Vol. 53 - Alaska Resources Library and Information Services

the curved lateral processes reach the posterior
margin of the third abdominal somite, but in Stage
I and II zoeae of C. bairdi, they are markedly
shorter."
Haynes' later paper thus emphasized the use of the curved lateral
process on the third abdominal segment [the length of
which was previously described for C. opilio by Kurata (1963)]
as a principal diagnostic feature for distinguishing between
both zoeal stages of the two species: one from the eastern
Pacific (C. bairdi) and one from the western Pacific (C.
opilio). However, Haynes (1981) acknowledged:
"Stage II zoea of C. opilio from the eastern Pacific Ocean
have not been identified, and it is not known if they
can be distinguished from Stage II zoeae of C. bairdi
by the length of their lateral processes."
Therefore, it remained unknown at that time how well these
observations would apply to specimens collected in the southeastern
Bering Sea.
Using the relationship of the length of lateral process on
the third abdominal segment to the posterior margin of that
segment (Haynes 1981), we were able to separate numerous
Chionoecetes zoeae from the southeast Bering Sea into two
groups, presumably corresponding to the two species of interest.
In many instances, then, the relationship recommended
by Haynes (1981) appears applicable when specimens of C. opilio
are from the eastern Pacific, as well. However, we have
found considerable variability in the relative length of the
lateral process and it frequently is not possible to distinguish
between the two species using this character alone.
Specifically, the more slender, longer processes do not always
reach the posterior margin of the segment, yet they clearly
differ in shape and length from the shorter processes on
other zoeae. We searched for additional characteristics in
specimens from the clearly separated zoeal groups (using the
above lateral process criterion of Haynes) to see if other
morphological features could be used to distinguish between the
two species when the lateral process length relationship did
not clearly indicate one species or the other. Two additional
characteristics have proven helpful in this respect: (1)
length from the distal end of the rostral spine to the distal
end of the dorsal spine and (2) the shape and relative length
of the carapace lateral spines. These characteristics are
described in the following section.
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