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article i nfo Drilling predation is one of the unique scenarios where past biotic interactions can be studied quantitatively and used to model behavioural evolution of the involved groups. Although it is recognized that hunger plays an im- portant role indetermining the behaviour of terrestrial predatory groups, its specifi ce ffect on drillinggastropods is largely unexplored. Muricids have been shown to demonstrate change in prey preference and foraging behav- iour when starved. Such behaviour is yet to be tested for naticid gastropods. In an experiment with live naticid gastropods,Natica tigrinaand their bivalve prey Cardium sp., we evaluated the effect of hunger on the following aspects of predation: 1. Drilling frequency, 2. Size selectivity, and 3. Site selec- tivity. Comparing gastropods between satiated controlled group and starved experimental group we demon- strated a positive effect of hunger on drilling frequency. Using different stages of hunger, we found that hunger plays an important role in dictating prey size-selectivity. While hunger increases drilling frequency, it reduces the degree of prey size selectivity. Hunger is not found to initiate edge-drilling or incomplete drilling in N. tigrina. It has been postulated that prey selection by gastropods are correctly modelled by cost-benefi ta nalysis; but the

Cannibalism is observed among the drilling gastropods in Recent and in the fossil record. However, the ecological factors triggering cannibalism are not well understood. While competition over food is considered a factor to initiate cannibalism in certain groups, it is yet to be tested for drilling gastropods. In an experiment with live naticid gastropods, Natica tigrina , we evaluated the effect of the following factors in controlling cannibalism: 1. availability of preferred prey, 2. size ratio of predator and prey, and 3. ontogenetic stage of the predators. Cannibalism is found to be quite rare when preferred bivalve prey ( Cardium sp.) is present. Size ratio among predator and prey is observed to play the most crucial role; cannibalism is maximum in a mixed group of small and large gastropods. While the incidence of cannibalism is much lower in groups of similar body size, the intensity differs with mean size. Cannibalism is relatively common in groups of larger size compared to those of smaller size. This indicates an ontogenetic threshold in cannibalism; the naticids seem to acquire such behavior only at a specific ontogenetic stage. Our findings are corroborated by observed drilling pattern in the Recent shells collected from Chandipur-on-sea, India. While the preferred prey Cardium sp. has the highest drilling frequency, the shells of N. tigrina often bear drill holes; the smaller size class of Natica has the highest drilling frequency among all size classes. The smallest drill holes in Natica are larger than those found in Cardium ; this pattern indicates that the Natica are less likely to attempt a cannibalistic attack in their early ontogeny. These behavioral patterns are also reported from a Miocene assemblage of N. tigrina from Poland (Zlotnik, 2001). It has been postulated that cannibalism should be observed in nutrient depleted conditions. However, our study demonstrates the relative importance of other ecological factors in guiding this behavioral trait. Moreover, the ontogenetic development of cannibalistic habit is closely linked to the evolutionary stable strategy (ESS). Therefore, such factors should also be taken into consideration while studying cannibalism in the context of drilling predation.

Dynamics in three deep-water populations, one northern and one southern at 100 m and one at 300 m, of the surface deposit-feeding bivalve Abra nitida (Muller) were studied during the period 1970–1980. Recruitment, growth in terms of length, mortality, and production of biomass were assessed by means of length frequency distribution analysis of quantitative samples. Recruitment success in different years was negatively correlated with adult density/population biomass at two of the localities, 100 and 300 m deep. The mortality of the 0-group was positively correlated with the size/density of the 0-group itself. Mortality among adults was considerably higher at 100 m, and for the southern 100 m population data are presented indicating a negative relationship between Abra and the predatory snail Natica. The average growth rates were considerably higher at 100 m compared with 300 m, which is attributed to a better food supply rather than higher temperature. Growth rates were negatively correlated with adult density/biomass at the two stations where Abra dominated. Production of biomass (shells included) was calculated for 9 consecutive yr at the southern 100 m station, and for 4 yr at 300 m. P ranged from 9.94 to 37.85 g dry wt· m−2 /sd yr−1 and P : B ratios from 0.54 to 1.46 at the former site, and the corresponding values from the latter site were 0.57–2.62 and 0.46–2.5. The production on the former site was high for a “deep” community. It was concluded that normally the factors regulating the Abra populations operated on the bottom rather than during the planktonic phase. The results strongly indicated that resource limitation on the bottom is a factor of prime importance in regulating the deepest (300 m) population, primarily acting through adult-larval interactions, while predation probably plays a greater role at 100 m. At the southern 100 m site where Abra may occasionally reach an adult density of 2000 ind. · m−2, both predation and resource limitation affected the dynamics of the species. Reasons for the “volatility” shown by the species are discussed, whereby a good competitive ability together with high susceptibility to predation are considered to be important. The findings demonstrate the importance of density-dependent factors in regulating these deep-water depositfeeding populations.

We determined causes of predation on an early Pleistocene assemblage of ten species of Naticidae in Fiji. Naticids preyed more frequently on the four Natica species (27% of shells drilled) than on Polinices, Eunaticina and Sinum (3% of shells drilled). Tertiary and Cretaceous naticids studied previously are generally less frequently drilled. The absence of incomplete boreholes indicates that drilling predation is typically successful. Predator size (based on borehole diameter) increased directly with prey size in all Natica species. Incidence of drilling predation decreased slightly with increasing prey shell size, but Natica species do not appear able to outgrow drilling predation. Unsuccessful crustacean predation, indicated by scar lines and shell repair, occurred frequently. In the eight commonest naticid species, 17–48% of the shells had healed fractures. The results identify two trophic links in the fossil community, naticids as generally successful predators and crustaceans as often unsuccessful predators, both on naticid prey.

Natica gualteriana, as observed on intertidal sand bars in Bantayan Island, Philippines, emerges from the sand at low tide when the bottom is exposed to the air, and hunts epifaunally for the trochacean gastropod Umbonium vestiarium. N. gualteriana captures U. vestiarium with a quick extension of the foot, triggered by direct contact with the prey. The shell aperture of the prey is subsequently plugged with a small amount of mucus, that forces U. vestiarium to remain retracted inside its shelf (chemically benumbed?), but neither kills nor permanently affects it. Drilling of the prey takes place infaunally, after burrowing. This seems to be the first record of subaerial hunting in naticid gastropods.

Boreholes produced by naticids and muricids can be recognized in molluscan prey from the Ameki Formation (Eocene) in southeastern Nigeria. Possible predators are four species of Naticacea and three species of Muricacea. A quantitative assessment of the occurrence and type (naticids or muricids) of borings in 1409 fossil shells belonging to seventeen species shows that there is a pronounced differential proneness to attack among the species. The most common prey species of naticids were the infaunal, feebly ornamented bivalve Tivelina newtoni and the infaunal, smooth gastropod Natica amekiensis. The principal prey of muricids was the epifaunal, strongly ornamented gastropod Bonellitia (A.) amekiensis.

Oxygen consumption in sea water increased with size and tissue weight of Natica maculosa Lamarck at ambient temperatures (28–29.5 dgC) and salinities (31–32‰) in a fashion comparable with other naticids. When measured in submerged shore sand, oxygen consumption resembled that in sea water among smaller and some larger Natica but was much lower in several larger snails. Even using the higher measurements, respiration accounted for a remarkably low proportion of the energy consumed in Umbonium prey, and this also matches previous findings with Polinices. Limited observations indicate that production of egg collars may account for > 30‰ of the consumption in adult females. Estimation of faeces and mucus were, however, unsuccessful. It is suggested that respiration in nature might be higher than recorded hitherto because of high metabolic costs and very long duration of drilling the shelled prey.

1. It is shown that Crepidula fornicata and Natica cataena are capable of synthesizing sterols from acetate and mevalonate respectively. 2. In this investigation N. cataena did not synthesize sterols from acetate. This phenomenon is discussed. 3. It is supposed that all Mesogastropoda possess the capacity of synthesizing sterols. 4. The composition of the sterol mixtures of C. fornicata and N. cataena is determined by means of gas-liquid chromatography. 5. These sterol compositions are compared with those of other mesogastropods.

On a sandy beach of the Dutch North Sea coast an experiment was carried out with 24000 brightly coloured artificial shell valves of Donax vittatus . Unperforated and perforated (artificial Natica -holes of 1, 2 or 3 mm inner diameter) left and right valves of three sizes (19.7, 24.2, and 28.7 mm shell-length) were used. It appeared that under the influence of waves and water currents a clear selection occurred according to size (“ size effect ”), symmetry (“ left-right phenomenon ”), presence or absence of a hole (“ hole effect ”), and diameter of the hole (“ diameter effect ”). The implication of these observations for studies of the biology of Naticid snails based upon valves collected along the beach are discussed. Furthermore, some remarks are made on the implications of this type of experimental work for sedimentology and marine palaeontology in general.

The river delta of Saloum is a complex system because of its channels and its rias. The meeting and ensuing mixture of the river water and sea water determines four biotopes: o 1) Sea-coast of high energy, 2) Tidal river of high to moderate energy, 3) Lagoon of moderate energy, 4) Estuary of low energy. Certain species of molluscs have characteristics relating to their particular biotope. The authors have studied the tropical lagunary species in particular (Tympanotonus fuscatus, Anadara senilis, etc…) and the zonation of Natica have been incated.