Chondrophore

Chondrophores
Blue button (Porpita porpita)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Anthoathecata
Suborder:	Capitata
Family:	Porpitidae Goldfuss, 1818
Type genus
Porpita
Genera
Porpita Velella
Synonyms
Velellidae Eschscholtz, 1829 Discalidae Haeckel, 1888 Porpalidae Haeckel, 1888 Porpitellidae Haeckel, 1888 Chondrophora Totton, 1954

The chondrophores or porpitids are a small and unusual group of hydrozoans. They are the family Porpitidae.

They all live at the surface of the open ocean, and are colonies of carnivorous, free-floating hydroids. Their life-style in the plankton is similar to that of pelagic jellyfish.

The chondrophores look like a single organism but are cooperatives of polyps.

The most familiar members of the family Porpitidae are the blue button (Porpita porpita) and the by-the-wind sailor (Velella velella).

Structure

Chondrophores may look like a jellyfish, but they really are not. Like the siphonophores they are not a single animal. They are a colony of clones, genetically identical zooids. These zooids are small, highly modified individual polyps. Though structurally similar to other cnidarians, the zooids do not live by themselves: they are attached to each other. Each type of zooid depends for survival on the others doing what it cannot do by itself.

This kind of set-up is also found in the siphonophores: the Portuguese man o' war. They evolved independently, and are classified in different orders.

Fossil record

A rare soft-bodied fossil was got from Mississippian strata in northeastern Kentucky. It was interpreted as a chondrophorine float. The origin of the group was probably in the Neoproterozoic era, some 650–540 million years ago.