|Nanomia bijuga (Chiaje, 1841) : Siphonophore
Phylum Cnidaria / Class Hydrozoa / Subclass Siphonophorae / Order Physonecta / Family Agalmidae
Many siphonophores, a group of chain-like hydrozoan predators, are difficult to identify to species. Nanomia is among the easier West Coast species to distinguish, and also one of the most common. As a physonect siphonophore, it possesses a gas-filled float known as the pneumatophore that aids buoyancy. Immediately behind the float are number of closely spaced swimming bells, the nectophores. These pulse to move the organism. The stem area posterior to this holds a series of feeding and reproductive components. The feeding structures deploy long tentacles that form a veil of death, ensnaring zooplankton prey as the siphonophore drifts in the water. The tentacles are fully extended only when the siphonophore is not actively swimming, and have a combined length that is many times the length of the stem. Nodules on the ends of tentacles appear to mimic copepods and may be a means for luring potential prey into a trap. The tentacles are highly contractile and when disturbed shorten considerably to facilitate a quick escape swimming response. By physonect standards Nanomia is tiny, with total chain length up to about 30 cm and nectophore region from 2 to 3 cm long. At times Nanomia can be incredibly abundant in nearshore surface waters of central California, but most of the time resides in deeper midwater habitats. It’s a cosmopolitan species, being found in tropical and temperate waters of the Atlantic, Indian and Pacific Oceans.
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