Pterygioteuthis giardi Fischer 1896

Introduction

P. giardi is a very distinctive species. It is easily recognized by the presence of hooks in both armature series on arms I-III, the distinctive hectocotylus and the lack of suckers on the ventral arms in females. These squids are more silvered than the other species in the genus and have extremely small tentacular clubs. In addition, adult females have relatively longer mantles and smaller head and arms.

Characteristics

1. Arms
   1. Hectocotylus (left arm IV) plate with two large teeth.
   2. Arms I, II and III with hooks in two series.
   3. Arms IV of females lack suckers and hooks.
   4. Right arm IV of males with one or two hooks and no suckers.
   

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   Figure. Left - oral view of the arms of a male P. giardi, 22.5 mm ML, from the tropical Eastern Pacific. Note the double series of hooks on arms I-III (the larger circles), the absence of suckers from the ventral arms (a few hooks are present), and the peculiar hectocotylus. Drawing from Okutani, 1974, with permission of the author. Right - Medial view of the hectocotylus of a P. giardi, preserved, male, 18 mm ML, from Hawaiian waters. The other arm is the right arm IV. Photograph by R. Young.

2. Photophores
   1. Tentacles with two embedded photophores (one large, spherical photophore at bend in base of tentacular stalk; one small spherical photophore near midpoint of tentacle).
   2. Eye with 10 large and five minute photophores.

Life history

Age and reproduction

Eggs are small (ca. 0.7 mm) but large in comparison to the small size of the spawning females. The oviduct holds only a few eggs (e.g., 11 in a 21 mm ML female). Presumably eggs are spawned in small batches and at frequent intervals due to the small storage capacity. The age at maturity and life-span are unknown.

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Figure. Ventral view of a paralarval P. giardi, 2.9 mm ML, from Hawaiian waters. Drawing modified from Young, et al., 1992.

Paralarvae

Due to similarities in general shape and the large size of the ocular-photophores, paralarvae are more easily confused with those of Pyroteuthis than other species of Pterygioteuthis. They are, however, distinguished from Pyroteuthis paralarvae by:

1. The large branchial photophores (equal to or larger than the anal photophores).
2. The lack of chromatophores on the tentacles except at the base.
3. More highly swollen tentacle base and slender distal tentacle.

Compare with paralarvae of Pterygioteuthis microlampas and Pyroteuthis addolux.

Distribution

Vertical distribution

In Hawaiian waters, this species vertically migrates from upper mesopelagic depths during the day to the upper 50 m at night (Young, 1978). Off Bermuda most captures were from 50-100 m at night while the few daytime captures suggested a depth range of 327-475 m (Roper and Young,1975). In the eastern North Atlantic captures were made mostly at 300-400m during the day and 50-200m at night (Clarke and Lu, 1974).

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Figure. Vertical distribution chart of P. giardi based on opening/closing trawls and open trawls taken off Hawaii. Yellow dots - Modal depth of trawl, day capture. Blue dots - Modal depth of trawl, night capture. Bars - Depth range of trawl for opening/closing tows. Red dots - Captures from open trawls that are assummed to be contaminants; that is, the squid were captured in an open trawl presumably while the trawl was being set or retreived and not at the modal fishing depth of the trawl. Distribution chart modified from Young, 1978.

Geographical distribution

This species was first described from the North Atlantic off Morocco (Fischer, 1896). It is the most widely distributed member of the Pyroteuthidae.

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Figure. Map showing some of the general localities (white circles) where P. giardi has been captured. Areas where other pyroteuthids have been captured are indicated by yellow crosses

Geographical variation

Nesis (1982/87) distinguishes two subspecies: P. giardi giardi (Atlantic) and P. giardi hoylei (Indo-Pacific; ) based on differences in the size of the hooks on the right arm IV of males. These forms were first given this taxonomic status by Pfeffer (1912) based on descriptions by Hoyle (1904) of the latter form from the Eastern Equatorial Pacific. A careful study, however, of speciation in this taxa has never been made.

Off Hawaii P. giardi appears to be a facultative mesopelagic-boundary species as it is twice as abundant as P. microlampas over bottom depths of less than 800 m but only 1/5 as abundant as its congener over more oceanic depths (Young, 1995).

References

Fischer, H. 1896. Note préliminaire sur le Pterygioteuthis Giardi, céphalopode nouveau recuelli dans le Cours de l'Expédition scientifique du Talisman (1883). Jour. Conchyliologie 43: 205-211.

Hoyle, W. E. 1904. Reportson the Cephalopoda. Bull. Mus. Comp. Zool., Harvard Coll, Cambridge. 43: 1-72.

Nesis, K. N. 1982. Abridged key to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

Okutani, T. 1974. Epipelagic decapod cephalopods collected by micronekton tows during the EASTROPAC expeditions, 1967-1968 (systematic part). Bull. Tokai Reg. Fish. Res. Lab., 80: 29-118.

Pfeffer, G. 1912. Die Cephalopoden der Plankton-Expedition. Ergebnisse der Plankton-Expedition der Humboldt-Stiftung. 2: 1-815.

Roper, C. F. E. and R. E. Young. 1975. Vertical distribution of pelagic cephalopods. Smithsonian Contributions to Zoolog, 209: 1-51

Young, R. E. 1978. Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters. Fishery Bulletin, 76: 583-615.

Young, R. E. 1995. Aspects of the natural history of pelagic cephalopods of the Hawaiian mesopelagic-boundary region. Pac. Sci. 49: 143-155.

Young, R. E., K. M. Mangold and M. Vecchione (1992). The enoploteuthid group of families. P. 55-66. In: Sweeney, M. J., C. F. E. Roper, K. M. Mangold, M. R. Clarke and S. V. Boletzky (eds.). "Larval" and juvenile cephalopods: a manual for their identification. Smithson. Contr. Zool., No. 513: 1-282.