350 
PACIFIC SCIENCE, VoL XVIII, July 1964 
As mentioned by Abbott (1907:47) . . 
measurements of Coeloplana are not of much 
value in an animal of such great mobility. When 
fully contracted the shape of the body ... is 
nearly circular. C. willeyi, in such conditions 
usually measures 1-2 cm. across. . . .” Komai 
( 1922:93 ) gives the range of the Misake repre- 
sentatives of this species as ". . . 20-60 mm. 
(in extended state).” The range of the Hawai- 
ian representatives is from 2 mm (contracted) 
to 32 mm (relaxed). 
Besides the well-developed tentacular appa- 
ratus, which may extend colorless, cydippid-like 
tentacles to many times the body diameter, 
numerous dorsal tentacles (papillae) are pres- 
ent. Komai (1922:9) gives the number of these 
dorsal papillae as commonly 20-30. Yet, these 
minute, club-shaped outgrowths of the gastro- 
vascular canals are not well developed in Ha- 
waiian representatives of this species for, as 
stated by Abbott (1907:48), "The body tissue 
of C. willeyi is so loose and the animal itself so 
'amoeboid’ in its movements that it is impossible 
to tell, in the living specimen, just what ar- 
rangement these dorsal tentacles have. . . 
They tend to disappear when the animal relaxes, 
and reappear, especially when contraction is 
along the tentacular axis. In such instances, two 
poorly defined sagittal "rows” appear, but it is 
difficult to determine which papillae are derived 
from paratentacular canals and which are de- 
rived from parastomacal canals. While dorsal 
papillae may be arranged on one side of the 
tentacular axis in a 2— 4-4-2 series, the other 
side may be arranged in a 2-3-4— 1 series. In 
other specimens only the 2-3 series is present 
on one side, while on the opposite side, a 2-3- 
5-1 series is present. Of the many specimens 
observed, not one exhibited a symmetrical ar- 
rangement of dorsal papillae. Their total number 
ranged from 18-24. Variations in size, number, 
and arrangement of dorsal papillae are not re- 
stricted to C. willeyi. Dawydoff (1938:160) 
says of C. perrieri: 
Close examination shows that the apparatus 
in question is based, in our species, on the most 
diffuse scheme in the Coeloplanidae, that is to 
say, that the aboral papillae are arranged in four 
irregular rows (each one containing 4 or 5 
papillae) so that the paratentacular papillae can- 
not be distinguished externally from the para- 
stomacal papillae. Moreover, in each row, the 
papillae have lost their usual alignment and 
generally show an embarrassing disorder to the 
observer. [Authors’ translation.] 
The aboral sense organ is clearly discernible 
as a small, unpigmented area in the center of the 
tentacular axis. Although Abbott (1907:47) 
states that the comparatively small otolith of 
living C. willeyi is frequently difficult to find, in 
Hawaiian representatives the pit in which it lies 
is closed by fleshy lips only when this region of 
the organism contracts. When this region re- 
laxes, the otolithic mass is clearly seen and dis- 
plays the usual, constant vibrating motion. The 
internal (concave) and external (convex) sur- 
faces of the two slightly elevated semicircular 
polar plates are devoid of digitiform papillae, 
thus conforming to Komai’s (1922:14) state- 
ment that in C. willeyi lobation of polar plates 
does not occur. Rudimentary ciliary bands are 
present, but beating cilia are seen only on polar 
plates and oral surface. 
As previously reported for C. duhosequii 
(Matthews, 1954:284), prominent excretory 
pores are located just outside the border of each 
polar plate. These pores appear and disappear as 
the gastrovascular system relaxes and contracts. 
In C. willeyi the region beneath an excretory 
pore forms a large temporary reservoir which, 
as it fills, protrudes as a light thin-walled hemi- 
sphere equal in size to the dorsal sense organ. 
The excretory "pore” is thus carried aloft and, as 
it opens, expulsion of materials quickly obliter- 
ates the reservoir. These "reservoirs” fill and 
empty neither simultaneously nor alternately; 
but, rather, one may function many times before 
the other becomes operative. 
Both living and stained (with acidulated 
borax-carmine and indulin) specimens show no 
trace of gonadal development, despite the fact 
that their size suggests sexual maturity. This, 
however, strengthens Komai’s (1922:32) con- 
tention that . . besides some negligible ex- 
ceptions, the breeding season of Coeloplana may 
be said to extend from early summer to early 
fall, the gonads developing in the main during 
summer months and the spawning taking place 
generally in late summer or in early autumn.” 
The fact that three urchins are now known to 
serve as hosts for platyctenids ( C . echinicola 
