Illustrated here is the hydromedusan
Cigar Jelly (Olindias phosphorica), a cnidarian, class
Hydrozoa. Hydromedusae may range in size from a few millimetres
to several centimetres in diameter when fully grown. They vary
in consistency from soft and gelatinous to firm and gristle-like.
Although the jelly is usually transparent, the manubrium, tentacles,
tentacle bulbs and gonads of living medusae may be delicately
and variously coloured, as exemplified here. Certain deep-sea
forms are heavily pigmented. In addition bioluminescence occurs
in some species, such as Aequorea
spp. Swimming is accomplished by rhythmic pulsations of the
umbrella, resulting from the opposing forces of muscular contraction
and mesogleal elasticity. A number of species are known to undergo
vertical migrations daily.
This Cigar Jelly has a bell about
4-5 cm in diameter and the tentacles of which are retracted during
the day (see above left). At night these appendages are fully
extended, often up to lengths of ten metres or so, for feeding
upon small fish and zooplankton (see above right). Their tips
are jigged as a form of lure to attract their plankton prey. This
species is commonly found in nearshore marine waters, over the
continental shelf. This particular individual was photographed
off Lizard Island on the Great Barrier Reef.