Abstract
Sacculina carcini is member of a highly-specialized group of parasitic cirripeds (Rhizocephala) that use crabs (Carcinus maenas) as hosts to carry out the reproductive phase of their life cycle. We describe the naupliar development of S. carcini Thompson, 1836 from a very precise monitoring of three different broods from three specimens. Nauplii were sampled every 4 h, from the release of the larvae until the cypris stage. Larval development, from naupliar instar 1 to the cypris stage, lasts 108 h at 18 °C. A rigorous sampling allowed us to describe an additional intermediate naupliar instar, not described previously. Naupliar instars are renumbered from 1 to 5. Nauplius 1 (N1) larvae hatch in the interna; N2 are released from the interna and last between 12 and 16 h; N3 appear between 12 and 16 h after release; N4 appear between 28 and 32 h; and N5 appear between 44 and 48 h. The cypris stage appears between 108 and 112 h. The redescribed morphologies allowed us to identify new characters. Antennular setation discriminates naupliar instars 3, 4 and 5. Telson and furca morphologies discriminate all naupliar instars. Furthermore, we demonstrate that the speed of larval development is similar within a single brood and between broods from different specimens, suggesting synchronization of larval development. From precise monitoring of broods every 4 h, we demonstrate that the life cycle of S. carcini includes five instars of naupliar larvae instead of four. The morphological characters of the larvae discriminate these naupliar instars and allow the identification of S. carcini from other Rhizocephala species. S. carcini larvae develop synchronously. Consequently, they might be an informative model to study larval development in crustaceans.
Highlights
Sacculina carcini is a highly specialized barnacle parasite of several Brachyura crabs including the green crab Carcinus maenas [1]
Sex‐specific dimensions of S. carcini larvae In single-sex broods, the measurements for each characteristic and each stage were distributed normally, which was consistent with populations containing a single sex
Male furcae were significantly longer than female furcae at Nauplius 2 (N2) (p < 0.001) and Nauplius 3 (N3) (p < 0.001)
Summary
Sacculina carcini is a highly specialized barnacle parasite of several Brachyura crabs including the green crab Carcinus maenas [1]. It belongs to the Rhizocephala, all of which present a highly altered morpho-anatomy at the adult stage, related to their endoparasitic lifestyle. The female adult consists of a root system that colonizes the crab cavity and is connected by a stalk running through the integument. The systematic positions of S. carcini and other Rhizocephala have been enigmatic. Thompson [3] described the S. carcini adult as a parasite and noted its affinity with cirripeds by studying the nauplius larvae.
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