Stenothecidae Explained

Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans.

The name of this taxon should not be confused with that of the class Stenothecoida, a group of problematic Cambrian invertebrates that have a bivalved (dorsal and ventral) shell.^[1]

Morphology

The group comprises conical laterally compressed shells that may be smooth or ornamented with folds or ribs.^[2] The shells are broadly limpet-like, which led to their initial consideration as monoplacophoran molluscs.^[1]

Taxonomy

The taxonomic position of the group is unclear; it has been classified as a Yochelcionelloid or Helcionelloid. It is not obviously in the stem group of any modern molluscan class, and has been referred to the monoplacophora,^[2] although the monoplacophora are no longer considered to be a clade, and thus that classification means little more than "primitive mollusc".^[3]

Genera

The family Stenothecidae consists of two subfamilies and the following genera:

• Stenothecinae Runegar & Jell, 1980 - synonym: Mellopegmidae Missarzhevsky, 1989^[4]
  • Stenotheca Salter [in Hicks], 1872 – type genus of the family Stenothecidae
  • Mellopegma Runegar & Jell, 1976
• Watsonellinae Parkhaev, 2001^[5]
  • Watsonella Grabau, 1900^[6] – type genus of the subfamily Watsonellinae
    • Watsonella crosbyi Grabau – type species of the genus Watsonella

Further reading

• Kouchinsky . A. V. . 1999 . Shell microstructures of the Early Cambrian Anabarella and Watsonella as new evidence on the origin of the Rostroconchia . Lethaia . 32. 2 . 173–180 . 10.1111/j.1502-3931.1999.tb00537.x.
• http://www.palaeos.org/Stenothecoida

Notes and References

1. 10.1111/j.1502-3931.1969.tb01250.x . Stenothecoida, A Proposed New Class of Cambrian Mollusca . 1969 . Yochelson . E. L. . Lethaia . 2 . 49–62.
2. B. . J.. Pojeta Jr. Molluscan Phylogeny: the Paleontological Viewpoint. 186. Runnegar. Science. 4161. 311–317. Oct 1974 . 1739764. 17839855. 10.1126/science.186.4161.311. 1974Sci...186..311R .
3. Budd . G. E. . Jensen . S. . 2000 . A critical reappraisal of the fossil record of the bilaterian phyla . 75 . 2 . 253–95 . Biological Reviews of the Cambridge Philosophical Society . 10.1111/j.1469-185X.1999.tb00046.x . 10881389.
4. Missarzhevsky. (after 10 July) 1989. Drevneishie skeletnye okamenelosti i stratigrafiia pogranichnykh tolshch Dokembriia i Kembiia. (English translation: Oldest skeletal fossils and stratigraphy of Precambrian and Cambrian boundary beds.) Trudy Geologicheskogo Instituta, Akademia Nauk SSSR, 443, 237 pp., 32 plates. Mellopegmidae is on the page 179.
5. Parkhaev 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.
6. [Amadeus William Grabau|Grabau A. W.]