(M. Sars, 1835)
Description
Umbrella bell-shaped, with moderately thick jelly, and a distinct apical chamber of varying shape, usually globular [Sarsia tubulosa ]. The umbilical canal is soon lost, the four radial canals pass through the mesogloea to enter the marginal bulbs somewhat abaxially, but only when fully mature.
[S.tubulosa-medusa ] Manubrium very long (about 2.5 times bell height), tubular, extending far beyond umbrella margin. Mouth circular, simple.
Gonads continuous, surrounding manubrium except for the swollen oral region and relatively long basal portion.
With four equally developed very long tentacles, not filiform, with numerous clusters of nematocysts. Marginal tentacle bulbs broad, with black or crimson ocelli on the abaxial side of the bulbs. Exumbrella without rows of nematocysts. Statocysts absent. Never with developing medusa buds.
Young medusa: S.tubulosa-young-habitus .
Size
Umbrella 18 mm high, somewhat higher than wide.
Colour
[S.tubulosa-habitus ] Species with brown, scarlet and blue forms; generally the manubrium is pinkish, the endoderm of the apical knob and bulbs an intense shade of red or brownish-red, tentacles and radial canals pale pink.
Ecology and depth range
Active swimmers in the upper water layers, more abundant in more sheltered coastal waters, correlated with the habitat of the hydroid. Hydroids are chiefly found near low watermark.
Young medusae begin to appear in March-April (sometimes even in February), mature specimens are present in April-June while small numbers persist until July (August). When in late winter-early spring the conditions are unfavourable, no medusae are produced, the hydroids saving their strength for an autumn generation.
Distribution in the North Sea
Northern and southern North Sea, including Skagerrak.
World distribution
North Atlantic Ocean including Arctic waters; N Pacific Ocean.
[After Russell, 1950b; Russell, 1953a; Kramp, 1959; Kramp, 1961; Edwards, 1983; Schuchert, 2001]