Burrow morphology of the ghost shrimp Nihonotrypaea petalura (Decapoda: Thalassinidea: Callianassidae) from western Kyushu, Japan

Abstract

The callianassid shrimp Nihonotrypaea petalura (Stimpson, 1860) is a common member on boulder beaches in Japanese waters. Its burrow morphology was investigated, based on 28 resin casts collected from a steeply sloping beach with dense boulders and 30 from a more gently sloping beach with less dense boulders in Ariake Sound, southern Japan. The structure and dimensions of the burrows from the two beaches were basically the same, and thus a combined mean value could be given to most of their constituent elements. In its entire dimensions, the burrow is greater in lateral extent than depth, with a mean maximum horizontal extension of 145 mm and a mean maximum depth of 119 mm for the shrimp with a mean total length of 31.8 mm. The burrow winds along boulders or cobbles and consists of, from top to bottom, a single surface opening with an ejected mound, a top shaft leading to the uppermost chamber at a mean depth of 48–56 mm, a passage with a regular cross section that is wider than that of the top shaft, and bulbous chambers (mean no.=4.7) with an irregular cross section associated with branches (mean no. per burrow=1.2). Bulbous chambers are much larger than the uppermost chamber and are usually connected by passages, with some directly attached to each other. The combined architecture of these features is unique and relatively simple among the burrows of all callianassid species, the majority of which inhabit bare soft sediments. The structure and function of the N. petalura burrow are discussed in relation to lifestyle.