December, 1999 
SCAMIT Newsletter 
Vol. 18, No.8 
NEW LITERATURE 
Our consideration of speciation in local Mytilus 
has just begun. In the last NL an e-mail from 
Dr. Jim Carlton opined that there was no 
morphological basis for separation of the 
species in the “edulis” group - M. edulis, M. 
galloprovincialis , and M. trossulus. He asserted 
that these three were morphologically one, and 
only separable genetically. Martel et al (1999) 
disagree, at least as far as juveniles are 
concerned, and present data to substantiate 
their claim of a method which allows 
identification of M. galloprovincialis, M. 
trossulus, and M. californianus juveniles (M. 
edulis was not included in their study). 
Separation of adult M. californianus from the 
remaining three species is not usually a 
problem as the former has shell ribbing absent 
in the other three. This is, however, not present 
in the newly recruited juveniles, and these have 
previously been identified as Mytilus spp. 
juveniles. 
Separation of the species hinges on only a few 
characters, although others might possibly be 
developed. Five characters were found to be 
useful: the location of the dorsal apex along the 
dorsal shell margin, the size of the posterior 
adductor scar, the relative distance of the 
posterior adductor scar from a line dropped 
from the dorsal apex, the dorsal angle of the 
dissoconch, and the presence/number of lateral 
hinge tooth demarcations. Identity of all the 
individuals used in the morphometric analysis 
was verified by DNA analysis. Statistically 
significant differences were found between 
species based on the selected characters, while 
differences between geographically separated 
populations of M. californianus were not 
significant. 
The samples examined were taken from areas 
which should support pure stands of either M. 
trossulus or M. galloprovincialis, and did not 
include areas of known hybridization of the 
two species along the Pacific coast. It remains 
to be shown that hybrids can be 
morphologically distinguished from the parent 
forms, and accurately assessed as hybrids. 
Previous work with adults in Europe, however, 
suggests that this may be the case. While not a 
completely definitive answer to our Mytilus 
dilemma, the present work represents a 
significant improvement in our ability to deal 
with this difficult group of animals. Additional 
work on Estuarine and intertidal communities 
in Southern California will give us all a chance 
to apply the techniques developed by Martel et 
al, and see if we can make them work . 
Imajima (1999) continues his long series of 
revisionary works on the Japanese polychaete 
fauna with a treatment of the Onuphidae 
(except the genus Onuphis itself). While many 
of the generic level taxa appear to be those 
represented in the Southern California Bight, 
there is little overlap at the specific level 
between our fauna and that of Japan. Dr. 
Imajima describes 10 new species in the 
monograph, and reports others from Japanese 
waters for the first time. The provided keys 
deal only with the Japanese fauna, and will not 
allow easy comparison of the Japanese species 
to a broader spectrum of species in each 
considered genus. Local workers should 
familiarize themselves with this fauna, which is 
sometimes introduced into local waters by the 
incessant flow of vessels from Japan to 
California ports. 
The small sipunculan worm Apionsoma 
misakianum is commonly reported from 
shallow coarse sediments in the Southern 
California Bight. It is also reported to occur in 
other widely separated areas of the Pacific, 
Atlantic, and Caribbean. Previous studies of 
early development in juveniles spawned by 
morphologically indistinguishable adults 
collected in eastern Florida suggested that large 
developmental differences existed within the 
populations of this species. Staton & Rice 
(1999) recently conducted an additional 
investigation to examine these differences 
using allozyme characterization of animals 
from different sources relative to the Florida 
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