Česká geologická služba
Virtual museum
Home  > Taxonomy > Animals > Metazoans > Molluscs > Hyoliths

Hyolitha (Hyoliths)

      Hyolitha are enigmatic animals with small conical shells known from the Palaeozoic Era. The calcareous shells have a cover (operculum) and two curved supports known as helens. Most are one to four centimeters in length and are triangular or elliptical in cross section. Some species have rings or stripes. Because hyoliths are extinct and do not obviously resemble any extant group, it is unclear which living group they are most closely related to. They may be molluscs; authors who suggest that they deserve their own phylum do not comment on the position of this phylum in the tree of life.Fossil traces showing a twisted, looped, intestine bear some resemblance to the gut of sipunculan worms. Despite the fact that hyolithid shells are common as fossils, little is known about their ancestry, internal structures, and life mode. They were probably benthic (bottom-dwellers). The first hyolith fossils appeared about 540 million years ago in the Purella antiqua Zone of the Nemakit-Daldynian Stage of Siberia and in its analogue the Paragloborilus subglobosus–Purella squamulosa Zone of the Meishucunian Stage of China. Hyolith abundance and diversity attain a maximum in the Cambrian, followed by a progressive decline up to their Permian extinction.

Source: http://en.wikipedia.org/wiki/Hyolithid
Img. 94:
Elegantilites JP1315
Elegantilites JP796
Elegantilites JP1137
Elegantilites JP791
Elegantilites JP627
Elegantilites JP1291
Elegantilites JP785
Elegantilites JP1292
Elegantilites JP663
Elegantilites JP794
Elegantilites JP805
Eumorpholites bouceki JP1117
Eumorpholites bouceki XA72
Gompholites cinctus CW266
Gompholites cinctus CW261
Gompholites cinctus CW263
Gompholites cinctus CW275
Gompholites cinctus CW273
Gompholites cinctus CW265
Gompholites cinctus CW269

Virtual museum of the Czech Geological Survey, www.geology.cz, (C) Czech Geological Survey, 2011, v.0.99 [13.12.2011]