Pterotrachea scutata Gegenbaur 1855

Introduction

Pterotrachea scutata is immediately distinguished from the other two species in the genus by the lateral expansion of the anterior portion of the trunk, forming a large cuticular disk. The eyes are rectangular in dorsal view, very similar to those in P. coronata. The visceral nucleus is relatively short, tear-drop shaped, similar to that in P. hippocampus, and markedly shorter than in P. coronata. Unique to the species is a wreath of two or three rows of peribuccal teeth located inside the mouth opening. Morphology of the central rachidian tooth on the radula is similar to that in P. hippocampus. The larva is unknown, but is probably either larva 2 or 3 of Richter (1968, see Pterotrachea larvae). The geographical distribution is cosmopolitan in tropical to subtropical waters.

Characteristics

1. Body morphology
   1. Anterior portion of the trunk greatly expanded, forming a cuticular disk, or bib (see title illustration)
   2. Proboscis narrow, cylindrical, and much shorter than in P. hippocampus or P. coronata; extending ventrally from beneath the anterior part of the cuticular disk, which overhangs the base of the proboscis
      
      

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      Figure. Dorsal view of the anterior part of the cuticular disk, with the proboscis extending ventrally from beneath the disk. ©

   3. Eyes rectangular in dorsal view, with the retinal base somewhat wider than the lens, as in P. coronata.
      
      

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      Figure. Dorsal view of the eyes in Pterotrachea scutata. ©

   4. Visceral nucleus tear-drop shaped; similar to that in P. hippocampus, and markedly shorter than in P. coronata
      
      

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      Figure. Lateral view of the tear-drop shaped visceral nucleus in Pterotrachea scutata. ©

   5. Swimming fin located on the middle of the trunk, but closer to the visceral nucleus than the eyes (see title illustration)
   6. Swimming fin sucker in males only; small and located anterior to the midpoint on the fin ventrum
      
      

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      Figure. Swimming fin and sucker (=s) in Pterotrachea scutata. Also noted is the location of the pedal ganglia (=p). © 1949 J. J. Tesch

   7. Wreath of two or three irregular rows of tiny peribuccal teeth inside the entrance of the mouth; not present in other species of Pterotrachea. The peribuccal teeth were first characterized by Vayssière (1904) and subsequently remarked upon and illlustrated by Tesch (1949; see figure below)
      
      

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      Figure. Drawing of the buccal cavity in Pterotrachea scutata, which was exposed by cutting along the ventral midline and removing the radula and its musculature. Immediately inside the mouth opening, the peribuccal teeth (p.t) form a ring, two or three rows deep. The much larger palatine teeth (pal.t) are located in the roof of the buccal cavity, along with the salivary glands (s.gl). © 1949 J. J. Tesch

2. Larva unknown but represented, most probably, by either larva 2 or 3 of Richter (1968); see Pterotrachea larvae
3. Radular morphology similar to that in the other species in the genus (see Pterotrachea radula), with a central tooth bearing a large, pointed medial cusp, flanked laterally by multiple short and pointed cusps.

Comments

Tesch (1949) reported that the lens in the eye of P. scutata was noticeably wider than that of P. coronata.  Comparison of the eyes in a 61 mm P. scutata with those in a 78 mm P. coronata (Seapy, 1985, Fig. 3E,F) provide supportive evidence for Tesch's observation; despite the shorter body length of the P. scutata specimen, its lens width was greater (1.4 mm) than in P. coronata (1.1 mm).

References

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. 1968. Heteropoden und Heteropodenlarven im Oberflächenplankton des Golfs von Neapel. Pubblicazioni della Stazione Zoologica di Napoli 36: 346-400.

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

Seapy, R.R. 1985. The pelagic genus Pterotrachea (Gastropoda: Heteropoda) from Hawaiian waters: a taxonomic review. Malacologia 26(1-2): 125-135.

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

Vayssiere, A. 1904. Mollusques Heteropodes provenant des campagnes de yachts l'Hirondelle et Princesse Alice. Resultats des campagnes scientifiquee du Prince Albert de Monoaco. No. 26.