| Mitrocoma cellularia
(A. Agassiz, 1865) : Cross Jelly Phylum Cnidaria / Class Hydrozoa / Order Leptomedusae / Family Mitrocomidae |
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The cross jelly is among the more common hydromedusae to
appear in the
waters of Monterey Bay and other West Coast locations. Typical of members of this group, the bell is transparent,
thus making it difficult to see without careful observation. The margin of the bell
(diameter up to 90 mm) is lined with several hundred fine, white tentacles. The most
conspicuous part of this jelly are the 4 radial canals to which are attached the white
gonads. They form the relatively conspicuous "cross" that gives the common
name to this species. The small stomach has 4 frilly lips. A strong bioluminescence is
produced around the bell margin. Fall and
winter months are the best times to find Mitrocoma in Monterey Bay. At times they
may form large aggregations that are easily visible from the surface. The
third photo shows a swarm that has invaded near-surface waters of a kelp forest
at Point Lobos in central California. Cross jellies are found in nearshore
waters from Alaska to
central California.Recent research has shown that cross jellies can actually detect chemicals in the water - they respond with changes in swimming behavior and extensions of tentacles when presented with traces of blended food. This may be implicated in their tendency to form large aggregations since they may be able to detect concentrations of prey. Other species presumably have similar chemical sensing abilities.
All photographs © David Wrobel and may not be used or copied without permission!