226
THE BIOLOGY OF EUPHAUSIIDS
of cephalopod molluscs examined; it was present mainly as the
ester and was concentrated in the liver and eyes. The concentrations
found in all the different organisms are considerably less than in the
euphausiids. Further, we have examined representatives of most
groups of crustaceans to discover if any of them also concentrate
vitamin A. No notable concentrations of vitamin A were present in
the four species of barnacles, the sixty-seven species of copepods, the
twenty-one species of ostracods, nor in the few species of isopods
examined. It occurred in only two species of the sixty-four species of
amphipods investigated ; these species were Brachyscelus crusculum
Bate and Parathemisto oblivia G. 0. Sars. More than twenty species
of mysids have been tested and although the vitamin was present in
many of them, the concentrations were notably lower than in the
euphausiids. The range in concentration of the vitamin in decapod
crustaceans, and we have examined more than one hundred species,
is lower than that of euphausiids; only two species, Lucifer typus
Milne-Edwards and Parapandalus richardi (Coutihre), had concentrations well within the range found in euphausiids. Several species
of decapods had no vitamin A while, in a few, it was occasionally
detected. Consequently, the main conclusion drawn from all this work,
much of which has already been published in the papers of Fisher, Kon
and Thompson, is that the populations of euphausiids in the oceans and
more coastal regions of the world form the main reservoirs of vitamin A.
We shall be discussing visual and other pigments in the eyes of
euphausiids in Chapter 8, but, on present evidence, there does not
seem to be any other function for the vitamin A present in the eyes
other than that of its aldehyde, retinene, in the visual pigment,
rhodopsin. The bulk of the vitamin is in the ester form and thus in a
store. This store is added to throughout the life of the animal and so
larger individuals of an euphausiid species have relatively greater concentrations of the vitamin present in the eyes than smaller individuals.
The vitamin is stored in the eyes of many decapods and mysids but, in
others, the bulk is not in the eyes but in the bodies. From an examination of the modes of life of the decapod crustaceans with the greatest
concentrations of vitamin A, and with a considerable fraction of it in
the eyes, and considering such groups as the mysids and euphausiids,
there is some tentative evidence to suggest that the pelagic species
are much richer in vitamin than neritic or benthic species. This
seems plausible because the visual sense is probably more important to
free-swimming animals than to those living close to the bottom or in
shallow waters where chemical and tactile senses may be of increasing
importance.
THE BIOLOGY OF EUPHAUSIIDS
of cephalopod molluscs examined; it was present mainly as the
ester and was concentrated in the liver and eyes. The concentrations
found in all the different organisms are considerably less than in the
euphausiids. Further, we have examined representatives of most
groups of crustaceans to discover if any of them also concentrate
vitamin A. No notable concentrations of vitamin A were present in
the four species of barnacles, the sixty-seven species of copepods, the
twenty-one species of ostracods, nor in the few species of isopods
examined. It occurred in only two species of the sixty-four species of
amphipods investigated ; these species were Brachyscelus crusculum
Bate and Parathemisto oblivia G. 0. Sars. More than twenty species
of mysids have been tested and although the vitamin was present in
many of them, the concentrations were notably lower than in the
euphausiids. The range in concentration of the vitamin in decapod
crustaceans, and we have examined more than one hundred species,
is lower than that of euphausiids; only two species, Lucifer typus
Milne-Edwards and Parapandalus richardi (Coutihre), had concentrations well within the range found in euphausiids. Several species
of decapods had no vitamin A while, in a few, it was occasionally
detected. Consequently, the main conclusion drawn from all this work,
much of which has already been published in the papers of Fisher, Kon
and Thompson, is that the populations of euphausiids in the oceans and
more coastal regions of the world form the main reservoirs of vitamin A.
We shall be discussing visual and other pigments in the eyes of
euphausiids in Chapter 8, but, on present evidence, there does not
seem to be any other function for the vitamin A present in the eyes
other than that of its aldehyde, retinene, in the visual pigment,
rhodopsin. The bulk of the vitamin is in the ester form and thus in a
store. This store is added to throughout the life of the animal and so
larger individuals of an euphausiid species have relatively greater concentrations of the vitamin present in the eyes than smaller individuals.
The vitamin is stored in the eyes of many decapods and mysids but, in
others, the bulk is not in the eyes but in the bodies. From an examination of the modes of life of the decapod crustaceans with the greatest
concentrations of vitamin A, and with a considerable fraction of it in
the eyes, and considering such groups as the mysids and euphausiids,
there is some tentative evidence to suggest that the pelagic species
are much richer in vitamin than neritic or benthic species. This
seems plausible because the visual sense is probably more important to
free-swimming animals than to those living close to the bottom or in
shallow waters where chemical and tactile senses may be of increasing
importance.