Onustus is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of large sea snail

Sea snail

Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....

s, marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 gastropod mollusks in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Xenophoridae

Xenophoridae

Xenophoridae, common name carrier shells, are a taxonomic family of medium-sized to large sea snails, marine gastropod mollusks in the clade Littorinimorpha....

, the carrier shells.

Description

Shells

Gastropod shell

The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...

 medium-sized to large (diameter of base without attachments 80-160 mm; height of shell 42-100 mm), thin-shelled, with wide peripheral flange, simple or weakly digitate, porcellanous ventrally. Umbilicus narrow to wide, sometimes plugged with callus. Foreign objects attached to periphery on few to all whorls

Whorl (mollusc)

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...

, usually small and inconspicuous, leaving most of the shell surface exposed.

Species

Species within the genus Onustus include:

• Onustus caribaeus
  Onustus caribaeus
  Onustus caribaeus is a species of large sea snail, a marine gastropod mollusk in the family Xenophoridae, the carrier shells.-Description:...
  
  (Petit de la Saussaye, 1857)
• Onustus exutus
  Onustus exutus
  Onustus exutus is a species of large sea snail, a marine gastropod mollusk in the family Xenophoridae, the carrier shells.-Distribution:...
  
  (Reeve, 1842)
• Onustus indicus
  Onustus indicus
  Onustus indicus is a species of large sea snail, a marine gastropod mollusk in the family Xenophoridae, the carrier shells.-Distribution:...
  
  (Gmelin, 1791)
• Onustus longleyi
  Onustus longleyi
  Onustus longleyi is a species of large sea snail, a marine gastropod mollusk in the family Xenophoridae, the carrier shells.-Distribution:...
  
  Bartsch, 1931