Firoloida demarestia Lesueur 1817

Introduction

Firoloida is a monotypic genus represented by the cosmopolitan species F. demarestia. It is the smallest (maximal body length of 40 mm) and most transparent species in the family Pterotracheidae. The visceral nucleus is terminal on the long trunk, followed by a very short ventral tail and either a permanent egg string (in females) or a tail filament (in males).  Prominent tentacles and a fin sucker are present in males, but are absent in females.

Brief Diagnosis

A pterotracheid with:

• Transparent body cylindrical, with a long trunk and a very short tail
• Visceral nucleus terminal on trunk
  
• Swimming fin anterior of the middle part of the trunk
• Small sucker on anterior margin of swimming fin in males only
• Prominent tentacles ahead of eyes in males only
• Tail filament only in males
• Permanent egg string in females

Characteristics

1. Body morphology
1. Body elongate, cylindrical
2. Trunk long; tail short and ventral
   
3. Visceral nucleus terminal on trunk
4. Swimming fin located about one-third the distance back from eyes on the trunk
   


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Figure. Body regions and selected structures in Firoloida demarestia. ©

2. Sexually dimorphic structures
1. Permanent egg string extends posteriorly from base of visceral nucleus in females; length of egg string commonly equal to the body length (Owre, 1964), with early cleavage stages at the proximal end and late-stage veliger larvae at the distal end
   

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   Figure. Posterior body region, right side in female Firoloida demarestia. ©

2. Filamentous extension of the very short tail in males highly contractile (compare the two figures below)
3. Club-shaped structure (illustrated in the literature by Tesch, 1949, but undescribed by any authors to my knowledge) of unknown function. The structure extends posteriorly from the visceral nucleus, and consists of a long, transparent stalk and a white "end bulb"
   
   

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   Figure. Posterior end of body in a male Firoloida desmaresti. At the end of the trunk, the tear-drop shaped visceral nucleus gives rise dorsally to a short (retracted) filamentous tail extension and ventrally to an elongate, club-shaped structure. ©

4. Sucker small and located on anterior margin of swimming fin in males
   
   

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   Figure. Drawing of male Firoloida desmaresti, from right side of body. Note the expanded filamentous tail extension. © 1949 J. J. Tesch

5. Tentacles prominent, located anterior to eyes in males (see drawing above and photo below)
3. Eye morphology
1. Eye shape narrowly triangular
2. Lens capsule oblong, with lens basal and distal portion slightly opaque
   


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Figure. Dorsal view of right eye in male Firoloida demarestia.©

4. Larval and radular morphology
1. Larva with four velar lobes that are colorless, except for lobe tips that usually have brown spots (Thiriot-Quiévreux, 1973a)
   

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   Figure. Drawing of Firoloida desmaresti larva, from Thiriot-Quiévreux (1973a, Fig. 8D).© 1973 Catherine Thiriot

2. Larval shell globular (see figure below), with about 2 whorls and an aperture that is rounded-ovoid (see second figure below)
   
   

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   Figure. Scanning electron micrograph of larval shell of Firoloida desmaresti, viewed from right side, angled toward the front of the shell. Modified from Thiriot-Quiévreux (1973; Fig. 6D). Scale bar - 100 µm. © 1973 Catherine Thiriot

   

   Figure. Scanning electron micrographs of Firoloida demarestia fossil larval shells. Left: right side (scale bar = 100 µm). Right: apertural view (scale bar = 50 µm). © 2007

3. Radula
1. Central rachidian tooth consists of a middle portion (with a long and thick median cusp, flanked on either side by three shorter and pointed cusps) and two large, broad-based lateral cusps (Thiriot-Quiévreux, 1973b)
   

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   Figure. Low (left) and high (right) views of the radula of Firoloida desmaresti. © 1973 Catherine Thiriot

References

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

Owre, H. B. 1964. Observations on development of the heteropod mollluscs Pterotrachea hippocampus and Firoloida desmaresti. Bulletin of Marine Science of the Gulf and Caribbean 14: 519-538.

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

Tesch, J. J. 1949. Heteropoda. Dana Rep. 34, pp. 1-53.

Thiriot-Quievreux, C. 1973a. Heteropoda. Oceanography and Marine Biology Annual Review 11:237-261.

Thiriot-Quievreux, C. 1973b. Observations de la radula des Heteropodes (Mollusca Prosobranchia) au microscope electronique a balayage et interpretation fonctionnelle. Comptes rendus de l'Académie des sciences, Serie D 276: 761-764.