268
THE BIOLOQY O F EUPHAUSIIDS
transverse muscles in the first four abdominal segments and these are
linked together by various central muscles which act in turn as support
for the important longitudinal oblique muscles. Each transverse muscle
is multiple in construction, being composed of elements subscribed by
muscles in its own segment as well as by muscles in the next anterior
segment. Above these systems of muscles are the dorsal muscles (Fig.
102) and below them the paired superjicial ventral muscles. Lateral
muscles only occur in the first two abdominal segments. The overall
musculature of the first five abdominal segments is similar but that of
the sixth abdominal segment is different. Here, the superJicia1 ventral
muscle is enlarged and extensor andJEexor muscles for the telson and
uropods are present. Oblique muscle 7 (Fig. 102, No. XXVI) and its
associated muscles traverse this segment to insertions posteriorly and
are also connected, by way of a tendon, to the ventral $exor muscle of
the telson.
Experimental studies with euphausiids have been hindered because
of the difficulty of keeping the animals alive and healthy in the laboratory (Komaki, 1966). The first problem is to catch the animals in such
a way that they suffer the least damage. Komaki suggests having a net
terminated by a lantern shape rather than a conical shape so that water
flow through the net is slowed down in the end regions. Hauls of short
duration a t slow speeds are best and collection of the animals when they
are in the surface layers is advantageous but, of course, impossible with
such deep living species as Bentheuphausia amblyops and Thysanopoda
cornuta which do not migrate into the surface layers even at night. No
filtering devices should be used in the bucket of the net but an ordinary
polythene, glass, or metal bucket should be attached so that, when the
net is raised to the deck after a short haul and the bucket detached,
the euphausiids are swimming around in the bucket and not lying
strained on a sieve a t the bottom of the bucket. They should then be
gently transferred to polythene or other suitable containers filled with
water whose temperature is close to that of the environment from which
the euphausiids were taken. The density of euphausiids in the containers should be low, about one per litre, and the containers should be
kept in the dark under controlled temperature conditions. No feeding
is necessary if the steaming time to the parent laboratory is only a few
days but if feeding is necessary then cultures of phytoplankton such as
Skeletonema costatum (Greville), or the nauplii of Artemia salina (L.),
are probably suitable. Meganyctiphanes norvegica has been kept at
Millport in large tanks cooled to 4°C for as long as three months but
the musculature of the abdomen has often been opaque a considerable
time prior to the actual death of the animal. Keeping M . norvegica and
THE BIOLOQY O F EUPHAUSIIDS
transverse muscles in the first four abdominal segments and these are
linked together by various central muscles which act in turn as support
for the important longitudinal oblique muscles. Each transverse muscle
is multiple in construction, being composed of elements subscribed by
muscles in its own segment as well as by muscles in the next anterior
segment. Above these systems of muscles are the dorsal muscles (Fig.
102) and below them the paired superjicial ventral muscles. Lateral
muscles only occur in the first two abdominal segments. The overall
musculature of the first five abdominal segments is similar but that of
the sixth abdominal segment is different. Here, the superJicia1 ventral
muscle is enlarged and extensor andJEexor muscles for the telson and
uropods are present. Oblique muscle 7 (Fig. 102, No. XXVI) and its
associated muscles traverse this segment to insertions posteriorly and
are also connected, by way of a tendon, to the ventral $exor muscle of
the telson.
Experimental studies with euphausiids have been hindered because
of the difficulty of keeping the animals alive and healthy in the laboratory (Komaki, 1966). The first problem is to catch the animals in such
a way that they suffer the least damage. Komaki suggests having a net
terminated by a lantern shape rather than a conical shape so that water
flow through the net is slowed down in the end regions. Hauls of short
duration a t slow speeds are best and collection of the animals when they
are in the surface layers is advantageous but, of course, impossible with
such deep living species as Bentheuphausia amblyops and Thysanopoda
cornuta which do not migrate into the surface layers even at night. No
filtering devices should be used in the bucket of the net but an ordinary
polythene, glass, or metal bucket should be attached so that, when the
net is raised to the deck after a short haul and the bucket detached,
the euphausiids are swimming around in the bucket and not lying
strained on a sieve a t the bottom of the bucket. They should then be
gently transferred to polythene or other suitable containers filled with
water whose temperature is close to that of the environment from which
the euphausiids were taken. The density of euphausiids in the containers should be low, about one per litre, and the containers should be
kept in the dark under controlled temperature conditions. No feeding
is necessary if the steaming time to the parent laboratory is only a few
days but if feeding is necessary then cultures of phytoplankton such as
Skeletonema costatum (Greville), or the nauplii of Artemia salina (L.),
are probably suitable. Meganyctiphanes norvegica has been kept at
Millport in large tanks cooled to 4°C for as long as three months but
the musculature of the abdomen has often been opaque a considerable
time prior to the actual death of the animal. Keeping M . norvegica and