182
THE BIOLOGY O F EUPHAUSIIDS
material is sucked posteriorly into the now open space (food basket)
between the knees of the limbs and the mouthparts. The mandibles then
macerate any large particles and the food passes to the mouth.
Euphausiids can also feed on such planktonic organisms as chaetognaths and copepods. Ponomareva (1954) describes the way in which
Thysanoessa longipes, T . inermis, and Euphausia paci$ca feed on
copepods and her results have been confirmed by observations on
Thysanoessa raschii and Meganyctiphanes norvegica. According to
Mauchline (1960) and David and Conover (1961) no hunting or stalking
of living prey seems to be carried out but a live copepod passing very
close to an euphausiid seems to place itself in danger because the
euphausiid suddenly spreads its thoracic limbs laterally and, as in the
case of lumps of bottom material held on the bases of the antennae, the
copepod is sucked into the food basket between the thoracic limbs and
the mouthparts. Ponomareva (1955) and Lasker (1966), however, did
find evidence of active hunting of prey organisms, the former finding
that luminescent copepods were selectively eaten by euphausiids, the
latter that Artemia nauplii were more frequently eaten than they would
have been if the catching techniques of Euphausia paci$ca had simply
involved random swimming and filtering of the water. Once the copepod
has been captured, it is then held by the mouthparts and its integument
pierced by them. The cusps of the mandibles and the spines on the
third joints of the maxillules are admirably adapted for this. The
" juices " are then sucked from the body of the copepod leaving an
empty husk that, according to Ponomareva, is as a rule not eaten;
these remains are ejected from the food basket and only a small quantity
of unidentifiable fragments of the exoskeleton enters the stomach of the
euphausiid. This is not always the case because recognizable portions
of copepods are encountered in stomachs of euphausiids but it is indeed
probable, as Ponomareva points out, that this is not common and that
consequently the role of copepods in the diet of these organisms tends
to be underestimated.
Nemoto (1 967), observing living Euphausia similis, found that the
maxillules and maxillae are important in handling food organisms in
the food basket and also in rejecting undesirable material in the food.
He further states that the pars molaris is responsible for crushing
diatoms, especially chains of species with hard frustules, Foraminifera,
and silicoflagellates. The pars molaris is largest, relative to the mandible
as a whole, in the more herbivorous Euphausia superba, smaller in more
omnivorous species, and smallest in a carnivorous species such as
Nematobrachion boopis. Nemoto measured the distances between the
setules on the setae of the ischium of the thoracic limbs of adult females
THE BIOLOGY O F EUPHAUSIIDS
material is sucked posteriorly into the now open space (food basket)
between the knees of the limbs and the mouthparts. The mandibles then
macerate any large particles and the food passes to the mouth.
Euphausiids can also feed on such planktonic organisms as chaetognaths and copepods. Ponomareva (1954) describes the way in which
Thysanoessa longipes, T . inermis, and Euphausia paci$ca feed on
copepods and her results have been confirmed by observations on
Thysanoessa raschii and Meganyctiphanes norvegica. According to
Mauchline (1960) and David and Conover (1961) no hunting or stalking
of living prey seems to be carried out but a live copepod passing very
close to an euphausiid seems to place itself in danger because the
euphausiid suddenly spreads its thoracic limbs laterally and, as in the
case of lumps of bottom material held on the bases of the antennae, the
copepod is sucked into the food basket between the thoracic limbs and
the mouthparts. Ponomareva (1955) and Lasker (1966), however, did
find evidence of active hunting of prey organisms, the former finding
that luminescent copepods were selectively eaten by euphausiids, the
latter that Artemia nauplii were more frequently eaten than they would
have been if the catching techniques of Euphausia paci$ca had simply
involved random swimming and filtering of the water. Once the copepod
has been captured, it is then held by the mouthparts and its integument
pierced by them. The cusps of the mandibles and the spines on the
third joints of the maxillules are admirably adapted for this. The
" juices " are then sucked from the body of the copepod leaving an
empty husk that, according to Ponomareva, is as a rule not eaten;
these remains are ejected from the food basket and only a small quantity
of unidentifiable fragments of the exoskeleton enters the stomach of the
euphausiid. This is not always the case because recognizable portions
of copepods are encountered in stomachs of euphausiids but it is indeed
probable, as Ponomareva points out, that this is not common and that
consequently the role of copepods in the diet of these organisms tends
to be underestimated.
Nemoto (1 967), observing living Euphausia similis, found that the
maxillules and maxillae are important in handling food organisms in
the food basket and also in rejecting undesirable material in the food.
He further states that the pars molaris is responsible for crushing
diatoms, especially chains of species with hard frustules, Foraminifera,
and silicoflagellates. The pars molaris is largest, relative to the mandible
as a whole, in the more herbivorous Euphausia superba, smaller in more
omnivorous species, and smallest in a carnivorous species such as
Nematobrachion boopis. Nemoto measured the distances between the
setules on the setae of the ischium of the thoracic limbs of adult females