Definitions

sweeping upward

Plesiocystiscus

Plesiocystiscus is a genus of minute sea predatory sea snails, marine gastropod mollusks or micromollusks in the infraorder Neogastropoda.

The genus name is taken is derived from the Greek plesios, near, in the sense of plesiomorphic, of characteres near the ancestor, combined with Cystiscus the name of another closely related genus. This indicates the relationship to the genus Cystiscus, type genus of the family. The gender of the name is masculine.

Sometimes this genus is simply left in the larger family Marginellidae.

(Note: Gastropod taxonomy has been in flux for more than half a century, and this is especially true currently, because of new research in molecular phylogeny. Because of all the on-going changes, different reliable sources can yield very different classifications.)

Habitat

This genus lives from the intertidal zone to 80m in depth.

Shell description

Shell minute to small (adult lengh 1,5-6.0mm). Color white, hyaline; surface smooth, glossy. Shape cylindrical, elliptic, or obovate; weakly to distinctly shouldered. Suture rapidly descending on last half of last whorl, then abruptly sweeping upward just before lip, giving characteristic shape to adult shell. Spire nearly flat to low. Aperture moderately narrow, broader anteriorly. Lip thin anteriorly, gradually thickening tower shoulder, smooth, lacking denticulation or lirae, external varix absent. Siphonal notch and poterior notch absent. Shell often with a weak parietal callus wash or weak parietal callus deposits. Columella multiplicate, with combined total of 3-8 plications, usually occupying less than half to slightly more than half the aperture length. Shell with cystiscid internal whorls.

The type species is P. jewettii (Carpenter, 1857).

Anatomy

The triserial radula, found in many other cystiscids, is the most primitive in this family. This is the only genus of marginelliform gastropods with a triserial radula. This group is considered to be the most primitive in the family based on the radula and type of animal. The radular and shell features, including the presence of odontophoral cartilage hoods, possession of cystiscid internal whorls, and lack of an external varix, place this group in the Cystiscidae.

Fossil record

This genus is found in the Eocene of France, the Miocene and Pliocene of Florida, and the Pleistocene of California, to the Recent.

Species within the genus Plesiocystiscus

  • Plesiocystiscus abbotti (de Jong & Coomans, 1988)
  • Plesiocystiscus alfiopivai Espinosa & Ortea, 2002
  • Plesiocystiscus alfredensis (Bartsch, 1915)
  • Plesiocystiscus aphanospira (Tomlin, 1913)
  • Plesiocystiscus atomus (E.A. Smith, 1890)
  • Plesiocystiscus bubistae (Fernandes, 1988)
  • Plesiocystiscus cinereus (Jousseaume, 1875)
  • Plesiocystiscus consanguineus (E.A. Smith, 1890)
  • Plesiocystiscus genecoani Espinosa & Ortea, 2000
  • Plesiocystiscus gutta (Gofas & Fernandes, 1987)
  • Plesiocystiscus jansseni (de Jong & Coomans, 1988)
  • Plesiocystiscus jewettii (Carpenter, 1857)
  • Plesiocystiscus josephinae (Fernandes & Rolan, 1991)
  • Plesiocystiscus larva (Bavay , 1922)
  • Plesiocystiscus ovatus Lussi & Smith, 1998
  • Plesiocystiscus palantirulus (Roth & Coan, 1968)
  • Plesiocystiscus politulus (Dall, 1919)
  • Plesiocystiscus pseudogranulina Lussi & Smith, 1998
  • Plesiocystiscus thalia (Turton, 1932)
  • Plesiocystiscus valae Lussi & Smith, 1998
  • Plesiocystiscus variegatus Lussi & Smith, 1998

References

2000. Descripción de un género y once especies nuevas de Cystiscidae y Marginellidae (Mollusca: Neogastropoda) del Caribe de Costa Rica. Aviccenia 12/13: 95-114.
2002. Nuevas especies de margineliformes de Cuba, Bahamas y el Mar Caribe de Costa Rica. Avicennia 15:101-128.

  • 1995. Revision of the Supraspecific Classification of Marginelliform Gastrapods. The Nautilus 109(2 & 3):43-110. (latest family review & original description)
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