A guide to the deep-water sponges of - NMFS Scientific Publications ...

31. Polymastia fluegeli Lehnert, Stone and Heimler, 2005
Description. This sponge is endopsammic and discshaped
with numerous fistules on the upper surface.
The surface is smooth with long protruding spicules
scattered about. The cortical layer is cartilaginous and
more resilient than the relatively soft choanosome. The
bottom side of the sponge is very firm and slightly elastic
and consists of a layer of spongin-cemented sediment.
In situ the plate is buried in the sediment; only the
fistules protrude. The fistules are cone-shaped with no
obvious opening. The disc is up to 52 cm in diameter
and about 1 cm in thickness (3–4 mm of the thickness
is due to the basal sediment layer). Color in life is light
yellow with bright yellow fistules; disc is light brown
after freezing.
Skeletal structure. SEM images of spicules are shown
in Appendix IV. Polyspicular tracts arise from the basal
sediment layer then widen, branch towards the surface,
and fan out in the cortical layer. Polyspicular tracts are
350–500 µm in diameter. The cortical layer is 500–700
µm in thickness and, except for the ends of the ascending
polyspicular tracts, consists of a mass of spicules
without orientation. The outermost layer is a palisade
of small tylostyles, oriented outward creating the microscopically
hispid surface. The papillae also show the
outermost palisade and the unorganized spicule mass
below, but differ insofar as the polyspicular tracts run to
the tip of the papillum. A central canal is visible in the
center of the papillae but there is no opening visible.
There are large fusiform tylostyles, in a wide size-range,
longest ones often with one or several subterminal
rings (180–1750 × 8–22 µm), and a small category of
tylostyles (65–110 × 3–6 µm).
Zoogeographic distribution. Locally common. In
Alaska – central Aleutian Islands. Elsewhere – not reported.
Habitat. Patchily distributed at depths between 81 and
338 m in generally low-relief (i.e., flat-bottomed) habitats
of small pebbles and coarse sand with moderate to
high current. Found at maximum densities up to eight
individuals per m 2 in coarse sand habitats at 82 m depth.
Photos. 1) Specimen collected at a depth of 82 m in
the central Aleutian Islands. Grid marks are 1 cm 2 . 2)
Same specimen as in photo 1 in situ during collection.
3) Specimen observed at a depth of 142 m in the central
Aleutian Islands. A prowfish (Zapora silenus) lies in a den
just below the specimen.
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