Rhabdocalyptus mirabilis Schulze, 1899

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 : 56-61

Rhabdocalyptus mirabilis Schulze, 1899

( Figs. 27 & 28 , Table 14)

Synonymy. Rhabdocalyptus mirabilis Schulze, 1899: 61 . Acanthascus (Rhabdocalyptus) mirabilis Stone et al., 2011: 28 .

Material examined. USNM# 1196563 , ROV ' Jason II' from RV ' Roger Revelle', dive J2105, 06 August 2004, Amchitka Pass , 11.4 km WNW of Cape Sajaka, Tanaga Island , Aleutian Islands , Alaska, 51º54.253'N, 178º23.235'W, 2311 m, dry & ethanol, base not collected .

Comparative material. Rhabdocalyptus mirabilis , holotype, USNM 07574, USFS 'Albatross', stn 3338, 28 Aug. 1890, S of Shumagen Bank, Alaska, 54º19'N, 159º40'W, 1143 m, ethanol; Rhabdocalyptus sp. , USNM 07573, USFS 'Albatross', stn 3008, 18 Mar. 1891, Gulf of California, 26º00'N, 111º06'W, 560 m, ethanol & dry.

Description. The specimen in situ ( Fig. 27A ) was a curved, white, tubular sponge, 15.5 cm long by 10.1 cm diameter, with well-developed spicule veil and large terminal osculum. The major part of the specimen, but not the basal attachment, was collected, and after drying ( Fig. 27B ) is 14.0 cm long by 6.8 cm in flattened width and wall thickness to 6.0 mm. Prostal diactins project 10–15 mm only from the oscular margin ( Fig. 27C ) and a narrow 12 mm wide band of lateral surface below it; they are not found on most of the lateral surface. Raised hypodermal pentactins forming the veil, all paratropal and thorned, project nearly continuously to 3.4 mm in the diactin zone around the oscular margin and as small groups of 3–8 pentactins to 7.3 mm from the tips of low conules over most of the lateral body surface ( Fig. 27D ). Conules are 4.2–6.5–9.2 (n = 36) mm apart and 0.8–1.2–1.5 (n = 16) mm high. Short extremely paratropal pentactins with all four tangential rays emanating as a tight bundle within 15° ( Fig. 27E ) occur in the dense veil near the oscular margin but not over the general lateral body veil. The dermal surface is turned in ca 2 mm at the osculum margin forming a narrow diaphragm. The lateral dermal surface ( Fig. 27F ) is covered by conspicuous inhalant canals, 1.1–2.1–3.0 (n = 41) mm in diameter, and, although these apertures are covered by a dermal lattice ( Fig. 27G ), it is irregular and so delicate and thin that it reflects very little incident light. The atrial surface bears apertures of larger exhalant canals, 1.6–2.9–5.9 (n = 62) mm in diameter, but they are covered by a firm, rather opaque lattice supported by hexactins with longest ray protruding into the atrium ( Figs. 27H, I ). Hypoatrial diactin strands do not support the atrial lattice over the exhalant apertures but are found below the lattice in the wall between the canal apertures. The sponge is very soft and delicate when fresh; color alive is white but when preserved or dried it is light tan.

Megascleres: (spicule dimensions are given in Table 14). Hypodermal pentactins ( Figs. 28A–C ) have considerable variation; all of those raised above the lateral surface are large, paratropal and thorned ( Fig. 28A ). Those within the general lateral surface include both large and small, tangential rays either thorned, smooth or shagreened, and paratropal or crucial in shape. Thorns, up to 94 µm long, are always nearly perpendicular proximally and gradually more inclined distally. Restricted to the dense suboscular veil are small hyper-paratropal ( Fig. 28B ) and very small crucial ( Fig. 28C ) forms, both with shagreened tangential rays. Dermalia ( Fig. 28D ) are mainly diactins (97%), with all other varieties, monactins, irregular diactins, triactins, tetractins, less than 1% each. These have slightly tapered rays ending in abruptly sharp or parabolic tips; they are entirely finely spined and vary in degree of formation of the knobs at the axial cross—typically the diactins have two, sometimes one reduced ray knob, but never indication of four reduced rays. Atrialia ( Fig. 28E ) are subpinular hexactins (99+%) and a very few pentactins (<0.1%); the projecting distal ray is longer and has larger spines than the other rays. Rays are tapered, entirely smooth only in the proximal third, and end in pointed tips. Parenchymal diactins ( Fig. 28F ) are here arbitrarily divided into thicker (> 35 mm thick, as principalia) and thinner (<35 µm thick) subgroups, but diactin length and width are probably continuously variable from prostal diactins to the smallest comitalia. Parenchymal diactins are mainly sinuously curved spicules, cylindrical and smooth, with rough ends terminating in rounded or very bluntly sharp tips. Prostal diactins ( Fig. 28G ), easily identified by their projection from the upper dermal surface, are mostly smooth, occasionally shagreened in patches, and have rough rounded tips; their axial cross could not be found.

Microscleres include one class of discoctasters, a suite of oxy-tipped forms consisting of oxyhexactins (80%), hemioxyhexasters (15%) and oxyhexasters (5%), and microdiscohexasters. The discoctasters ( Fig. 28H ) have short primary rays, each bearing 5–9–12 long, rough terminal rays that splay strongly outward in floricoidal pattern and end in marginally serrate discs with 4–7 marginal teeth that project proximally. Interradial knobs are short and hemispheric. Discoctasters occur primarily in atrial and subatrial tissues and are entirely absent in dermal or subdermal tissues. Oxyhexactins ( Fig. 28I ) have straight, tapering, finely rough rays that lack a basal inflation. The reclined spines are more dense basally, but they do not form a striking skirt at the centrum. Hemioxyhexasters ( Fig. 28J ) have extremely short primary rays, each supporting 1–3 terminal rays with same form and orientation as those of oxyhexactins. Oxyhexasters ( Fig. 28K ) are similar, with each primary ray supporting 2–4 terminal rays. Very few smaller oxyhexasters with hooked ray ends occur in spicule preparations, but it remains uncertain if these are proper or contaminants. The size gradation of smaller hexasters, larger hemihexasters, and largest hexactins seen in most lyssacinosids is exhibited here. Microdiscohexasters ( Fig. 28L ) have short, very thick primary rays, each supporting numerous (6–12) straight, curved or sinuous terminal rays ending in minute discs. They occur only in dermal tissues.

Remarks. The new described specimen has large thorned hypodermal pentactins distributed sparsely within the outer lateral body surface and discoctasters and is thus a member of the genus Rhabdocalyptus . The new specimen can be excluded from four of the five known species of the genus that have diactins as their principal dermal spicules. Rhabdocalyptus australis Topsent, 1901 , from Antarctica, has atrial spicules with equal ray lengths, has octasters with cylindrical terminal ray tufts, and has no discohexasters. Rhabdocalyptus capillatus Ijima, 1897 , from Japan, has smaller atrial spicules (tangential ray length 126–220 µm vs 191–316 µm here) and much smaller discoctasters (diameter 76–94–110 µm vs 144–163–180 µm here). Rhabdocalyptus mollis Schulze, 1886 , from Japan, has atrialia with equal length rays, discoctasters that are mainly subdermal, and smaller discohexasters (diameter 22–27 µm vs 21–40 µm here). Rhabdocalyptus unguiculatus Ijima, 1904 , from Japan, shares the floricoidal form of discoctasters with the new form but has much thicker principal diactins (to 175 µm vs 113 µm here), much larger discohexasters (diameter 175–190 vs 145–163–180 µm here), and smaller microdiscohexasters (22–30 µm vs 21–40 µm here). The new specimen agrees completely with the original description of R. mirabilis Schulze, 1899 , from south of the Alaska Peninsula, and is confidently assigned to that species. The specimen, USMN 07573, from the Gulf of California is listed as R. mirabilis on label and catalogue, but although it was compared to R. mirabilis by Schulze (1899), he concluded that it must remain R. sp.; he did not provide reasons for that conclusion. In review of the extremely damaged specimen, we find it has discoctasters (diameter 127–167–205 µm, n = 64) very similar in size and shape to those of R. mirabilis , but it does not have diactin dermalia nor does it have oxyhexactins as the major microsclere; it has pentactins and oxyhexasters respectively. The Gulf of California specimen is clearly not R. mirabilis and must remain as R. sp. until that local fauna is better known. Justification for description of the new Aleutian specimen is the fact that this is only the second reported specimen of R. mirabilis , and the first known since Schulze's original 1899 description of a partial top end of the original specimen. We also provide the first SEM figures and complete spicule data set for this species.

Review of all video footage collected with the ROV 'Jason II' indicate that it is a rare species occurring singly on bedrock at depths between 1984 and 2790 m.

Figures

FIGURE 27. Rhabdocalyptus mirabilis Schulze, body and surfaces. A. Specimen in situ before collection (laser spacing 10 cm). B. Two sides of main specimen after drying. C. Margin and associated prostal diactins and pentactin veil. D. Lateral body surface in profile with low conules supporting pentactins of veil; note absence of prostal diactins. E. Closer view of submarginal exterior spicules with several extreme paratropal pentactins. F. Lateral dermal surface showing apertures of inhalant canals and surface conules as small stellate figures. G. Closer view of dermal surface showing extremely fine, irregular dermal lattice between three conules. H. Atrial surface showing apertures of exhalant canals covered by loose spicule lattice. I. Closer view of atrial surface showing regular hexactin mesh with protruding distal rays. All from USNM# 1196563.

FIGURE 28. Spicules of Rhabdocalyptus mirabilis Schulze, from the Aleutian Islands (SEM). A. Prostal paratropal hypodermal pentactins from side and top, with enlargements of proximal and distal parts of thorned tangential rays. B. Prostal paratropal hypodermal pentactin from submarginal zone with four tightly grouped tangential rays and enlargement of part of a thornless tangential ray. C. Prostal crucial hypodermal pentactin from same area, with enlarged ray end. D. Dermalia, including main diactins with enlarged ray end, irregular diactin, triactin, stauractin and monactin. E. Atrialia, whole hexactin and pentactin (rare), with enlarged distal and tangential ray tips. F. Parenchymal diactins, whole and enlarged ray tips from thinner (above) to thicker (below) forms. G. Prostal diactin, whole and enlarged middle and end. H. Discoctaster, whole and enlarged centrum and terminal ray tips. I. Oxyhexactin, whole and enlarged centrum. J. Hemioxyhexaster. K. Oxyhexaster. L. Microdiscohexaster.