Anthoathecata

Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known and heavily discussed group. It has also been called Gymnoblastea and (with or without an emended ending -ae), Anthomedusa, Athecata, Hydromedusa, and Stylasterina. There are about 1,200 species worldwide.^[1]

These hydrozoans always have a polyp stage. Their hydranths grow either solitary or in colonies. There is no firm perisarc around the polyp body. The medusae, or jellyfish, are solitary animals, with tentacles arising from the bell margin, lacking statocysts but possessing radial canals. Their gonads are on the manubrium ("handle").^[2]

Except in Eudendriidae and Laingiidae, prey can be captured by discharging harpoon-like structures (desmonemes) from chambers (cnidae) in specialized cells (nematocysts) on the tentacles. In hydrozoans, these are nearly always adhesive and entrapping, rather than puncturing and venomous as in other jellies.^[2]

Systematics

The close relationship of the orders Anthoathecata and Leptomedusae has been long known, but formerly it was also believed that these two were close to the order Limnomedusae. However, their closest relatives are the highly advanced Siphonophorae, whereas the Limnomedusae are a rather primitive group, and not very closely related to these three Leptolinae, and might instead belong to the subclass Trachylinae.^[3][4]

Some uncertainty existed regarding the taxonomy of the order Anthoathecata. The most simple scheme, used until recently by most authors since it was proposed in 1913, divided the order into a smaller suborder (Filifera) and a second larger one (Capitata), but several unusual Anthoathecatae did not fit into this arrangement, and a considerable number did so awkwardly.^[5][6] The Porpitidae, for example, are a highly aberrant group, and were at one time even considered a separate order "Chondrophora". However, they are currently considered to be derived from Zancleida.^[7][8] In the early 21st century, the well-known Hydra and its relatives – and most of the supposed filiferan infraorders Tubulariida and Moerisiida – were determined to be a very ancient lineage, recognized as suborder Aplanulata.^[9][10][11] Although not all Anthoathecatae have been firmly placed in the phylogeny, most are fairly certainly assigned at least to one of the major subdivisions. As a notable exception, a prehistoric family, the Heterastridiidae, is still highly disputed regarding its relationships to the extant taxa, as are a small number of very aberrant and/or little-known species such as the aptly named Saccohydra problematica.

The family Clathrozoellidae is placed with the Filifera here; in others it is placed in the Leptomedusae and sometimes even synonymized with their family Clathrozoidae. By contrast, the supposed filiferan genus Anthohydra is in fact the leptomedusan Eugymnanthea; similarly, "Gammaria" is also a leptomedusan and properly spelled Grammaria.

The supposed athecate family Monobrachiidae is apparently a close relative of the Olindiasidae, and belongs in the Limnomedusae. Halammohydridae and Otohydridae, sometimes placed here, appear to be trachyline hydrozoans of the order Actinulidae.

^[12]

Infraorders and families

References

1. ^ Schuchert, P. (2014). Anthoathecata. Accessed through: Schuchert, P. (2014) World Hydrozoa database at http://www.marinespecies.org/hydrozoa/aphia.php?p=taxdetails&id=13551 on 2014-10-31
2. ^ Bouillon, J.; Gravili, C.; Pagès, F.; Gili, J.-M.; Boero, F. (2006). An introduction to Hydrozoa. Mémoires du Muséum national d'Histoire naturelle, 194. Muséum national d'Histoire naturelle: Paris, France. ISBN 2-85653-580-1. 591pp. + 1 cd-rom
3. ^ Schuchert, Peter (2010). "The Hydrozoa (Cnidaria) of the World: A Review of Classification and Phylogeny". Zootaxa. 2463: 1–248. Retrieved 2025-10-08. Phylogenetic analyses indicate a close relationship between Anthoathecata, Leptomedusae, and Siphonophorae, with Limnomedusae placed among Trachylinae.
4. ^ Cartwright, Paulyn & Nawrocki, Ann M. (2010). "Character Evolution in Hydrozoa". Integrative and Comparative Biology. 50 (3): 456–472. doi:10.1093/icb/icq089. Retrieved 2025-10-08. Comparative molecular data show that Anthoathecata and Leptomedusae form a clade sister to Siphonophorae, while Limnomedusae are basal Trachylinae.
5. ^ Petersen, Kai W. (1990). "Evolution and Taxonomy in Anthomedusae (Hydrozoa, Cnidaria)". Zoological Journal of the Linnean Society. 100 (2): 101–231. doi:10.1111/j.1096-3642.1990.tb01863.x The Filifera and Capitata subdivision, established in 1913, has been widely used until recent molecular revisions.
6. ^ Schuchert, Peter (2007). "The European Athecate Hydroids and their Medusae (Hydrozoa, Cnidaria): Filifera Part 2". Revue Suisse de Zoologie. 114 (2): 195–396. Retrieved 2025-10-08. Historical divisions of Anthoathecata into Filifera and Capitata remain of limited phylogenetic significance.
7. ^ "World Hydrozoa Database". World Register of Marine Species. Schuchert, P. (ed.). Retrieved 2025-10-08. Porpitidae are listed under Anthoathecata and derived from Zancleida.
8. ^ Govindarajan, Ann F. (2006). "Phylogenetic Relationships within Hydrozoa Inferred from 16S rRNA Data". Marine Biology. 149 (5): 889–904. doi:10.1007/s00227-006-0263-9 Molecular analyses indicate that Porpitidae belong within Anthoathecata, derived from the Zancleida lineage.
9. ^ Collins, A. G., Winkelmann, S., Hadrys, H. and Schierwater, B. (2005), Phylogeny of Capitata and Corynidae (Cnidaria, Hydrozoa) in light of mitochondrial 16S rDNA data. Zoologica Scripta, 34: 91–99. doi:10.1111/j.1463-6409.2005.00172.x
10. ^ Cartwright, Paulyn (2008). "Phylogenetics of Hydroidolina (Hydrozoa, Cnidaria) Using 16S and 18S rDNA Sequences". Molecular Phylogenetics and Evolution. 46 (1): 118–134. doi:10.1016/j.ympev.2007.09.005 Hydra and related taxa form an ancient lineage distinct enough to warrant recognition as the suborder Aplanulata within Anthoathecata.
11. ^ Cornelius, Paul F. S. (1995). "Hydroid, Hydromedusa and Siphonophore Phylogeny and Classification". Hydrobiologia. 308: 17–44. doi:10.1007/BF00007593 Comparative morphology and molecular data suggest the Aplanulata lineage includes Hydra and several former Filifera taxa.
12. ^ Schuchert (2014), World Hydrozoa database.
13. ^ New name is required for the remaining Tubulariida, because Tubulariidae has been moved to Aplanulata.

Bibliography

• Buecher, E., Goy, J. & Gibbons, M.J. 2005. Hydromedusae of the Agulhas Current. African Invertebrates 46: 27-69.[1]

External links

• North East Atlantic Taxa
• Family, genus and species list
• A page about Hydromedusae