(biology, obsolete) Any of various shellfish, especially those of the obsolete orders Vermes or Acephala, or the suborder Thecosomata.
1722, John Jones (tr.), Oppian's Halieuticks of the Nature of Fishes and Fishing of the Ancients, page 231:
ANAIMONA, Aquatilia Exanguia, Bloodless Fishes, are divided into Mollia Soft Fishes without Shells; Crustata, those that are covered with thin pliant Shells; and Testacea, those which have thick, hard brittle Shells.
1829, Andrew Ure, A New System of Geology, page 285:
The echinite family […] may be deemed characteristic of the chalk formation, affording of itself as many shells as the other testacea do.
1832, Charles Lyell, chapter I, in Principles of Geology[…], volume II, London: John Murray, page 11: