1 
Studies on the Internal Defense Mechanisms of Sponges 
I. The Cell Types Occurring in the Mesoglea of Terpios 
zeteki (de Laubenfels) (Porifera: Demospongiae ) 1 
Thomas C. Cheng, Herbert W. F. Yee, and Erik Rifkin 2 
It is well known that various morphological 
types of free cells occur in the mesoglea of 
sponges. Collectively, these cells are generally 
designated as amoebocytes since they are all 
assumed to be capable of amoeboid movement 
although their functions may vary. According- 
ing to Hyman (1940), in those poriferan 
species in which there are much mesoglea and 
relatively few cells, the mesenchyme, that is, 
the mesoglea together with the cells embedded 
therein, may be referred to as the collenchyma, 
while in those in which there are numerous 
ceils, the mesenchyme may be designated as the 
parenchyma. The mesenchyme of the species 
under consideration may be considered paren- 
chymatous. A search of the literature pertaining 
to the mesenchymal cells of sponges reveals that 
a variety of names have been coined to designate 
the various cell types (Tuzet, 1932; de Lauben- 
fels, 1932; Wilson and Penney, 1930; and 
others). This practice has led to considerable 
confusion for those interested in cell homolo- 
gies and analogies. During our investigation of 
the parenchymal cells of Terpios zeteki (de 
Laubenfels), we have found the designations 
used by Minchin (1900), Galtsoff (1925), 
and Hyman (1940) categorizing the free cells 
as archaeocytes, collencytes, chromocytes, theso- 
cytes, and scleroblasts, to be the most useful. 
Therefore, we have used these names for the 
cells encountered in T. zeteki. 
Our interest in poriferan collenchymal or 
parenchymal cells stems from inquiries into the 
types of internal defense mechanisms occurring 
in sponges, whether in response to abiotic for- 
1 This study was supported in part by a grant 
from the American Cancer Society and in part by a 
grant (Contract 14-17-007-662G) from the Bureau 
of Commercial Fisheries, U. S. Department of the 
Interior. Manuscript received July 7, 1967. 
2 Laboratory of Symbiology, Department of Zool- 
ogy, University of Hawaii, Honolulu, Hawaii 96822. 
eign particles or to microsymbionts, including 
parasites. Although studies of this nature, par- 
ticularly the various aspects of cellular defense 
mechanisms (leucocytosis, phagocytosis, pino- 
cytosis, and encapsulation) have been examined 
extensively among the higher coelomate inver- 
tebrates, especially the Mollusca and Arthro- 
poda, very few comparable studies have been 
carried out among the Porifera. In this paper 
are described the various types of free amoebo- 
cytes normally found in the parenchyma of 
T. zeteki, and the ratio of each type of cell 
present is reported. 
We are grateful to Dr. Sidney J. Townsley 
for identifying the sponge used in this study. 
. MATERIALS AND METHODS 
Terpios zeteki is one of the two or three 
most abundant species of sponges in Hawaii 
(de Laubenfels, 1950). Specimens collected 
from pilings at Ala Wai Yacht Harbor, Hono- 
lulu, were brought into the laboratory and main- 
tained in aerated filtered sea water with a salin- 
ity of 35 % 0 at 20 °C. The parenchymal cells 
were examined by two methods: in histological 
sections, and in smears of living tissues. 
Histological sections of T. zeteki were pre- 
pared by fixing segments of whole sponges, 
each approximately 10 cm in length, for 12 
hours in 10% neutral formalin. These were 
subsequently dehydrated via a closely graded 
ethanol series, cleared in xylene, and embedded 
in high temperature paraffin (melting point 
56°C) . The sections were cut at lOp and stained 
with Harris’ hematoxylin and counters tained 
with eosin. After the morphological characteris- 
tics of each type of cell found in the mesoglea 
were determined, comparable cells were sought 
in smear preparations of small pieces of living 
sponges, each piece measuring approximately 
0.5 cm 3 . Examinations of living dissociated 
395 
