Aphrocallistes vastus Schulze, 1886
Shape and size: A specimen and a small fragment firmly fixed to a Coral has been found. This last one is apparently of similar structure, and probably belong to the same specimen. They represent parts of the lateral wall of a large cup. Instead of the glove-finger-like sacculations which occur in Aphrocallistes beatrix, there is here a simple folding of the wall. Whether the tolerably irregular, bulging folds, which are here and there attached to the Coral branch were directed longitudinally or transversely to the axis of the entire cup could not be certainly determined, though I am inclined to believe that they were longitudinal.
Since the thickness of the cup wall amounts to 5 mm, the mesh spaces, which are about 1 mm. in width, have become canals, which penetrate the wall transversely in a radial direction.
Surface: The dermal membrane, which is still clearly visible in these dried specimens, extends in the form of a delicate skin over the whole outer surface. With a lens one can recognize a fine quadrate lattice-work formed of apposed dermalia. A quadrate lattice-like network of this kind is indeed entirely absent on the inner side of the partially-preserved gastral membrane, which has rather an irregular streaky appearance.
Skeletal elements: A more accurate examination of the dictyonal framework of the septa between the radial six-sided prismatic canals, shows that it consists of a single-layered network, with meshes predominantly three- or four-sided. The beams of the network bear rays directed at right angles or obliquely to the dermal surface, and projecting freely into the lumen of the canals. From an examination of the often very obviously marked axial canals, it may be seen that the rays of adjacent dictyonalia are partly fused in the
familiar longitudinal fashion (somewhat as in Farrea), partly in a more irregular arrangement, crossing one another arbitrarily, or connected at the intersections. Sometimes all the six rays are concerned in the formation of the network, which lies approximately in one plane - an arrangement which is obviously only possible through the great curvature of some rays. Usually, however, one ray is bent at right angles or obliquely inwards, and is provided with a free point, which projects into the canals on either side. Where the margins of three adjacent canals meet one another, the lattice like networks are slightly separated, and an irregular interspace is thus formed.
As in Aphrocallistes beatrix, the dermal marginal pegs of the dictyonal framework stand at right angles to the dermal membrane, while the longer gastral marginal pegs are in part curved inwards. The pegs on the inner surface sometimes project obliquely towards the dermal surface into the lumen of the canals, and are sometimes applied quite close to the surface of the wall, but the free tuberculated end is always directed outwards towards the dermal membrane. The beams of the meshwork often appear almost entirely smooth, while in other cases they are more or less richly beset with small tubercles. The freely projecting pegs all exhibit a rough or tubercled surface.
The dermal skeleton is distinguished by the strong development of the distal fir-tree like ray of the dermal hexacts. This is richly pronged and more bushy than in the other species of the Aphrocallistes. The numerous scopules, which are present in the dermal skeleton, exhibit a shaft which runs to a point beneath, and forks externally into two, more rarely into three branches, after forming a simple expansion or an annular thickening. The branches are rough on their outer extremities, and terminate either in a simple rounded manner, or in a very slight knob-like thickening.
In the gastral membrane, as in Aphrocallistes beatrix, the hexacts are replaced by simple, straight, rough or pronged diacts of variable length, with rounded extremities and central knots; pin-like monacts are also scattered here and there. Whether the scopules, which are entirely absent in the gastral skeleton of Aphrocallistes beatrix, occur in the present instance remains doubtful. It is true that in the dried specimen and on the inner side of the cup-wall scopules occur which, like the dermal, consist of a terminally pointed shaft, and of two, more rarely three knobbed and externally roughened branches, but I am not sure that these are not subsequent extrinsic intrusions.
The uncinates are distinguished by their length and also by the fact that their greatest dilatation usually lies much nearer the dermal than the gastral extremity. This latter appears much more slender, and usually runs out into a smooth point, which is less frequently beset with lateral prongs. It is important to note that the irregularly scattered loose parenchymal hexasters, which are present in large numbers, all bear terminal rays the ends of which are knobbed or provided with small thick transverse discs. The diameter of these discohexasters varies from 0.08 to 0.03 mm. The principal rays remain, as a rule, uniformly short and crowded, but the two rays of one axis are often greatly prolonged in comparison with the others, and it is just in such cases that the latter usually remain simple, while the former become divided into two to four terminal rays.
Synonymised taxa: Aphrocallistes whiteavesianus Lambe, 1892 (junior synonym)
Ecology and Distribution
Canadian Exclusive Economic Zone [Pacific part] (from synonym); Japan
Links and Resources
World Porifera Database : http://www.marinespecies.org/porifera/porifera.php?p=taxdetails&id=171632