Advanced Larval Development of Callianassa Tyrrhena (Decapoda: Thalassinidea) and the Effect of Environmental Factors

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Abstract
The larval development of Callianassa tyrrhena was studied under laboratory conditions. Sixteen salinity-temperature combinations were used (14, 18, 22, 25.degree.C and 40, 60, 80, 100% sea water of S = 37.permill.). Since only 2 zoeal stages and a megalopa were observed, the postembryonic development can be characterized as advanced. Morphological changes between stages are prominent, while size does not seem to increase. Salinity mainly affects successful molting to zoea II and metamorphosis, while temperature dominates the development rate. Low salinities and temperatures prohibit or do not favor larval development, but when these factors approximate natural conditions (S .ltoreq. 80% sea water and T .gtoreq. 18.degree.C) metamorphosis is completed in a percentage equal to or greater than 70%. With increasing temperature, the zoeal duration is shortened drastically, but also the participation of the 2 zoeal stages in the total zoeal duration is equalized. The shortening of the larval duration up to 3.2 days (in 25.degree.C and 100% sea water) is considered as advantageous for a species which, as adult, lives in a restricted habitat in the upper coastal zone.