What is the Difference Between Sarcopterygii and Actinopterygii?

Sarcopterygii and Actinopterygii are two major groups of osteichthyans, which include vertebrate bony fish. The key difference between the two lies in their fin structure:

• Sarcopterygii: This class of bony fish consists of lobed fish with fleshy, lobed, and paired fins. They are characterized by their fleshy pectoral and pelvic (paired) fins that articulate with the skeleton. Some examples of sarcopterygians are coelacanths, lungfishes, and their fossil relatives.
• Actinopterygii: This class of bony fish consists of ray-finned fish with fins supported by horny spines. They have only skin-covered bony spines (lepidotrichia) supporting the fins. Actinopterygii includes the Teleostei, which comprise 95% of surviving fish species, representing approximately half of all extant vertebrate species.

Similarities between Sarcopterygii and Actinopterygii include:

• Both are classes of bony fishes.
• Both are vertebrates and chordates, and are aquatic in nature.
• They belong to the group osteichthyans, sharing a common ancestor.
• They have a three-chambered heart.
• Both classes have fin structures.
• They possess swim bladders.

However, the rate of extinction in Sarcopterygii is higher compared to Actinopterygii. Additionally, the types of scales present in the two groups vary, with Actinopterygii fish having lepidotrichia.

Comparative Table: Sarcopterygii vs Actinopterygii

Here is a table comparing the differences between Sarcopterygii and Actinopterygii fish:

Sarcopterygii fish are lobed-finned fish, with fleshy fins and a single bone connecting the body. Their scales are true scaloids, and they have teeth covered by true enamel. Many Sarcopterygii species have a symmetrical tail. These fish are mostly extinct and can be found in the West Indian Oceans.

Actinopterygii fish, on the other hand, are ray-finned fish with fins supported by horny spines. They are marine fish with a wide distribution.