PATTERN, NUMBER, VARIABILITY, AND TAXONOMIC
SIGNIFICANCE OF INTEGUMENTAL ORGANS
(SENSILLA AND GLANDULAR PORES) IN THE GENUS
EUCALAMS (COPEPODA, CALANOIDA)
Abraham Fleminger'
ABSTRACT
Methods for study of bilaterally symmetrical, serially homologous sets of integumental organs
comprising hair, peg, and pit sensilla and the pores of integumental glands as well as their
number and distribution in the genus Eiicalanus are described.
A survey of these organs was carried out on geographically representative samples of the
17 discrete populations I recognize as valid species in the genus. The survey concentrated on
adult females, but smaller numbers of adult males and some younger copepodid stages were
also examined. Numbers and arrangement of these organs, estimates of variability, and their
relationship to total length were established for each species. Phenetic similarity in integu-
mental organ arrangement is shown to concur with other morphological features within the
genus. Comparison is also made between number and arrangement of integumental organs
and the geographical relationships among the members in each species group. Several new
species in the attenuatus group are described on the basis of integumental organs and geo-
graphical distribution. A preliminary study of geographical variation in the circumglobal,
broadly tropical species £. suhtenuis is used to estimate the general complexity of genetic
control and the use of these organs to study gene flow and population variability in plank-
tonic species.
The integument of arthropods bears numerous
organs that fall into two general classes:
sensory receptors or sensilla, and glands. Sen-
silla are composed of one to several sensory
neurons and generally two accessory cells, the
latter forming the external features which may
be in the form of an outgrowth, i.e., a hair, a
cone, or a peg, or an ingrowth such as a pit or
plate organ with sensory cell bodies located
underneath (Laverack, 1969; Schneider, 1969;
Stiirckow, 1970). The regular presence of sen-
silla containing nerve fibers has been demon-
strated histologically in a variety of different
copepods (e.g., Fahrenbach, 1962; Elofsson,
1971).
In terrestrial arthropods integumental glands
are highly variable in number, in distribution,
and in morphological detail (Eisner and Mein-
wald, 1966). Integumental glands described
from copepods tend to be rather simple sacs
' Scripps Institution of Oceanography, University of
California at San Diego, La Jolla, CA 92037.
underlying the integument and communicate
with the environment via a simple pore penetrat-
ing the integument (e.g., Clarke et al., 1962;
Fahrenbach, 1962; Park, 1966).
On the body of copepods as in mystacocarids
and other arthropods, sensilla and glands are in
general distributed in bilaterally symmetrical
patterns that are somewhat redundant on suc-
cessive body segments, i.e., they appear to be
serially homologous (Sewell, 1929, 1932, 1947;
Fahrenbach, 1962; Hessler, 1969). It is highly
probable that chemical communication via integ-
umental organs, a widespread means for ex-
changing information among arthropods and
vertebrates (e.g., cf. Johnston, Moulton, and
Turk, 1970) is essential to copepods. Dioecious
and nonparthenogenetic copepods must locate
and correctly identify a potential mate without
visual aids. This search and contact procedure is
mediated by pheromones in Eiinjtemora and
called "mate-seeking behavior" (Katona, 1973).
Moreover successful culmination of the mating
act requires attachment of the spermatophore
Manuscript accepted May 1973
FISHERY BULLETIN: VOL. 71, NO. 4, 1973.
965
Pattern, number, variability, and taxonomic significance of integumental organs (sensilla and glandular pores) in the genus Eucalanus (Copepoda, Calanoida)
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