Pacific Species of "Lar” ■ — Hand 
59 
In life this medusa is nearly colorless, pig- 
ment being restricted to the tentacle bulbs 
and the wall of the stomach. These areas are 
brown to orange brown. The tentacle bulbs 
appear to develop before pigment is depos- 
ited in them so that the small tentacle bulbs 
are colorless or nearly so. The older tentacle 
bulbs are usually a bright orange-brown color. 
The gonads are very lightly colored, those of 
the males being white and of the females a 
light creamy color. The sexes are separate. 
The nematocysts of adult P. circumsabella 
are as follows: 
Large macrobasic euryteles 17— 26X8— 12/x 
Small macrobasic euryteles 7 — 10X4 — 5iU 
Desmonemes 5 — 7X4 — 6/x 
The large macrobasic euryteles are restricted 
to the cnidothylacies, whereas the small ma- 
crobasic euryteles occur in the tentacles. The 
desmonemes are present in both the tentacles 
and cnidothylacies. The large macrobasic eu- 
ryteles occur in very small numbers, and not 
all cnidothylacies were found to possess them 
(Fig. id-f). 
THE hydroid: The hydroid is similar to 
other species of Prohoscidactyla in that the 
colony possesses two major types of indivi- 
duals, the two-tentacled gastrozooids and the 
gonozooids, which are without tentacles and 
bear the medusa buds. Small gonozooids or 
dactylozooids occur at the margins of the 
hydrorhizal network. The gonozooids occur 
as scattered individuals arising from the hy- 
drorhizae and are never arranged in a row 
immediately behind or on the gastrozooids, 
as in P. flavicirrata or P. stellata. Up to a 
maximum of four medusa buds may be borne 
upon a single gonozooid. The individuals of 
a colony seldom are as much as 1 millimeter 
tall and are commonly about 0.8 millimeter 
tall by about 0.1 millimeter in diameter. The 
hydrorhizal network is devoid of any covering 
and may form extensive anastomosing nets 
running along the tube for as much as 15 
millimeters. 
The nematocysts of the hydroid are as 
follows : 
Macrobasic euryteles 16— 24X9— 12^ 
Large microbasic euryteles 9 — 12X3 — 4/i 
Small microbasic euryteles 5— 6X2— 3 m 
D esmonemes 6— 8X3— 4 m 
The macrobasic euryteles occur only in the 
cap of the gastrozooid and the tip of the 
gonozooid. The other three types of nemato- 
cysts occur in most areas of the gastrozooid 
and gonozooid although no small microbasic 
euryteles were found in the gonozooids. Fig- 
ure ‘be-h illustrates the nematocysts of the 
hydroid. 
THE HOSTS: Prohoscidactyla circumsabella oc- 
curs most commonly on the sabellid Pseudo- 
potamilla ocellata. Careful observation of other 
sabellids, such as Eudistylia polymorpha and 
Sabella media which sometimes occur with 
Pseudopotamilla ocellata, have failed to reveal 
the presence of a single "Lar” on the tubes 
of these other worms. This may be due to the 
fact that these worms commonly grow to a 
considerably larger size than the common 
host and are for this reason an unsuitable 
substrate. Other sabellids, such as Myxicola 
and Eudistylia vancouveri, have tubes whose 
consistency or structure make it impossible 
for this hydroid to live upon them. Of the 
several different sabellids examined from 
Monterey Bay and vicinity only a single ex- 
ample of "Lar” upon any host other than 
Pseudopotamilla ocellata has been found, and 
this was a small colony on the tube of Pseudo- 
potamilla intermedia. This worm had built its 
tube of elongate, rather pointed, sand grains 
and presented a much more irregular sub- 
strate to the hydroid than the tubes of its 
regular host. It appears that Prohoscidactyla 
circumsabella is limited to hosts whose tubes 
do not reach very large sizes, whereas P. 
flavicirrata may be found upon tubes up to 
about 1 centimeter in diameter. The largest 
worm tube upon which P. circumsabella has 
been found was about 4 millimeters in 
diameter. 
