Scientia Marina, Vol 74, No 3 (2010)

Tentacle cnidae of the sea anemone Metridium senile (Linnaeus, 1761) (Cnidaria: Anthozoa)

Carina Östman
Animal development and Genetics, Evolutionary Biology Centre (EBC), Uppsala University , Sweden

Jens Roat Kultima
Uppsala University , Sweden

Carsten Roat
Department of Ecology, Environment and Geology, Umeå University , Sweden


Tentacle cnidae of Metridium senile (Linnaeus, 1761) were examined by light microscopy. In addition to spirocysts, feeding-tentacles had 3 nematocyst categories grouped into medium and small size-classes, including 5 types. Spirocysts dominated, especially distally, followed by medium b-mastigophores. The density of cnidae decreased towards the tentacle base. Early cnidoblasts were numerous on the tentacle tip. Late cnidoblasts appeared in a moderate number on the mid-tentacle. Catch-tentacles, found in two Metridium specimens, had a maturity gradient of isorhizas and gland cells along their length. Their tip had two distinct types of mature isorhizas in great numbers and large gland cells, but lacked spirocysts. Mature isorhizas and gland cells decreased in number towards the tentacle base. On the mid-tentacle differentiating ages of isorhizas were numerous. Ordinary feeding-tentacle cnidae, abundant at the tentacle base, decreased in number distally along the tentacle.


sea anemone; nematocysts; cnidae; catch-tentacles

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