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Characteristics, distribution and ecology
Taxonomische classification
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(Quoy and Gaimard, 1827)

Description
Umbrella hemispherical, about as wide as high or wider; jelly thick [M.rotunda-adult ]. Velum about 1/10 of bell radius.
Stomach short, with pyramidal apex attached to subumbrella along edges of cross-shaped furrow [M.rotunda-drawing ]. Mouth with slightly crenulated margins [M.rotunda-medusa ]. Radial canals four, issuing from stomach at ends of cross-shaped furrows. Ring canal narrow, widening opposite each marginal tentacle.
Gonads transversely folded along sides of cross-shaped furrow.
Marginal tentacles usually 16, up to 28(?32), hollow, smooth, with large conical basal bulbs. 1-3(4) spindle-shaped, hollow cordyli between adjacent marginal tentacles, with abundant nematocysts [M.rotunda-margin ]. No ocelli.

Size
Diameter up to ca 22 mm.

Colour
Stomach, radial canals, gonads, and marginal tentacle bulbs carmine red to violet.

Ecology
There is little information about the reproductive season: probably October-December (Edwards, 1973b).

Depth range
Medusa typically deep-sea oceanic.
— Hydroid recorded on variety of substrates, commonly colonial hydroids; coastal and across Continental Shelf, some deeper records to 681 m (Ramil and Vervoort, 1992a).

Distribution in the North Sea
Recorded from the North Sea (Kramp, 1947); probably common nowhere every year.

World distribution
Boreal to tropical parts of Atlantic and Indo-Pacific Oceans (Ramil and Vervoort, 1992a).
Medusa recorded in Atlantic Ocean from mid-Norway, Iceland and W Greenland south to Patagonia, W Africa and off Antarctic continent (Edwards, 1973b).
— Hydroid recorded in Atlantic Ocean from the same areas as medusa, but also north to Barents and Kara Seas (Naumov, 1969).

[Description after Cornelius, 1995a]

Modeeria rotunda