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

28 Professional Paper NMFS 12
14. Acanthascus (Rhabdocalyptus) mirabilis (Schulze, 1899)
Description. This species was known previously only
from the holotype, which was the distal portion (about
1/3 of total specimen) of a soft saccate sponge. Surface
is overtly smooth but evenly covered with small
conic protuberances and bears a veil of pentactins and
diactins; large single terminal osculum with marginal
fringe. Consistency is soft and compressible. From the
holotype fragment, the original specimen was thought
to be ca. 30 cm in length and 15 cm in diameter with a
1-cm thick wall; a new Aleutian specimen is 15.5 cm in
length and 10.1 cm in diameter. Color in life is white;
light brown when preserved in ethanol.
Skeletal structure. Skeleton is composed entirely of
loose spicules. Megascleres are thick prostal diactins to
2 cm long; hypodermal pentactins with mostly thorned
paratropal tangential rays to 1 cm long; principal diactins
(11.7–21.0 mm long); dermal diactins (plus a few
stauractins and hexactins) (204–462 mm long); atrial
hexactins (free ray 249–447 µm long, tangentials and
parenchymal rays 153–316 mm long). Microscleres are
oxyhexactins and a few oxyhexasters and hemioxyhexasters
(72–232 mm in diameter with 33–87 mm long
terminal rays); discoctasters (144–180 mm in diameter)
with very short primary rays (20–28 mm long),
each bearing 8–12 straight or s-curved, divergent terminal
rays; microdiscohexasters mainly near or in the
dermal surface (21–40 mm in diameter).
Zoogeographic distribution. Rare. Known only from
Alaska – central Aleutian Islands and Gulf of Alaska.
Elsewhere – not reported.
Habitat. Central Aleutian Islands – occurs singly on
bedrock at depths between 1984 and 2790 m. Southern
Alaska – attached to cobbles at depths near 1143 m.
Remarks. Our specimen recently collected in the
Aleutian Islands is only the second known verified
specimen of this species. It is very likely that A. (R.)
unguiculatus Ijima, 1904 is a junior synonym of A. (R.)
mirabilis. This species is similar in appearance to A.
dawsoni but likely differs in depth distribution and
can be distinguished by its much larger discoctasters
(144–180 vs 56–82 µm diameter).
Photos. 1) Fragment of preserved (frozen) specimen
collected at a depth of 2311 m in the central Aleutian
Islands. Grid marks are 1 cm 2 . 2) Same specimen as in
photo 1 in situ. The separation between the red laser
marks is 10 cm.