Pterotrachea is a taxonomic 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 medium-sized to large floating sea slugs, 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...

 pelagic gastropod molluscs 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...

 Pterotracheidae

Pterotracheidae

Pterotracheidae is a family of medium-sized to large floating sea snails, pelagic gastropod molluscs. They are in the superfamily Pterotracheoidea along with two other similar pelagic families, the Atlantidae and the Carinariidae....

, which is in the infraorder Littorinimorpha

Littorinimorpha

Littorinimorpha is a large clade of gastropods within Hypsogastropoda consisting primarily of marine species, but also aquatic and terrestrial species as well....

. As such they are quite closely related to such families as the tritons (Ranellidae

Ranellidae

Ranellidae, common name the triton shells or tritons, is a taxonomic family of small to very large predatory sea snails, marine gastropod mollusks in the clade Littorinimorpha.-Subfamilies:...

) and the tun shells (Tonnidae

Tonnidae

Tonnidae is a family of medium-sized to very large sea snails, known as the tun shells. These are marine gastropod molluscs in the clade Sorbeoconcha and the clade Littorinimorpha.- Taxonomy :...

).

These pelagic slugs are not at all closely related to the pelagic opisthobranch gastropods such as the sea angel

Sea angel

Sea angels previously known as one kind of pteropod, are a large group of small swimming sea slugs in six different families. These are pelagic marine opisthobranch gastropod molluscs in the clade Gymnosomata within the larger clade Heterobranchia....

s and sea butterflies.

Species within the genus Pterotrachea

• Pterotrachea coronata
  Pterotrachea coronata
  Pterotrachea coronata is a species of large floating sea snail, a pelagic gastropod mollusc in the family Pterotracheidae.This pelagic snail is not at all closely related to the pelagic opistobranchs such as the sea angels and sea butterflies...
  
  Forskål
  Peter Forsskål
  Peter Forsskål, sometimes spelled Pehr Forsskål, Peter Forskaol, Petrus Forskål or Pehr Forsskåhl, was a Swedish explorer, orientalist, naturalist and an apostle of Carl Linnaeus.-Early life:...
  
  , 1775
• Pterotrachea hippocampus Philippi
  Rodolfo Amando Philippi
  Rodolfo Amando Philippi was a German-Chilean paleontologist and zoologist....
  
  , 1836
• Pterotrachea keraudrenii J. E. Gray, 1850
• Pterotrachea minuta
• Pterotrachea scutata Gegenbaur, 1855