The Three Sub-Classes
Actinopterygii (Ray-Finned Fish)
The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines ("rays").
- These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).
Sarcopterygii (Lobe-Finned Fish)
Early lobe-finned fishes have fleshy, lobed, paired fins, which are joined to the body by a single bone.
- Their fins differ from those of all other fish in that each is borne on a fleshy, lobe like, scaly stalk extending from the body. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs.
Dipnoi (Lung-Fish)
Lungfish (also known as salamander-fish) are freshwater fish belonging to the subclass Dipnoi.
- Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton.
