Shell form and niche occupation in Nucella lapillus (L.) (Gastropoda)

Collections of Nucella lapillus (L.) from various eastern Atlantic areas have been measured, and shell shape has been analysed by D'Arcy Thompson's method in terms of whorl ratio, apical angle, and spiral angle. In southwestern Ireland N. lapillus varies greatly from tall and narrow in sheltered situations to short and wide at very wave-exposed sites. A local population is described for a bay near Crookhaven, County Cork. In northwestern Spain the open-sea form is developed only weakly. In southwestern Ireland N. lapillus effectively populates mussel beds in the lower littoral on open coasts, whereas in Spain it is sparse or absent from such situations but plentiful high up on the shore on barnacles in places where there is some local shelter from rocks or crevices. It is suggested that failure to develop the open-sea type in Spain is responsible for this difference in niche. Both in Spain and at a site in Scotland N. lapillus feeding on mussels in sheltered situations is of the tall narrow type, so that a diet of mussels cannot alone be responsible for the development of the open sea type, although it still might be a necessary condition. It is to be expected that the genetic composition of populations will vary regionally and will contribute to variation in shell form, but the part which it plays on a purely local scale remains uncertain.     

Some observations on the spawning behaviour and larval development in the limpet,Cellana Radiata (Born) (Gastropoda: Prosobranchia)

Some observations were made on the spawning behaviour, fertilization and larval development from fertilization to the veliger stage in the common tropical limpet Cellana radiata, of the Visakhapatnam coast. Attempts have also been made to compare the present observations with those in the temperature climate limpets.     

Spawning in Littorina littorea (L.) (Gastropoda: Prosobranchiata)

Data on the amount of ‘spawn’ of Littorina littorea (L.) held in the laboratory for varying periods of time during the breeding season have been used for an analysis of the pattern of egg production. It has been shown that there is good evidence for seasonality of breeding in the population studied, and that there are both diurnal and longer time scale fluctuations in spawn output. There is a strong indication of a lunar/tidal rhythm in spawning, but this is not conclusively proved. A limited number of experiments have failed to show any effect of temperature fluctuations on spawning, and there is no evidence of the entrainment of a rhythm when the snails are brought into the laboratory.     

Salinity detection by Hydrobia ulvae (Pennant) and Potamopyrgus jenkinsi Smith (Gastropoda:Prosobranchia)

Both Hydrobia ulvae (Pennant) and Potamopyrgus jenkinsi Smith climb vertically in the laboratory but stop or crawl horizontally if presented with a sharp salinity drop. 50% of Hydrobia ulvae respond to a difference of 18–26% from the original solution. 50% of Potamopyrgus jenkinsi respond to a difference of 53–55%. In both species, the response is impaired at high temperatures, and in Hydrobia ulvae it is also impaired at low temperatures. From 9–22 °C no temperature influence is evident.From acclimation experiments it is suggested that the snails respond not to the gradient across the interface, but to the gradient between body fluids and the upper solution presented. Snails respond to non-ionic gradients when these are presented either as density gradients or as solutions separated by a semi-permeable membrane, and it is argued that they detect osmotic pressure directly. The sense organs are probably located in the tentacles.     

Shell colour variation in Bullia digitalis, a sand-dwelling, intertidal whelk (Gastropoda: Prosobranchia)

Bullia digitalis is an intertidal whelk that lives on sandy beaches in South Africa. It is highly variable in shell colour, with individuals varying from white to dark brown. This paper describes shell colour variation of B. digitalis at seven sites, along a 230 km coastline east of the Cape Peninsula. Seven colour forms were found: striped, violet, banded violet, banded brown, orange, pale yellow and white. These forms are probably genetically determined morphs. The striped form is the most common at all sites, constituting 53–62% of each sample. The violet is the second most common morph. Its frequencies are remarkably stable at 15–17%. The striped form blends well into the sandy environment and may therefore be of considerable cryptic value in concealing B. digitalis from predators. The violet form is highly conspicuous. Its stable frequency throughout the study area may represent a genetic balance that is not relevant to any visual advantages of the violet colour.     

Water balance and the mantle cavity fluid of Nucella lapillus(L.) (Mollusca: Prosobranchia)

When uncovered by the tide Nucella lapillus (L.) retains fluid in the mantle cavity which accounts for ≈ 39% of the total water content of the attached animal. This extra-corporeal fluid reservoir retained in the mantle cavity has been investigated in relation to desiccation. Volume changes of mantle cavity fluid (m.c.f.) and concentration changes in Cl^?, Na⁺ and total osmotic pressure of m.c.f. and blood, suggest that the m.c.f. reduces the full effects of desiccation on the animal by restricting those effects to the external compartment. The blood of Nucella living in normal sea water was found to be hypo-osmotic and an hypothesis is presented which links this to the rôle of the m.c.f. during desiccation.     

The control of mating behaviour in Helix pomatia L. (Gastropoda: Pulmonata)

I examined how extirpations of various parts of the reproductive system affected the mating behaviour of Helix pomatia. The integration of the sequence of activities in the mating behaviour was not affected by any of the extirpations performed. It is concluded that the sequence is mainly controlled centrally. The simultaneousness of the performance of dart shooting behaviour and the initiation of a new bout of mating activity was found to be independent of the presence of the dart. The mating activity was decreased by mechanical stimulation of the duct of the bursa copulatrix and increased by extirpation of the digitiform glands. It is concluded that the mating behaviour cycle is caused partly by mechanical effects of dart shooting and copulation.     

Thermal preference and tolerance of Megastrea (Lithopoma) undosa (Wood, 1828; Gastropoda: Turbinidae)

The thermoregulatory behavior of the wavy turban snail Megastrea (Lithopoma) undosa was determined in a horizontal thermal gradient and was 16.31 in day cycle and 14.4 °C in night cycle. Displacement velocity of adults was 29.3±4.2 cm h⁻¹ during the light phase and 26.1±3.2 cm h⁻¹ during the dark phase. The critical thermal maxima of the wavy turban snail were determined. As a measure of thermal tolerance, snails were subjected to increasing water temperatures at a rate of 1 °C every 30 min until they were detached from the substrate. The critical thermal maximum at 50% was 29.7 °C.     

Revision of the Arctic-Atlantic Rissoidae (Gastropoda, Prosobranchia)

The present paper contains a revision of the Arctic-Atlantic Rissoidae (Gastropoda, Prosobranchia). Twenty-two species are recognized. Two new species, Alvania obliqua and Alvania pseudoareolata are described, both previously wrongly identified. One new genus, Frigidoalcania , is established with Rissoa janmayeni as type-species.     

Cold,freezing, and desiccation tolerance of the limpet Acmaea digitalis (Eschscholtz)

Cold, freezing, and desiccation tolerance were examined in the limpet, Acmaea digitalis (Eschscholtz). Fifty percent of the experimental population survived freezing at temperatures between ?10 ° and ?12 °C for at least 24 hr. In this temperature range, 60–80 % of the body water was frozen. The LD₅₀ for water loss by desiccation was 76.5% ± 1.3_δ. At 70–80% body water loss, solutes were concentrated between 350 and 500%. Some limpets failed to survive immersion in 450% seawater for 6 hr (100% scawater = salinity of 31‰), suggesting that much of the damage from freezing and desiccation was from an increased solute concentration. No glycerol could be detected in extracts of the foot and the visceral mass of A. digitalis during winter, confirming similar results in studies carried out on other intertidal molluscs.     

Absorption of ferritin by cells of the digestive gland in Nassarius tegula (Gastropoda : Prosobranchia)

Within 12 min after the prosobranch snail, Nassarius, begins feeding on ferritin-labeled food, ferritin reaches the lumen of the digestive gland and is absorbed by the digestive cells lining the gland. Within the digestive cells, the ferritin is present in coated pinocytotic vesicles, in microvesicles and in macrovesicles. It is probable that ferritin (and components of the food as well) progresses rapidly in order from the gland lumen to the pinocytotic vesicles to the microvesicles to the macrovesicles. The macro vesicles are presumably an important site of intracellular digestion.     

Basal bodies in the odontoblasts of the limpet,Patella coerulea L. (Gastropoda)

Summary The odontoblasts in the long radular gland of Patella coerulea L. are arranged in a terminal position; therefore newly formed teeth already have an upright position. The long and slender odontoblasts have only one to three lengthy and ramifying apical microvilli. Between these pinnate microvilli a fine filamentous material appears which probably corresponds to chitin microfibrils. Therefore, the pattern of chitin microfibrils seems to depend on the arrangement of odontoblasts' microvilli. For the first time, basal bodies were found in the apical part of odontoblasts which led to the assumption that the radular gland originally might have been a mucous gland, the secretion of which was transported by cilia.     

The characterization of N-acetylglucosaminidases from the limpet Patella vulgata (L.)

The α- and β-N-acetylglucosaminidase activity of the limpet Patella vulgata (L.) is due to two enzymes. One of these enzymes hydrolyses both α- and β-N-acetylglucosaminidases and is referred to α,β-N-acetylglucosaminidase. The other is a β-N-acetylglucosaminidase (EC 3.2.1.30). Both enzymes have been isolated and characterized as glycoproteins containing 12% hexose, mainly galactose. The amino acid, neutral sugar and amino sugar content of the two enzymes is very similar, and the main difference lies in the presence of 9% sialic acid in β-N-acetylglucosaminidase. The molecular weight of α,β-N-acetylglucosaminidase is 217 000 and that of β-N-acetylglucosaminidase is 136 000. Evidence has been obtained for the presence of an additional sub-unit in the α,β-enzyme.     

Feeding in some Australasian Cymatiidae (Gastropoda:Prosobranchia)

Of the four common Australasian cymatiids studied, Cabestana spengleri and Mayena australasia feed almost entirely on simple ascidians. Monoplex australasiae feeds on bivalves as well as on ascidians and Charonia rubicunda feeds on a variety of echinoderms. All species locate their prey by chemoreception of current born prey substances. Charonia rubicunda is a nocturnal predator while the other species feed almost continually.     

Spermiogenesis in the vermetid gastropod Dendropoma petraeum (Gastropoda,Prosobranchia)

The structure and maturation of the male gonad of the Mediterranean vermetid gastropod Dendropoma petraeum are described. Histological sections of the gonads were made throughout development and gonad activity was monitored at regular monthly intervals. During the autumn months the gonad is very small and is surrounded by a large quantity of connective tissue; it becomes more voluminous from December to August, with the highest growth peak in springtime. The stages of spermatogenesis were also observed and described.     

Reproduction in some New Zealand Cymatiidae (Gastropoda:Prosobranchia)

The behaviour during reproduction of four species of New Zealand cymatiids is described revealing a year-long courtship period in Cabestana spengleri. Charonia species, Mayena australasia and Monoplex australasiae have only a brief period of courtship prior to egg laying. The female of all species remains with the egg mass until the embryos hatch. This period may be as long as three months in the case of Mayena australasia. Protection of the egg mass seems to be the reason for this brooding behaviour as development proceeds normally in the absence of the female. Anatomically, the genital system of these mesogastropods is approaching the condition seen in more advanced neogastropods particularly with regard to the female.     

Locomotion of the filiform sperm of Littorina (Gastropoda,Prosobranchia)

Summary The filiform sperm of Littorina sitkana swims effectively in sea water and more viscous fluids, overcoming the problems of a non-uniform flagellar beat with an unusual mechanism, which involves three main events: (1) the sperm rotates anti-clockwise (looking from tail to head); then (2) stops rotating and stiffens itself to form a screw-shape, with the tail being held perpendicular to the middle piece, and finally; (3) reverses its rotation and propels itself forward in a clockwise spiral. The average velocity of sperm is approximately 185 ms with a rotational frequency of 24 revs. The mechanism of propulsion may involve two kinetic centers at opposite ends of the sperm, which coordinate their movements to produce anti-clockwise rotation, stationary twisting, or clockwise rotation, in a manner reminiscent of spirochaetes. Littorina sperm also exhibit slower methods of propulsion including swimming backwards (tail first) at 18 m, and gliding at about 30 m.The adaptive significance of the rapid propulsion is not obvious, because Littorina copulate and fertilize internally and at each stage in the transfer there are external aids to sperm transport, such as ciliary action (oviduct) and muscular expulsion (bursa and seminal receptacle). The filiform shape, however, is well-adapted for long-term storage in the female body. These points are discussed.     

The diet of the dog-whelk, Nucella lapillus (Gastropoda Prosobranchia)

The information at present available suggests that, when adult, Nucella lapillus may prey upon a considerable number of different species, but that the diet of recently hatched dog-whelks is rather more restricted. The food preferences of young Nucella have been investigated and it has been concluded that, while the diet of young and adult animals may differ to some extent, it is probably equally varied at all ages, and that cannibalism may be a frequent occurrence amongst all age groups.
It has been determined that the size of the prey influences the selective predation of Mytilus by Nucella. Dog-whelks show a marked preference for mussels in the 1 to 3 cm size range which may possibly be identified chemotactically.     

Viral pyrogen affects thermoregulatory behavior of wintering Planorbarius corneus (L.) snails (Mollusca: Gastropoda)

Exogenous pyrogens, isolated from viruses, bacteria and fungi, are widely used in research on fever in endotherms. The present study investigates the use of viral pyrogen poly (I:C) for inducing the symptoms of so-called behavioral fever in ectothermic animals Planorbarius corneus (Mollusca: Gastropoda). The observations of thermoregulatory behavior of the snails placed in the temperature gradient showed that the snails which were injected with 750 ng g⁻¹ polyinosinic-polycytidylic acid-poly (I:C), after remaining latent for more than 24 h, moved to warmer areas (with the temperature around 30 °C) and stayed there until the end of the experiment. Transferred to the culture, they lived for a period similar to that of the control snails. Our observations indicate that P. corneus snails can exhibit a symptoms of fever response to poly (I:C) and could be used as model animals in the research on behavioral fever in invertebrates.