Lovén, 1836
Description
Umbrella hemispherical [L.clausa-male-habitus ] with moderately thick jelly, diameter 5-9 mm; velum ca 1/4 bell radius; stomach short and small; without peduncle; manubrium short; mouth with four small unfolded lips.
Radial canals four, they and ring canal narrow.
Gonads on distal ends of radial canals, oval, longitudinally divided [L.clausa-medusa ].
Marginal tentacles 16-24, with large conical bases [L.clausa-marginal tentacle ]; one to three spiral cirri on either side of each tentacle base. 16-23 closed marginal vesicles, alternating approximately with marginal tentacles, each with one concretion.
Young specimen: L.clausa-newly-habitus.
Size
Diameter of bell of adult 5-9 mm; no more data on adult available. Russell, 1936b, Russell, 1936c, Russell, 1953a recorded dimensions of young medusae at various bell diameters.
Colour
Manubrium recorded as pale greenish yellow, gonads with greenish tinge, bases of marginal tentacles orange with core of bright green and with reddish summit.
Ecology
In W English Channel medusa recorded January, March-April, June-September, but commonest in autumn (Russell, 1953a; Marine Biological Association, 1957; Teissier, 1965); gonothecae noted April, NW Spain (Ramil, 1988).
Depth range
— Medusa in coastal plankton.
— Hydroid recorded especially on Turritella communis (Gastropoda), sometimes occupied by Phascolion strombi (Sipunculoidea) (Teissier, 1965) but most published records mention only 'mollusc'; recorded depths range 0-50 m.
Distribution in the North Sea
Recorded sparsely, possibly overlooked. Probably occurs throughout the area except Norway, but known from W Sweden.
— Medusa recorded from Elbe estuary (Russell, 1953a; Russell, 1970a), Helgoland (where common, Russell).
— Hydroid reported from Norfolk (where colonies tiny and often moribund, Hamond, 1957); SW Denmark (Kramp, 1935a), W Sweden (Lovén, 1836; Jäderholm, 1909; Kramp, 1935a). No records from Belgium, Netherlands, the Baltic Sea or Norway.
World distribution
Reported from the British Isles (Hincks, 1868; Hincks, 1871; Marine Biological Association, 1957), Portugal (Da Cunha, 1944), Roscoff (Teissier, 1965), SE Spain (Garcia Corrales et al., 1979) and NW Spain (Ramil, 1988). Furthermore apparently unknown outside Europe except Agadir, Morocco (Patriti, 1970; Ramil, 1988) and one possible record from Beaufort, N. Carolina (Fraser, 1944). Kramp, 1959 regarded the species as endemic to the area outlined above.
[After Cornelius, 1995a]