Anatomy

Like other sea cucumbers, Apostichopus japonicus has a roughly cylindrical shape. It is radially symmetrical along its longitudinal axis, and has weak transversal bilateral symmetry with defined dorsal and ventral surfaces. There are five ambulacral zones along the length of the body from the mouth to the anus – two on the dorsal surface, and three on the ventral surface. The anterior end of the animal, bearing the mouth, corresponds to the oral pole of other echinoderms (e.g., sea urchin and sea star). The posterior end, where the anus is located, corresponds to the aboral pole. A. japonicus has a well-developed respiratory tree, but no Cuvierian organ. This chapter describes and discusses the anatomy of the body wall, endoskeleton, coelom and coelomocytes, as well as the nervous, digestive, respiratory, water vascular, hemal, and reproductive systems of A. japonicus. The macrostructural, microstructural, and ultrastructural aspects are covered in detail.