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

23. Plakina tanaga Lehnert, Stone and Heimler, 2005
Description. Sponge is encrusting. Convoluted surface
has deep grooves between strands with a microtuberculated
surface. Consistency is cheese-like. Circular
oscula flush with the surface are visible in situ. This
sponge may cover large areas (up to 1 m 2 ) with a thickness
of approximately 1 to 1.5 cm. Color in life is beige
to light brown.
Skeletal structure. SEM images of spicules are shown
in Appendix IV. The ectosome is packed with lophocalthrops
with a layer 20–250 µm thick. Spicules are
characteristically bent diods, often centrotylote or with
a reduced third ray in the form of a spine (85–97 ×
2–4 µm); two categories of triaxons, smooth, thinner
triods (24–50 × 2–5 µm/ray) and thicker triods, often
with one short, slender spine near the base of each ray
(22–38 × 7–9 µm). Rare smooth calthrops have rays of
the same dimensions as those of the triods. There are
abundant trilophose calthrops with each ray tetrafurcate
and, again microfurcate at the points, somewhat smaller
than the triods and concentrated in the ectosome. Total
length of lophocalthrops is 28–42 µm. Non-lophose rays
are sometimes bifurcate.
Zoogeographic distribution. Uncommon. In Alaska –
known only from the type locality in Little Tanaga Strait,
central Aleutian Islands. Elsewhere – not reported.
Habitat. Encrusts vertical and overhanging surfaces of
bedrock and boulders at depths between 140 and 383 m.
May cover relatively large areas (up to 1 m 2 ).
39
Remarks. Plakina tanaga can be distinguished from
the similar P. atka by its strongly convoluted and microtuberculated
surface compared to the relatively smooth
surface of the latter species, and by the presence of trilophose
lophocalthrops compared to the tetralophate
lophocalthrops of P. atka.
Photo. 1) P. tanaga encrusting a bedrock scarp at a
depth of 146 m in the central Aleutian Islands.