Hexactinella carolinensis, Reiswig & Dohrmann & Pomponi & Wörheide, 2008

Reiswig, Henry M., Dohrmann, Martin, Pomponi, Shirley & Wörheide, Gert, 2008, Two new tretodictyids (Hexactinellida: Hexactinosida: Tretodictyidae) from the coasts of North America, Zootaxa 1721 (1), pp. 53-64 : 59-61

Hexactinella carolinensis n. sp.

Figs. 6–9 , Table 2.

Material examined. Holotype: USNM 1110009 , coll. J. Reed using HBOI manned submersible Johnson-Sea- Link II, Dive 2339, Charleston Lumps, off Charleston , South Carolina, 32°44.068'N, 078°05.955'W, 213 m, 25 May 1992.

Diagnosis. Hexactinella with body of branching tubules with microscleres as stellate discohexasters, oxyhexasters and onychohexasters.

Description. The complete body form remains unknown but 8 broken fragments collected ( Fig. 6A ) are short branching tubules, 6.3-10.6-18.6 mm diameter (n=50). Those fragments that are clearly end branches have terminal oscula leading into atrial tubes 3–4 mm in diameter; tubule walls are 1.5–4.8 mm in thickness. It is possible, but unlikely that atrial tubes are continuous throughout the entire branching body. The outer surface is regularly nodulose due to the coarse schizorhysial skeletal framework ( Figs 6B , 7A ) consisting of a system of branching and anastomosing ridges outlining irregular surface gaps (grooves) 0.4–1.0–1.7 mm in width (n = 50). When alive, the grooves are covered by a lattice formed by loose pentactine and subhexactine dermalia. The texture is stony hard; the color of the dried fragments is dirty white.

Dictyonal framework. Dimensions of framework elements are given in Table 2. The skeletal framework is constructed of a primary frame of longitudinal strands ( Fig. 7C ), which run straight or curve to the dermal surface. Internal meshes are mainly rectangular; beams are sparsely spined and internal nodes are not thickened ( Fig. 7D, F ). A thin cortex is formed on the dermal (distal) and lateral surfaces of ridges where meshes are irregularly 3–5-sided, beams are sparsely spined and nodes are thickened and bear strong conical spines ( Fig. 7B, D ). Spurs on dermal and lateral ridge surfaces are long, thin and finely rough ( Fig. 7D ). The atrial framework surface consists mainly of exposed primary strands, but in places small spiny hexactins are fused to the bounding surface forming a dense mat as a thin cortical layer ( Fig. 7E ).

Spicules. Spicule forms are shown in Figs 8 and 9 ; dimensions are given in Table 2. Megascleres are pentactins, subhexactins, strongyloscopules and small uncinates in both dermal and atrial surfaces. Dermalia and atrialia are pentactins and hexactins with very short distal rays. They are entirely finely rough, and have cylindrical rays that end in abruptly sharp or rounded tips. Irregular step-like reductions in ray diameter are common. The proximal ray may be longer or much shorter than the tangential rays. Scopules occur as a single type; they are entirely rough but often spination can only be resolved on the head with light microscopy. Tines, 3–4 in number, are very slightly splayed and end simply in rounded or indistinct button tips ( Fig. 9B ). The shaft ends proximally in a sharp tip without inflation or conspicuous increase in spination. Small uncinates occur in bundles oriented vertical to the surface. In light microscopy they appear as structureless sharptipped rhaphides, but in SEM their shallow brackets and very short barbs are clear. Many have a small central swelling, but an axial cross is not detectable.

Microscleres consist of discohexasters, oxyhexasters and onychohexasters. The stellate lophodiscohexasters ( Figs. 8E , 9A ) are the most abundant microsclere; they are entirely rough, with relatively long primary rays each bearing 6–16 short terminal rays ending in small, marginally-toothed discs. The degree of splay of the terminal tuft is highly variable. Diaster variants of this microsclere type are rare. Oxyhexasters ( Figs. 8F , 9D ) are the same size as the discohexasters; they are also entirely rough (in SEM) but their primary and terminal rays are almost equal in length. Each primary ray carries 2–3 or rarely 4 terminals ending in sharp, slightly hooked tips. The spherical onychohexasters ( Fig. 8G ) are rarer, smaller, and thinner than the other microscleres. Each short primary ray bears 2–4 long terminals, ornamented with recurved hooks and tipped with a whorl of 3–5 recurved claws.

Etymology. The species name, carolinensis , refers to the location of collection, off S. Carolina, USA.

Remarks. The specimen was originally used for biochemical analysis (identified as " Farrea (?) sp.") in Thiel et al. (2002), and in the forthcoming first molecular phylogenetic study of Hexactinellida by Dohrmann et al. (in press).

Within the genus Hexactinella , spiculation of three Indonesian forms, H. rugosa Ijima , H. spongiosa Ijima and H. vermiculosa Ijima , remain unknown. Their geographic location and body form exclude them from receiving the Carolina specimen. Stellate discohexasters are known to occur in only three Hexactinella species , H. grimaldi Topsent , H. lata (Schulze) , and H. lingua Ijima. Of these, the only one occurring in the Atlantic region, H. grimaldi , as redescribed by Ijima (1927), differs from the Carolina specimen in its platelike body form, probably when entire consisting of a large cup or bowl. It also has oxy-tipped microscleres, but as oxyhexactins instead of oxyhexasters. The Pacific H. lata differs from the Carolina specimen in its mas- sive rather than branching body shape and possession of discohexactins and spherical discohexasters instead of stellate ones. The Indonesian form, H. lingua , differs from the Carolina specimen in its large plate body form (known only as fragments), and its complete lack of oxy-tipped microscleres. The S. Carolina specimen clearly represents a member of a new species of Hexactinella .

Figures

FIGURE 6. Hexactinella carolinensis n. sp. A. wet body fragments immediately after capture, courtesy of Harbor Branch Oceanographic Institution. B. freeze-dried branch tips.

FIGURE 7. Dictyonal framework of Hexactinella carolinensis n. sp. (all SEM). A. dermal surface with ridge/groove system. B. swollen nodes of the dermal surface. C. longitudinal section through septum showing longitudinal strands, dermal side up. D. beams, nodes and spurs of the outer sides of septum. E. deposition of small spined spicules on the atrial wall. F. magnified view of longitudinal septal section C showing internal beams, nodes, spurs.

FIGURE 8. Spicules of Hexactinella carolinensis n. sp. A. various forms of surface pentactins and subhexactins. B. tangential ray of dermal pentactin. C. scopule. D. small uncinate and magnified central part. E. stellate lophodiscohexaster with magnified ray tip. F. oxyhexaster with magnified ray tip. G. onychohexaster with magnified ray tip.

FIGURE 9. SEM micrographs of spicules of Hexactinella carolinensis n. sp. A. stellate lophodiscohexaster. B. scopule head. C. central part of small uncinate. D. oxyhexaster.