Siphonophora
Eschscholtz 1829
Taxonomy
| Phylum | Cnidaria |
| Superclass | Hydrozoa |
| Class | Siphonophora |
Distinguishing characteristics
- Siphonophores are complex colonial hydrozoans comprising different types of medusoid and polypoid individuals.
- Medusoid zooids form clear gelatinous swimming bells (nectophores), floats (pneumatophores) or protective shields called bracts.
- The various polyps have diversified as feeding polyps (gastrozooids), as stinging tentacles, fishing or sensory tentacles (dactylozooids), and reproductive zooids (gonophores).
- All zooids bud from a single stem that contains a gastrovascular canal connected to all zooids in the colony.
Distribution
- Most siphonophores are oceanic and are not common in coastal samples. However, bluebottles are often washed into inshore waters and beaches where they can be a nuisance to bathers.
Ecology
- There are three orders.
- The Calycophorae generally have one or two nectophores each 1 to 2 cm in size and have no apical float (pneumatophore).
- The Physonectae have a distinct apical gas-filled float and numerous swimming bells underneath with the stem running down the centre.
- The Cystonectae have a very large float, no nectophores, and tentacles and zooids hang below the float. The most familiar member of this order is Physalia utriculus, the Portuguese man-o'-war or bluebottle.
- The other siphonophores are easily damaged during sampling and may only be identified by the presence of their nectophores.