Hydroidomedusae (Cnidaria: Hydrozoa) symbiotic radiation

Abstract

Hydroids can establish symbiotic relationships with most marine phyla. Almost entire genera or even families are associated with specific groups (e.g. Hydractiniidae and Cytaeididae with gastropods and hermit crabs, Zancleidae with bryozoans, Dipurena with sponges, Ralpharia with octocorals, Eugymnanthea with bivalves, Proboscidactyla and Teissiera with serpulids, Bythotiara with tunicates). Generally, the symbiotic groups belong to the Anthomedusae that, due to the absence of theca, are more plastic in establishing trophic relationships with the hosts. Nevertheless a number of scattered species, mainly Leptomedusae, are strictly associated to algae or sea grasses: in these cases no evident morphological or behavioural adaptations were observed. In animal symbiosis several unrelated symbiotic species show polymorphic colonies or a strong reduction in number and/or size of the tentacles, which are sometimes completely lost. Moreover, these symbiotic species may lack perisarc even in the hydrorhiza.In this paper we summarize the morphological and behavioural adaptations of symbiotic species suggesting that the described aptitude of hydroids to establish relationships with other organisms is not only the result but also the source of the evolutionary radiation of this group.

Symbiotic association between Solanderia secunda (Cnidaria, Hydrozoa, Solanderiidae) and Medioantenna variopinta sp. nov. (Annelida, Polychaeta, Polynoidae) from North Sulawesi (Indonesia)

“…The Class Hydrozoa includes a large variety of life forms that are often involved in symbiotic relationships with other invertebrates (Boero and Bouillon 2005;Gili and Hughes 1995;Puce et al 2008). Their rather rich symbiotic fauna includes polychaetes (Genzano and San Martín 2002;Lagardère and Tardy 1980), and some species of Teissiera or Hydractinia tend to be specifically associated with polychaetes (Bouillon and Boero 1987;Bouillon 1994;Galea et al 2007).…”

A tubulariid hydroid associated with anthozoan corals in the Mediterranean Sea

“…Within this family, there are several species reported in association with other organisms (Puce et al 2005): Hybocodon includes species mainly associated with sponges and one associated with a scleractinian, Zyzzyzus includes only species associated with sponges and a further species of Ectopleura, E. exxona, lives associated with an unidentified sponge (Watson 1978). All of these evidences strongly suggest that the tubulariid evolution may have had a role in the possibility to establish symbiotic relationships with different benthic groups (Puce et al 2008a). …”

“…The previously described cases of hydroids associated with living portions of anthozoans involved a number of species (Puce et al 2008a) (Table I), of which six were tubulariids belonging to the genus Ralpharia. To these records must be added Hybocodon cfr.…”

“…In some cases, this epibiotic aptitude may shift to a mutualistic or parasitic relationship (Boero & Bouillon 2005;Puce et al 2008b). Symbiotic associations involving hydroids and anthozoans were recently reviewed by Puce et al (2008a) (Table I). Associations with living octocorals are well described, with 12 species belonging to six families (Asyncorynidae, Cladocorynidae, Corynidae, Ptilocodiidae, Tubulariidae, and Zancleidae) found associated with these corals.…”

“…Associations with living octocorals are well described, with 12 species belonging to six families (Asyncorynidae, Cladocorynidae, Corynidae, Ptilocodiidae, Tubulariidae, and Zancleidae) found associated with these corals. Particularly, the genus Ralpharia (Tubulariidae) is almost exclusively known to be associated with octocorals, with two species living on soft corals and four on gorgonians (Puce et al 2008a). In contrast to associations with octocorals, the relationships between hydroids and hexacorals are almost unknown, with the exception of Zanclea margaritae Pantos and Bythell, 2010, which was recently described associated with Acropora muricata (Linnaeus, 1758) (Pantos & Bythell 2010).…”