Cnidae in the sea anemone Sagartiogeton viduatus (Muller, 1776) (Cnidaria, Anthozoa); A comparison to cnidae in the sea anemone Metridium senile (Linnaeus, 1761) (Cnidaria, Anthozoa)

Abstract

The cnidom of the sea anemone Sagartiogeton viduatus (Muller, 1776) is described from interference‐contrast light micrographs (LMs) and scanning electron micrographs (SEMs). Special attention is given to nematocyst maturation, including the differentiation of the shaft into proximal and main regions as helical folding of the shaft wall proceeds. Comparisons are made with Metridium senile (Linnaeus, 1761), whose cnidom, with a few exceptions, is closely similar to that of S. viduatus. The two anemones possess b‐ and p‐mastigophores, p‐amastigophores, isorhizas and spirocysts. Although the majority of cnidae in S. viduatus is smaller than corresponding ones in M. senile, they are grouped into the same size classes as those of M. senile, namely small, medium and large. The main differences from M. senile cnidae are the followings: (1) Large acontia p‐amastigophores are the largest nematocysts in S. viduatus. (2) They are noticeably larger than the large acontia b‐mastigophores, and (3) they are separated from the p‐amastigophores of M. senile by the sinusoid pattern of their U‐shaped capsular matrix. (4) The large acontia b‐mastigophores are microbasic and not mesobasic as in M. Senile, and (5) they do not produce darts. (6) Another difference from M. senile is the absence of catch‐tentacle isorhizas.

The cnidome and internal morphology of Lophelia pertusa (Linnaeus, 1758) (Cnidaria, Anthozoa)

“…A), as previously noted in the sea anemones Metridium senile and Sagartiogeton viduatus (Östman et al . ,b, ).…”

“…The different developing stages observed in this study are to a large extent congruent with previous descriptions of cnidogenesis (Slautterback and Fawcett ; Westfall ; Skaer ; Holstein ; Tardent and Holstein ; Östman et al . ,b, ). The location of cnidoblasts mainly in the basal epidermis below mature cnidae is in agreement with Möbius () and Slautterback and Fawcett (), although cnidoblasts were also found among mature cnidae.…”

“…Documentation of the morphology of developing cnidae (cnidoblasts) in different stages of maturation has been carried out for the anthozoans Metridium senile and Sagartiogeton viduatus by Östman et al . (,b, ). Möbius () suggested that cnidoblasts differentiate beneath the mature cnidocytes (commented in Robson ).…”