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:
Bactrotheca MD101
Bactrotheca VK87
Bactrotheca MD100
Bactrotheca PB1186
Bactrotheca VK111
Bactrotheca CW1498
Bactrotheca teres CW103
Bactrotheca teres CW100
Bactrotheca teres CW104
Bactrotheca teres CW108
Bactrotheca teres CW106
Bactrotheca teres XA226
Bactrotheca teres p2368
Bactrotheca teres XB591
Bactrotheca teres YA984
Bactrotheca teres CW107
Buchavalites ValentFatka a Kozák (2014) CW10
Buchavalites Valent CW226
Buchavalites Valent CW228
Buchavalites Valent CW224

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