Torrey, 1909
Description
Umbrella rather flat, 3-4 times wide as high [P.diegensis-habitus ]; jelly thin, being thickest in apical region. Velum narrow, less than 1/4 of bell radius.
Stomach very short, with short conical gastric peduncle, which reaches to about limit of bell [P.diegensis-habitus ]. Mouth with four very short perradial lips with crenulate margins. Radial canals four, extending from margin to end of gastric peduncle; they and ring canal narrow.
Gonads on radial canals limited to subumbrellar disc, linear, extending from base of gastric peduncle nearly to ring canal, without median furrow [P.diegensis-habitus ].
Marginal tentacles 16-28, perhaps more in some specimens, with elongate conical bases. 3-9 rudimentary and triangular marginal bulbs and, similarly, 3-9 short marginal cirri, between adjacent tentacles; no lateral cirri. 2-5 closed marginal vesicles between adjacent tentacles each with 2-6 concretions.
Size
Diameter of bell '20-30 mm or over' (Russell, 1953a); apparently no more information
Colour
Gonads and stomach opaque milky white, otherwise colourless.
Ecology
The only specimens taken in the NW European area were from the Western Approaches in April. Dates of collection have otherwise been recorded from off San Diego May-July and in the south and equatorial Atlantic Ocean in September (Russell, 1953a).
Probably typically amongst oceanic plankton. Though usually taken over deep water the species might presumably be carried into coastal areas by suitable currents.
Depth range
Although poorly known, this species has been recorded sporadically over most of the open oceans of the world and so is among the most widespread of all animals. Its apparently predominantly oceanic distribution is unusual among Leptomedusa; and Russell's (1953a) record of a specimen with two actinian larvae attached is paradoxical in a species habitually occurring in water of great depth. Possibly it spends part of its life in deep water near the bottom.
Distribution in the North Sea
May occur in the northern North Sea, just from outside the Continental Shelf.
World distribution
Reported widely from cool to equatorial waters of the Atlantic and Indo-Pacific Oceans; in the Atlantic Ocean the recorded northerly and southerly extremes are from the Irminger Current south of Iceland, and off the Cape of Good Hope (Kramp, 1961).
Remark
Hydroid unknown.
[After Cornelius, 1995a]