Arthropods: Crustaceans and Pycnogonids

Arthropods are the largest phylum in the animal kingdom and in the sea they are mainly represented by Crustaceans and Pycnogonids.
Crustaceans are specialized for aquatic life and many of them have gills for breathing. Their chitinous exoskeleton is strengthened by calcium carbonate. The different appendices are specialized for movement, reproduction and feeding.
Crustaceans of the Italian Seas, belonging to the taxa Cumaceans, Tanaids, Isopods, Amphipods and Decapods, consist of about 1044 species.
Pycnogonids are cheliceriformes pantopods, "relatives" of terrestrial spiders, of which maintain the aspect (they are also known as sea spiders). Pycnogonids of the Italian seas reach a lengths of 2 or 3 mm and include about 44 species. Their body consists of a thoracic segment, bearing the legs, and a cephalic segment, with the ocular tubercle, a proboscis equipped with the mouth, chelicerae and ventral palps. On the ventral side of the cephalic segment a pair of ovigers are present in both sexes or in some cases only in males. In addition to removing the debris from the appendages, in  males such ovigers are used to carry the eggs.