Calycophoran siphonophores are distinguished by the presence of a swimming bell (or bells) and the lack of an apical gas-filled float.   Whereas some members of this order form lengthy chains, many calycophorans are tiny and inconspicuous like the species pictured here.  These types possess a characteristic "rocket-shaped" swimming bell with relatively powerful musculature.  Rapid pulsing of the bell leads to a swift, darting swimming pattern.   The  stem trailing from the bell is highly contractile.  When disturbed, it can be retracted close to the swimming bell, thus enabling more streamlined propulsion.   As the stem is extended, tentacles are set in very specific patterns to act as a net in capturing zooplankton prey.  Most calycophorans in this group are members of the family Diphyidae.  They can be very difficult to identify to species or even genus, particularly since only pieces of the organism are usually all that is available.   You are unlikely to see one while boating or scuba diving since they are small and transparent.  These calycophorans are frequently collected with plankton nets but are usually damaged in the process - often only the relatively tough swimming bell remains intact.

All photographs © David Wrobel and may not be used or copied without permission!