Velella velella
ORDER
Capitata
FAMILY
Porpitidae
TAXONOMY
Medusa velella Linnaeus, 1758, Mediterranean Sea.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
Hydroid: the colony is a flattened oval to slightly S-shaped float, with a triangular sail and concentric air chambers; up to 1.5 in (40 mm) long and 0.78 in (20 mm) wide, higher in the center than at the edges. Float and sail are supported by chitin covered by mantle tissue; margin of float is soft and flexible. The center of colony underside is a single large gastrozooid encircled by a ring of medusa-producing gastro-gonozooids and a peripheral band of dactylozooids. Central-feeding zooid oval, with an elongated hypostome, without tentacles or medusa buds. Gastro-gonozooids are spindle shaped, with a swollen mouth region, lacking tentacles, but with warts of cnidocyst clusters concentrated in distal half; on proximal half of hydranth, numerous medusa buds growing in groups from short blastostyles. Dactylozooids are mouth less, long, and tapering, oval in cross section, with cnidocysts concentrated in two lateral bands on the narrow sides. The float is deeply blue when alive, medusa buds yellow-olive from symbiotic algae.
Medusa: with four exumbrellar cnidocyst rows, four radial canals; two pairs of opposite, perradial tentacles, a short adaxial one and a long abaxial one, each with a large terminal cnidocyst cluster; two perradial marginal bulbs without tentacles; manubrium conical with quadrate base; mouth tubular; gonads irregularly arranged perradially and interradially.
DISTRIBUTION
Atlantic and Indo-Pacific. (Specific distribution map not available.)
HABITAT
The hydroid floats, with the sail out of the water and the zooids hanging down in the hyponeuston. The medusae are planktonic, in shallow water and possibly in deep water as well, where the young colonies have been recorded, before climbing to the surface.
BEHAVIOR
Nothing is known.
FEEDING ECOLOGY AND DIET
The hydroid colony feeds on surface plankton, from crustaceans to appendicularians, and especially on fish eggs.
REPRODUCTIVE BIOLOGY
Floating hydroids can occur in immense offshore swarms, sometimes stranding along shorelines. The colonies liberate rarely observed young medusae that sink toward the bottom. Development of new colonies occurs in deep waters.
CONSERVATION STATUS
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
The massive strandings can entrap sand and protect the shore from erosion. Feeding on fish eggs makes Velella a potential competitor for man in the use of fish resources.
