Sponges of Palau, I — BERGQUIST 
Fig. 32. Stelletta durissima n. sp. Sta. 64. Holotype. 
USNM 23704. Spicules: 1, Oxeas. 2, Plagiotriaenes. 
3, Anatriaenes. 4, Tylasters. 
Microscleres are distributed sporadically 
throughout the sponge and are frequent lining 
the subcortical channels. 
spicules: Megascleres. (a) Plagiotriaenes, 
often tending toward orthotriaenes, with stout 
shaft tapering abruptly in the posterior third 
to a stylote or oxeote termination. Many of the 
larger triaenes are incipient dichotriaenes; the 
bifurcation of the axial canals in the clads often 
can be seen, but dichotriaenes are rarely formed. 
The tips of the clads are often reflexed at an 
acute angle to the shaft. 
Smaller triaenes often have irregular clad- 
omes; four-branched forms are common and 
occasionally one or two abbreviated clads pro- 
ject from the shaft below the actual head of the 
spicule. Frequently the angle between clads is 
unequal, giving the cladome a two-dimensional 
appearance. 
195 
(b) Anatriaenes with strongly recurved and 
exceedingly stout clads. These spicules rarely 
have perfect form; the cladome can be slightly 
subterminal, with the shaft projecting as a nub- 
bin beyond the point from which individual 
clads diverge, or both the angle between clads 
and the curvature of the rays may vary greatly 
on a given spicule. 
( c ) Oxeas, which are frequently strongyloxe- 
ote; these spicules make up the entire endoso- 
mal skeleton. 
(d) Fine, spindle-shaped cortical oxeas, not 
sufficiently abundant to form a distinct layer. 
Microscleres. Tylasters, with 5-10 long fine 
rays. 
DIMENSIONS : Plagiotriaenes : 5 00- ( 8 3 5 ) - 
1398 X 19- ( 38) -70/*; cladome: 60-487g. An- 
atrianes: 787- ( 1134)— 1375 X 23- ( 32 ) -37/*;. 
cladome: 125-150/*. Oxeas: 587- ( 1009) -1460 
X 16- (32) -50/*. Cortical oxeas: 200-(223)- 
240 X 2- (2.8) -4 /*. Tylasters: 8- (9.7) -10.5/*. 
HISTOLOGY: The cortex is a distinct layer, 
125—17 5/x deep, composed of a dense collen- 
chymatous matrix in which spindle-shaped cells 
are relatively abundant. The inner boundary of 
this layer is marked by a zone of cells with 
coarsely granular cytoplasm; these line the roof 
of subcortical channels but are also dispersed 
between and below them. The fleshy tissue of 
the endosome is granular. 
DISCUSSION: Stelletta durissima is closest in 
spiculation and morphology to Stelletta clavosa 
Ridley and particularly to S. ( Myriastra ) cla- 
vosa var. quadrata Sollas, which has similar 
anatriaenes. 
The chief differences are that S. durissima 
has incomplete, malformed dichotriaenes where 
S. clavosa has normal dichotriaenes as the sur- 
face spicules; plagiotriaenes are present in S. 
durissima and absent from S. clavosa; anatri- 
aenes are often irregular in form in S. durissima 
and all megascleres are substantially shorter and 
stouter in this species than in S. clavosa. The 
single, circular, depressed osculum described for 
S. clavosa by all authors has not been observed 
in S. durissima. The latter is further distin- 
guished by the presence of a double layer of 
triaenes. 
The decision taken by Dendy ( 1905 ) and 
de Laubenfels (1936) to separate Stelletta 
