A guide to the deep-water sponges of - NMFS Scientific Publications ...
A guide to the deep-water sponges of - NMFS Scientific Publications ...
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38 Pr<strong>of</strong>essional Paper <strong>NMFS</strong> 12<br />
22. Plakina atka Lehnert, S<strong>to</strong>ne and Heimler, 2005<br />
Description. Sponge is encrusting. Surface is convoluted<br />
but less distinctively so than Plakina tanaga. Single<br />
strands have a smooth surface, not microtuberculate.<br />
This sponge may cover large areas (up <strong>to</strong> 30 cm 2 ) with<br />
a thickness <strong>of</strong> approximately 0.3 <strong>to</strong> 0.8 cm. The ec<strong>to</strong>some<br />
is reddish brown (Aleutian Islands), beige, or light<br />
brown (eastern Gulf <strong>of</strong> Alaska).<br />
Skeletal structure. SEM images <strong>of</strong> spicules are shown<br />
in Appendix IV. Ec<strong>to</strong>somal dense spicule crust averages<br />
100 µm in thickness. Choanosome is somewhat<br />
less densely packed with spicules, roughly arranged in<br />
tracts <strong>of</strong> varying orientation and with many spicules in<br />
between. Characteristic plakinid oxeas are slightly bent<br />
and thickest in <strong>the</strong> center (70–108 × 3–6 µm). A thicker<br />
category <strong>of</strong> diods, always with relatively long spines at<br />
<strong>the</strong> center, is probably derived from <strong>the</strong> spined category<br />
<strong>of</strong> triods (82–95 × 8–10 µm). Triods also occur in two<br />
distinct types: relatively rare simple triaxons (28–33 µm/<br />
ray) and much more abundant, robust triaxons with a<br />
row <strong>of</strong> large spines on each ray close <strong>to</strong> <strong>the</strong> center <strong>of</strong> <strong>the</strong><br />
spicule (23–40 × 3–6 µm/ray). Calthrops are rare and<br />
have a reduced fourth ray only. Tetralophose calthrops<br />
have tetrafurcate, occasionally pentafurcate rays, with<br />
micr<strong>of</strong>urcate ends (18–23 µm in <strong>to</strong>tal length).<br />
Zoogeographic distribution. Locally abundant. In<br />
Alaska – central Aleutian Islands, eastern Gulf <strong>of</strong> Alaska<br />
(continental shelf <strong>of</strong>f Cape Ommaney, Baran<strong>of</strong> Island),<br />
and sou<strong>the</strong>rn Sou<strong>the</strong>ast Alaska (Portland Canal). Elsewhere<br />
– nor<strong>the</strong>rn British Columbia (Portland Canal).<br />
Habitat. Encrusts bedrock, boulders, cobbles, pebbles,<br />
and hexactinellid skele<strong>to</strong>ns at depths between 82–180 m<br />
(Aleutian Islands) and 95–253 m in <strong>the</strong> eastern Gulf <strong>of</strong><br />
Alaska. May cover relatively large areas (up <strong>to</strong> 30 cm 2 ).<br />
Remarks. Plakina atka can be distinguished from<br />
<strong>the</strong> similar P. tanaga by its relatively smooth surface<br />
compared <strong>to</strong> <strong>the</strong> strongly convoluted and microtuberculated<br />
surface <strong>of</strong> <strong>the</strong> latter species, and by <strong>the</strong> presence<br />
<strong>of</strong> tetralophate lophocalthrops compared <strong>to</strong> <strong>the</strong><br />
trilophose lophocalthrops <strong>of</strong> P. tanaga.<br />
Pho<strong>to</strong>s. 1) Specimen collected at a depth <strong>of</strong> 118 m in<br />
<strong>the</strong> central Alautian Islands. Grid marks are 1 cm 2 . 2)<br />
Specimen collected at a depth <strong>of</strong> 167 m in <strong>the</strong> eastern<br />
Gulf <strong>of</strong> Alaska. 3) Specimen at a depth <strong>of</strong> 118 m in <strong>the</strong><br />
central Aleutian Islands.