Sigmaxinella hipposiderus, Mitchell, Kirsty D., Hall, Kathryn A. & Hooper, John N. A., 2011

Mitchell, Kirsty D., Hall, Kathryn A. & Hooper, John N. A., 2011, A new species of Sigmaxinella Dendy, 1897 (Demospongiae, Poecilosclerida, Desmacellidae) from the Tasman Sea, Zootaxa 2901, pp. 19-34 : 23-29

Sigmaxinella hipposiderus sp. nov.

Figs 2–5

Holotype. QM G323175, Big Horseshoe Canyon ( West Bank), Bass Canyon system, Tasman Sea, Australia, - 38.1148 S, 149.3565 E, depth 159.6 m, coll. CSIRO ‘Southern Surveyor’ cruise SS0404, Sherman sled, 26.iv.2004.

Diagnosis. Sigmaxinella with a single category of styles as megascleres (mean length 791 μm, mean width 19.2 μm); microscleres include a single category of sigmas (mean length 19.6 μm) and microxeas singly or in bundles (mean length 42 μm).

Taxon # QM α GenBank β SBD γ Reference Registration Accession Accession

Poecilosclerida

Mycalina

Desmacellidae

Biemna fistulosa (Topsent, 1897) AM076982 Rot et al. (2006) Biemna saucia Hooper, Capon & Hodder, 1991 G303281 JF7731346 1054 δ Neofibularia hartmani Hooper & Lévi, 1993 A G306606 642/592 B G206628 644/594 C G324632 JF773145 1055 δ Neofibularia irata Wilkinson, 1978 G307266 650/600 Neofibularia nolitangere (Duchassaing & Michelotti, EF519653 156/156 Erpenbeck et al. (2007) 1864)

Sigmaxinella hipposiderus sp. nov. G323175 JF773147 1053 δ

Esperiopsidae

Esperiopsis challengeri (Ridley, 1885) G306063 732/762

Isodictyidae

Coelocarteria singaporensis ( Carter, 1883) G319331 669/619

Mycalidae

Mycale fibrexilis (Wilson, 1894) AJ843890 Hess et al. (direct submission) Mycale (Arenochalina) laxissima (Duchassaing & EF519649 Erpenbeck et al. (2007) Michelotti, 1864)1

Mycale (Arenochalina) mirabilis (Lendenfeld, 1887) G 300561 572/522 Mycale (Mycale) sulcata Hentschel, 1911 G304666 693/719

Podospongiidae

Diacarnus spinipoculum (Carter, 1879) AY561975 Nichols (2005)

Microcionina

Microcionidae

Artemisina melana Van Soest, 1984 EF519575 Erpenbeck et al. (2007) Clathria (Clathria) prolifera (Ellis & Solander, 1786) 2 AJ843888 Hess et al. (direct submission) Clathria (Thalysias) oxeota (Van Soest, 1984) 3 EF519606 Erpenbeck et al. (2007) Clathria (Thalysias) schoenus (de Laubenfels, 1936)4 EF519607 Erpenbeck et al. (2007) Pandaros acanthifolium Duchassaing & Michelotti , EF519662 Erpenbeck et al. (2007) 1864

continued next page Taxon # QM α GenBank β SBD γ Reference Registration Accession Accession Queensland Museum; not all specimens have vouchers in the Queensland Museum collection.

NCBI database, available at: http://www.ncbi.nlm.nih.gov/

Sponge Barcoding Database, available at: http://www.spongebarcoding.org/; number provided as record number then sequence number (xxx/xxx).

sequence generated newly in this study as Mycale laxissma 9 as Tedania ignis

as Microciona prolifera 10 as Tedanis klausi

as Clathria oxeota 11 this species is undescribed but has been identified as an operational taxonomic unit as Clathria schoenus by the Queensland Museum, as designated by an OTU number. as Strongylacidon bermudae 12 as Pseudaxinella reticulata

as Lissodendoryx isodictyalis 13 as Halichondria magniconulosa

as Lissodendoryx sigmata 14 as Halichondria melanodocia

as Holopsamma helwigi 15 as Halichondria panicea

Description. Growth form arborescent, erect, flattened into one plane, branching dichotomously, but irregularly, basal attachment small and on well formed stalk (now detached in fixed specimen); branches cylindrical, laterally compressed, ellipsoidal in cross-section, matting of spicules gives appearance of external segmentation in fixed specimen ( Fig. 2 B). Dimensions: overall height 103.0 mm; maximum breadth 69.0 mm; stalk length is approximately 15 mm; width of main axis 1.5 mm at base, widening to 3.8 mm at first bifurcation and 5.7 mm at apex; longest branch 62.2 mm in length from point of bifurcation to branch apex, maximum width 7.5 mm; shortest branch 35.7 mm in length, maximum width 2.6 mm. Colour light beige to pale grey in ethanol. Oscules inconspicuous, shallow, less than 1mm diameter, few, roughly circular; fine oscules observed on proximal portion of main axis in fixed specimen.

Surface uneven, velvety, hispid, with hair-like conulose projections forming a pile which becomes matted distally on branches, axial region villose. Texture barely compressible, tough, difficult to tear although easily cut; branches flexible, pliable; main axis flexible, but more resistant to bending than branches.

Skeleton with markedly differentiated axial and extra-axial construction; axis strongly compressed, extra-axial region plumose ( Fig. 3 ). Compressed axial core occupies approximately half the diameter of the sponge in the region of the stalk, and one third the diameter in the branches. Choanosomal skeleton an axially condensed reticulation of multispicular tracts enclosed in abundant collagenous spongin; extra-axial skeleton plumose, with ends of terminal spicules forming brushes at the surface; microscleres densely packed along and between megascleres in plumose tracts; packing of microscleres more dense near axis than in periphery of skeleton, and density of microscleres decreases towards ectosome. Ectosome indistinct from choanosome, without any conspicuous specialisation aside from plumose terminal spicule bundles protruding from the choanosomal extra-axial skeleton.

Spicules (n = 25) (Table 1, Fig. 5 ):

Megascleres: single category of styles as megascleres, occasionally bent, 500–1300 (791.0) × 15–25 (19.2) μm.

Microscleres: single categories of both sigmas and microxeas; sigmas c-shaped, elongate, entirely smooth, 10– 41 (19.6) × 1–2 (1.4) μm (chord length and widest axis), microxeas single or in compact bundles, isodiametric, completely smooth, tips hastate, 27–55 (42.1) × 1–1.5 (1.2) μm (length and maximum width).

Ecology and distribution. Known only from the holotype collected from the shallower margins of the Big Horseshoe Canyon, a side canyon to the Bass Canyon system off the eastern Victorian boarder, lying on the edge of the southeastern continental shelf. The specimen was collected from 160 m in a habitat dominated by rock and silt.

Etymology. The epithet is made as a masculine noun in apposition from the ancient Greek hipposideros (= horseshoe) in reference to the type locality, Big Horseshoe Canyon, Tasman Sea.

DNA sequence data. 1 sequence: COI mt DNA (partial, Folmer fragment, 658 bp, 1 replicate).

Remarks. This species is clearly assigned to Sigmaxinella on the basis of its compressed axial and plumose extra-axial skeletons, which is otherwise similar to Biemna . By having a single category of unmodified style megascleres, and single categories of both sigmas and microxeas, and in specific sizes of its spicules, this species differs from the 12 valid species of Sigmaxinella as follows (refer to Table 1 for the comparison among species of Sigmaxinella ).

Sigmaxinella hipposiderus sp. nov. clearly differs from the type species, S. australiana Dendy, 1897 , in having a single category of styles, sigmas and microxeas. The latter has much smaller styles, some of which are modified into strongyles and oxeas, two categories of sigmas and one category of much thinner raphides (i. e. those in the present species are thicker and more obviously microxeas than raphides, and, even though they form bundles, these bundles are not trichodragmata) (Table 1, Fig 5 B). Nevertheless, both species have a similar external morphology (see Fig. 2 , 6 A) and a differentiated axial and extra-axial skeletal architecture, features which can only be described as ‘typical’ of Sigmaxinella .

In growth form, S. hipposiderus also vaguely resembles S. dendroides Whitelegge, 1907 from southern New South Wales ( Fig. 6 C), but the latter has distinctly smaller megascleres, two categories of sigmas, all s-shaped, and rare microxeas not forming bundles (Table 1). The present species should also be compared to the Atlantic S. cearense Salani et al., 2006 ; both species show simple, reduced spiculation, but the present species also has microxeas and sigmas. The sigmas of S. hipposiderus lack the Paresperella -like spines on the outer edge as is seen in the Atlantic species.

There has been some confusion by previous authors in the descriptions of some species of Desmacellidae (including Sigmaxinella and Biemna ) about the possession of raphides versus microxeas. Usually these spicule categories have been combined into a single category (e. g.: Hooper 1984; Salani et al. 2006), yet they are differentiated clearly under electron microscopy (e. g.: Hooper & Lévi 1993). This is the case for S. flabellata Carter, 1885 sensu Dendy, 1897 redescribed by Hallmann (1916). This species was described as having two categories of raphides, yet further examination indicates that the larger category, occurring both in bundles and singly, are microxeas, not raphides.

A further note on S. flabellata is appropriate, as re-examination of one of the syntypes of Axinella flabellata Carter, 1885 (BMNH 1886.12.15.471 from Port Phillip Heads, Victoria), the type species of the genus Sigmaxia Hallmann, 1916 , shows this to actually be a species of Raspailia (Raspailia) Nardo, 1833 . Unfortunately, the other syntype (BMNH 1886.12.15.143 wet) has not yet been located in the collections of the BMNH. Therefore, for the time being, we must use the concept of Sigmaxinella flabellata in the sense of Dendy (1897: 241). Hallmann (1916: 535) subsequently redescribed S. flabellata much more comprehensively based on new material, which he also stated he compared to “one of Dendy’s specimens”. Carter’s (1885) original concept of A. flabellata remains uncertain.

Figures

FIGURE 2. Sigmaxinella hipposiderus sp. nov. Holotype (QMG 323175), habitus, scale bar = 25 mm. A, specimen on deck; B, specimen after preservation in ethanol (70 %).

FIGURE 3. Schematic representation of skeletal arrangement of Sigmaxinella hipposiderus sp. nov., scale bars = 1000 μm. A, schematic of cross-section taken through upper branch of specimen (as indicated by the double-arrow ‘ a’ on whole specimen image); B, schematic of cross-section taken through lower stalk of specimen (as indicated by the double-arrow ‘ b’).

FIGURE 4. Scanning electron micrographs of skeleton structure from Sigmaxinella hipposiderus sp. nov. A, overview of skeleton, showing axial compression and plumose extra-axial region, scale bar = 1000 μm; B, extra-axial region, showing plumose tracts of styles radiating from central axis, scale bar = 1000 μm; C, axial region, showing strong compression with styles arranged in parallel into tightly packed bundles surrounded by dense spongin, scale bar = 200 μm; D, styles arranged in plumose brushes in extra-axial region and penetrating ectosome, scale bar = 500 μm.

FIGURE 5. Scanning electron micrographs of spicule complement from Sigmaxinella hipposiderus sp. nov. A, megascleres are represented by two types of styles, with the long straight styles dominant, scale bar = 200 μm; B, image of microscleres in the mesohyl, showing microxeas forming bundles, but not organised into true trichodragmata, scale bar = 50 μm; C, microxea, smooth and isodiametric, scale bar = 10 μm; D, sigma, c-shaped and without any spines on hooks, scale bar = 10 μm.

FIGURE 6. Comparison of gross morphology of species of Sigmaxinella Dendy, 1897 found in Australian waters. A, S. australiana Dendy, 1897; B, S. soelae Hooper, 1984; C, S. dendroides Whitelegge, 1907; D, S. viminalis Hallmann, 1916; E, S. flabellata (Carter 1885) sensu Dendy, 1897; F, S. ramosa (Carter, 1883); image A from Hallmann (1916, pl. XXXIII, Fig. 1); image B from Hooper (1984, p. 8, Fig. 1); image C from Whitelegge (1907, pl. XLVI, Fig. 42); image D from Hallman (1916, pl. XXXIII, Fig. 4); image E from Hallmann (1916, pl. XXXIII, Fig. 5); image F original, syntype of Phakellia ramosa Carter, 1883, specimen BMNH 1884.4. 14.2, collected from Sydney region; images A – D and E – F to same proportion, both scale bars = 50 mm.