hydroid Monocaulus microrhiza

Monocaulus microrhiza is found in Antarctica at depths from 33 to 761+ meters [1,3,5,6]. M. microrhiza is up to eighteen centimeters long [3]. M. microrhiza is colored greyish to brown-violet to black with a distinct constriction between its head and caulus (stalk); the caulus (stalk) is tightly covered with a transparent greyish firm perisarc which leaves free the darkened 'neck' region of the caulus, giving it a characteristic split-colored appearance [3,7].



Monocaulus microrhiza has 30-50 longer basal aboral tentacles up to seven centimers long, arranged in one row, and about 100-200 short, densely crowded oral tentacles around the hydroid's mouth [3].

M. microrhiza is a conspicuous organism in Cape Armitage's third benthic faunal zone below 33 meters depth [5].



The small tentacle-fringed structure rising up in the middle of the gonophores of Monocaulus microrhiza is the hypostome with the hydroid's mouth and smaller oral tentacles at the end. The white to greyish beads are the reproductive sex cells (gonophores) which arise in the space between the oral and aboral tentacles [3]. After fertilization, those Monocaulus gonophores containing eggs develop free-swimming medusae borne from stalks above the aboral tentacles; the medusae have a pointed apex and apical canal, with one extensile marginal tentacle with beads of sting-cells [4].




Here Monocaulus microrhiza is living in an ice pocket. M. microrhiza has been observed heavily colonizing iceberg scours [3].

M. microrhiza is anchored by root filaments [3,7]. Juveniles of M. microrhiza may settle on rooting filaments of adults [3].

Taxonomic Note: Genus was previously Lampra or Corymorpha, and is now Monocaulus [2,3,6,7].

1: British National Antarctic Expedition 1901-1904. Natural History. Volume 3 Zoology and Botany, Part 2 Hydroid Zoophytes. Hickson, SJ & Gravely FH. London : British Museum, 1907; 2: Gidroidi Pribrezhnikh vod Moria Deivtssa po Materialam XI Sovetskoi Antarkticheskoi Ekspeditsii 1965/1966 gd. [Hydroids of Coastal Waters of the Davis Sea from the Materials of the 11th Soviet Antarctic Expedition]. SD Stepanjants. Rezultaty Biologicheskikh Issledovanii Sovetskoi Antarkticheskoi Ekspeditsii , 5. [Biological Results of the Soviet Antarctic Expeditions, 5] Issledovaniia Fauny Morei 11 (19). [Explorations of the Fauna of the Seas 11 (19)]. Leningrad, Academy of Sciences of the USSR, 1972. pp. 56-80.; 3: Marine Ecology 22(1-2):53-70, 2001 (has in situ color photos); 4: Monograph on the Hydroida of Southern Africa. NAH Millard. Annals of the South African Museum 68, 1975; 5: Antarctic Ecology, Volume 1. MW Holdgate, ed. NY: Academic Press, 1970. pp. 244-258; 6: Polar Biology 20(4):229-247, 1998; 7: Proceedings of the Zoological Institute, Russian Academy of Sciences, Volume 281. Zoological Sessions, Annual Reports 1998, St. Petersburg, Russia : Zoological Institute, 1999. pp. 47-54

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