264
MALCOLM R. CLARKE
may be developed into large hooks. Nesis (1965) found that fish are
more important in the diet of Gonatus fabricii after the tentacle hooks
have developed, but otherwise the relationships between diet and such
features have not been studied. The carpus of the tentacle club in many
species bears smooth suckers and ‘‘ press-studs ” which interlock with
those of the other tentacle; this certainly enables the tentacles to be
used together as tongs ” in some species (Fig. 8). Such studs and
suckers sometimes extend the whole length of the tentacle stalk in
species having very long tentacles such as Architeuthis. There is some
variation in beak shape (Clarke, 196213) and reference has already
been made to the poisonous and non-poisonous bites delivered by
different species (pages 113 and 145). All species are probably
exclusively carnivorous.
Photophored varying from a simple, sub-cutaneous lump of luminescent tissue to complex organs with reflector, diaphragm, pigment
screen and lens are widespread within the group. They are found on
the eye bulb, on the head and mantle surface, on the tips of the arms
and tentacles and within the mantle cavity. The eyes and apparently
the liver cannot be made transparent and it is interesting to note
that in the transparent squids there are photophores on the ventral
side of these organs and their lateral and dorsal surfaces are silver.
Such an arrangement of photophores would break up the outline of
the organs when seen against weak daylight from below (W. D. Clarke,
1963) and the silver sides would blend with any intensity of background
light (Denton in press). Photophores are predominantly ventral in
position with the exception of the photophores on the tips of arms and
on the tentacles which possibly act as lures and the large dorsal photophores of some ommastrephids which possibly warn others of danger.
Eyes of squids are large relative to the body and the reason for
some modifications remain a mystery. For example, species of Calliteuthis possess a left eye which is much larger than the right eye.
Sound production in oegopsids has been noted in the literature
several times. Steenstrup (1881) quoted old descriptions which described the sounds of ommastrephids as squeaks and moans ’’ and
those of Gonatus as wailing noises and Bartsch (1916) noted the popping
sound when squids jumped clear of the water. Recording and analysis
of sounds beneath the water was not made before Nishimura (1961)
recorded swimming noises of 1 000-4 000 c/s with a peak a t 1 500 c/s.
Hashimoto and Maniwa (1963) also recorded squid school noises a t
40-6 000 c/s with a peak a t 1 000-2 000 c/s. Iversen et al. (1963)
recorded individual squids and found that they produce pulses of
500-2 500 c/s a t intervals of 31-48 msec. These pulses were produced
MALCOLM R. CLARKE
may be developed into large hooks. Nesis (1965) found that fish are
more important in the diet of Gonatus fabricii after the tentacle hooks
have developed, but otherwise the relationships between diet and such
features have not been studied. The carpus of the tentacle club in many
species bears smooth suckers and ‘‘ press-studs ” which interlock with
those of the other tentacle; this certainly enables the tentacles to be
used together as tongs ” in some species (Fig. 8). Such studs and
suckers sometimes extend the whole length of the tentacle stalk in
species having very long tentacles such as Architeuthis. There is some
variation in beak shape (Clarke, 196213) and reference has already
been made to the poisonous and non-poisonous bites delivered by
different species (pages 113 and 145). All species are probably
exclusively carnivorous.
Photophored varying from a simple, sub-cutaneous lump of luminescent tissue to complex organs with reflector, diaphragm, pigment
screen and lens are widespread within the group. They are found on
the eye bulb, on the head and mantle surface, on the tips of the arms
and tentacles and within the mantle cavity. The eyes and apparently
the liver cannot be made transparent and it is interesting to note
that in the transparent squids there are photophores on the ventral
side of these organs and their lateral and dorsal surfaces are silver.
Such an arrangement of photophores would break up the outline of
the organs when seen against weak daylight from below (W. D. Clarke,
1963) and the silver sides would blend with any intensity of background
light (Denton in press). Photophores are predominantly ventral in
position with the exception of the photophores on the tips of arms and
on the tentacles which possibly act as lures and the large dorsal photophores of some ommastrephids which possibly warn others of danger.
Eyes of squids are large relative to the body and the reason for
some modifications remain a mystery. For example, species of Calliteuthis possess a left eye which is much larger than the right eye.
Sound production in oegopsids has been noted in the literature
several times. Steenstrup (1881) quoted old descriptions which described the sounds of ommastrephids as squeaks and moans ’’ and
those of Gonatus as wailing noises and Bartsch (1916) noted the popping
sound when squids jumped clear of the water. Recording and analysis
of sounds beneath the water was not made before Nishimura (1961)
recorded swimming noises of 1 000-4 000 c/s with a peak a t 1 500 c/s.
Hashimoto and Maniwa (1963) also recorded squid school noises a t
40-6 000 c/s with a peak a t 1 000-2 000 c/s. Iversen et al. (1963)
recorded individual squids and found that they produce pulses of
500-2 500 c/s a t intervals of 31-48 msec. These pulses were produced