January, 2000 
SCAMIT Newsletter 
Vol. 18, No. 9 
endoparasites favored by Mackenzie. I 
personally have great sympathy for use of less 
common species in benthic analysis, having 
chafed over the years at exclusion rules in 
analysis of benthic data sets. Many discussions 
(or arguments if you prefer) with Dr. Bob 
Smith have convinced me that rarity is a 
concept which is difficult to pin down and even 
more difficult to evaluate in a sampling 
context. There are a multitude of possible 
explanations for a species absence or 
occurrence at low density in a given sample. 
The authors seize on one of them (range 
extreme density attenuation) and discuss it 
here. Since they provide a single operational 
definition of rarity in the article they are able to 
conveniently ignore the other possible, and 
possibly contradictory, explanations for 
observed low population density. Their 
methodology does offer utility in that they 
examine “rare species” collectively, but this is 
tantamount to maintaining that the same cause 
is responsible for low density in each of the 
collectively considered populations - an 
exceedingly unlikely case. So, while I feel that 
they are on to something, I think the proposed 
method is only a suggestive first effort. Before 
a more serious attempt to refine such an 
approach is made, the theoretical bases of 
“rarity” need more thorough examination and 
much more explicit discussion. 
Investigations continue on the ecology of one 
of the lab rats of the benthic infaunal world, 
Capitella sp. I. Cohen & Pechenik (1999) 
report on the species relation with sediment 
organic carbon, while Horng & Taghon (1999) 
discuss particle selection in contaminated 
sediments. The effects of different levels of 
sediment organic carbon on larval settlement 
and metamorphosis, and the post-metamorphic 
growth of the animals were experimentally 
examined by Cohen & Pechenik. They found 
that larvae apparently responded to some 
fraction of the sediment organic load, but did 
not select either the most organically enriched 
sediments or those which would provide 
optimal subsequent growth. 
10 
While Horng and Taghon found that Capitella 
sp. I fed on the smallest available particles, 
they also found that they did so regardless of 
sediment phenanthrene concentration. As 
organic pollutants are adsorbed to surfaces of 
fine particles they tend to be more concentrated 
(in equal weights of sediment) on sediments 
composed of the finest particles. In 
consequence the feeding of particle selective 
sediment consumers such as Capitella may 
help lengthen the time taken to degrade organic 
compounds in nature. As selective feeders on 
the particles which have the highest percentage 
of contaminants by weight, they package 
(digestion is inefficient, passing most items 
through unaltered) particulates in long lasting 
fecal pellets, potentially preventing other 
biologically or chemically mediated 
breakdown of included organics. Glass beads 
were used to determine that the preferred 
particle size for the species was 17±4pm. 
The pyramidellid mollusks have long been a 
thorn in the side of practical marine monitoring 
in the Southern California Bight. A large 
number of species in several genera have been 
described from the area and others from the 
north and south are either known or suspected 
to occur here as well. The group, by all 
accounts, was seriously over described on 
conchological grounds by W. H. Dali and Paul 
Bartsch in the late 19 th and early 20 th centuries. 
Since these are generally small animals, few 
were willing to undertake the study of the soft 
parts which might contradict the tales told by 
the shells. In the last two decades a few 
courageous individuals have begun putting the 
nomenclature of the group on a more sensible 
basis. Schander et al (1999) contribute to this 
by examining two of the odostomiid genera, 
Odostomella and Herviera. Members of both 
genera are predominantly Indo-Pacific in 
distribution with no representatives in our area. 
However, the nature of the character states 
examined, the analysis, and the biological 
notes provided by the authors are all of interest 
to any mollusk student dealing with the family 
and this thorough treatment is recommended. 
