Morphology and distribution of setae used for decorating on the dorsal carapace of the spider crab, Pugettia quadridens quadridens (De Haan) (Brachyura: Majidae)

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Examination of the morphology and distribution of setae of Pugettia quadridens quadridens, using SEM and stereomicroscopy reveals two types of setae (hooked and simple) distributed in different areas on the dorsal surface of the carapace. Hooked setae bear regularly arranged oblique striae with both spinules and a median groove along the inner curve. These setae are loosely arranged in double rows along the rostrum, in the orbital region, and at the anterolateral border of the carapace. Simple setae are not curved and are found in the gastric, mesobranchial and intestinal regions of the carapace. The distribution of hooked setae on the carapace varies considerably according to crab size and sex. They are more widely distributed on the dorsal carapace of smaller crabs than on larger ones, and on females compared to males. These spider crabs can be classified into four types based on setal distribution pattern.