August, 1999 
SCAMIT Newsletter 
Vol. 18, No.4 
populations. They report that the relationship 
between environmental stresses and parasite 
impact on hosts is not the simple linear one 
assumed in most monitoring. Parasite load is a 
stressor of both individuals and populations 
which may either augment or offset the effects 
of other stressors. They even discuss the case 
in which stress associated reductions in the 
host populations drop the host density beyond 
the threshold necessary for the parasite to exist, 
leading to its local extinction. Parasites are 
everywhere, and are usually under-examined in 
routine monitoring. We need to pay more 
attention to them, and the current review is 
helpful in fitting them into the broader 
ecological framework. 
“...and bigger fleas have smaller fleas...” is the 
case with the parasitism of a lithodid crab by 
the barnacle Briarosaccus callosus in the south 
Atlantic (Watters 1998). The barnacle is in its 
turn parasitized by an undescribed liriopsine 
cryptoniscid isopod hyperparasite. What is 
particularly interesting about this case is the 
isopod uses the same hormonal tricks to control 
it’s barnacle host as the barnacle uses to control 
the crab. Thus the barnacle, which has 
hormonally sterilized the crab, is hormonally 
sterilized by the isopod. Local king crabs in the 
genus Paralithodes host ostensibly the same 
barnacle, but no isopod hyperparasites have yet 
been noted. 
Bight ‘98 trawling around Catalina and the 
northern Channel Islands yielded several 
specimens of the hexactinellid sponge 
Rhabdocalyptus dawsoni. Ecological 
information on this form has been virtually 
non-existent. Now Leys & Lauzon (1998) 
discuss features of its natural history derived 
from monitoring of populations in the waters 
of Saanich Inlet and Barkley Sound in British 
Columbia. From their measured growth rates 
they estimated the age of average sized 
individuals at 35 yrs., and of specimens lm 
long at 220 yrs. They studied a number of 
individual sponges in situ, revisiting them over 
a three year period. 
An examination of nemertean 
interrelationships using data from 
mitochondrial 16S rDNA is provided by Envall 
(1998). Although a nemertean group is used as 
the test case, the test actually is of the method. 
Envall tests the impact of use and non-use of 
probability weighting of ribosomal DNA data 
on most parsimonious tree topology. Weighting 
has been used to counteract the differences in 
mutation frequency in different regions along 
this molecule. He reports that the greater the 
genetic distance between two organisms, the 
greater the impact of weighting. At genetic 
distances of less than 19% the weighted and 
unweighted treatments produced concordant 
results. 
Paucity of data is always a potential problem in 
this relatively early stage of genetic sequencing 
of invertebrates. Siddall et al (1998) definitely 
found this to be a problem in determining the 
phylogenetic position of the Echiura and 
Pogonophora. They present an examination of 
the results reported by McHugh (1997) which 
reported echiurans and pogonophores were 
derived annelids. While the current authors are 
not averse to that position, they found that 
McHugh’s analysis was laced with 
methodological problems, largely stemming 
from the nature of the selected gene, the EF-1 
gene (elongation factor 1), and/or the 356 base 
pair fragment of it used. One of the approaches 
used by Siddall et al was inclusion of 
additional taxa for which equivalent molecular 
data was available. In so doing they found that 
the results presented by McHugh lost 
significance or were contradicted by 
information from the additional taxa. They 
conclude that reassessment of the relationship 
between annelids, echiurans, and 
pogonophorans should not be based on EF-1 
data, and that McHugh’s conclusions were not 
sufficiently supported. 
The resolution of sibling species complexes 
using molecular evidence mentioned in the last 
newsletter continues apace. Simison & 
Lindberg (1999) tackle the Notoacmea 
3 
