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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 subglobosusPurella 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
Hyolitha
Img. 94:
Hyolitha Marek, 1963 M3048
Hyolitha Marek, 1963 M3050
Hyolitha Marek, 1963 M3075
Hyolitha Marek, 1963 M3077
Hyolitha Marek, 1963 M3086
Hyolitha Marek, 1963 M3090
Hyolitha Marek, 1963 M3023
Hyolitha Marek, 1963 M3047
Hyolitha Marek, 1963 M3057
Hyolitha Marek, 1963 M3068
Hyolitha Marek, 1963 M3071
Hyolitha Marek, 1963 M3081
Hyolitha Marek, 1963 M3092
Hyolitha Marek, 1963 VL1437
Hyolitha Marek, 1963 VL317
Hyolitha Marek, 1963 VL1608
Hyolitha Marek, 1963 VL1302
Hyolitha Marek, 1963 VL1432
Hyolitha Marek, 1963 VL1532
Hyolitha Marek, 1963 VL1539

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