382
THE BIOLOGY OF EWHAUSIIDS
found, in the case of laboratory experiments on the accumulation of
"Zn, that the cuticle of E. pacijica contained, on average, 41% of
the total body content of this isotope. Cuticles cast in the surface
layers during the night when E . pacijica has migrated upwards are
then available for ingestion by surface living organisms which then
gain access to the 65Zn. This work suggests that vertically migrating
animals may play a major part in the movement of certain radioisotopes or other substances and materials vertically, and even through
density gradients, in the open ocean.
Euphausiids are able to synthesize vitamin A and store it, primarily
in their eyes, as was described in Chapter 7. This vitamin is characteristic of all vertebrates but does not occur in all invertebrates. It does not
occur, as far as is known, in protozoans nor was it found in the sponge,
Haliclona oculata (Pallas), nor in any coelenterates (Fisher and Kon,
1959). It was present in the chaetognath, Eukrohnia fowleri RitterZahony, but not in samples of Sagitta species and probably is not
present in polychaete worms or echinoderms. Vitamin A is present in
many species of molluscs, low concentrations being found in members
of the Loricata, Bivalvia, and Gastropoda (Fisher et al., 1956a),
and mainly located in the digestive gland or in the visceral mass ; all
species of cephalopod molluscs analysed contained vitamin A (Fisher
et al., 195613). Vitamin A only occurred in a few species of the sixty-nine
species of copepods analysed (Fisher et al., 1964) and was not detected
a t all in the very important copepod, Calanus finmarchicus. The little
information available a t present suggests that the vitamin probably
does not occur to any great degree in representatives of the Branchiopoda, Cirripedia, or Ostracoda but this view may be modified by future
results. It is present in some amphipods, isopods, and mysids (Fisher
and Kon, 1959), in most of the penaeid and sergestid prawns
analysed (Fisher et al., 1957), and in many anomuran, brachyuran
and astacuran crustaceans (Fisher and Kon, 1959). Its presence or
absence in tunicates, species of which (salps and doliolids) are important
members of the plankton, requires further investigation (Fisher and
Kon, 1959).
Thus euphausiids are the only group of organisms in which all the
species contain vitamin A and the concentrations of the vitamin in these
animals are much greater than those of other invertebrates. Further,
from our extensive analyses for vitamin A in copepods it appears that
this very important group of planktonic crustaceans, although extremely
rich in the carotenoid astaxanthin, cannot contribute significantly to
the vitamin A cycle in the sea. Consequently, it follows that the
euphausiids must be an extremely important source of this vitamin for
THE BIOLOGY OF EWHAUSIIDS
found, in the case of laboratory experiments on the accumulation of
"Zn, that the cuticle of E. pacijica contained, on average, 41% of
the total body content of this isotope. Cuticles cast in the surface
layers during the night when E . pacijica has migrated upwards are
then available for ingestion by surface living organisms which then
gain access to the 65Zn. This work suggests that vertically migrating
animals may play a major part in the movement of certain radioisotopes or other substances and materials vertically, and even through
density gradients, in the open ocean.
Euphausiids are able to synthesize vitamin A and store it, primarily
in their eyes, as was described in Chapter 7. This vitamin is characteristic of all vertebrates but does not occur in all invertebrates. It does not
occur, as far as is known, in protozoans nor was it found in the sponge,
Haliclona oculata (Pallas), nor in any coelenterates (Fisher and Kon,
1959). It was present in the chaetognath, Eukrohnia fowleri RitterZahony, but not in samples of Sagitta species and probably is not
present in polychaete worms or echinoderms. Vitamin A is present in
many species of molluscs, low concentrations being found in members
of the Loricata, Bivalvia, and Gastropoda (Fisher et al., 1956a),
and mainly located in the digestive gland or in the visceral mass ; all
species of cephalopod molluscs analysed contained vitamin A (Fisher
et al., 195613). Vitamin A only occurred in a few species of the sixty-nine
species of copepods analysed (Fisher et al., 1964) and was not detected
a t all in the very important copepod, Calanus finmarchicus. The little
information available a t present suggests that the vitamin probably
does not occur to any great degree in representatives of the Branchiopoda, Cirripedia, or Ostracoda but this view may be modified by future
results. It is present in some amphipods, isopods, and mysids (Fisher
and Kon, 1959), in most of the penaeid and sergestid prawns
analysed (Fisher et al., 1957), and in many anomuran, brachyuran
and astacuran crustaceans (Fisher and Kon, 1959). Its presence or
absence in tunicates, species of which (salps and doliolids) are important
members of the plankton, requires further investigation (Fisher and
Kon, 1959).
Thus euphausiids are the only group of organisms in which all the
species contain vitamin A and the concentrations of the vitamin in these
animals are much greater than those of other invertebrates. Further,
from our extensive analyses for vitamin A in copepods it appears that
this very important group of planktonic crustaceans, although extremely
rich in the carotenoid astaxanthin, cannot contribute significantly to
the vitamin A cycle in the sea. Consequently, it follows that the
euphausiids must be an extremely important source of this vitamin for