Life history of the Japan-endemic crab, <i>Pseudopinnixa carinata</i> (Ortmann, 1894) (Decapoda: Brachyura: Varunidae)

Abstract Pseudopinnixa carinata (Ortmann, 1894) (Decapoda) is a small-size brachyuran endemic to Japan and placed within, or near, Varunidae. It inhabits primarily sandy intertidal flats in sheltered inner bays. We aimed to elucidate the life history and habitat use of this species on a tidal flat at Nishio City, Aichi Prefecture, central Japan. Burrowing individuals were collected monthly from sediment cores (10 cm diameter × 25 cm high) extracted from the sand flat between January and December 2016. The presence of burrows and biological traces did not significantly affect the number of individuals collected and the possibility of the sediment sample containing crabs. This species lives freely, excavating only shallowly into the sand rather than constructing its own burrows. Differences in monthly frequencies between the upper and lower intertidal zones showed that the species appears to vacate the upper intertidal zone in summer and shift its distributional core into the subtidal zone. Recruits with a carapace width (CW) of less than 3 mm were collected during April and May, resulting in a bimodal CW frequency distribution. Ovigerous females were observed only in October and November, and in each of these months their CWs fell within the largest size classes among females collected concurrently.