Overview

Brief Summary

Introduction

All pterotracheids lack a shell as adults, although they possess one as larvae (the shell is shed following metamorphosis). Their bodies are elongate and basically cylindrical, consisting of a proboscis, trunk and tail. The maximal recorded body length (in Pterotrachea coronata) is 33 cm. The head lacks tentacles anterior to the eyes, except in male Firoloida desmarestia. 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. All pterotracheid species have cosmopolitan distributions in tropical to subtropical waters.

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 following 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.

Brief Diagnosis

Heteropod molluscs with:

  • Body elongated and basically cylindrical, divided into proboscis, trunk and tail
  • Viscera compacted into a pyriform visceral nucleus
  • Shell lacking in adults; larval shell shed after metamorphosis
  • Cosmopolitan distribution in tropical to subtropical waters

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Comprehensive Description

Characteristics

  1. Shell present in larvae only; cast off following metamorphosis
  2. Body morphology
    1. Elongate, basically cylindrical; streamlined for rapid swimming
    2. Proboscis, trunk and tail regions well developed

      Figure. Body regions in Pterotrachea coronata. © R. R. Seapy

    3. Viscera compacted into pyriform visceral nucleus
    4. Esophagus elongated, extending from the buccal mass to the visceral nucleus

      Figure. Location of buccal mass, esophagus, and visceral nucleus in Pterotrachea coronata. © R. R. Seapy

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

      Figure. Pterotrachea coronata. Left: swimming fin in female, viewed from right side of body. Right: swimming fin and sucker in male, viewed from right side. © R. R. Seapy

  4. Head
    1. In dorsal view, shape of eyes either rectangular (with a narrow retinal base) or triangular (with a broad retinal base that curves upward toward the lens)
    2. Figure. Dorsal views of eyes in Pterotrachea. Left: rectangular eye of P. coronata. Center: narrowly triangular eye in juvenile P. hippocampus. Right: broadly triangular eye in adult P. hippocampus. © R. R. Seapy

    3. Tentacles absent, except in Firoloida desmarestia males

  5. Radula
    1. 24-30 tooth rows
    2. Central rachidian tooth (lower center in photo below) polycuspid with a prominent middle cusp that is flanked on either side by numerous short cusps

      Figure. High magnification view of central rachidian tooth (lower, middle) and elongate, pointed lateral teeth (upper left and right in photo) from radula of Pterotrachea hippocampus. Scale bar = 20 µm. © G. Richter

  6. Comments

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

    Genus Tail Tentacles anterior to the eyes
    Posterior egg string
    Pterotrachea well developed
    absent in both sexes
    absent
    Firoloida very short, ventral present in both sexes
    present

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Wikipedia

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.

These pelagic snails are not at all closely related to the pelagic heterobranch opistobranchs such as the sea angels and sea butterflies. They are in the clade Littorinimorpha, and as such they are related to such families as the tritons (Ranellidae) and the tun shells (Tonnidae), in the clade Caenogastropoda.

According to taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Pterotracheidae has no subfamilies.

Genera

Genera within the family Pterotracheidae include:

References

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Source: Wikipedia

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