Plakina atka, Lehnert, Helmut, Stone, Robert & Heimler, Wolfgang, 2005

Lehnert, Helmut, Stone, Robert & Heimler, Wolfgang, 2005, Two new species of Plakina Schulze, 1880 (Porifera, Plakinidae) from the Aleutian Islands (Alaska, USA), Zootaxa 1068, pp. 27-38: 32-37

publication ID 10.5281/zenodo.170249

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scientific name

Plakina atka


Plakina atka  n.sp.

Material: holotype: 6220 ­ 3 B­ 1, collected by Dave Carlile south of Atka  Island (51 ° 55`1.4 ``N, 175 ° 17`35.5 ``W) at 118 m depth. The holotype is deposited at the Senckenberg Museum, Frankfurt/Main, Germany under the registration number SMF 10324View Materials.

Description: In life it is a pink to reddish­brown coloured sponge ( Fig. 5View FIGURE 5). The sponge is light brown in ethanol. It is similar in growth form to Plakina tanaga  n. sp. but with a slightly less convoluted surface and a different color. Single strands of the sponge have a smooth surface which is not microtuberculate like Plakina tanaga  n.sp. The material consists of a single specimen encrusting a cobble. Thickness of encrustations is 0.3–0.8 cm. Consistency is more soft than P. tanaga  and elastic. The specimen has an ectosomal dense spicule crust, averaging 100 µm in thickness. The choanosome is somewhat less densely packed with spicules. Spicules are vaguely arranged in tracts of varying orientation and with many spicules in between. Spiculation consists of diods, triods, calthrops and trilophose calthrops. Diods occur in two categories. Thin, smooth diods are typical plakinid diods, slightly bent and thickest in the center. Their dimensions are 70– 108 x 3–6 µm ( Fig. 6View FIGURE 6). The thick, spined category of diods, is possibly derived from the the spined category of triods and measures 82– 95 x 8–10 µm ( Fig. 7View FIGURE 7). Triods also occur in two distinct categories: relatively rare thin, smooth triods (28–33 µm/ray) and, much more abundant, thick, spined triods (23– 40 x 3–6 µm/ray). These have a row of large spines on each ray, close to the center of the spicule. ( Fig. 6View FIGURE 6). Calthrops are rare and were observed with a reduced fourth ray only ( Fig. 8View FIGURE 8). Tetralophose calthrops ( Fig. 9View FIGURE 9) have tetrafurcate, occasionally pentafurcate rays, with microfurcate ends ( Fig. 10View FIGURE 10) and measure 18–23 µm in total length.

Discussion: P. a t k a n.sp., also a member of the trilopha  –species­complex, differs from other Pacific species of Plakina  in the conspicuous convoluted surface, shared only with P. tanaga  n.sp. P. microlobata  and P. pacifica  have dilophose and monolophose calthrops respectively, so conspecifity can be excluded. P. fragilis  , P. bioxea  , and P. tetralophoides  are also members of the trilopha  species­complex and should be discussed further. P. fragilis  differs in color and in being an extremely thin encrustation (0.3 mm). It does not have the conspicuously spined category of triods and is also lacking the tetralophose calthrops of P. a t k a n.sp. P. bioxea  differs in having two categories of diods, the large category much longer than in P. a t k a n.sp. Lophose calthrops occur in P. bioxea  as mono­, di­ and trilophose calthrops, in contrast to only tetralophose calthrops in P. a t k a n.sp. P. tetralophoides  shares the spined triods and tetralophose calthrops of P. a t k a n.sp. and appears to be the most closely related species to P. a t k a n.sp but differs in the species habit. Furthermore, P. a t k a n.sp. has, in addition to the spined triods present in both species, the usual smooth diods and triods. As argued above, P. monolopha sensu Tanita & Hoshino, 1989  is likely to belong to the trilopha  species­complex and therefore should be discussed here. P. monolopha sensu Tanita & Hoshino  differs in growth form, in having trilophose calthrops and in lacking the spined triods of P. a t k a n.sp. Remarkably, both new species described here have both smooth triods and a second category with spines at the base of the rays; a character shared only with P. tetralophoides  . Based on these observations we conclude that P. tetralophoides  is the most closely related species to P. a t k a n.sp, perhaps not surprising since it is the geographically the closest record of another species of Plakina  .

Plakina atka  differs from P. tanaga  in growth form, color, surface structure and spiculation. In the pink colored Plakina atka  single strands of the sponge have a less distinctive outline and are more widely spaced than in the beige colored P. tanaga  (cf Figs. 1View FIGURE 1 & 5View FIGURE 5). P. a t k a is softer than P. tanaga  . The spined spicule categories of P. a t k a are considerably more strongly spined than the ones in P. tanaga  (cf Figs. 3View FIGURE 3, 7View FIGURE 7 & 8View FIGURE 8). The lophocalthrops of P. a t k a is a tetralophose calthrops of roughly half the size (tab. 1) of the trilophose calthrops of P. tanaga  (cf Figs. 4View FIGURE 4 & 9View FIGURE 9).

Distribution: Known only from the type­locality.

Etymology: Named after Atka  Island close to where the holotype was found.


Forschungsinstitut und Natur-Museum Senckenberg