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

13. Acanthascus (Rhabdocalyptus) dawsoni dawsoni (Lambe, 1893)
Description. Soft straight or curved tube or barrellike
sac, occasionally partially divided into two or three
conjoined tubes, is attached basally to hard substrate.
Surface is smooth but usually bearing a 1-cm tall veil of
pentactins and diactins which may be clean but usually
covered with small epizoans and sediment; large single
terminal osculum has marginal fringe. Consistency is
soft and compressible. Height is to 1 m and diameter to
30 cm. Color in life is white but often coated with sediment,
epizoic organisms, and flocculent material, giving
it a brown to greenish brown appearance.
Skeletal structure. Skeleton is composed entirely of
loose spicules. Megascleres are thick prostal diactins to
6 cm long; hypodermal pentactins with some smooth
and some thorned tangential rays (0.9–4.1 mm long)
and smooth proximal rays (0.9–4.1 mm long); principal
diactins (4.2–11.4 mm long); thin short diactins
(0.35–1.62 mm long); dermal stauractins (50–101 mm
ray length), dermal pentactins with tangential rays
(54–99 mm long) and proximal rays (44–100 mm long);
atrial hexactins (55–177 mm ray length). Microscleres
are oxyhemihexasters (48–104 mm in diameter); small
discoctasters with straight terminals (56–82 mm in diameter);
microdiscohexasters (17–28 mm in diameter).
Zoogeographic distribution. Locally common and
abundant. In Alaska – eastern Gulf of Alaska. Elsewhere
– British Columbia to southern California.
Habitat. In Alaska – attached to bedrock, cobbles, and
pebbles at depths between 82 and 255 m. Elsewhere
– attached to bedrock, cobbles, and pebbles on flat,
inclined, or vertical surfaces (e.g., fjord walls), and following
detachment may survive loose as roller sponges
(Reiswig, unpubl. data, 2010) at depths between 10 and
437 m.
Remarks. The species presently contains three subspecies:
A. (R.) d. dawsoni (reviewed here); A. (R.) d. alascensis
Wilson and Penney, 1930 (known only from Cape
Spencer, Gulf of Alaska); and A. (R.) d. horridus Koltun,
1967 (from the Bering Sea). A. (R.) d. dawsoni can be
distinguished from A. solidus by the presence of at least
some heavily thorned hypodermal pentactins; the latter
species possesses only smooth hypodermal pentactins.
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A. (R.) d. dawsoni is similar in appearance to A. mirabilis
but likely differs in depth distribution and can be
distinguished by its much smaller discoctasters (56–82
vs. 144–180 µm diameter). We have observed a very
similar species in the central Aleutian Islands at depths
between about 400 and 1238 m attached to cobbles and
hexactinellid skeletons. This species is preyed upon by
the sea star Poraniopsis inflata and possibly by the sea star
Henricia longispina in the eastern Gulf of Alaska.
Photos. 1) Whole specimen collected at a depth of
168 m in the eastern Gulf of Alaska. Grid marks are 1
cm 2 . 2) Specimen (indicated by the white arrow) at a
depth of 165 m in the eastern Gulf of Alaska.