Plicatellopsis borealis Lehnert & Stone 2017, n. sp.

Plicatellopsis borealis n. sp.

(Figs. 2 & 3; Table 1)

Material examined: Holotype ZSM 20170015, whole specimen in ethanol, 28 June 2013, 102 m depth, 110.2 km E of Tolstoi Pt., St. George Island, Pribilof Islands, eastern Bering Sea (56°39.510´N, 167°40.338´W). Bottom water temperature = 1.0 °C. Paratypes ZSM 20170016, same collection data as holotype; ZSM 20170017, whole specimen dry (sample in ethanol), 28 June 2015, 80 m depth, 111 km NE of St. Paul Island, Pribilof Islands, eastern Bering Sea (57°00.828´N, 168°20.220´W). Bottom water temperature = 3.7 °C. ZSM 201700178, whole specimen dry (sample in ethanol), 15 July 2013, 117 m depth, 99.3 km WSW of Southwest Pt., St. Paul Island, Pribilof Islands, eastern Bering Sea (57°00.470´N, 172°02.112´W). Bottom water temperature = 3.6 °C. ZSM 20170019 whole specimen dry (sample in ethanol), 28 June 2015, 76 m depth, 91 km E of Polovina Pt., St. Paul Island, Pribilof Islands, eastern Bering Sea (57°10.806´N, 168°38.580´W). Bottom water temperature = 3.9 °C.

Other material examined ZSM 20170020 and ZSM 20170021, whole specimens dry (samples in ethanol), 2 July 2014, 66 m depth, 159 km NE of Northeast Pt., St. Paul Island, Pribilof Islands, eastern Bering Sea (58°00.852´N, 167°49.134´W). Bottom water temperature = -0.4 °C. ZSM 20170022 (4 bases coalesced into one funnel), whole specimen in ethanol, 28 June 2013, 102 m depth, 110.2 km E of Tolstoi Pt., St. George Island, Pribilof Islands, eastern Bering Sea (56°39.510´N, 167°40.338´W). Bottom water temperature = 1.0 °C. ZSM 20170023, whole specimen dry (sample in ethanol), 28 June 2013, 102 m depth, 110 km E of Tolstoi Pt., St. George Island, Pribilof Islands, eastern Bering Sea (56°39.510´N, 167°40.338´W). Bottom water temperature = 1.0 °C. ZSM 20170024, whole specimen dry (sample in ethanol), 27 June 2015, 66 m depth, 78 km NE of St. Paul Island, Pribilof Islands, eastern Bering Sea (57°49.812´N, 169°21.300´W). Bottom water temperature = 3.6 °C. ZSM 20170025 (2 specimens), whole specimen dry (sample in ethanol), 8 June 2015, 66 m depth, 211 km N of Cape Krenitzin (Alaska Peninsula), eastern Bering Sea (56°59.226´N, 163°23.220´W). Bottom water temperature = 4.0 °C. ZSM 20170030, whole specimen dry (sample in ethanol), 13 July 2015, 112 m depth, 224 km NW of St. Paul Island, Pribilof Islands, eastern Bering Sea (58°39.912´N, 173°00.540´W). Bottom water temperature = 2.4 °C.

Specimens collected. All specimens were collected by Jerry Hoff, Bob Lauth, Dan Nichol, and Dave Somerton with a research survey bottom trawl from the FV Alaska Knight and FV Vesteraalen.

Description. The species is polymorphic and also grows on very different substrates. Three specimens were found growing on the carapaces of live crabs; two of the specimens were found on the same crab. The larger specimen is designated as the holotype (ZSM 20170015, Fig. 2A, left) and the smaller specimen designated as one of four paratypes (ZSM 20170015, Fig. 2A, right). The holotype is attached to the crab carapace by two stalks which start at the shell with diameters of 0.6 and 0.8 cm respectively. The stalk gradually broadens, converges at a height of 2.5 cm and then forms one single funnel with undulating walls 0.3–0.7 cm thick, The largest diameter of the specimen is 4.7 cm, maximum height of the specimen is 9.2 cm. Small circular oscules are about 1 mm in diameter and flush with the surface. The consistency is relatively soft and moderately elastic, breaking when bent under pressure. The sponge is crumbly in the dry state. The smaller specimen (paratype, ZSM 20170016), growing on the same crab as the holotype also starts from two bases, 4 mm and 6 mm in diameter. The two stalks meet at a height of 1.1 cm and grow into two broadening bodies agglutinated in the middle but not forming a single funnel. The larger body reaches a height of 5.9 cm and a diameter of 2.7 cm at the top and is closed at the top. The smaller body is 4.2 cm in height, 1.5 cm in diameter and has an apical osculum 0.9 cm in diameter (Fig. 2A, right). The third specimen also growing on a crab carapace (ZSM 20170022) has a single funnel with a maximum height of 9.6 cm and supported by four separate stalks. In paratype, ZSM 20170017 (Fig. 2B) the stalk starts from a bulbous base, 1.5 x 2.3 cm with several root-like processes, 1–1.5 mm in diameter and up to 1.2 cm long (some look broken so longer roots are likely to occur). The wiry stalk has a diameter of 0.5–0.7 cm and splits at a height of 4.8 cm into three branches each producing a triangular plate or blade. The triangular blades are of three different sizes; the smallest 7.2 cm in height, gradually widening from the stalk to a width of 7.2 cm at the top. The largest blade reaches a height of 11.2 cm and is broken at the sides so we cannot give an exact width. The thickness of all blades is rather uniform between 4 and 7 mm. In the dry state the consistency of all specimens is hard, inelastic and crumbly. The largest specimen (paratype ZSM 20170018, Fig. 2C) is massively encrusting, covering an area of 40 x 25 x 1–4 cm. It has no obvious stalks on the basal side, although they may have been removed upon collection with the trawl. The very uneven, undulating surface and the varying thickness of the specimen might be the result of several agglutinated specimens. Paratype ZSM 20170019 is a funnelled specimen (Fig. 2D) originating from a basal plate (4.2 x 2.7 x 0.3 cm) attached to the substrate, and from there gradually widens from a diameter of 1.6 cm, branching near the base into two large funnels, 16–18 cm in diameter and a height of 21–23 cm, thickness of the walls 0.7–1.2 cm with the largest diameter on the upper rim, walls are undulating near the upper end. The surface is irregularly scattered with circular apertures, flush with the surface and approximately 1 mm in diameter. These specimens demonstrate the variability of growth forms in this species.

Skeletal architecture: The choanosomal skeleton consists, as pictured by Burton, 1932 for the type species P. arborescens and P. flabellata, of polyspicular tracts running longitudinally through the center of the plates (Fig. 3A, right). Exactly like the definition of the genus, given by Van Soest (2002, p. 232), this axially condensed skeleton of tylostyles supports an extra-axial skeleton of spicule tracts from the central axis to the surface. These extra-axial tracts diverge obliquely to the surface (Fig. 3A, left), fanning out at the surface to form brushes (Fig. 3B). The surface skeleton consists, again as requested by the definition of the genus of Van Soest, 2002, of “a dense palisade of smaller spicules”. Due to the high spicule density the consistency of the stalk is wiry. Here polyspicular tracts with diameters of 70–110 µm run longitudinally through the stalk, in between the tracts are many spicules without recognizable orientation. Spaces between tracts vary between 160–350 µm. In addition, there is a smaller category of spicules forming a palisade at the surface (Fig. 3A, dark area on the left, Fig. 3B, darker area on the right).

Megascleres. Spicules are fusiform subtylostyles (Fig. 3C), often almost looking like styles, sometimes with a subterminal ring (Fig. 3D, center), sometimes more easily recognisable as tylostyles. The small category of tylostyles forms the ectosomal palisade, the large category is found in the spicule tracts. Large tylostyles, 445–553 x 14–24 µm (Fig. 3E, small tylostyles, 165–270 x 9–11 µm (Fig. 3F).

Discussion. The WPD lists five species of Plicatellopsis worldwide, all from the southern hemisphere (Van Soest et al. 2017). Aside from obvious zoogeographical reasons the new species differs from the other five in sizes of the tylostyle categories (Table 1). The type species (Plicatellopsis arborescens Burton, 1932) and the new one presented here are the only stalked species known in the genus. Tyles of the tylostyles in P. borealis are weakly developed and only in a few spicules easily recognizable. This seems to be true for other species as well: Burton, 1932 reported styles for the type species in his original description while a re-examination revealed tylostyles (after Van Soest, 2002, p. 234). In fact when introducing the genus Plicatellopsis in 1932 Burton published a drawing of the skeletal architecture which resembles so closely the skeletal architecture of P. borealis that it could have been drawn from sections of the species described here (compare Burton, 1932, p. 332, Figs. 36A & B). Koltun (1964) made his description on fragments and mentions that intact specimens must be funnel-shaped but did not describe a stalk, so we assume there was no stalk present. His species is described as friable which differs from the species described by us which is, even in the dry state, quite resilient and somewhat elastic.

The new Plicatellopsis differs from other congeners in the following characteristics:

P. antarctica (Carter, 1876) (Antarctica), “leaden grey colour”, only one category of tylostyles. P. arborescens Burton, 1932 (Falkland Islands), dichotomously branched, both categories of tylostyles are larger. P. expansa (Thiele, 1905) (Chile), plate-shaped, intermediate-sized categories of spicules present, both spicule

categories are larger.

P. flabellata Burton, 1932 (Falkland Islands), flabellate growth form, smaller and thinner spicules, third category of tylostyles present.

P. fragilis Koltun, 1964 (Antarctica), probably no stalk, friable, both categories of spicules larger.

Note 1: “possessing a pin-like spicule, in which the head is for the part spherical and much larger than any other part of the spicule” (p. 391–392)

Note 2: Our translation

Note 3: translated from Russian (Israel Program for Scientific Translations)

Distribution and ecology. Apparently a common and widespread species ranging over more than 600 km on the eastern Bering Sea shelf in habitats of mixed unconsolidated sediments (pebble, sand, shell). Found at depths between 66 and 117 m. Attached to pebbles, shell including the whelk Neptunea ventricosa Gmelin, 1791 and to the carapace of ovigerous Arctic lyre crabs (Hyas coarctatus Leach, 1815). Female lyre crabs, like other spider crabs (family Majidae), have a terminal molt at maturity and may then carry epibionts like sponges with them for the remainder of their life. Little is known about the biology of H. coarctatus but females are thought to produce two clutches of eggs after the terminal molt with each clutch taking just under one year to hatch (Wicksten 2010). The two crabs had moderately worn (old-shell, 13–24 months post ecdysis shell age of Jademec et al. 1999) carapaces (each 33.6 mm in width) and had clutches of new (orange and uneyed) eggs. The sponges on the crabs ranged from 70 to 96 mm in height, possibly representing a single cohort (i.e. year class). Juvenile but not adult Arctic lyre crabs are known to decorate their carapaces (Wicksten 2010) and the local congener, H. lyratus, carries few or no decorations (Jensen 1995) so we assume that the sponges settled directly on the crabs. So the sponges are either relatively fast growing (70–96 mm year -1) or the life history information for the crabs is not accurate and the sponges grow more slowly. For example, female Arctic spider crabs (H. araneus) carry egg masses for approximately two years (Schiffer et al. 2014) so if H. coarctatus has a similar brooding period then the sponges would grow half as fast (~ 3.5 to 5 cm per year). Regardless, there is no doubt that the sponge(s) greatly impede the mobility of the crabs by the end of their lifetime.

Etymology. From the Latin boreus —northerly, the species is the only member of the genus from the northern hemisphere.