OSTEICHTHYES

Major Sub-groups in the Phylum


There are two subclasses of Osteichthyes:

  1. ACTINOPTERYGII
  2. SARCOPTERYGII

The distinguishing character is the paired fins. The fins of Sarcopterygii are fleshy and their skeletal/muscular supports project externally. The fins of Actinopterygii are formed by dermal fin rays, where the endoskeleton and muscles control the fins internally.

Anarrichthys ocellatus, right. Picture taken from http://members.aol.com/bafiler/Osteichthyes.html (with permission)

ACTINOPTERYGII

The ray-finned fishes. Most of today's fish are actinopterygians. There are three infraclasses: the CHONDROSTEANS, the HOLOSTEANS, and the TELEOSTS. The actinopterygians are very diverse and successful, especially the teleosts, and can be found in nearly all aquatic environments. Actinopterygian fishes are oviviparous and lay many thousands of tiny eggs at one time, which are then fertilised externally.

SARCOPTERYGII

The lobe-finned bony fishes. The sarcopteryians are a very ancient subclasses of fishes with three orders: RHIPIDISTIA, ACTINISTIA, and DIPNOI. All sarcopterygians are viviparous, i.e. they give birth to one or two highly developed young at one time.