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Roger R. Seapy
taxon links [down<--]Carinarioidea Interpreting the tree
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Containing group: Carinarioidea


All pterotracheids lack a shell as adults, although they possess one as larvae (the shell is shed at metamorphosis). Their bodies are elongate and basically cylindrical, consisting of a proboscis, trunk and tail. The maximal recorded body length is 33 cm. The head lacks tentacles anterior to the eyes, except in male Firoloida. The viscera are compacted into a fusiform visceral nucleus. The swimming fin is large, located about midway between the anterior and posterior ends of the trunk, and bears a sucker only in males (presumably used in mating). Pterotracheids are mostly epipelagic (dwelling in the upper several hundred meters of the water column), although the vertical ranges of two species of Pterotrachea extend into the mesopelagic. Nocturnal vertical migration is seen in Pterotrachea.

The Pterotracheidae are widely regarded as the most highly derived of the heteropod families. Features supporting this contention include: (1) enlargement, elongation and narrowing (to a  basically cylindrical shape) of the body in the anterior-posterior axis, resulting in a streamlined body with enhanced swimming abilities, (2) shedding of the larval shell at metamorphosis, with the result that buoyancy problems are reduced since a calcareous shell (present in the adults of the other two families) is lacking, (3) compaction of the viscera into a pyriform visceral nucleus, which is largely enveloped by the gelatinous body at the posterior end of the trunk.


Heteropod molluscs with:


  1. Shell
    1. Present in larvae
    2. Cast off at metamorphosis
  2. Body morphology
    1. Elongate, basically cylindrical; streamlined for rapid swimming
    2. Proboscis, trunk and tail body regions
       image info

      Figure. Body regions in Pterotrachea coronata.

    3. Viscera compacted into pyriform visceral nucleus
    4. Esophagus elongated, connecting buccal mass with visceral nucleus
       image info

      Figure. Location of esophagus in Pterotrachea coronata

  3. Swimming fin
    1. Located about midway between head region and visceral nucleus
    2. Fin sucker small; present only in males
       image info

      FigurePterotrachea coronata.  Left: swimming fin in female. Right:  swimming fin sucker in male.

  4. Head
    1. Shape of eye (in dorsal view) rectangular to triangular
    2.  image info

      Figure. Dorsal views of Pterotrachea eyes. Left: P. coronata adult. Middle: P. hippocampus juvenile. Right: P. hippocampus adult.

    3. Tentacles absent, except in Firoloida males
  5. Radula
    1. 24-30 tooth rows
    2. Rachidian (central) tooth polycuspid with prominent central cusp


Two genera are included in the Pterotracheidae, one of which, Firoloida, is monotypic. The genera can be distinguished by the following characters:

Genus Tail Posterior egg string or filamentous extension Tentacles
Pterotrachea prominent absent absent in both sexes
Firoloida very short, ventral present present in males


Lalli, C. M. and R. W. Gilmer. 1989. Pelagic snails. The biology of holoplanktonic gastropod mollusks. Stanford Unive. Press, Stanford, pp. 1-259.

Richter, G. and R. R. Seapy. 1999. Heteropoda, pp. 621-647. In: D. Boltovskoy (ed.), South Atlantic Zooplankton. Leiden: Backhuys Publ.

Spoel, S. van der, L. Newman and K. W. Estep. 1997. Pelagic molluscs of the world. World Biodiversity Database, CD-ROM Series. Expert Center for Taxonomic Identification (ETI), Amsterdam, The Netherlands, UNESCO, Paris.

Tesch, J. J. 1949. Heteropoda. Dana Rep., 34: 1-54.

Title Illustrations
Scientific Name Pterotrachea coronata
Location Hawaiian Islands
Specimen Condition Live Specimen
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About This Page

Roger R. Seapy
California State University, Fullerton, California, USA

Correspondence regarding this page should be directed to Roger R. Seapy at

Citing this page:

Seapy, Roger R. . 2006. Pterotracheidae. Version 30 May 2006 (under construction). http://tolweb.org/Pterotracheidae/28734/2006.05.30 in The Tree of Life Web Project, http://tolweb.org

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