Hyolitha

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Hyolitha

 

a class of extinct animals conventionally assigned to the phylum Mollusca. (Some scientists classify the animals as an independent phylum.) The Hyolitha lived from the beginning of the Cambrian to the Permian. The conical or pyramidal shell ranged from 0.1 to 15 cm in length and was sealed at the narrow end. The stoma of the shell closed with an operculum. In most species the dorsal and ventral sides of the shell were highly sculptured. In many the shell cavity was divided by transverse septa into a number of air chambers and one dwelling chamber. Some scientists believe that the shell was bivalved, that is, it consisted of conical and flat valves. The wall of the shell is calcareous and two-layered. Some species had a pair of long slender appendages departing from the stoma. The Hyolitha lived in the sea. They are very important in the stratigraphy of Cambrian deposits.

REFERENCE

Drushchits, V. V. Paleontologiia bespozvonochnykh. Moscow, 1974.
References in periodicals archive ?
Well-diversified trilobites, brachiopods, gastropods, echinoderms, phyllocarids, ostracods, bivalves, agnostids, hyoliths, cephalopods and conulariids, associated with graptolites and ichnofossils, have been studied for more than 150 years (see Barrande 1872; Havlicek & Vanek 1966, 1990; Mikulas 1991; Mergl 2002; Chlupac 2003; Kraft & Kraft 2003; Budil et al.
Comparatively well diversified trilobites, brachiopods, bivalves, bryozoans, gastropods, ostracods, echinoderms, hyoliths, cephalopods, conulariids, rare agnostids and graptolites, associated with locally abundant ichnofossils from the Bohdalec Formation, have been studied for more than 150 years (see Barrande 1872; Havlicek & Vanek 1966, 1990; Mikulas 1988; Fatka & Mergl 2009).
Dense patches of mesoclots are the dominant fabric and the occurrence of hyoliths is sporadic.
The spongiostromate-oncoid peloidal microbialite is composed of 40% spongiostromate oncoids, parautochthonous archaeocyaths (10%) and hyoliths (5%), all surrounded by homogeneous fine peloidal micrite (40% of the rock volume -microbial peloids up to 40 um in size).
Skeletal microstructures of hyoliths from the Early Cambrian of Siberia.