(M. Sars, 1835)
Description
Umbrella slightly higher than wide, pyriform with solid, rounded apical projection [Rathkea octopunctata ]; jelly moderately thick, especially apical ; velum broad. Four radial canals and ring canal narrow.
Gastric peduncle well developed, conical; manubrium shorter than length bell cavity, cylindrical to four-sided. Mouth with four lips armed with lateral and stalked terminal clusters of nematocysts.
Gonads surrounding manubrium. Asexual budding from manubrium wall [R.octopunctata-asexual-habitus ].
Eight groups of marginal tentacles spreading from eight marginal tentacular bulbs; four perradial each with five tentacles, four interradial each with three tentacles. Ocelli absent.
Development: R.octopunctata-development.
Size
Umbrella 3-4 mm high.
Colour
Manubrium brownish yellow; marginal tentacle bulbs pale yellowish, dark yellowish brown, or deep Vandyke brown appearing black under transmitted light [R.octopunctata-male-habitus ].
Ecology and depth range
Typically a winter and spring planktonic species, first medusae appearing in January to February, becoming abundant by April and disappearing from the plankton by June-July. Asexual reproduction ceases when the medusae reach sexual maturity in April-May.
Distribution in the North Sea
World distribution
E North Atlantic Ocean, Mediterranean Sae.
[After Russell, 1953a; Russell, 1953b; Kramp, 1959]