Calyptoptomatida
Calyptoptomatida (phylum Mollusca) Extinct Palaeozoic class of marine molluscs, with bilateral symmetry, in which the shell shape is variable: most are subtrigonal in cross-section. The walls are generally thick, and composed of laminated calcium carbonate. The apertural end is the widest; the narrowest is the closed apex, which may be pointed or blunt. The juvenile portion is chambered with imperforate septa. Externally the shells are smooth, or ornamented with growth lines and/or longitudinal and transverse ridges. The aperture is usually protected by an operculum possessing paired muscle scars. Individuals are 1–150 mm long. The class ranges in age from Lower Cambrian to Middle Permian, and contains two orders.
More From encyclopedia.com
Rhynchonellids , Rhynchonellida (rhynchonellids; class Articulata) Order of brachiopods (Brachiopoda), with rostrate shells, a functional pedicle, and a delthyrium pa… Terebratulida , Terebratulida (terebratulids; class Articulata) Order of Brachiopoda with punctate shells, rounded hinge lines, functional pedicle, deltidial plates,… Hemichordata , Hemichordata (Stomochordata) A phylum first encountered in the Middle Cambrian Burgess Shale, British Columbia, Canada. The hemichordates are related… Sauropterygians , Nothosauria (nothosaurs; subclass Archosauria, order Sauropterygia) A suborder of marine reptiles that flourished during the Triassic. They possessed… Decapoda , Decapoda
Decapoda (crabs, crayfish, lobsters, shrimps; subphylum Crustacea, class Malacostraca) Order of crustaceans, most of which are marine, but s… Tusk Shells , Scaphopoda (tooth shells, tusk shells; phylum Mollusca) A class of elongate, bilaterally symmetrical, burrowing, marine molluscs which have a taperin…
You Might Also Like
NEARBY TERMS
Calyptoptomatida