Hypertext Webster Gateway: "Acephala"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Lamellibranchia \La*mel`li*bran"chi*a\, Lamellibranchiata
\La*mel`li*bran`chi*a"ta\, n. pl. [NL. See {lamella}, and
{Branchia}, {Branchiate}.] (Zo["o]l.)
A class of Mollusca including all those that have bivalve
shells, as the clams, oysters, mussels, etc.
Note: They usually have two (rarely but one) flat,
lamelliform gills on each side of the body. They have
an imperfectly developed head, concealed within the
shell, whence they are called {{Acephala}}. Called also
{Conchifera}, and {Pelecypoda}. See {Bivalve}.
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Acephala \A*ceph"a*la\, n. pl. [NL., fr. Gr. ?, adj. neut. pl.,
headless. See {Acephal}.] (Zo["o]l.)
That division of the Mollusca which includes the bivalve
shells, like the clams and oysters; -- so called because they
have no evident head. Formerly the group included the
Tunicata, Brachiopoda, and sometimes the Bryozoa. See
{Mollusca}.
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