The key difference between Sarcopterygii and Actinopterygii is that sarcopterygii is a class of bony fish, consisting of lobed fish that have fleshy, lobed and paired fins. Meanwhile, actinopterygii is a class of bony fish, consisting of ray-finned fish that have fins supported by horny spines.
Fish that belong to the group osteichthyan are vertebrates. Their fins and the body structure may vary depending on the group. Sarcopterygii and actinopterygii are two classes of osteichthyans. Sarcopterygii fish are lobed finned fish while actinopterygii fish are ray-finned fish. Most species belonging into sarcopterygii are extinct in comparison to species belonging into actinopterygii.
CONTENTS
1. Overview and Key Difference
2. What is Actinopterygii
3. What is Sarcopterygii
4. Similarities Between Sarcopterygii and Actinopterygii
5. Side by Side Comparison – Sarcopterygii vs Actinopterygii in Tabular Form
6. Summary
What is Sarcopterygii?
Sarcopterygii is a group of bony fish containing lobe-finned fish. They belong to the group of Osteichthyan. Sarcopterygii group includes two species: coelacanths and lungfish. The sarcopterygii species are fleshy fish. They have paired dorsal fins, and the body joins by one single bone. The scales of the sarcopterygians are true scaloids, and they consist of a lamellar bone. They are also tetrapod limbs.
Figure 01: Sarcopterygii
Many sarcopterygians have a symmetrical tail and teeth covered by true enamel. The species of sarcopterygii are mostly extinct species. They are commonly found in the West Indian Oceans.
What is Actinopterygii?
Actinopertygii is the second major grouping member of the Osteichthyans. They are also called ray-finned fish due to the presence of the bony or horny spines in their skin. The actinopterygian fins are directly attached to the proximal skeletal elements. They are also called the basal skeletal elements. They are vertebrates. And, this group includes about 30,000 species of fishes. The distribution of these fish varies in both marine and freshwater.
Figure 02: Actinopterygii
The types of scales present in actinopterygii vary, unlike in sarcopterygii. They all belong to the group teleosts. They have bony ridges, and the inner part is composed of fibrous connective tissue.
The reproduction of the ray-finned fish may show complex patterns. In most species, the sexes are separated. They undergo external fertilization. The species belonging to the actinopterygii have a free-swimming larval stage. However, in certain species, there is switching of sexes where the lifecycle begins as a female and ends as a male. Some species are also capable of self – fertilizing.
What are the Similarities Between Sarcopterygii and Actinopterygii?
- Sarcopterygii and Actinopterygii are two classes of bony fishes.
- Both are vertebrates and chordates and are aquatic in nature.
- They belong to the group osteichthyas, so their last common ancestor is Osteichthyes.
- They have a three-chambered heart.
- Moreover, both of these classes have fin structures.
- They have swim bladders.
What is the Difference Between Sarcopterygii and Actinopterygii?
Sarcopterygii and actinopterygii are two groups of osteichthyans. The key difference between sarcopterygii and actinopterygii relies mainly on their fin structure. Sarcopterygii fish species have lobed fins, while the actinopterygii fish species have ray fins.
Moreover, the rate of extinction in sarcopterygii is higher in comparison to actinopterygii. So, this is another significant difference between sarcopterygii and actinopterygii. Furthermore, the types of scales present in the two species also vary; actinopterygii fish have horny spines while sarcopterygii fish do not have horny spines.
Summary – Sarcopterygii vs Actinopterygii
Sarcopterygii and actinopterygii are two major groups of osteichthyans, which include vertebrate bony fish. Most of these species are marine. Sarcopterygii are extinct organisms that have a pair of lobed fins. Actinopterygii, in contrast, have a pair of ray fins. So, this is the key difference between sarcopterygii and actinopterygii. In addition, the sarcopterygii species do not have horny spines in the skin, while, the horny spins are present in actinopterygii species.
Reference:
1. “Sarcopterygii and Actinopterygii” GEOL431 – Vertebrate Paleobiology, University of Maryland. Available here.
Image Courtesy:
1. “Sarcopterygii” By Prehistoricplanes – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Rose fish” (Public Domain) via Commons Wikimedia