Farrea aspondyla, Reiswig & Stone, 2013

Reiswig, Henry M. & Stone, Robert P., 2013, <strong> New glass sponges (Porifera: Hexactinellida) from deep waters of the central Aleutian Islands, Alaska </ strong>, Zootaxa 3628 (1), pp. 1-64 : 11-15

Farrea aspondyla n. sp.

( Figs. 5 & 6 , Table 3)

Synonymy. Farrea kurilensis ssp. nov. Stone et al., 2011: 16.

Material examined. Holotype: USNM# 1196549 , ROV ' Jason II' from RV ' Roger Revelle' , dive J2099, 31 July 2004, Adak Canyon , 15.9 km SW of Cape Yakak, Adak Island, Aleutian Islands, 51º28.091'N, 177º03.055'W, 2105 m, partial, dry & ethanol.

Comparative material examined. Farrea kurilensis Okada, 1932 , holotype, USNM 22034 , USFS ' Albatross' , stn 4804, SE of Shimushir Island, Kurile Islands, 24 June 1906, 46º42'N, 151º47'E, 419 m ; Farrea beringiana Okada, 1932 , holotype, USNM 22037 , USFS ' Albatross' , stn 4790, Cape Monati , Bering Island, Bering Sea, 14 June 1906, 54º38'45"N, 167º11'45"E, 117 m ; Farrea kurilensis, BMNH 1938.07.04.119 (from Zoological Institute of the Academy of Sciences , Leningrad), stn 248, Sea of Okhotsk, other data unavailable .

Description. The new species holotype consists of over 100 fragments, the largest being 80 mm long, from a stock of very tightly branching and anastomosing tubes, with internode length less than or about the same as tube diameter, hence appearing nearly lettuce-like, with individual tubular components difficult to distinguish ( Figs. 5A, B ). Apertures of tube openings on the outer surface are 22±3 (20–28; 6) mm; wall thickness is 2.0±0.4 (1.5–2.5; 10) mm. The color of the preserved fragments is white. Both inner and outer surfaces are smooth, without channelization ( Fig. 5B ).

The skeletal framework is a typical farreoid dictyonal type easily seen by naked eye ( Fig. 5C ), with smooth beams ( Figs. 5D, E ). Dictyonalia are mainly restricted to a single layer but a second layer may occasionally be added on the dermal side. Meshes are mostly rectangular, approximately square, so longitudinal and transverse beam lengths do not differ. Spurs are rough, tapered to a fine point, and usually gently curved downstream (to exhalant flow; Figs. 5E, F ), but in many areas they project directly perpendicular to the plane of the framework without curvature. Framework measurements are given at the top of Table 3.

Megascleres are pentactins, regular hexactins, anchorate clavules and uncinates (dimensions given in Table 3). The pentactins ( Fig. 6A ) of dermal and atrial surfaces are regularly cruciate and indistinguishable; all rays are straight, slightly tapered, finely rough (moderately dense microspines), and end in abruptly pointed tips. A short rudiment represents an undeveloped sixth (distal) ray; its length is generally less than twice its width and the spicules are here considered to be pentactins. Regular hexactins ( Fig. 6B ) occur as parenchymal spicules with rays similar to those of the surface pentactins; they are too rare to provide data for Table 3 but the one figured has rays 227 µm long by 11.2 µm thick. Anchorate clavules ( Figs. 6C–F ) occur on both surfaces; their caps have a small central prominence, raised to varying degrees and often with a few coarse spines; the 3–10, 23–93 µm long marginal spines projecting backwards are rarely straight and more commonly flared outwards or s-shaped. Outer surfaces are mostly smooth, but spines occur across the cap and on the distal spines of some clavules. Darkened surfaces on outer and inner surfaces of some caps ( Figs. 6E–F ) appear due to incomplete silicification where the nanospherular silica is seen at higher magnification. The shafts are straight, robust and smooth, ending in blunt parabolic tips without inflation; large shaft spines are absent. Uncinates are of moderate size but thin ( Fig. 6G ); barbs and brackets are well developed in the middle and barbs are moderately inclined from the spicule surface.

Microscleres consist of only stellate discohexasters of two distinct size and form classes (dimensions given in Table 3). Both are entirely rough and bear terminal discs with 4–7 marginal teeth. The smaller, more abundant discohexasters ( Fig. 6I ) generally have long primary rays bearing 3–7 shorter secondary rays, usually bundled very tightly together, but many are slightly flared at the tips and some flare outwards directly from their insertion on the primary ray. The larger discohexasters ( Fig. 6H ) have relatively shorter primary rays that bear 6–8 long straight secondary rays. The bases of the secondary rays are fused for a short distance forming a calyx-like base. Most of the discohexasters are easily assigned to these two classes, but a few intermediates occur as verified by a plot of spicule diameter vs 1º ray length/2º ray length (not shown).

Etymology. The species name, aspondyla , reflects the absence of spines on the clavule shafts.

Remarks: The new Aleutian Islands specimen is clearly closely related to F. kurilensis Okada, 1932 based on the shared characteristic shape of its anchorate clavules as well as the form of its dermal and atrial pentactins. It differs from F. k. forma kurilensis Okada, 1932 , as modified by Koltun (1967), in the larger caliber of its tubular body components (22 vs. 10 mm diameter in the latter), lack of pileate clavules, complete absence of shaft spines on its anchorate clavules, absence of oxyhexaster microscleres (the dominant microsclere of the latter), and presence of a large class of discohexasters (absent in the latter). It differs from F. k. forma beringiana, Okada, 1932 , as modified by Koltun (1967), in absence of pileate clavules (although these were absent in Okada's original Bering Sea specimen), absence of shaft spines on the anchorate clavules, and presence of a much larger class of discohexasters (91–293 vs. 80–150 µm diameter in the latter) with calyx-like fusion of the secondary ray bases. Koltun (1967) noted, after examination of seven previously unreported specimens, that F. kurilensis is a polymorphous species but he still maintained distinction between the two forms, now considered subspecies ( Reiswig 2002). Other species of Farrea with only anchorate clavules include F. aculeata Schulze, 1899 , from Oregon and F. campossinus Lopes et al., 2011 from Brazil; both differ from Farrea aspondyla n. sp. in having their main microsclere as oxyhexasters. The special characters of the new Aleutian Islands form, absence of pileate clavules, absence of shaft spines on anchorate clavules, and presence of a very large class of stellate discohexasters with calyx-like secondary ray bases, are here considered sufficient evidence for genetic isolation and its recognition as a new species, Farrea aspondyla .

Review of all video footage collected with the ROV 'Jason II' indicates that this is a common species, locally abundant in some areas and occurring on bedrock, mudstone, boulders, cobbles, and other hexactinellid skeletons at depths between 1887 and 2249 m (likely much shallower but difficult to determine due to presence of conspecifics from which it cannot always be distinguished in situ). When encountered in situ, the majid crab Chionoecetes angulatus was using the sponge as cover; other associated fauna include juvenile crabs ( Paralomis and Lithodes spp. ). The skeleton of this and other Farrea spp. provide important substrate for gorgonian corals ( Primnoidae and Acanthogorgia sp. ).

Figures

FIGURE 5. Farrea aspondyla n. sp., body and framework A. Frame grab from video footage of the holotype in situ before collection. B. Three largest fragments of the collected holotype (dry). C. Mass of smaller fragments in which the meshes of the dictyonal framework can just be resolved (dry). D. Plane view of the dictyonal framework showing relative regularity of square meshes (SEM). E. Magnified view of the framework showing smooth beam surfaces and sharp-pointed spurs (SEM). F. Oblique atrial view of framework showing longitudinal strands running away from the viewer and downstream curvature of the spurs (SEM).

FIGURE 6. Farrea aspondyla n. sp., spicules, all from holotype (SEM). A. Surface pentactin, whole and enlarged tangential ray end. B. Parenchymal hexactin. C. Range in size of anchorate clavules in side view, all to same scale. D. Magnified side view of anchorate clavules. E. Magnified end view of anchorate clavule heads. F. Proximal view of broken anchorate clavule head showing pattern of dark incompletely smoothed silica surface. G. Uncinate, whole and enlarged middle segment. H. Large discohexaster, whole and enlarged view of calyx-like base of secondary rays and terminal discs. I. Small discohexasters, whole and magnified view of secondary ray ends.