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THE BIOLOGY O F EUPHAUSIIDS
and nauplius eye are present in all except Bentheuphausia amblyops and
Stylocheiron abbreviatum. No dorsal frontal organ was present in any of
the species of euphausiids examined. There is, unfortunately, no information on the function of these organs in euphausiids and conjecture
about their use as background illumination sensing organs is probably of
FIG. 78. Sagittal section through the anterior part of the head of Thysanopoda trieuspidata. 1, brain; 2, ventral frontal organ; 3, nauplius eye s e n m stricto; 4 , musculus
oculi basalis distalis ; 5, musouli compressores ; 6, antennule. (After Elofsson, 1965.)
littlevalue at present. The presence of rhabdoms in these organs and the
fact that they are present throughout the malacostracous Crustacea
suggests that they are useful to the organisms but only further work will
define their function or functions in the daily life of the organisms.
The compound eyes of Bentheuphausia amblyops are degenerate and
do not have distinct, well-developed ommatidia nor is there a photo-