Anatomy of Bathyacmaea secunda Okutani, Fujikura & Sasaki, 1993 (Patellogastropoda: Acmaeidae)

Abstract

Anatomy of a vent-endemic patellogastropod limpet, Bathyacmaea secunda ,w as examined by gross dissection and serial sections. It was revealed that B. secunda is anatomically distinct from other patellogastropod taxa in that (1) the intestine runs through the ventricle; (2) the ventral approximator muscle of odontophoral cartilages is ventrally single-layered; (3) there is a pair of radular teeth with long shafts; and (4) the statocysts are isolated from pleural and pedal ganglia. In addition, the species is characterized by short pallial margin papillae, lack of pallial streaks, presence of a ctenidium, obliquely tubular salivary glands, simple gut configuration and acmaeoidean type of buccal mass musculature and odontophoral cartilages. The comparison in anatomical and shell microstructural characters suggests that B. secunda shares no unique similarities with the Patelloidea or Neolepetopsidae and, therefore, is not closely related to these groups. In contrast, a number of similarities were found between B. secunda and acmaeid species. These results support the current systematic position of Bathyacmaea within the Acmaeidae, although anatomical data from some related genera are still insufficient.