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Idealized cross-sections of a sea anemone, left one at the level of
the actinopharynx, right nearer the base. In the latter cross-section,
the numeral 1 indicates primary mesenteries, of which there are six pairs;
the numeral 2 indicates secondary mesenteries, of which there are six pairs;
and the numeral 3 indicates tertiary mesenteries, of which there are 12
pairs. Polyps of some species have fewer cycles of mesenteries and some
have many more. In the former cross-section, three cycles of mesenteries
are also represented. The primary mesenteries are complete (they connect
to the actinopharynx) whereas the secondary and tertiary mesenteries are
incomplete (they do not connect to the actinopharynx). The number of cycles
of complete mesenteries is a character of systematic importance - in some
actiniarians mesenteries of several cycles are complete. Note that two
diametrically opposite pairs of primary mesenteries connect to the siphonoglyphs;
the retractor muscles of these directive mesenteries lie on the outer side
of the mesenteries whereas the retractor muscles of all other mesentery
pairs (the non-directive mesenteries) face one another. (Adapted from Hyman,
1940)
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To return to the main page: Illustrated Glossary of Sea Anemone Anatomy
To view our home web site, please follow this link: Division of Invertebrate Zoology
Please send any questions or comments to Bryan McCloskey.