Scientia Marina, Vol 74, No 3 (2010)

Acontia and mesentery nematocysts of the sea anemone Metridium senile (Linnaeus, 1761) (Cnidaria: Anthozoa)

Carina Östman
Animal Development and Genetics, Evolutionary Biology Centre, Uppsala University , Sweden

Jens Roat Kultima
Uppsala University , Sweden

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

Karl Rundblom
Uppsala University , Sweden


Acontia and mesentery nematocysts of Metridium senile (Linnaeus, 1761) are described from interference- contrast light micrographs (LMs) and scanning electron micrographs (SEMs). The acontia have 2 nematocyst categories grouped into small, medium and large size-classes, including 5 types: of these, large b-mastigophores and large p-amas- tigophores are the largest and most abundant. Mesenterial tissues, characterised by small p-mastigophores and medium p-amastigophores, have 3 nematocyst categories grouped as small and medium, including 6 types. Attention is given to nematocyst maturation, especially to the differentiation of the shaft into proximal and main regions as helical folding of the shaft wall proceeds. Groups of differentiating nematoblasts occur along acontia, and near the junction between acontia and mesenterial filaments. Nematoblasts are sparsely found throughout mesenterial tissues.


cnidae; SEM; acontia; mesenterial filaments

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