C. septemvalvis was originally described from a disfigured specimen with seven valves. Montagu believed its missing valve to be a characteristic of an undescribed species of chiton; it was a specimen of a new species, but characterised by other features in normal individuals that have eight valves. (Some authorities have criticised the name 'septemvalvis' as being mis-leading, but as it was the first epithet used to describe a valid species, the name remains valid.)
Length: to 22 mm (up to 14 mm broad)
Tegmentum colour: orange to brick red, often with white markings, or with shades of green, bright yellow, or bright orange.
Sculpture: smooth and glossy to the naked eye, diagonal ridges set with black dots (the pigment cups of the ‘shell-eyes’); under magnification the valves are sculptured with small granules arranged in quincunx
Girdle: wide (about 1/3 of the animal’s width) and covered in spicules, with a short marginal frince of spicules. The girdle is coloured yellow or orange with red markings.
Bathymetric range: shallow subtidal to 1000 m (usually from 10-100 m)
Geographic range: uncommon, but distributed on all coasts of Europe from Scandinavia and the Shetland Islands to the Meditteranean and the Red Sea.
Similar species: Tonicella rubra
Taxonomy and Synonymy:
Ischnochitonidae Dall 1889
GENUS: CALLOCHITON Gray 1847
Callochiton septemvalvis (Montagu 1803 : Chiton)
= Chiton achatinus Brown 1827
= Chiton euplaeae Costa O.G. 1829
= Chiton doriae Capellini 1859
= Chiton laevis var. navicula Jeffreys 1865
= Callochiton achatinus euboecus Kattoulas, Koukouras & Economidis 1973
? Chiton scytodesma Scacchi 1836
! Chiton laevis Pennant 1777 sensu Montagu, 1803
Synonyms (=); Dubious synonyms (?); Mis-identifications (!)