In the last post, I wrote about brooding sea anemones. In this gallery I’ll cover some of the diversity in brooding species and show the various ways in which offspring are brooded. The following are images of animals from the field and of preserved specimens. Click or tap any of them for larger versions.
Some species brood offspring internally. In this case, the young simply develop within the body of the adult. Internally brooding animals usually aren’t readily noticeable as such. However, under certain conditions one can sometimes see offspring within the adult.
External brooding is usually more conspicuous in the field than internal brooding. In this behavior, developing offspring are held upon the adult’s body. There may be specializations in the structures of the adult that increase retention and/or protection of the offspring. In other cases, the young may simply be attached to the adult as they would any other surface. Epiactis prolifera offers an example of the simplest case.
In other cases, the offspring are held in modifications of the adult’s body wall. These modifications appear in three general forms:
Pits are depressions in the body wall which hold individual offspring. They can be all over the adult’s column or restricted to certain areas.
Grooves surround the adult somewhat like a moat around a castle. A groove may be open or closed and is formed by a circular depression in the adult’s body wall.
Chambers are one of the most unusual and interesting structures that sea anemones use to protect externally developed offspring. They are pouches that go deep into the adult’s body and house many offspring simultaneously. Unfortunately, due to their rarity (only two or possibly three species produce chambers) and Antarctic distribution I have never seen a sea anemone with chambers, so a drawing made from a previously published figure (Carlgren 1901) will have to suffice.
Carlgren, O., 1901. Die Brutpflege der Actiniarien. Biol. Centralbl., Bd. XXI. Leipzig 468–484.
About the Author: Paul Larson is a PhD candidate at the Department of Evolution, Ecology and Organismal Biology at The Ohio State University studying evolution of marine invertebrates.