No common name

Craspedacusta sowerbyi

ORDER Limnomedusa

FAMILY Olindiidae

TAXONOMY

Craspedacusta sowerbyi Lankester, 1880, found on a water-lily in a tank at Regent's Park, London.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

Hydroid: freshwater, solitary or forming small colonies of 2-4, rarely 7 polyps; hydranths without tentacles, cylindrical, with apical mouth (hypostome) surrounded by cnidocysts forming a spherical capitulum under which the polyp is slightly tapering, forming a distinct neck; basal portion of hydranths with periderm covering, attaching colony to substrate; medusa buds lateral, on the middle or lower part of body column, often becoming terminal by hydranth reduction; asexual reproduction by frustules, transversal division and resting stages (cysts).

Medusa: umbrella 0.39-0.78 in (10-20 mm) wide, slightly flatter than a hemisphere; mesoglea fairly thick; with well-developed, marginal cnidocyst ring; velum broad and well developed; manubrium large, upper portion conical with broad square base, tapering downwards to cross shaped distal region; mouth with four simple or slightly folded lips, extending beyond umbrella margin; four straight radial canals and circular canal broad and massive; four large, smooth, triangular pouchlike gonads, with rounded comers, hanging down into subum-brellar cavity from points of junction of radial canals with manubrium; with 200-400 or more hollow marginal tentacles, in several series situated at different levels on umbrella margin; oldest four perradial marginal tentacles being largest and highest; bases of marginal tentacles adherent to exumbrella; surface of marginal tentacles covered with evenly distributed papillae, each with 3-10 cnidocysts; 100-200 or more statocysts, usually about half number of marginal tentacles; statocysts situated in velum, forming centripetal tubes with basal enlargements near umbrella margin.

Numerous species of Craspedacusta have been described, mainly from China; it is not excluded that they represent anything more than variations of a single species.

DISTRIBUTION

Cosmopolitan in freshwaters and sometimes in brackish waters of temperate and tropical areas. (Specific distribution map not available.)

HABITAT

Freshwater surfaces and calm rivers, often found in tanks and aquaria.

BEHAVIOR

Hydroids live on water plants; the medusae are active swimmers, living usually near surface.

FEEDING ECOLOGY AND DIET

Feed on small freshwater planktonic organisms, mainly protozoa, rotifers, crustaceans, worms, and fish larvae.

REPRODUCTIVE BIOLOGY

Dioecious, sex cells released in freshwater; the planula gives rise to polyp colonies.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

The medusae may damage and injure fishes in fish farms. ♦

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