The moulting cycle and changes in body density in larvae of the snow crab Chionoecetes opilio (Brachyura: Majoidea) under laboratory conditions

The moulting cycle and the time course of changes in body density from hatching to the end of the megalopal stage in snow crab (Chionoecetes opilio) larvae were investigated in laboratory-reared specimens. Morphological changes in the epidermis and cuticle were photographically documented to characterize the moult-cycle stages: A–B (postmoult), C (intermoult), D (premoult) and E (ecdysis). Moult-stage characteristics were based on a microscopical examination of integumental modifications, particularly of the telson. During stages A–C, the larval cuticle changed from a spongy structure to become conspicuously thicker and more solid in appearance. In stage D, the epidermis retracted from the cuticle and new setae and appendages were formed. The body densities of larval snow crabs were lowest just after moulting; they increased greatly during stage C, and then gradually increased to reach a plateau at 1.0897–1.0931 g cm^?3 during stage D. Over the whole larval period, they have a density greater than that of seawater. These observations will assist in understanding of larval distribution and transport in snow crabs in their natural habitat, and provide a useful tool to determine the developmental stages of larvae sampled from the plankton and from larval cultures.     

Morphological features of the larvae of spider crab <Emphasis Type="Italic">Pugettia quadridens</Emphasis> (Decapoda: Majidae) from the Northwestern Sea of Japan

The entire cycle of larval development of the spider crab Pugettia quadridens (de Haan, 1850) (Decapoda: Majidae), widespread in Peter the Great Bay (Sea of Japan) is studied under the laboratory conditions. The development cycle of this species comprises prezoea, zoea I, zoea II, and megalopa. At a temperature of 18–20° C larval development took from 11 to 15 days. Zoea II is described in detail for the first time. Many morphological characters are found distinguishing zoea and megalopa of P. Quadridens in Russian waters from the larvae of this species in Japanese and Korean waters. Some characters of larvae are similar in P. Quadridens and the related species of the genus Pugettia. The larvae of P. Quadridens occur in the plankton of Vostok Bay from late June to late October with a density up to 5 ind/m³ at a surface water temperature of 13–21°C. They are easily distinguished from the other brachyuran larvae of this region by the absence of lateral spines on the carapace.Original Russian Text Copyright © 2004 by Biologiya Morya, Kornienko, Korn.