192 
PACIFIC SCIENCE, Vol. XIX, April 1965 
FlG. 31*. Ancorina acervus (Bowerbank). Sta. 
220A. 
granular; in places it is coarsely hispid and is 
microhispid over-all Oscules are small, concen- 
trated in dorsal or lateral oscular areas which 
measure up to 1.8 X 1.0 cm. Individual oscules 
are circular or oval, ranging from 0.4-2 .0 mm 
in maximum dimensions. In specimen 798 from 
Ifaluk, skeletal pores approximately 0.1 mm in 
diameter are visible over most of the surface. 
skeleton: The endosomal skeleton is made 
up of radially disposed oxeas which vary greatly 
in size and abundance; near the surface oxeas 
give way to small orthotriaenes with rare pro- 
triaenes, anatriaenes, and large orthotriaenes in 
that order. Between the cladomes of the surface 
orthotriaenes is a layer of radially disposed small 
oxeas. The most abundant microscleres are 
microspined microrhabds and these are aggre- 
gated at the surface to form a dense crust. The 
sponge is weakly corticate. The cortex is the 
region containing the clads of the triaenes and 
the radial oxeas, a densely spiculiferous zone 
containing some collenchymatous tissue; it is 
clearly separate from the endosome in the 
deeper region of which fleshy tissues predomi- 
nate over skeletal elements. 
Apart from the microrhabds which occur 
abundantly throughout the sponge, the distri- 
bution, relative abundance, and form of micro- 
scleres is extremely variable. 
In the holotype of Hezekia walkeri (usnm 
22925) and the two specimens from the Pa- 
laus, anthasters occur in tracts deep in the endo- 
some; these spicules are very sporadically dis- 
tributed and only fortuitously seen in sections. 
Fine tylasters also occur, chiefly in the endo- 
some lining large canals, but they are occasion- 
ally present in superficial spicule preparations. 
In all of the Ifaluk specimens anthasters are 
lacking, and tylasters with long, fine rays and 
small tylospherasters are the endosomal micro- 
scleres. In addition the microrhabds of these 
specimens are thinner and more finely spined 
than those of the Palau group. The specimens 
having anthasters can be compared with Stel- 
letta tmncata Kieschick (1898), those with 
tylospherasters approach very . closely to Ecio- 
nemia acervus Bowerbank. Burton (1937) has 
produced evidence for the view that these two 
types are extremes in a single variable species. 
SPICULES: Megascleres (Table 15). These 
spicules are essentially the same as described by 
all earlier authors, the only variability being in 
the presence or absence of protriaenes (present 
but rare in all specimens from the Palaus) and 
in the length of the cladi of the anatriaenes, 
which are somewhat longer in the Palau speci- 
mens than in the Ifaluk group. 
Microscleres. Three types are present in each 
sponge: (a) spined microrhabds, which are 
uniformly abundant, varying slightly in diame- 
ter and degree of spining; they are thicker and 
have more pronounced spination in the Palau 
specimens; (b) tylasters, with extremely fine 
rays usually 5-8 in number; in the Palau speci- 
mens forms of these spicules occur which grade ] 
toward a chiaster by thickening of the rays and 
even toward an anthaster by these rays becom- | 
ing rugose; (c) large anthasters, found only in I 
the Palau specimens, and ranging from two- to 
eight-rayed forms, the triact being particularly 
common; (d) tylospherasters found only in the j 
Ifaluk sponges, extremely tiny spicules, 4-6/x ! 
in diameter, with a pronounced centrum and 
up to 16 short rays. In this whole complex of ( 
sponges asterose microscleres are relatively rare l 
