CHAPTER 8
VISION AND BIOLUMINESCENCE
The eyes of euphausiids are prominent features of the external
morphology and are the basis for the only British common name for an
euphausiid-suil dhu (black eyes), the name given by Gaelic-speaking
fishermen to Meganyctiphanes norvegica. I n discussing vision, consideration must be given to the photophores and, consequently, an
examination of the structure and function of the eyes is followed by a
discussion of the photophores and their possible importance to these
animals. Many organisms are sensitive to light which strikes the body
and not the eyes (Steven, 1963). The eyes of euphausiids, however,
appear to be their only means of sensing light because Kampa et al.
(1959) only recorded nerve impulses, by electrical means, when the eyes
were illuminated; no such impulses were recorded when parts of the
body, other than the eyes, were exposed to light.
Elofsson (1963, 1965) has made a comparative study of the bee
ocellaire, nauplius eye and the frontal organs of malacostracous
Crustacea. The bee ocellaire is the name given to the structure within
which the nauplius eye is always found; it lies a t the most anterior
point of the animal, between the compound eyes, and extends ventrally
to the dorsal origins of the two antennules (Fig. 78), that is in the same
position in which it occurs in the decapod Crustacea. Externally, it is
a small conical protuberance, smaller than in the decapods. It has an
internal muscular and nervous system, fully described in many
Crustacea by Elofsson and reference should be made to his papers.
The nauplius eye of euphausiids consists of nine cells in three groups
of three, the groups being separated by small lumps of pigment. A
rhabdom, the degree of development varying from species to species, is
present. The nauplius eye connects with the epidermis by way of tubes
formed by extensions of the epineurium covering the eye and nerve to
it. Paired frontal organs are present as two cell-filled tubes, parallel to
the nerve to the nauplius eye (Fig. 78) and having one, two or several
rhabdoms. Elofsson examined Bentheuphausia amblyops, Thysanopoda
tricuspidata, Meganyctiphanes norvegica, Euphausia gibboides, E .
hemigibba, Thysanoessa inermis, Nematobrach~on Pexipes, NematosceZis
microps, and Stylocheiron abbreviatum and found that the bee ocellaire
227
VISION AND BIOLUMINESCENCE
The eyes of euphausiids are prominent features of the external
morphology and are the basis for the only British common name for an
euphausiid-suil dhu (black eyes), the name given by Gaelic-speaking
fishermen to Meganyctiphanes norvegica. I n discussing vision, consideration must be given to the photophores and, consequently, an
examination of the structure and function of the eyes is followed by a
discussion of the photophores and their possible importance to these
animals. Many organisms are sensitive to light which strikes the body
and not the eyes (Steven, 1963). The eyes of euphausiids, however,
appear to be their only means of sensing light because Kampa et al.
(1959) only recorded nerve impulses, by electrical means, when the eyes
were illuminated; no such impulses were recorded when parts of the
body, other than the eyes, were exposed to light.
Elofsson (1963, 1965) has made a comparative study of the bee
ocellaire, nauplius eye and the frontal organs of malacostracous
Crustacea. The bee ocellaire is the name given to the structure within
which the nauplius eye is always found; it lies a t the most anterior
point of the animal, between the compound eyes, and extends ventrally
to the dorsal origins of the two antennules (Fig. 78), that is in the same
position in which it occurs in the decapod Crustacea. Externally, it is
a small conical protuberance, smaller than in the decapods. It has an
internal muscular and nervous system, fully described in many
Crustacea by Elofsson and reference should be made to his papers.
The nauplius eye of euphausiids consists of nine cells in three groups
of three, the groups being separated by small lumps of pigment. A
rhabdom, the degree of development varying from species to species, is
present. The nauplius eye connects with the epidermis by way of tubes
formed by extensions of the epineurium covering the eye and nerve to
it. Paired frontal organs are present as two cell-filled tubes, parallel to
the nerve to the nauplius eye (Fig. 78) and having one, two or several
rhabdoms. Elofsson examined Bentheuphausia amblyops, Thysanopoda
tricuspidata, Meganyctiphanes norvegica, Euphausia gibboides, E .
hemigibba, Thysanoessa inermis, Nematobrach~on Pexipes, NematosceZis
microps, and Stylocheiron abbreviatum and found that the bee ocellaire
227