Order Actinulida Swedmark & Teissier, 1959

how to recognize?

Microscopic animals living in the sand interstitial. Check for statocysts and more than four tentacles. 

However, not all interstitial hydrozoans belong to this taxon.

The genera Siphonohydra and Psammohydra  belong to the family Corymorphidae (Anthomedusae).

The family Armorhydridae (genus Armorhydra) is here classified among the Narcomedusae, although its position is not entirely clear.

organization

longitudinal section of a the aboral part of a Halammohydra species

Families

Halammohydridae

Body composed a tubular manubrium with a terminal mouth, on aboral end a small cone separated from manubrium by a neck, bearing an adhesive organ; above neck one whorl of tentacles, alternating with statocysts; gonochoristic; without brood pouch.

Otohydridae

Umbrella much reduced and fused to manubrium so that tentacles and statocysts are arranged around oral end of manubrium; one ring of marginal tentacles of two kinds: adhesive and armed ones; with or without a brood pouch (= subumbrellar cavity); hermaphroditic, viviparous.

References

Bouillon, J. 1994. Les Hydrozoaires. In Traité de Zoologie, vol. 3(2) (ed.P. Grassé & J. Doumeng), pp. 29-416. Paris: Masson.

Clausen, C. 1971. Interstitial Cnidaria: present status of their systematics and ecology. In: N.C. Hulings, ed., Proceedings of the first international conference on Meiofauna. Smithson. Contr. Zool. 76: 1-8.

Clausen, C. 1967. Morphological studies of Halammohydra remanei (Hydrozoa).Sarsia 29: 349-370.

Clausen, C. 1971. Interstitial Cnidaria: present status of their systematics and ecology. In: N.C. Hulings, ed., Proceedings of the first international conference on Meiofauna. Smithson. Contr. Zool.76: 1-8.

Remane, A. 1927. Halammohydra, ein eigenartiges Hydrozoon der Nord-und Ostsee. Z. Morph. oekol. Tiere 7: 643-677.

Swedmark, B.G.T. 1950. Développement d'un hydrozoaire aberrant Halammohydra schulzei Remane. Comptes rendus hebdomadaires des séances de l'Académie des sciences de Paris 231: 173-174.

Swedmark, B. 1956. Variation morphologique des différentes populations régionales d'Halammohydra. In: Colloque international de biologie marine. Station Biologique de Roscoff (27 juin - 4 juillet 1956). Année Biol. 33: 183-189.

Swedmark, B. 1959. On the biology of sexual reproduction of the interstitial fauna of marine sand. Proc. XV. int. Congr. Zool. 327-330.

Swedmark, B. 1964. The interstitial fauna of marine sand. Biol. Rev. 39: 1-42.

Swedmark, B., & Teissier, G. 1957. Organisation et développement des Halammohydra (Hydrozoaires). C. r. hebd. séanc. Acad. Sci., Paris 244: 501-504.

Swedmark, B., & Teissier, G. 1958a. Halammohydra vermiformis n. sp. et famille des Halammohydridae Remane. Bulletin de la Société Zoologique de France 82: 38-49, pls 1-2.

Swedmark, B., & Teissier, G. 1958b. Armorhydra janowiczi n. g.,n. sp. hydroméduse bentique. Comptes rendus hebdomadaires des séances de l'Académie des sciences de Paris 247: 133-135.

Swedmark, B., & Teissier, G. 1958c. Otohydra vagans n. g., n.sp.,hydrozoaire des sables, apparanté aux Halammohydridées. Comptes rendus hebdomadaires des séances de l'Académie des sciences de Paris 247: 238-240.

Swedmark, B., & Teissier, G. 1959. Halammohydra et Otohydra, hydrozoaires de la microfauna des sables et l'ordre des Actinulides. Proc. XV. int. Congr. Zool 330-332.

Swedmark, B., & Teissier, G. 1967. Structure et adaptation d'Halammohydra adherens. Cah. Biol. mar. 8: 63-74.

Swedmark, B. G. T. 1966. The Actinulida and their evolutionary significance.In: W.J. Rees, ed., The Cnidaria and their evolution. Symp. zool. Soc. Lond. 16: 119-133.