Hawaiian Crangonidae — Banner 
7 
tube worms. Lack of data prevents the tabu- 
lation of the habitats of the deeper- dwelling 
species, but the few I have collected in dredge 
hauls from deeper water were either living in 
dead coral boulders or in sponges. 
Although the general habitats of the spe- 
cies are known, very little is known of their 
actual ecology. For example, what are their 
food habits.^ They are reported to be carnivor- 
ous, yet the digestive tracts of specimens kept 
in aquaria with Ulva turn a bright green. In 
the case of a dozen species living in one dead 
coral head, are there zones typical of each spe- 
cies, and, if so, what factors determine this 
selection? Does a pair found living together 
in a single tube represent a pair mated for life? 
What are the food and defensive relationships 
of this pair in which the smaller male has the 
larger chela? What is the biological signifi- 
cance of the sexual dimorphism of the small 
chela of some species? Why are the two close- 
ly related species, Crangon crassimanus (Heller) 
and C. pad fica (Dana), which seem to inhabit 
the same type of coral in the same zone, al- 
most never found together in the same coral 
head? What are the limitations of the distri- 
butional range of C. diadema (Dana)? To my 
knowledge, none of these problems has ever 
been investigated. 
VARIATION WITHIN SPECIES 
A number of species reported upon in this 
study are noted to show great variation, a var- 
iation which transcends the limits previously 
accepted to be of subspecific and, in some 
cases, of specific worth. These variations are 
encountered particularly in the armature and 
proportions of the appendages, characteristics 
that have been accepted as stable within quite 
narrow limits for a single species. Some of the 
species from Hawaii, especially those that 
have been collected in large numbers, like 
Synalpheus paraneomeris (Coutiere), Crangon 
hrevtpes (Stimpson) , and C. dypeata (Coutiere) , 
show great variation; many of those that are 
less plentiful, such as S. charon (Heller) and C. 
edmondsoni Banner, show less variation. There 
are occasional species that appear to be rather 
constant and do not show as much variation 
as would be expected from observation of re- 
lated species collected in similar numbers, 
e. g., C. pad fica (Dana), C. nanus Banner, and 
C. collumiana (Stimpson). 
This apparently unusual degree of variation, 
reported in detail in the text, may be due to 
three factors: 
The first possibility is the lack of discrimi- 
nation on my part, resulting in my confusing 
several discrete but narrowly separated spe- 
cies and considering them as a single species. 
However, whenever during this study any 
considerable variation of a species was noted, 
that species was examined critically, and, in 
instances of complicated variations, tables of 
measurements were prepared to facilitate the 
drawing of conclusions. Characters which ex- 
hibited a more or less continuous spectrum of 
variation were not considered as of specific 
worth. Although other workers have some- 
times used a combination of variable charac- 
ters as a basis for distinguishing species, I do 
not believe that, even if the procedure is valid, 
the knowledge of the family is sufficiently ad- 
vanced to warrant the use of such criteria. 
A second possible cause of the variation is 
a species radiation in Hawaii. This would be 
caused by the immigration of one or a few 
species to an isolated location and then the 
rapid evolution of the species to fit into the 
unoccupied ecological niches. When suffi- 
cient time has elapsed, this process should 
produce many new but closely related spe- 
cies; when the process is just starting, it should 
be noticeable as variations within a species. It 
is true that the Hawaiian Archipelago has 
fewer species than other parts of the Pacific; 
for example, de Man (1911) reported 38 spe- 
cies of the genus Synalpheus from the area vis- 
ited by the Siboga Expedition, whereas in Ha- 
waii the genus is represented by only six 
species, three of which are common. There- 
fore, those three species in Hawaii may be in 
the process of evolution to fit the ecological 
niches filled by the 38 species of the Nether- 
