Staurocalyptus tylotus, 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 : 52-56

Staurocalyptus tylotus n. sp.

( Figs. 25 & 26 , Table 13)

Synonymy. Acanthascus (Staurocalyptus) sp. nov. 1. Stone et al., 2011: 30.

Material examined. Holotype: USNM# 1196561 , RV ' Velero IV', stn T-5E, 6-m shrimp trawl, 02 July 2004, Adak Canyon, 6.6 km SSE Cape Tusik, Kanaga Island , Aleutian Islands , Alaska, 51º37.322'N, 177º14.350'W, 155 m, dry & ethanol; paratype: USNM# 1196562 . same trawl/location, dry & ethanol.

Description. The holotype is a thick-walled sac ( Figs. 25A, B ), fresh on deck measuring 20.7 cm long by 12.8 cm diameter; wall thickness is up to 2.8 cm in the middle. The large terminal osculum has a slight marginal fringe of spicules that do not differ from the sparse lateral prostalia. The outer surface of this trawled specimen is exceptionally ragged with most areas bearing conspicuous bud-like digitate papillae or lobes ( Fig. 25C ), which are terminally rounded, each bearing a tuft of prostalia projecting up to 5 mm. Papillae have wide or narrow (stalk-like) attachments to the general body surface; they are 1.3–4.0– 8.6 mm in width (n = 54) and 1.9–5.3– 8.7 mm in height (n = 51). Valleys between the papillae are often deep and extensive, but in areas where papillae are laterally fused to form ridges, the valleys become shorter and, ultimately, in places, rounded holes, 2.9–4.2–7.0 mm in diameter (n = 14). The paratype ( Figs. 25D, E ) is very similar in all characters to the holotype except it is smaller, 8.0 cm long by 6.3 cm diameter, wall thickness to 2.1 cm at middle, has much denser cover of slightly longer prostal diactins (project to 7 mm) and less papillar fusion. Neither specimen has a veil; hypodermal pentactins remain within the outer wall. Exposed surfaces such as tops and sides of papillae, as opposed to the valley floors, are covered by an irregular quadrate lattice of loose spicules with mesh size of 45–82– 113 mm ( Figs. 25F, G ); inhalant canals are not visually apparent. The atrial surface is smooth, with visually obvious exhalant canals covered by a coarse irregular spicular lattice formed of hypodermal diactin trains with atrial spicules scattered along those, not forming a rectangular grid; mesh size is 115–420–883 µm ( Figs. 25H–J ). Body texture is soft and pliable; color alive is golden brown, light brown when preserved or dried.

Megascleres: (spicule dimensions are given in Table 13). Prostal diactins ( Fig. 26A ) are slightly curved and taper to rounded or pointed finely roughened tips. No middle swelling occurs and an axial cross was not found. Hypodermal pentactins are never in a raised position (no veil) and occur in two forms, those with normal proportions (proximal ray length ca 1.5 x tangential ray length) and proximal ray not swollen and those with short tangential rays (proximal ray>5x tangential ray length) and proximal ray swollen along upper half ( Fig. 26B ). Tangential ray tips are parabolic-rounded and proximal ray tips are pointed; both are rough at ends only. Both are strictly crucial and all tangential rays are smooth, never thorned. Dermalia are relatively small, entirely rough spicules occurring as hexactins (55%), often with short distal ray, pentactins (36%) and stauractins (9%) ( Fig. 26C ). Rays are cylindrical and tips are often rounded, but some are parabolic. Atrialia are larger and less rough, occurring as hexactins (94%) with distal (projecting) ray longer or shorter than tangential rays, pentactins (3%), and triactins (3%) ( Fig. 26D ). Rays are very slightly tapering and end in sharp tips. Atrial and parenchymal diactins are generally longer and thinner than hypodermal diactins, but they have great overlap. Their measurements are presented separately, but they are morphologically similar ( Fig. 26E ), mainly smooth with sharp rough tips, with or without a slight axial swelling. A distinct class of short, stout, rough diactins (not figured) is associated with both subdermal and subatrial areas, but absent from parenchymal tissues. While these are shorter than the normal diactins, they are larger than dermalia and atralia and are not here considered to be part of those assemblages.

Microscleres consist of one size of discoctasters, a suite of oxy-tipped forms as mostly oxyhexactins (99%) and few hemioxyhexasters (1%), but no fully developed hexasters. All forms are equally abundant in subdermal and subatrial locations. The discoctasters are relatively small, with outcurved floricoidal secondary rays ( Fig. 26F ). Primary rays are very short, each supporting 3–10 terminal rays ending in symmetric or asymmetrical discs with 10–12 marginal teeth. The eight corner projections of the central cube are developed as short digital rays, occasionally bifurcate, instead of the short knobs on most discoctasters. The oxyhexactins ( Fig. 26G ) and hemioxyhexasters ( Fig. 26H ) are fairly robust and appear smooth in LM, but are found to be sparsely spined in SEM ( Fig. 26I ). Hemihexasterous forms have a total of 7–10 rays. Small spurs up to 12 µm long occur on about 3% of oxyhexactins at any point on their rays. Irregular oxy-tipped spicules as pentactins, tetractins, triactins and diactins do occur very rarely. No microdiscohexasters or their parts were found in extensive searches.

Etymology. The species name, tylotus , is derived from Greek " tylotos " meaning knobby, appropriate to the condition of the outer papillate surface.

Remarks. Only 2 of the presently recognized 15 Staurocalyptus species have discoctasters less than 100 µm in diameter, S. fasciculatus Schulze, 1899 and S. rugocruciatus Okada, 1932 . Review of type specimens and original descriptions of both show neither of these species is suitable for assignment of the new Aleutian specimens. The discoctasters of both species have short, straight, tightly bundled terminal rays in contrast to the out-curved, long terminal rays in the floricoidal forms of the Aleutian specimens. Other differences are that both species are thinwalled, 3 mm and 8 mm respectively, in contrast to the 28.0 mm and 20.8 mm of the new specimens. Staurocalyptus fasciculatus has no projecting prostalia and S. rugocruciatus has a veil of projecting hypodermal pentactins, both features differing from those of the new specimens. These differences indicate that the Aleutian specimens represent a new species, here designated S. tylotus .

Floricoidal discoctasters also occur in Rhabdocalyptus unguiculatus Ijima, 1904 , and R. bidentatus Okada, 1932 . If this similarity is seriously considered or proven to be phylogenetically shared, it could serve as an argument for discounting the importance of hypodermalia thorns and lead to a reorganization of the present grouping of acanthascid species.

The new specimens were collected on relatively flat seafloor composed of sand, pebbles, and cobbles. They were attached to small cobbles and pebbles imbedded in the sediment. Review of all video footage collected with the ROV 'Jason II' indicate that it is a common species, locally abundant in some areas and occurring at depths between 139 and 183 m. No in situ images are available for this species.

Genus Rhabdocalyptus Schulze

Synonymy. Rhabdocalyptus Schulze, 1886: 51 . Part of Acanthascus - Tabachnick 2002: 1447. Part of Acanthosaccus - A. tenuis Schulze, 1899: 65 . Subgenus Rhabdocalyptus Tabachnick 2002: 1449 .

Type species: Rhabdocalyptus mollis Schulze, 1886

Genus diagnosis. Acanthascinae with large pentactins that form a continuous hypodermal lattice supporting smaller dermal spicules; some hypodermal pentactins bear large thorns on their tangential rays (modified from of Tabachnick 2002: 1450 for subgenus Rhabdocalyptus ).

Remarks. The taxon Rhabdocalyptus is reinstated as a genus-level group as proposed above under Acanthascinae .

Figures

FIGURE 25. Staurocalyptus tylotus n. sp., body and surfaces. A. Holotype, dry, both sides. B. Holotype, dry, terminal osculum view. C. Papillate lateral surface of holotype, dry. D. Paratype, dry, both sides. E. Paratype, closer view of oscular margin, projecting prostalia and upper atrial surface. F. Dermal surface of holotype. G. Closer view of dermal surface of holotype showing spicule lattice. H. Atrial surface of holotype with exhalant canals covered. I. Closer view of H. J. Closer view of atrial surface cover (compare with dermal surface G -- same scale).

FIGURE 26. Spicules of Staurocalyptus tylotus n. sp., holotype from the Aleutian Islands (SEM). A. Whole prostal diactin and enlarged tips. B. Hypodermal pentactins in lateral views, with enlarged tangential and proximal ray ends. C. Dermalia; hexactins with short distal rays, pentactin, stauractin and enlarged ray ends. D. Atrialia, whole and enlarged ray end. E. Parenchymal diactins including enlarged ends. F. Two subdermal discoctasters not differentiated as size classes with enlarged terminal ray ends. G. Oxyhexactin, H. Hemioxyhexaster. I. Enlarged center of oxyhexactin to show spines.