Pyroteuthis Hoyle, 1904

Introduction

Members of this genus are similar in appearance to those of Pterygioteuthis except that they are larger as adults and tend to have broader heads. They are most easily separated from their congener by the more numerous hooks on the arms and the presence of small hooks on the tentacular clubs.

Characteristics

Lateral arm of P. addolux from Hawaiian waters.

1. Arms
   1. Arm hooks in two series.
   2. More than 13 hooks/arm.
   3. Arms IV with >16 hooks.
   4. Right arm IV hectocotylized; toothed plate absent.
      
      
2. Tentacles
   1. Tentacular club with one series of hooks and three series of suckers on manus.
      image info

      Figure. The Pyroteuthis addolux club shows the presence of a single series of hooks in the proximal portion of the club.

3. Photophores
   1. Eyeball without a lidded photophore.
   2. Six or seven separate photophores in tentacular stalk.
   3. Three anterior abdominal and small branchial photophores.
      
      
4. Oviducts.
   1. Both present; right may be reduced.

Comments

The major differences between the species lie in:

1. the arrangement of tentacular photophores.
2. the form of the hectocotylus.
3. the shape of the hooks on the hectocotylus.

Discussion of Phylogenetic Relationships

P. addolux is more similar to P. serrata than to P. margaritifera in the arrangement of tentacular photophores and in the structure of the hectocotylus (Riddell, 1985).

Behavior

The quick, brilliant bioluminescent flashes observed in Pterygioteuthis spp. have not been seen in Pyroteuthis spp. This is not surprising since comparable photophores in Pyroteuthis are either absent (lidded ocular photophore) or less specialized (branchial photophores). However, we have seen P. addolux produce a peculiar, long-duration flash where all tentacular photophores, among others, glow for up to 4 or 5 seconds. We call this the Y-pattern display since the photophores are aligned in a pattern of this shape. All of the photophores involved have not been clearly identified but include four tentacular photophores and some ocular and visceral organs. To produce the Y-pattern, the tentacles are held straight and rigid at angles of approximately 45° to the body axis. This behavior is illicited when the squid is distrubed without direct physical contact. When physical contact is involved (i.e., squid touched or grabbed), the same photophores seem to be involved but the tentacles undulate instead of being held rigid.

Pyroteuthis addolux has been shown in the laboratory to counterilluminate (i.e., use bioluminescence to match the dim downwelling light and thereby eliminate the squid's silhouette) (Young and Roper, 1977). The photophores involved were, apparently, the ocular and anal organs.

Distribution

Species of Pyroteuthis are found throughout most of the tropical and temperate regions of the world's oceans but they are apparently absent from the Tropical Eastern Pacific (Nesis, 1982).

image info

This map shows the general localities (white circles) where Pyroteuthis has been captured. Areas where pyroteuthids, other than members of this genus, have been captured are represented by yellow crosses. (Records are listed here).

References

Nesis, K. N. 1982/87. 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.

Riddell, D. J. 1985. Enoploteuthidae of the New Zealand Region. Fisheries Research Bulletin. New Zealand Ministry of Agriculture and Fisheries, No.27: 1-52.

Young, R. E. and C. F. E. Roper (1977). Intensity regulation of bioluminescence during countershading in living midwater animals. Fish. Bull., U.S., 75: 239-252.