Antho (Acarnia) ridgwayi, 2019

Stone, Robert P., Lehnert, Helmut & Hoff, Gerald R., 2019, Inventory of the eastern Bering Sea sponge fauna, geographic range extensions and description of Antho ridgwayi sp. nov., Zootaxa 4567 (2), pp. 236-250 : 245-249

Antho (Acarnia) ridgwayi n. sp.

( Figs. 2 & 3 ; Table 2)

Material examined. Holotype USNM2084685 , largely intact specimen originally frozen then dried, collected by Jerry Hoff with a research survey bottom trawl from the FV Cape Flattery; 21 June 2016, 210 m depth, haul station #27, 97.5 km WSW of St. Paul Island, Pribilof Islands , upper slope of the eastern Bering Sea (56°54.5880' N, 173°21.9390' W). Water temperature = 3.9 °C. A fragment of the holotype is deposited at the Zoologische Staatssammlung München, Germany under the registration number ZSM 20190188 .

Description. A foliaceous or flabellate, golden brown sponge with an irregular outline and lobes in several directions ( Fig. 2A ), maximum dimensions 130 x 120 x 2–3 mm. The consistency is flexible and resilient. No oscules visible, surface is smooth.

Skeletal architecture. The relatively narrow sheet of the sponge has a reticulation of acanthostrongyles in its center ( Figs. 2B & 3A ), near the two surfaces, plumose tracts composed of two categories of styles rise towards the ectosome ( Figs. 2B, 2C , & 3A ). The smaller category of subtylostyles with microspined heads also occurs in bundles in between the tracts. The ectosome consists of a thin organic veneer ( Figs. 2B & C ) and contains abundant palmate isochelae, toxa and tylotes with microspined heads.

Spicules. Megascleres are ectosomal tylotes with microspined heads ( Fig. 3C ), 223–254 x 6–9 µm, choanosomal acanthostrongyles ( Figs. 3B & D ), 195–228 x 14–24 µm, choanosomal, echinating smooth, thick styles ( Figs. 2B, 2D , & 3B ), 620–805 x 2 5–38 µm, and choanosomal thin (subtylo-)styles ( Fig. 3B ) with microspined heads, 378–466 x 8–10 µm. Microscleres are palmate isochelae ( Fig. 3F ), 20–24 µm and toxa in two size categories, small, 10–42 µm, and large, 136–182 µm ( Figs. 2D & 3E ).

Discussion. A well-structured choanosome with megascleres differentiated in geometry and distribution, more than one category of choanosomal megascleres, one greatly modified and accessory spicules that consist of acanthostrongyles and are accompanied by ascending plumose tracts of styles clearly indicate the assignment of the new species within the family Microcionidae , the genus Antho , and the subgenus Acarnia . A comparison of the new species with congeners from the Bering Sea, North Pacific Ocean, Arctic Ocean, and North Atlantic Ocean indicate that there are no other Antho species in the area with two categories of toxa and none with large styles of comparable size and geometry. The new species differs from all compared congeners in the following characters ( Table 2):

Antho arctica has thinner large styles that have spined heads, much thinner acanthostrongyles (approximately one third), tornotes instead of tylotes that are much longer, and lacks toxa.

A. bakusi has shorter styles, an additional category of thin styles and shorter acanthostyles, shorter and thinner acanthostrongyles, no ectosomal tylotes, and three distinct categories of toxa.

A. circonflexa has acanthostyles instead of styles that are shorter and thinner, lacks a second category of styles, much shorter acanthostrongyles, lacks tylotes although the subtylostyles mentioned by Lévi (1960) could be regarded as tylotes based on the figure in the publication, and has shorter isochelae.

A. coriacea has shorter styles (both acanthostyles), much shorter acanthostrongyles, and lacks tylotes although we regard the subtylostyles mentioned by Lévi (1960) as ectosomal spicules.

A. elegans has much shorter styles and acanthostyles, shorter acanthostrongyles, ectosomal subtylostyles intead of tylotes, shorter isochelae, and different sizes of the two toxa categories.

A. illgi has shorter and thinner styles (both categories), short styles without microspined heads, shorter and thinner acanthostrongyles, and lacks tylotes.

A. planoramosa has only one category of styles (acanthostyles), thinner acanthostrongyles spined only at the ends, and lacks toxa.

A. signata has shorter and thinner acanthostrongyles, ectosomal subtylostyles instead of tylotes, anisochelae and only one category of toxa.

A. spinulosa has shorter and thinner thick styles with microspined heads, more slender thin styles that do not have microspined heads, strongyles to tylotes (with spines at the ends only) rather than acanthostrongyles, lacks ectosomal tylotes, smaller isochelae (described as arcuate by Tanita), and only one category of toxa in a size category intermediate to the two in A. ridgwayi .

Etymology. We name this new species in memory of Michelle Ridgway who made major contributions to the conservation of Alaska’s marine resources, particularly in the Bering Sea, and whose passion inspired many.

Figures

FIGURE 2. Antho ridgwayi n. sp. A, Holotype. Grid marks are 1 cm. B, Light microscopic section perpendicular to the surface. Ectosome visible as dark band on upper right. Ascending tracts of styles and reticulation of acanthostrongyles visible below, appearing as darker area. C, Close-up view of section perpendicular to surface. Ectosomal veneer with numerous isochelae (upper right) and ascending tracts of styles (below). Reticulation of acanthostrongyles visible at the right. D, Small and large toxa within the ectosomal organic veneer.

FIGURE 3. SEM images. A, a section through the complete blade of the sponge perpendicular to the surface. In the center of the sponge blade, the reticulation of acanthostrongyles is visible, towards both surfaces of the sponge blade plumose tracts of styles run towards the two surfaces ending at the ectosome. B, Large and small style, acanthostrongyles and ectosomal tylotes. C, Ectosomal tylote with microspined head detail in inset at upper right. D, Acanthostrongyle. E, Small category of toxon. F, Isochelae.