CHAPTER 6
FOOD AND FEEDING
The food of euphausiids can be roughly divided into three classes :
(1) material such as diatoms, dinoflagellates, and tintinnids filtered by
the mouthparts from the water, (2) zooplankton, and (3) detrital
material obtained with bottom sediments. These three classes of food
are obtained by different methods of feeding in which all or only some
of the appendages are involved.
A comprehensive study of the feeding appendages of the species in
the different genera is given by Mauchline (1967b) and Nemoto (1967),
and so a brief summary of this work is all that is required here.
Euphausiids are maxillary feeders but the other appendages also play
an important part. The appendages which are most important in
feeding are the labrum, and the paired mandibles, labia, maxillules,
maxillae, and first and second thoracic limbs. All except the second
thoracic limbs are illustrated in Pig. 59 in which they have been spaced
out to show the positions of the filtering setae.
The labrum, anterior to the mouth, forms a pad and has a covering
of very short, hair-like setae on its posterior surface which fits into the
concave anterior faces of the mandibles (Fig. 59) ; it is soft in texture
and has no sclerotized plates on its posterior face. The mandibles, on
the other hand, are hard and have strong cusps, the pars incisiva, in
the ventral region and grinding surfaces, the pars molaris, in the dorsal
region (Fig. 59). They also have a palp (Fig. 59), composed of three
joints, in most genera, but the size of the palp relative to the rest of
the mandible varies somewhat in different genera and species. The
labium (Fig. 59) is plate-like and fits against the posterior face of the
mandible; it has short, hair-like setae along the whole length of the
inner edge (next to the food groove). The maxillule (Figs 59, 61)
usually has four parts-the lobe of the first joint, the third joint, the
endopod, and the pseudexopod. The pseudexopod is absent in some
species (Fig. 61). The lobe of the first joint bears plumose setae but the
third joint has strong spines. The maxilla is the mouthpart that shows
the most variation in morphology throughout the Euphausiacea
(Fig. 62). The lobe of the first joint and the third joint may or may not
be further subdivided and in Stylocheiron species these lobes plus the
174
FOOD AND FEEDING
The food of euphausiids can be roughly divided into three classes :
(1) material such as diatoms, dinoflagellates, and tintinnids filtered by
the mouthparts from the water, (2) zooplankton, and (3) detrital
material obtained with bottom sediments. These three classes of food
are obtained by different methods of feeding in which all or only some
of the appendages are involved.
A comprehensive study of the feeding appendages of the species in
the different genera is given by Mauchline (1967b) and Nemoto (1967),
and so a brief summary of this work is all that is required here.
Euphausiids are maxillary feeders but the other appendages also play
an important part. The appendages which are most important in
feeding are the labrum, and the paired mandibles, labia, maxillules,
maxillae, and first and second thoracic limbs. All except the second
thoracic limbs are illustrated in Pig. 59 in which they have been spaced
out to show the positions of the filtering setae.
The labrum, anterior to the mouth, forms a pad and has a covering
of very short, hair-like setae on its posterior surface which fits into the
concave anterior faces of the mandibles (Fig. 59) ; it is soft in texture
and has no sclerotized plates on its posterior face. The mandibles, on
the other hand, are hard and have strong cusps, the pars incisiva, in
the ventral region and grinding surfaces, the pars molaris, in the dorsal
region (Fig. 59). They also have a palp (Fig. 59), composed of three
joints, in most genera, but the size of the palp relative to the rest of
the mandible varies somewhat in different genera and species. The
labium (Fig. 59) is plate-like and fits against the posterior face of the
mandible; it has short, hair-like setae along the whole length of the
inner edge (next to the food groove). The maxillule (Figs 59, 61)
usually has four parts-the lobe of the first joint, the third joint, the
endopod, and the pseudexopod. The pseudexopod is absent in some
species (Fig. 61). The lobe of the first joint bears plumose setae but the
third joint has strong spines. The maxilla is the mouthpart that shows
the most variation in morphology throughout the Euphausiacea
(Fig. 62). The lobe of the first joint and the third joint may or may not
be further subdivided and in Stylocheiron species these lobes plus the
174