What are the typical signs of the external structure of arachnids?

A characteristic feature of spiny-finned or perch-like fish is a variety of color and appearance. They have a special structure of fins, which are located not in the belly area, but under the pectoral fins, and sometimes on the throat. All fins have spines, their number is small. They have different lengths and weights: from 1 cm to 5 meters, and from tenths of a gram to nine hundred kilograms. Some do not have a swim bladder.

The fin on the back has two parts: soft and prickly. The anal fin has two spines. The teeth are bristly, some have canines. The adipose fin is absent, there are spines in the head area. Scales are often absent, or ctenoid.