana Philippi (Gastropoda,Prosobranchia) of southern Vancouver Island (British Columbia,Canada)

The microdistribution of Littorina scutulata and L. sitkana on the rocky shores of Vancouver Island can be related to their feeding characteristics. Their gut contents, studied with light and fluorescence microscopy, showed that both species are opportunistic herbivores. However, L. scutulata can feed on the sparse epi- and endolithic microflora of the supralittoral zone, while L. sitkana is confined to special microenvironments, with abundant epilithic growth.     

The anatomy of Addisonia (Mollusca,Gastropoda)

Summary The organization of Addisonia lateralis (Requien, 1848) and A. brophyi McLean, 1985 is described. Addisonia species have a thin, asymmetrical, cup-like shell and a very simple shell muscle. Eyes, oral lappets and epipodial tentacles are absent and the right cephalic tentacle is also used as a copulatory organ. Most characteristic is the enormously developed gill which is enlarged into the right subpallial cavity. It is composed of about 30 leaflets with skeletal rods and its epithelia are uniquely arranged. The heart is large and the single auricle is situated anteriorly left. There are two kidneys: the left is small, while the right forms large coelomic cavities and has no connection with the pericardium or the hermaphroditic genital system. Testis and ovary are separate: both have a simple duct proper (vas deferens, oviduct). They are connected to the copulatory organ by an open seminal groove; a small receptaculum is present. The mouth opening is typically triangular, with no jaws or subradular sense organs. Addisonia possesses tuft-like salivary glands, a radula diverticulum and distinct, tubular oesophageal glands. The oesophagus itself is simple. The radula and the posterior alimentary tract are unique; the stomach is completely reduced and the intestine forms a pseudostomach. The streptoneurous, hyoathroid nervous system has pedal cords with three commissures. The visceral loop is also cord-like. A single (left) osphradium is present and the small statocysts have several statocones.The peculiarities and unique combination of primitive and advanced characters in Addisonia reflect a highly enigmatic organization among the Archaeogastropoda. Possible relationships to other archaeogastropod groups are discussed.     

Phylogeny of the Cocculinoidea (Mollusca, Gastropoda)

Abstract. The superfamily Cocculinoidea is a group of marine, deep-water, limpet-like gastropods. Recent speculation surrounding their affinities has concentrated on their placement within the Gastropoda. However, phylogenetic relationships within the Cocculinoidea, especially the monophyly of families and genera within the group, remain poorly understood. Phylogenetic analysis of 31 morphological characters for 15 cocculinoidean taxa and 2 outgroups resulted in a single most parsimonious tree, length=70, CI=0.62, and RI=0.71. Monophyly of the Cocculinoidea, Cocculinidae, and the genera Cocculina and Coccopigya was supported; Paracocculina and Coccocrater were found to be paraphyletic. Character optimization demonstrates that many characters often cited as diagnostic of various taxa, are often homoplastic and/or synapomorphies at different hierarchical levels.     

Dart formation in Helix aspersa (Mollusca,Gastropoda)

Summary Dart formation in Helix aspersa has been investigated by SEM of isolated darts at progressive stages in their development, and by histology of dart sacs at the same times. Dart formation begins at the tip of a tubercle where a small group of epithelial cells secrete an organic material filling a small CaCO₃ cone that is the first mineralized part of the shaft. Subsequent secretory activity by an increasing area of the tubercle epithelium results in an increase in the diameter and anterior lengthening of the shaft. Continued secretion by the tubercle and dart sac epithelium produces the flare and finally the corona. A pattern of deposition is also evident in the fine structure of the mineral. In the shaft and vanes there is an inner layer of spherulitic prismatic structure which is covered by a layer of irregular patches of simple prismatic structure. The outermost layer of the shaft and vanes has a continuous simple prismatic structure. Two layers are present in the flare, an inner granular amorphous layer and an outer spherulitic prismatic layer. The corona consists of a single rarefied prismatic layer. A mechanism of dart formation is suggested that involves two types of organic matrix, calcifying and non-calcifying. Measurements of the calcium content of darts, dart sacs, and collars indicate that the hemolymph is the probable source of calcium for the dart.     

A new species of hydrobiid snails (Mollusca, Gastropoda, Hydrobiidae) from central Greece

Anew minute valvatiform species belonging to the genus Daphniola Radoman, 1973, Daphniola eptalophossp. n., from mountain Parnassos, Greece is described. The new species has a transparent valvatiform-planispiral shell, wide and open umbilicus, grey-black pigmented soft body and head and a black penis with a small colorless outgrowth on the left side near its base. A comparative table of shell dimensions and a key to the species known for this endemic genus for Greece are provided.     

Inheritance of longitudinal shell bands in the snails Littorina obtusata and Littorina saxatilis (Gastropoda, Prosobranchia)

The hypothesis of a monogenic inheritance of dark longitudinal bands on the shell in the gastropods Littorina obtusata and L. saxatilis was checked. One gene having two alleles proved to be responsible for the shell banding pattern in both of the species. The presence of bands was a dominant character in either case.     

The maintenance of shore-level size gradients in an intertidal snail (Littorina sitkana)

Summary The size of many intertidal animals varies with tidal height. These size gradients could be produced by growth or survival varying with tidal height, or by animals moving to a preferred tidal level. The body size of the snail, Littorina sitkana, increases steadily with tidal height in rocky high intertidal habitats of British Columbia. To determine how size gradients were maintained in L. sitkana, I quantified how growth, survival, and snail movement varied with tidal height. I studied populations of L. sitkana found on sheltered pebble beach and exposed basaltic shelf habitats. Mark-recapture studies and experimental transplants showed that growth could not have produced the size gradients because snail growth rates in both habitats were as fast or faster at low tidal levels (where the snails were the smallest) than at high tidal levels. However, survival rates were lowest at low tidal levels. On pebble beaches, this was due to size selective predation on large snails by the pile perch, Rhacochilus vacca. On basaltic shelves, heavy wave action at low tidal levels may have caused the poor survival rates. Transplanted snails moved homeward on pebble beaches, but not on basaltic shelves. Reduced survival rates at low tidal levels cause size gradients in both habitats, and snail movement helps to maintain size gradients on pebble beaches.     

Specific dynamic action demonstrated in the herbivorous marine periwinkles,LIttorina littorea L. and Littorina obtusata L. (Mollusca,Gastropoda)

• 1.1. Respiration rates of starved periwinkles, Liltorina littorea and Littorina obtusata, increased by 40–60% when fed their preferred algal food for 1 hr, or after having been exposed for the same period to an aqueous extract of the alga.
• 2.2. The stimulus causing the rise in metabolic rate by algal extracts is therefore thought to be chemosensory in nature, and possibly composed primarily of dissolved free amino acids.
• 3.3. The respiration rates of L. littorea responded only to the green alga Enteromorpha intestinalis while L. obtusata demonstrated an increase in respiration rates when fed the ubiquitous brown alga, Ascophyllum nodosum, and to a lesser degree to Enteromorpha.
• 4.4. These results compare very well to postprandial increases in oxygen consumption demonstrated in vertebrates and marine bivalves where the components of specific dynamic action (SDA) are thought to be chiefly biosynthetic costs of digestion and assimilation.