Acantholid

The term "Acantholid" seems to be a misspelling or variation of "Acanthodii," which refers to an extinct class of fish known as acanthodians.

These creatures are often called "spiny sharks" due to their shark-like appearance and the presence of prominent spines supporting their fins.

However, they are not true sharks.

Acanthodians are considered a paraphyletic group, meaning they consist of various fish lineages that are basal to modern cartilaginous fish like sharks, rays, and chimaeras.

Acanthodians had a mix of characteristics shared with both bony fish (osteichthyans) and cartilaginous fish (chondrichthyans).

Their bodies were generally streamlined like modern sharks, and their skin was covered with tiny rhomboid platelets similar to the scales of certain bony fish.

These fish first appeared in the Early Silurian period and lasted until the Permian.

Initially marine, some species later adapted to freshwater environments.

Fossilized spines and scales are often all that remains of these fishes, providing valuable insights into their structure and the environments they inhabited.

Acanthodians are divided into several orders, including Acanthodiformes, Climatiiformes (a paraphyletic group), Diplacanthiformes, and Ischnacanthiformes.

Each order had distinct features, such as the robust bony shoulder girdles and multiple small sharp spines of Climatiiformes, or the tooth plates fused to the jaws of predatory Ischnacanthiformes.

In summary, "Acantholid" likely refers to the acanthodians, a fascinating and diverse group of early jawed fishes that played a significant role in the evolution of modern fish species.

Their study helps scientists understand the transition from early fish to the diverse array of species we see today.