athecate hydroid, Tubularia sp.

Tubularia hydroids are colonial, have long stalks with a thickened perisarc covering, and are attached to the substrate by stolons [1,2,4]. Tubularia hydroid colonies do not anchor by rooting filaments as do the solitary Corymorpha hydroids [1,2,3].

Tubularia has two sets of filiform tentacles (long, slender tentacles with stinging cells scattered along their length): the short, numerous, and densely crowded oral tentacles and the longer basal aboral tentacles in a single whorl [1,2,3].



Here's a closer view of the hydranth (head) of these Tubularia hydroids. The small beaded area between the oral and aboral tentacles are the reproductive sex cells (gonophores). The tentacle-fringed conical structure rising up in the middle of the gonophores is the hypostome with the hydroid's mouth and smaller oral tentacles at the end.



A prominent McMurdo hydroid is Tubularia ralphii (with T. hodgsoni synonymized under T. ralphii in 1979) [5,6].

T. ralphii is colonial, with a few to several hundred mostly smooth stems arising from a mat [9]. T. ralphii is found at depths from 0 to 234 meters and has been collected up to seventeen centimeters in length [6,7,8.9]. T. ralphii has white or greenish stems, orange red hydranth and gonophores, and white tentacles [9]. T. ralphii can form creeping colonies on stones [10]. T. ralphii has a diet dependent on the water column, capturing planktonic prey like copepods and invertebrate eggs [10].


Hydroids have a complex life cycle -- a sexual reproduction stage involving medusae or is medusoid in character, and an asexual reproduction stage, often colonial, involving asexual budding.


This could be a newly settled and growing Tubularia sp. hydroid.

1: Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening 111:183-215, 1949; 2: Monograph on the Hydroida of Southern Africa. NAH Millard. Annals of the South African Museum 68, 1975; 3: South African Journal of Antarctic Research 23(1-2):3-24, 1993; 4: Hydroids and Hydromedusae of the USSR. (Gidroidy i Gidromeduzy Morskikh, Solonovatovodnykh i Presnovodnykh Basseinov SSSR). DV Naumov. Jerusalem: Israel Program for Scientific Translations / NTIS. 1969; 5: Ecological Monographs 44(1):105-128, 1974; 6: Hydroids of the Antarctic and Subantarctic Waters. SD Stepanjants. Rezultaty biologicheskikh issledovanii Sovetskoi antarkticheskoi ekspeditsii , 6. [Biological Results of the Soviet Antarctic Expeditions Volume 6]. Issledovaniia fauny morei 20(30). [Explorations of the Fauna of the Seas 20(30)]. Academy of Sciences of the USSR, Zoological Institute. 1979; 7: Some Ecological Peculiarities of the Hydroid Tubularia ralphii Bale, 1884, in Antarctic Waters (from the Material of the 16th Soviet Antarctic Expedition) [Nekotorye osobennosti ekologii gidroida Tubularia ralphii Bale, 1884 v priantarkticheskikh vodakh (po materialam XVI Sovetskoi antarkticheskoi ekspeditsii)]. Stepaniants, SD. IN: Teoreticheskoe i prakticheskoe znachenie kishechnopolostnykh (Theoretical and Practical Significance of Coelenterates) edited by D.B. Naumov and S.D. Stepaniants: Leningrad, 1980. pp.109-113; 8: Antarctic Hydroids. Broch, H. Scientific results of the Norwegian Antarctic Expeditions, 1927-1928. Number 28. Oslo, I Kommisjon hos J. Dybwad, 1948; 9: Marine Invertebrates of Southern Australia, Part 1. SA Shepherd & IM Thomas. Adelaide, South Australia: DJ Woolman Government Printer, 1982; 10: Polar Biology 24(8):620-627, 2001

Text ©Peter Brueggeman. Photographs ©Canadian Museum of Nature (Kathleen Conlan), Jim Mastro, & M Dale Stokes. Photographs may not be used in any form without the express written permission of Canadian Museum of Nature (Kathleen Conlan), Jim Mastro, & M Dale Stokes.