Acanthopleura gemmata Seashell Chiton Polyplacophora Amphineura

Acanthopleura gemmata mm 42-50 Seashell Chiton Polyplacophora Amphineura.
Family: Chitonidae.
Common name:  Gumboot Sea, Cradle, Coat-of-Mail Shell or Loricate.
Syn. Chiton gemmatus, Acanthopleura balansae, Acanthopleura bergenhayni, Acanthopleura glareosa, Acanthopleura rawakiana, Acanthopleura spiniger, Acanthozostera virens, Chiton macgillivrayi, Chiton spiniger.

Polyplacophora, normally called Chitons from the name of the type genus (Chiton), are algae-eating marine molluscs with evident primitive characteristics.
The identification is simple thanks to the oval dorsal shell, consisting of imbricated and articulated plates (8 in the current species) which also give the name to the class. These plates, consisting of three main layers, are included in the mantle which extends to the edge of the animal forming a flap that surrounds and connects the plates and allows them to articulate, given its flexibility.
Equipped with radula and pseudotrocophore larva, they preserve the metamery, already detected in the Monoplacophora, in the shell valves and in the gills repeated in series. The animal, seen from below, has a distinct head, devoid of tentacles, the typically elongated foot, surrounded by a groove containing the gills.
The polyplacophores are an ancient group, already existing in the Cambrian with 430 identified fossil forms, and survived to the present day with about 940 marine species, typical of intertidal environments, where they resist the violence of the waves thanks to the foot that exerts a powerful sucker function. and flattened form. The large muscular foot that has a firm grip on the rocks, the flexible body and the articulated plates allow these molluscs to bend and anchor strongly adapting to any roughness and irregularity of the rock.
polyplacophores are exclusively marine animals. They live on the seabed (they are benthic) and prefer rocky or compact soils. Some species populate the intertidal zones such as above and are therefore exposed to air and light for significant periods.
Polyplacophores are distributed across all three oceans and connected seas. They are also present in the Mediterranean and especially in the Italian seas. However, it is estimated that the greatest diversity of species is found in the Pacific.