Farrea aleutiana, 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 : 8-10

Farrea aleutiana n. sp.

( Figs. 3 & 4 , Table 2)

Synonymy. Farrea sp. nov. Stone et al., 2011: 18.

Material examined. Holotype: USNM# 1196548 , ROV ' Jason II' from RV ' Roger Revelle' , dive J2102, 03 August 2004, 26.7 km W of Amatignak Island, Delarof Islands , Amchitka Pass, Aleutian Islands, 51º18.549'N, 179º31.693'W, 887 m, partial, dry & ethanol.

Description. The holotype consists of 15 fragments, the largest being 35 mm long, of a dichotomously branching tubular stock, with internode length greater than tube diameter, hence appearing spindly for a farreid ( Figs. 3A, B ); evidence of anastomosis is lacking in either the in-situ image ( Fig. 3A ) or the recovered fragments ( Fig. 3B ). Outer tube diameter is 8.5±1.5 (6.9–12.7; n = 13) mm; wall thickness is 1.08±0.16 (0.78–1.32; n = 10) mm. The color of the preserved fragments is light tan or beige. Both inner and outer surfaces are smooth, without channelization.

The skeletal framework is a typical farreoid dictyonal type, with smooth beams. Dictyonalia are mainly formed in a single layer ( Fig. 3C ) but in the thicker fragments a second layer may occasionally be added on the dermal side. Meshes are mostly rectangular, elongate in the longitudinal axis, but nearly square meshes are also quite common. Spurs are rough, tapered to a fine point and overwhelmingly curved toward the growth margin, in downstream exhalant water flow ( Fig. 3D ), although in some areas they are straight ( Fig. 3C lower). Framework measurements are given at the top of Table 2.

Megascleres are pentactins, pileate clavules, and uncinates (dimensions given in Table 2). The pentactins ( Fig. 4A ) of dermal and atrial surfaces are regularly cruciate and indistinguishable; all rays are slightly tapered and finely rough (moderately dense microspines); tangential rays are slightly curved towards the body wall (down) and appear in LM to be slightly inflated distally; proximal rays are abruptly tapered at the tip without inflation. A rudiment of the sixth (distal) ray is present. Pileate clavules ( Fig. 4B ) occur on both surfaces; their necks are barely swollen; the cap is smooth, bordered by 23–25 short, sharp marginal teeth, 3.2±0.6 (2.2–4.3; n = 19) µm long. The shaft is entirely covered with short spines inclined away from the head; the proximal tip is not inflated but abruptly tapered to a sharp point. Uncinates are moderate in size but thin ( Fig. 4C ); barbs and brackets are well developed in the mid-area and barbs are only moderately inclined from the spicule surface.

Microscleres are mainly oxyhexasters and hemioxyhexasters (59%), discohexasters and hemidiscohexasters (23%). Oxyhexactins (12%) and discohexactins (5%) constitute the less common regular forms (dimensions given in Table 2). Oxyhexasters ( Fig. 4D ) and hemioxyhexasters ( Fig. 4E ) have short primary rays (1°/2° ray length = 0.316). Branched rays have 2–3 secondary rays; both primary and secondary rays are tapered to sharp tips and smooth except for short spurs representing undeveloped secondary rays. Discohexasters ( Fig. 4G ) and hemidiscohexasters ( Fig 4H ) have short primary rays (1°/2° ray length = 0.392). Branched rays have 2–4 secondary rays; both primary and secondary rays are cylindrical and ornamented with fine reclined spines ( Fig. 4J ) although they are sparse on the primary rays. Terminal discs have 4–7 marginal spines. Oxyhexactins ( Fig. 4F ) and discohexactins ( Fig. 4I ) are totally unbranched forms of the oxy- and disco-tipped branched forms. Their rays are similar to those of their branched counterparts in shape and ornamentation, but they are slightly longer in both types. Microscleres with onychoid ray tips are rare (<1%); they are the size of discohexasters but have thin rays. They are interpreted to be young stages of discohexaster development and not a distinct microsclere category. All fragments are contaminated with spicules of Regadrella okinoseana , collected at the same station, but these are quite easily recognized as foreign in origin.

* includes hemioxyhexaster and hemidiscohexaster respectively.

Etymology. The species name, aleutiana , reflects the name of its occurrence location, the Aleutian Islands.

Remarks. This new Aleutian Islands form of Farrea is unique among the local Alaskan Farrea forms in lacking anchorate clavules. Six forms of Farrea have previously been described as lacking anchorate clavules, but the new form is easily distinguished from each of these. The North Atlantic F. laminaris Topsent, 1904 has an undulatory blade body form and pentactins with macrospines, while the new Aleutian form has a branching tubular body form and microspines on its pentactins. In F. microclavula Tabachnick, 1988 , from the Western Pacific Mountains, the major microscleres are disco-tipped (here oxy-tipped), oxyhexasters have longer primary rays (calculated from figures 1°/2° ray length = 0.6 vs 0.316 here), discohexactins are absent (present here), and oxyhexactins are only attached to the framework (free here). Unfortunately megasclere dimensions were not provided in the description of F. microclavula , but the qualitative differences noted indicate that the two forms are clearly distinct. The south Australian form assigned to Farrea occa occa by Reiswig, 1992 has no disco-tipped microscleres (28% here). The form described from off Gibraltar, Atlantic Ocean, by Boury-Esnault et al. (1994) as F. occa , but clearly not assignable to that species, is nearly identical in pattern of spiculation to the new form, but the uncinates are much smaller, mean length 582 µm (2050 µm here); the clavules are much shorter (230–270–310 µm vs 333–411–490 µm), and both microsclere classes differ significantly in shape (primary rays longer than terminals in the former but those rays very much shorter in the new form). The New Zealand species, F. anoxyhexastera Reiswig & Kelly, 2011 , has no oxyote microscleres (dominant here), and F. ananchorata Reiswig & Kelly, 2011 has two size classes of oxyhexasters (largest with diameter 102–216 vs 61.5–116.7 µ m here) and discohexasters with long primary rays (1°/2° ray length ratio 1.82 vs 0.39 here). Based upon the differences from all known Farrea lacking anchorate clavules, the new Aleutian form is considered here to be a new species, designated as Farrea aleutiana .

Review of all video footage collected with the ROV 'Jason II' indicates that this is a rare species, known only from a few locations in Amchitka Pass and near Bobrof Island in the central Aleutian Islands, occurring on small boulders, cobbles, and pebbles at depths between 397 and 1353 m. The skeletons of this and other Farrea spp. provide important substrate for gorgonian corals ( Primnoidae and Acanthogorgia sp. ).

Figures

FIGURE 3. Farrea aleutiana n. sp., body and framework. A. Frame grab from video footage of the holotype in situ before collection; the holotype is outlined by white line; arrowheads mark laser spots 10 cm apart. B. Largest fragments of the holotype, USNM# 1196548. C. Cleaned dictyonal framework viewed from atrial side showing relatively straight spurs at bottom (SEM). D. Higher magnification of framework showing smooth beam surfaces and spurs curved toward the growing margin (left) (SEM).

FIGURE 4. Farrea aleutiana n. sp., spicules (all SEM). A. Surface pentactin, whole, with enlarged tangential and proximal ray ends. B. Pileate clavule, whole, side and end view of the upper end. C. Uncinate, whole and enlarged middle segment. D. Oxyhexaster. E. Hemioxyhexaster. F. Oxyhexactin. G. Discohexaster. H. Hemidiscohexaster. I. Discohexactin. J. Magnified side and end views of terminal ray ends of disc-tipped microscleres.