Acrothoracica

Article By:

Stubbings, H. G. Admiralty Materials Laboratory, Poole, United Kingdom.

Last reviewed:August 2019

DOI:https://doi.org/10.1036/1097-8542.007700

A subtaxon of burrowing barnacles in the subclass Thecostraca. All members of the Acrothoracica burrow into shells of mollusks and thoracican barnacles, echinoderm tests, bryozoans, dead coral, and limestone. The entrance to the burrow is slitlike. In thin shells, the burrow and animal are strongly compressed (see illustration). The mantle lacks calcareous plates and is attached to the burrow by calcareous cement from glands in the dorsal part of the mantle. The attached area becomes thickened by the buildup of successive layers of chitin, which cannot be shed at molting. The normal three pairs of cirriped mouthparts are present: mandibles, maxillules, and maxillae. Four to six pairs of cirri (jointed appendages) occur, often greatly reduced in size, with the first pair close to the oral appendages and the remainder packed together at the posterior end of the body. The sexes are separate; dwarf males are found on the mantle or wall of the burrow of the female. Naupliar larval stages may be omitted, but a cypris larva always occurs in the life cycle. Three families, 10 genera, and about 60 species are recognized. Detailed examination of shell debris, especially from warmer seas, has revealed many new species; without a doubt, many more exist. Fossils, known from burrows only, occur from the Carboniferous to Recent (Holocene). See also: Cirripedia; Crustacea

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