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

38 Professional Paper NMFS 12
22. Plakina atka Lehnert, Stone and Heimler, 2005
Description. Sponge is encrusting. Surface is convoluted
but less distinctively so than Plakina tanaga. Single
strands have a smooth surface, not microtuberculate.
This sponge may cover large areas (up to 30 cm 2 ) with
a thickness of approximately 0.3 to 0.8 cm. The ectosome
is reddish brown (Aleutian Islands), beige, or light
brown (eastern Gulf of Alaska).
Skeletal structure. SEM images of spicules are shown
in Appendix IV. Ectosomal dense spicule crust averages
100 µm in thickness. Choanosome is somewhat
less densely packed with spicules, roughly arranged in
tracts of varying orientation and with many spicules in
between. Characteristic plakinid oxeas are slightly bent
and thickest in the center (70–108 × 3–6 µm). A thicker
category of diods, always with relatively long spines at
the center, is probably derived from the spined category
of triods (82–95 × 8–10 µm). Triods also occur in two
distinct types: relatively rare simple triaxons (28–33 µm/
ray) and much more abundant, robust triaxons with a
row of large spines on each ray close to the center of the
spicule (23–40 × 3–6 µm/ray). Calthrops are rare and
have a reduced fourth ray only. Tetralophose calthrops
have tetrafurcate, occasionally pentafurcate rays, with
microfurcate ends (18–23 µm in total length).
Zoogeographic distribution. Locally abundant. In
Alaska – central Aleutian Islands, eastern Gulf of Alaska
(continental shelf off Cape Ommaney, Baranof Island),
and southern Southeast Alaska (Portland Canal). Elsewhere
– northern British Columbia (Portland Canal).
Habitat. Encrusts bedrock, boulders, cobbles, pebbles,
and hexactinellid skeletons at depths between 82–180 m
(Aleutian Islands) and 95–253 m in the eastern Gulf of
Alaska. May cover relatively large areas (up to 30 cm 2 ).
Remarks. Plakina atka can be distinguished from
the similar P. tanaga by its relatively smooth surface
compared to the strongly convoluted and microtuberculated
surface of the latter species, and by the presence
of tetralophate lophocalthrops compared to the
trilophose lophocalthrops of P. tanaga.
Photos. 1) Specimen collected at a depth of 118 m in
the central Alautian Islands. Grid marks are 1 cm 2 . 2)
Specimen collected at a depth of 167 m in the eastern
Gulf of Alaska. 3) Specimen at a depth of 118 m in the
central Aleutian Islands.