The ecology, biology and taxonomy of Addisonia excentrica (Tiberi, 1855) (Cocculiniformia: Addisoniidae) from southern Spain

Abstract

This study of Addisonia excentrica (Tiberi, 1855) is the first on the population dynamics of any cocculiniform limpet. We conducted 2 years of monthly sampling by trawling off the coast of Malaga province, Spain (Western Mediterranean), at 47-311 m. We sampled 482 egg cases of the lesser spotted dogfish (Scyliorhinus canicula), in which A. excentrica lives and feeds, which yielded 987 specimens of A. excentrica. Of capsules containing A. excentrica, 70.3 were collected between 50 and 100 m depth, where the mean percentage of occupied capsules (incidence) was 32.8; the greatest incidence was found between 100 and 150 m (42.1). The maximum depth of living A. excentrica was 222 m. In samples collected at 50-100 m recently settled individuals (<2 mm) predominated throughout the year. Larvae and apohermaphroditic specimens with mature oocytes (>7.2 mm) were scarce, but they were also present almost all year round, suggesting continuous reproduction. A positive correlation between the relative age of the egg case and the mean length of limpets was found. The long embryonic development of dogfish and the slow decay of egg cases provides enough time for larvae or young individuals to mature within a single egg case. Once mature, the limpets leave the capsule and spawn on the nearby bottom. Continuous reproduction and aggregated egg laying areas of the dogfish may improve the chances of larvae finding the egg cases during what is presumably a short larval life, and facilitate emigration of juveniles or large specimens to neighbouring capsules. Addisonia enodis Simone, 1996 is considered to be a junior synonym of A. excentrica. The larval shell of A. excentrica is described; it is very similar in shape and sculpture to the larval shell of Lepetella species, but larger. Newly settled specimens start to discard the protoconch at a size smaller than 0.4 mm. © The Author 2010.