REVIEW OF THE SYSTEMATICS AND ECOLOGY OF OCEAMO SQUIDS
241
XX. SPIRULIDAE
The single species within this family, Spirula spirula, is the only
truly oceanic member of the Sepioidea.
A. Spirula
Bruun (1943) was unable to detect specific or geographical
differences between the cuttlefish referable to this genus.
1. Spirula spirula Linnaeus, 1758
Bruun (1941, 1943, 1955) made a detailed study of this species
and most of the following details are based on his work. The shells
are regularly washed up on shores in very large numbers and a8 such
strandings occur in regions not frequented by the animal it is pointless
to list the large number of records in the literature. The living animal
occurs in tropical and subtropical regions in the Atlantic, Indian and
Pacific Oceans (Fig. 53). Bruun (1955) considered that the water
temperature is the principal factor in determining the distribution
while food availability is perhaps also important. All catches have
been in regions where the temperature at 400 m is 10°C or higher.
On the other hand, it does not occur in the Mediterranean, the Sula
Sea or the Red Sea which may be due to the high temperatures (of
over 10°C at 1 000 m) in these regions. It seems to be most numerous
off the north-west African coast. Although it lives as a true pelagic
species it is usually taken near continental slopes and the neighbourhood
of islands is particularly favourable for its occurrence. Over 55% of
specimens were taken in water less than 2 600 m deep and over 70%
in water less than 3 500 m deep.
The vertical distribution corresponds to the continental slope.
The youngest specimens less than 0.6 cm in length are concentrated
at 1 000-1 750 m, while the larger ones are found at as little as 100 m*
at night and down to 1 750 m. The upper limit corresponds to water
at less than 19°C. The lower limit of 1 750 m is the limit to which the
shell can go without imploding due to the pressure and this wag
determined by finding the pressure resistance of dead shells (Bruun,
1943). Bruun (1955) later considered that 1 750 m is probably too
deep and Spirula possibly does not live below the thermocline. He
concluded that it lives in the aphotic zone of the thermosphere and
therefore falls within his definition of a mesopelagic animal.
Spirula probably moves about in shoals, swims upright in the
water and can control its buoyancy (Denton, 1961). A light organ on
the apex of the body (posterior end) (Chun, 1910b) emits a pale,
yellowish-green light (Bruun, 1943).
* ThereIis a:record of Spirula 0ccurring:at the surface by J. S.:Gardiner;in the narrative
of “ The Fauna and Geography of the ;Maldive ~d-Leccedive:Archipelagoea.” 1, p. 6,
Cambridge University Press.
241
XX. SPIRULIDAE
The single species within this family, Spirula spirula, is the only
truly oceanic member of the Sepioidea.
A. Spirula
Bruun (1943) was unable to detect specific or geographical
differences between the cuttlefish referable to this genus.
1. Spirula spirula Linnaeus, 1758
Bruun (1941, 1943, 1955) made a detailed study of this species
and most of the following details are based on his work. The shells
are regularly washed up on shores in very large numbers and a8 such
strandings occur in regions not frequented by the animal it is pointless
to list the large number of records in the literature. The living animal
occurs in tropical and subtropical regions in the Atlantic, Indian and
Pacific Oceans (Fig. 53). Bruun (1955) considered that the water
temperature is the principal factor in determining the distribution
while food availability is perhaps also important. All catches have
been in regions where the temperature at 400 m is 10°C or higher.
On the other hand, it does not occur in the Mediterranean, the Sula
Sea or the Red Sea which may be due to the high temperatures (of
over 10°C at 1 000 m) in these regions. It seems to be most numerous
off the north-west African coast. Although it lives as a true pelagic
species it is usually taken near continental slopes and the neighbourhood
of islands is particularly favourable for its occurrence. Over 55% of
specimens were taken in water less than 2 600 m deep and over 70%
in water less than 3 500 m deep.
The vertical distribution corresponds to the continental slope.
The youngest specimens less than 0.6 cm in length are concentrated
at 1 000-1 750 m, while the larger ones are found at as little as 100 m*
at night and down to 1 750 m. The upper limit corresponds to water
at less than 19°C. The lower limit of 1 750 m is the limit to which the
shell can go without imploding due to the pressure and this wag
determined by finding the pressure resistance of dead shells (Bruun,
1943). Bruun (1955) later considered that 1 750 m is probably too
deep and Spirula possibly does not live below the thermocline. He
concluded that it lives in the aphotic zone of the thermosphere and
therefore falls within his definition of a mesopelagic animal.
Spirula probably moves about in shoals, swims upright in the
water and can control its buoyancy (Denton, 1961). A light organ on
the apex of the body (posterior end) (Chun, 1910b) emits a pale,
yellowish-green light (Bruun, 1943).
* ThereIis a:record of Spirula 0ccurring:at the surface by J. S.:Gardiner;in the narrative
of “ The Fauna and Geography of the ;Maldive ~d-Leccedive:Archipelagoea.” 1, p. 6,
Cambridge University Press.