Stenothecidae is an extinct family of fossil univalved Cambrian

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s which may be either

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s or

monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

ns. The name of this taxon should not be confused with that of the class

Stenothecoida Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs. Affinity Their affinity is uncertain. They were considered by E. L. Yochelson 1968 to belong to Mollus ...

, a group of problematic Cambrian invertebrates that have a bivalved (dorsal and ventral) shell.

Morphology

The group comprises conical laterally compressed shells that may be smooth or ornamented with folds or ribs. The shells are broadly

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

-like, which led to their initial consideration as monoplacophoran molluscs.

Taxonomy

The taxonomic position of the group is unclear; it has been classified as a

Yochelcionelloid Yochelcionelloidea is an extinct superfamily of paleozoic molluscs of uncertain position (Gastropoda or Monoplacophora). The earliest yochelcionellids are known from the Middle Tommotian, but they are most diverse from the Botomian through the ea ...

Helcionelloid Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about in the late Nemak ...

. It is not obviously in the stem group of any modern molluscan class, and has been referred to the monoplacophora, although the monoplacophora are no longer considered to be a clade, and thus that classification means little more than "primitive mollusc".

Genera

The family Stenothecidae consists of two subfamilies and the following genera: * Stenothecinae Runegar & Jell, 1980 - synonym: Mellopegmidae Missarzhevsky, 1989 ** '' Stenotheca'' Salter n Hicks 1872 – type genus of the family Stenothecidae ** '' Mellopegma'' Runegar & Jell, 1976 * Watsonellinae Parkhaev, 2001Parkhaev P. Yu. 2001. ''Molluscs and siphonoconchs''. In: Alexander E. M. et al. (eds.) ''The Cambrian biostratigraphy of the Stansbury basin, South Australia''. Transactions of the Paleontological Institute, Russian Academy of Sciences, 282: 133–210, plates 24–54. Watsonellinae on the page 187. ** '' Watsonella''

Grabau Grabau is a surname. Notable people with the surname include: * Aaron Grabau (born 1978), Australian basketball player * Amadeus William Grabau (1870–1946), geologist * Charles Grabau, jurist * Johannes Andreas August Grabau (1804–1879), theo ...

, 1900 Grabau A. W. 1900. ''Palaeontology of the Cambrian terranes of the Boston Basin''. Occasional Papers of the Boston Society of Natural History 4:601–694. – type genus of the subfamily Watsonellinae *** '' Watsonella crosbyi'' Grabau – type species of the genus ''Watsonella''

Morphology

Taxonomy

Genera

References

Further reading