Pacific Species of "Lar" — Hand 
63 
of hydroids exists which possesses reduced 
numbers of tentacles, and some have none. 
Such forms as Hydrichthys, Icthyocodhm, and 
Nudiclava are tentacleless, whereas Mono- 
hrachium has but one and Prohoscidactyla but 
two tentacles. The possibility exists that the 
tentacleless forms exhibit a true parasitism 
in which the hydroid uses the hosts’ tissues 
for its food, as was claimed for Hydrichthys 
by Warren (1916). The exact manner in which 
Monobrachium is adapted to its bivalved host 
is not clear inasmuch as living specimens have 
not been studied, but for at least two of the 
2 -tentacle Prohoscidactyla we have adequate 
descriptions of tie living animal (Gosse, 1857; 
Hand and Hendrickson, 1950). From these 
descriptions we can see how well fitted these 
animals are for their special way of life, but 
they seem to have sacrificed certain usual 
hydroid traits and the versatility of substrate 
requirements of most hy droids for the limited 
substrate offered by certain sabellids. The 
known genera upon which these hydroids 
occur represent but a small number of those 
which appear to be available. Only Potamilla, 
Pseudopotamilla, and Schizobranchia have so far 
been reported as bearing Prohoscidactyla. Stud- 
ies concerning host choice and relationships 
among this group would appear to be worth 
pursuing. 
In most respects the life history of Probosci- 
dactyla differs but little from that presented 
in freshman biology as characteristic of the 
Hydrozoa. However, a life history such as 
this, with two well-developed, relatively long- 
lived phases, is rather unusual in the animal 
kingdom and presents certain difficulties to 
the student of the group. The hydroid phase 
is, in general, a sessile stage, adapted to its own 
environment, whereas the medusoid stage is 
pelagic and is adapted to a completely differ- 
ent mode of life. Most students of the Hy- 
drozoa look upon the hydroid phase as a 
stage in development specialized for asexual 
propagation and upon the medusa as the 
adult, sexually reproducing stage of the life 
history. Because of this curious division of 
the life history, students of the Hydrozoa 
have developed two "schools,” the one a 
group of specialists in hydroids, the other 
in hydromedusae. Therefore, we find today 
that in many instances there are two sets of 
nomenclature referrable to a given animal, 
and there is no immediate hope of reducing 
this gigantic taxonomic snarl to a satisfactory 
systematic treatment. The prime hope would 
seem to be the study of life histories in this 
group so that the medusae may be referred 
to their proper hydroids, and then gradually 
the two systems will become one. 
In the nearly 100 years since Gosse (1857) 
described the first "Lar,” only three additional 
species have been described. These three all 
occur along the Pacific coast of North Amer- 
ica, with one of them ranging to Japan. The 
actual number of species which exist cannot 
be determined at this time, but the possibility 
that as many as a dozen occur is not im- 
probable. Uchida and Okuda (1941) list four 
certain species of medusae of Prohoscidactyla 
with a fifth, originally described by Uchida 
(1927) as Misakia typica, also included as a 
distinct species. The status of several of the 
ten species and varieties of Prohoscidactyla and 
WilUa of Mayer (1910) certainly remains in 
doubt, although the present study validates 
Fewkes’ Willia occidentalis and adds a new 
species, Prohoscidactyla circurnsabella. Foerster 
(1923), in an excellent study of the hydro- 
medusae of the west coast of North America 
and particularly of the Vancouver Island re- 
gion, lists four species of Prohoscidactyla. Of 
these, two are merely cited from the literature 
(P. occidentalis and P. ornata var. stolonifera) , 
but the other two (P. flavicirrata and P. poly- 
nema) concern specimens taken in the Van- 
couver Island area. Foerster reported ocelli on 
the tentacle bulbs of P. flavicirrata; however, 
this statement and that of Uchida and Okuda 
(1941) are the only known instances where 
ocelli have been reported for proboscidac- 
tylans. In each instance, however, the report 
has concerned P. flavicirrata, so ocelli may 
occur in that species although specimens ex- 
