254
MALOOLM R. CLARKE
minimum depths of species in the separate families (Fig. 57). From
these curves, which are each based on rather few species, it is clear
that all the ommastrephid squids are found in the upper 100 m a t
times; half the onychoteuthids are found in the superficial 100 m,
most of the rest are deeper than 100-500 m; 56% of cranchiids extend
into the upper 100 m and the family would seem to have a fairly
large depth range; almost a third of the histioteuthid species are
. .
.- . - - . - - - .
. -
100 500 1000
2000
3000
4 0 0 0
5000
Depth in metres
FIQ. 67. Cumulative percentage curves of species i n various oogopsid families having
their upper limits shallower than each selected depth. The numbers of species
included in each are Ommaatrephidae 12, Onychoteuthidae 10, Histioteuthidae 10,
Cranchiidae 41 and Chiroteuthidae 3 I .
sometimes found in the upper 100 m but 40% of the species of the
family live only deeper than 500 m and 20% only deeper than 1 000m;
the Chiroteuthidae is the deepest-living family, only 16% extend into
the upper 100 m, only 42% into the upper 1000 m and the upper
limits of over 20% lie deeper than 2 000 m.
Collection of squids by closing nets has only been reported two or
three times and therefore provides little evidence on vertical distribution.
The evidence of photography and tentacles caught in reversing water