Staurocalyptus psilosus, 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 : 48-52

Staurocalyptus psilosus n. sp.

( Figs. 23 & 24 , Table 12)

Synonymy. Acanthascus (Staurocalyptus) sp. nov. 2, Stone et al., 2011: 31.

Material examined. Holotype: USNM# 1196560 , ROV 'Jason II' from RV 'Roger Revelle', dive J2104, 05 August 2004, N Amchitka Pass, 50.9 km WSW of Gareloi Island, Aleutian Islands , Alaska, 51º39.403'N, 179º35.041'W, 711 m, dry & ethanol.

Description. The specimen encountered in situ ( Fig. 23A ) was a white, flask-shaped sac with large slightly flaring osculum bordered by a narrow brown fringe, and smooth external surface. Basally it tapered abruptly to a short narrowed stalk ending in a narrow attachment to hard substrate. The collected specimen ( Figs. 23B–C ) is 36.5 cm long, 24.5 and 16.3 cm in major and minor diameters (slightly flattened), 3.5 cm thick wall at middle, osculum 15.8 x 8.1 cm in diameters. The general dermal surface, sporting a very few scattered prostal diactins, has evenly distributed 1.9–4.0– 5.9 mm diameter inhalant canals covered by a delicate spicule lattice ( Figs. 23D–F ). The atrial surface has a somewhat similar aspect with 2.5–4.0– 7.1 mm diameter exhalant canals but these are covered by a lattice of thick tissue bands ( Figs. 23H, I ). Dense prostal diactins, projecting 2.4–5.8– 9.7 mm, and a raised pentactin veil, projecting 0.6–1.5– 2.3 mm, occur only in a narrow band adjacent to the oscular margin and extending only 17 mm below it ( Figs. 23G, J ). Sediment trapped in the narrow veil is seen as a brown band in the in-situ image ( Fig. 23A ). Special marginalia are not present. In the basal area near the attachment site there occur a few patches of projecting hypodermal pentactins, most with short tangential rays clearly adapted for anchorage rather than supporting dermalia ( Fig. 23K ). The entire sponge is fairly firm when fresh and dry; color alive is white, light tan when dried or preserved in ethanol.

Megascleres: (spicule dimensions are given in Table 12). Prostal diactins ( Fig. 24A ) are slightly curved and taper to rounded finely roughened tips. No middle swelling occurs and an axial cross was not found. Hypodermal pentactins ( Fig. 24B ) are abundant in raised position in the submarginal band but not on the lateral body wall. They are moderate in size and mostly paratropal (69%) but crucial forms are common (27%). Surfaces are either smooth or shagreened. These spicules are not abundant within the lateral body wall surface, but can be found to occur at ca 3 cm - 2 in digests of large peels. Dermalia ( Fig. 24C ) are small, entirely rough pentactins (85%), with unpaired ray directed inward and small knob in place of sixth ray, hexactins (15%) and rare stauractins (<1%); rays are stout and nearly cylindrical and tips are rounded. Atrialia are exclusively regular hexactins ( Fig. 24D ) with ornamentation and ray shape like dermalia. Hypodermal diactins ( Fig. 24E left) are slightly curved, with an inflation at the axial cross and rough ends with parabolic tips. Atrial and parenchymal diactins ( Fig. 24E right) are somewhat longer in mean length, but overlap with the hypodermal diactins is extensive. They have similar tips but generally lack the inflation at the axial cross.

(dimensions in µm unless otherwise indicated).

Microscleres include two sizes of discoctasters, a suite of oxy-tipped hexactins and hexasters, and microdiscohexasters. The discoctasters ( Fig. 24F ) have short primary rays and long, straight, rough terminal rays ending in marginally serrate discs. When measured diameters are frequency-plotted ( Fig. 24F inset graph) it is very clear that the two size classes have virtually no overlap, the dermal and parenchymal octasters being only 65% as large as the atrial octasters. The atrial octasters have proportionately longer terminals. The relatively robust oxytipped microscleres consist of only 10% oxyhexasters with 2–4 terminal rays per primary ( Fig. 24G ), 45% hemioxyhexasters with 1–2 terminal rays per primary ( Fig. 24H ) and 45% oxyhexactins ( Fig. 24I ). All have rough terminal rays with reclined spines that do not reach the size and density noted above in Acanthascus koltuni . The oxyhexactins are the smallest of these spicules, an unusual condition among Acanthascinae where the oxyhexactins are generally larger than oxyhexasters. The spherical microdiscohexasters ( Fig. 24J ) are typical of the subfamily; the very numerous terminal rays end in discs with 4–8 marginal teeth.

Etymology. The species name, psilosus , is derived from Greek " psilos " meaning smooth, bare, bald, naked, as appropriate to the condition of the extensive outer body surface of the single known specimen.

Remarks. The described specimen has discoctasters and large smooth hypodermal pentactins distributed sparsely within the outer lateral body surface and is thus a member of the genus Staurocalyptus . The new specimen can be excluded from the following 7 of the 15 presently accepted species in having mainly pentactin dermalia: S. celebesianus Ijima, 1927 , S. glaber Ijima, 1897 , S. heteractinus Ijima, 1897 , and S. microchetus Ijima, 1898 , all have stauractins as the main dermal spicules, while S. hamatus Lendenfeld, 1915 , and S. pleorhaphides Ijima, 1897 , both have diactins, and S. fuca Tabachnick, 1989 has both diactins and stauractins. By its abundant oxyhexactins, the new specimen can be excluded from S. entacanthus Ijima, 1904 where these are absent or very rare. By its relatively large octasters (162–369 µm diam.) the new species is excluded from S. fasciculatus Schulze, 1899 (<100 µm), S. roeperi Schulze, 1886 (120–180 µm), S. rugocruciatus Okada, 1932 (<100 µm), S. solidus Schulze, 1899 (134–225 µm) and S. tubulosus Ijima, 1904 (130–213 µm). Among other qualitative differences, the new form has atrial apertures traversed only by hypoatrial diactine strands while these apertures are either entirely covered by an atrialia lattice in S. fasciculatus or entirely uncovered in S. roeperi , S. tubulosus and S. solidus . The lateral body of the new form lacks a pentactin veil while it is well developed in S. rugocruciatus and S. solidus . This leaves only S. affinis Ijima, 1904 and S. dowlingi Lambe, 1894 , both of which are very similar to the new specimen in their known characters. The new species differs from S. affinis in its covered exhalant canals (vs open canals in S. affinis ), its lack of hypodermal veil over most of its smooth lateral surface (vs well-developed veil on papillae), its largest hypodermal tangential ray as 3.4 mm x 59 µm (vs 12 mm x 100 µm), its atrial hexactin rays 69–132 µm (vs 140–240 µm), and its parenchymal diactins to 9.5 mm x 46 µm (vs to 35 mm x 80–600 µm). The new species differs from S. dowlingi in its covered exhalant canals (vs open in S. dowlingi ), its large atrial canals to 7 mm diameter (vs 0.75 mm), its much smaller prostal diactins to 17 mm (vs to 35 or 60 mm), its hypodermal pentactins being mostly paratropal (vs all crucial), and its larger oxyhexasters 111–169–212 µm diameter (vs 100–159, the largest not reaching the mean of the new specimen). With this suite of differences between the new Aleutian specimen and all present Staurocalytpus species, we conclude that it is a new species, here designated S. psilosus n. sp.

The collected specimen was attached to a cobble that was buried in a consolidated mix of cobble and sand. Review of all video footage collected with the ROV 'Jason II' indicates that it is a common species, locally abundant in some areas and occurring singly on bedrock, mudstone, and cobbles at depths between 190 and 1556 m.

Figures

FIGURE 23. Staurocalyptus psilosus n. sp., body and surfaces. A. An in situ image of the collected holotype. B. Nearly complete dried holotype in front and back views. C. Oscular view of the dry holotype. D. Outer lateral surface with inhalant canals below a spicule lattice cover. E. Closer view of the inhalant canals and their lattice cover. F. The delicate lattice cover over one inhalant canal. G. Oscular margin viewed from outer (dermal) surface showing projecting prostal diactins. H. Inner atrial surface with exhalant canals covered by thick tissue lattices. I. Close-up of the lattice over one exhalant canal. J. Profile of the submarginal hypodermal pentactin veil and prostal diactins, arrow marks the oscular margin which lacks projecting spicules. K. Hypodermal pentactins with short tangential rays in the basal area near the attachment site.

FIGURE 24. Spicules of Staurocalyptus psilosus n. sp., from the Aleutian Islands (SEM). A. Whole prostal diactin and one tip enlarged. B. Hypodermal pentactins in end and lateral views, with enlarged tangential and proximal ray ends. C. Dermalia; whole pentactin and stauractin with enlarged ray ends. D. Atrialium, whole and enlarged ray end. E. Internal diactins, including short forms from hypodermal strands (left) and longer parenchymal thin and thick examples (right), with enlarged ends and an enlarged centrum of the dermal form. F. Whole examples of the two discoctaster size classes, dermal left (smaller) and atrial right (larger), with enlarged terminal ray ends and inset size-frequency plot of spicule diameters. G. Oxyhexaster with enlarged central area showing spine arrangement. H. Hemioxyhexaster. I. Oxyhexactin. J. Microdiscohexaster, whole and enlarged terminal ray ends.