Theonella xantha ( Sutcliffe, Pitcher & Hooper, 2010 ) Hall & Ekins & Hooper, 2014

Hall, Kathryn A., Ekins, Merrick G. & Hooper, John N. A., 2014, Two new desma-less species of Theonella Gray, 1868 (Demospongiae: Astrophorida: Theonellidae), from the Great Barrier Reef, Australia, and a re-evaluation of one species assigned previously to Dercitus Gray, 1867, Zootaxa 3814 (4), pp. 451-477 : 461-463

Theonella xantha ( Sutcliffe, Pitcher & Hooper, 2010) n. comb.

Figs 1 , 4 , 6

Dercitus xanthus Sutcliffe, Hooper & Pitcher, 2010, p. 6

Dercitus (Stoeba) xanthus Sutcliffe, Hooper & Pitcher, 2010 ; van Soest, Beglinger & de Voogd, 2010, p. 38 (subgenus reassignment); van Soest 2012c (online resource)

Material examined. Holotype: QM G329976 (=SBD513022), Australia, Great Barrier Reef , inter-reef sea floor, south-east of Rock Cod Shoal , 23.7249°S 151.665°E, 34.3 m (depth), coll. CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 20.Sep.2004, epibenthic sled . Paratypes: QM G329977 (=SBD513042), Australia, Great Barrier Reef, inter-reef sea floor, west of Fairfax Island , 23.8849°S 152.105°E, 41.8 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Gwendoline May, 13.Apr.2004, epibenthic sled ; QM G329978 (=SBD505424), Australia, Great Barrier Reef, inter-reef sea floor, west of Old Reef , 19.4049°S 147.935°E, 42.0 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 27.Nov.2003, epibenthic sled .

Other material: QM G329095 (=SBD500449), Australia, Great Barrier Reef, inter-reef sea floor, east of Davies Reef , 18.8349°S 147.685°E, 62.9 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 22.Sep.2003, trawl ; QM G329183 (=SBD517180), Australia, Great Barrier Reef, inter-reef sea floor, north-west of Devlin Reef , 11.805°S 143.825°E, 37.9 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 5.Feb.2005, trawl ; QM G329186 (=SBD517310), Australia, Great Barrier Reef, inter-reef sea floor, north-west of Devlin Reef , 11.805°S 143.825°E, 34.7 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 4.Feb.2005, trawl ; QM G329283 (=SBD537784), Australia, Great Barrier Reef, inter-reef sea floor, east of Gladstone , 23.8349°S 151.585°E, 26.9 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 14.Nov.2005, trawl; G331398 (=SBD500399), Australia, Great Barrier Reef, inter-reef sea floor, south-west of Little Broadhurst Reef , 19.045°S 147.3949°E, 14.9 m (depth) , QM coll. CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 21.Sep.2003, epibenthic sled ; QM G331401 (=SBD500654), Australia, Great Barrier Reef, inter-reef sea floor, west of Big Broadhurst Reef , 18.925°S 147.525°E, 17.2 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 22.Sep.2003, epibenthic sled ; QM G331411 (=SBD506498), Australia, Great Barrier Reef, inter-reef sea floor, south-west of Rudder Reef , 16.245°S 145.6149°E, 21.0 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 9.Oct.2003, epibenthic sled ; QM G331426 (=SBD512852), Australia, Great Barrier Reef, inter-reef sea floor, south-west of Lamont Reef , 23.625°S 151.875°E, 27.3 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 21.Sep.2004, epibenthic sled ; QM G331429 (=SBD513056),vAustralia, Great Barrier Reef, inter-reef sea floor, north-west of Tryon Island , 23.2249°S 151.7049°E, 28.0 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 22.Sep.2004, epibenthic sled ; QM G331436 (=SBD513964), Australia, Great Barrier Reef, inter-reef sea floor, north-east of Magnetic Island , 18.995°S 147.095°E, 35.0 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 26.Apr.2004, epibenthic sled; G331463 (=SBD525255), Australia, Great Barrier Reef, inter-reef sea floor, east of Gladstone , 23.935°S 151.9333°E, 51.0 m (depth) , QM coll. CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 19.Sep.2004, epibenthic sled ; QM G331662 (=SBD524169), Australia, Great Barrier Reef, inter-reef sea floor, north-east of Mumford Reef , 22.1549°S 150.385°E, 79.2 m (depth), coll . CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Lady Basten, 9.May.2004, epibenthic sled ; QM G331964 , Australia, Great Barrier Reef, inter-reef sea floor, south-west of Polmaise Reef, 23.6383°S 151.5025°E, 26.0 m (depth), coll. Vicki Hall, Northern Fisheries, Cairns (former Department of Employment , Economic Development and Innovation , Queensland Government), 22.Nov.1999, epibenthic sled .

Redescription. Based on examination of holotype, 2 paratypes and 16 vouchers; all specimens post-fixed in ethanol (70%) after initial frozen storage.

Growth form and gross morphology: sponge consists of very thin sheets, thickness ~ 30 µm; sheets encrust over assorted non-specific substrates, cements a variety of unidentified broken gastropod shells, polychaete tubes, diatoms, broken coral debris into single mass; incorporates large amounts of quartz sand and debris, small amounts of filamentous algae; holotype mass measures ~ 4 × 5 × 3 cm (total mass dimensions) ( Figs 1C , 6A–B )

Colour: unknown in life; dark orange to yellow portions of sponge mixed with green algae and dirty cream to brown sand and debris when frozen; colour retained in ethanol; stains ethanol dark golden yellow; yellow pigment greasy.

Oscules: unobserved macroscopically in frozen and fixed material; visible microscopically, few, inconspicuous, shallow, discrete, broadly elliptical, ~ 100 µm (diameter), distributed sparsely.

Texture: difficult to determine because of large amounts of debris in sponge mass; mass friable, fragile; sponge soft, very fragile, friable, granular, flaccid, limp, highly compressible, slowly resilient, spongy.

Surface ornamentation: even, smooth.

Ectosomal skeleton: indistinguishable from choanosome.

Choanosomal skeleton: lax, vague; rigid skeleton entirely absent; skeleton consists only of confused arrangement of interstitial microscleres scattered throughout mesohyl; microscleres sparse in patches, distributed singularly, concentrated in other regions, sometimes forming very dense carpet; collagen homogenous; occasional foreign megascleres (oxeas, regular triacts) incorporated into mesohyl ( Figs 6B–C ).

Megascleres: nil.

Microscleres: single category of microrhabd; microrhabds as highly spined microxeas, small, isodiametric, robust, generally straight but rarely slightly curved, curvature irregular, tips rounded, rhabd covered with profuse, small, blunt, conical spines; spines shorter than rhabd width, raised obviously from spicule shaft, arise perpendicular to axis; shaft straight, lacks torsion; dimensions 8.1–21.5 (14.7) × 1.3–2.9 (2.2) µm ( Fig. 6D ).

DNA sequence data. 15 COI barcode sequences were obtained for specimens of T. xantha , including the holotype and both paratypes (GenBank Accession: KJ494361 – KJ494375 ; see Table 1); each of these sequences was 709 bp in length (including primers), except 4 which were shorter ( KJ494367 : 597 bp; KJ494365 & KJ494369 : 631 bp; KJ494361 : 634 bp (including primers)).

Ecology and distribution. Specimens of T. xantha have, to date, been found associated with the seabed only in the inter-reef areas of the Great Barrier Reef. Sutcliffe et al. (2010) draw attention to enormous biomass that specimens of T. xantha represent; they are distributed widely across the entire span of the Great Barrier Reef, extending from regions of low to high latitude, and are found in high densities in the inter-reef area. Sutcliffe et al. (2010) did not find any major correlation between the presence or prevalence of T. xantha and the composition of the underlying substrate, although specimens were not recovered commonly in areas with a high proportion of mud in the sediment.

Remarks. We re-examined the holotype and both paratypes, in addition to 16 vouchers, of T. xantha using SEM and light microscopy. In no specimen were we able to observe any native megascleres; all specimens were found to contain only small, microspined microrhabds. The samples were morphologically homogeneous, with large amounts of debris incorporated into the structure of all specimens, including non-active polychaete tubes and shells, fragments of diatoms, and coralline and siliceous rubble. Small amounts of filamentous algae (or bacteria) were incorporated into the mass also.

The measurements of the microrhabds were consistent among the samples we examined. The average microrhabd length was 14.8 µm (range 8.1 to 21.5 µm); three outlier measurements were detected (7.0 µm, 23.2 µm and 24.1 µm). The lengths fitted a normal distribution, which was not skewed appreciably. The median spicule length was 14.6 µm; there were relatively few spicules which measured less than 13.1 µm. The majority of microrhabds reached lengths of between 13 and 17 µm.

Comments. This species was attributed initially to Dercitus Gray, 1867 by Sutcliffe et al. (2010) based on their interpretation of the morphology of this species as comprising sanidasters and three-rayed calthrops (calthrops reported in 20% of their samples). Van Soest et al. (2010) and van Soest (2012c) classify D. xanthus within the subgenus Dercitus (Stoeba) Sollas, 1888 . We have been unable to replicate the sighting of any native calthrops in the holotype or paratypes, nor in any other specimens we examined. We can confirm the common occurrence of broken calthrops distributed sporadically in several of the samples we investigated, however, in no specimen could these be interpreted as native; indeed, in one specimen of T. deliqua , dense rafts of non-native broken calthrops were found aggregated in portions of the sponge mass of this species also (as noted above). The geometry of regular calthrops and triods and the thickness of the rays of these megascleres may make these particular spicule morphologies exceptionally robust; the tumbled edges, however, support their foreign origins. The absence of calthrops, and the interpretation of the microscleres as microrhabds, rather than sanidasters, renders the placement of this species within Dercitus unjustified. We interpret the morphology of this species as being consistent with other megasclere-lacking species of Theonella , and this interpretation is supported by DNA-based studies (see below); based on these data, we designate this species within Theonella , as T. xantha ( Sutcliffe, Hooper and Pitcher, 2010) n. comb.

Morphologically, specimens of T. xantha are very similar to those of T. deliqua and T. maricae , however, they may be distinguished by the shape of the microrhabds and ecological characteristics. Specimens of T. xantha are recognisable immediately from those of T. maricae by the size of the microrhabds; the spicules of T. maricae are more than twice as long as those of T. xantha . Discrimination between T. xantha and T. deliqua is subtler; boxplots comparing the microrhabd lengths ( Fig. 4 ) show that the range of lengths of the microscleres of both species are broadly equivalent. The microrhabds of T. xantha , however, are more robust in appearance than those seen in T. deliqua . The spines along the shaft of the microrhabds of T. xantha are bluntly conical and generally shorter than the width of the rhabd. Contrastingly, the microrhabds of T. deliqua are less robust in appearance, being slender and bearing sharply pointed spines, which are longer than the length of the underlying rhabd. Structurally, T. xantha , like T. maricae , consolidates the seabed substrates and cements a variety of rubble types, however, these two species can be distinguished from T. deliqua by this characteristic, which contrasts the aggregation of only one species of Tenagodus shell by specimens of T. deliqua .

Figures

FIGURE 1. Photographs of fixed whole specimens of desma-less species of Theonella Gray, 1868. A. Theonella deliqua n. sp., habitus, part of holotype (QM G329195), fixed in ethanol; scale bar = 2 cm. B. Theonella maricae n. sp., habitus, three parts of holotype (QM G331427), fixed in ethanol; scale bar = 2 cm. C. Theonella xantha (Sutcliffe, Hooper and Pitcher 2010) n. comb., habitus, part of holotype (QM G329976), fixed in ethanol; scale bar = 2 cm.

FIGURE 4. Summaries of statistics for sets of measurements of microrhabds from Theonella deliqua n. sp., Theonella maricae n. sp. and Theonella xantha (Sutcliffe, Hooper and Pitcher, 2010) n. comb. The boxes for each species include the minimum, maximum, mean, standard deviation and variance. A boxplot has been used to demonstrate the distributions of the means of the measurements for each species and to indicate significant differences among them. Outliers are indicated by asterisks (*). The ranges of the measurements for T. deliqua and T. xantha can be seen to be approximately equivalent, and are normally distributed. Stronger skew and Kurtosis are shown for the measurements for the specimens of T. maricae. Most measurements of the microrhabd length for T. maricae greatly exceed those of the other two species, as illustrated in the boxplot.

FIGURE 6. Theonella xantha (Sutcliffe, Hooper and Pitcher, 2010) n. comb. Micrographs (SEM) of paratype, QM G329978, and voucher specimen, QM G329095. A. QM G329095, overview of a fragment of sponge, showing large amounts of organic and inorganic debris, including coral rubble and empty polychaete tubes; scale bar = 500 µm. B. QM G329978, detail of sheets of sponge, showing oscules and carpets of microrhabds; scale bar = 200 µm. C. QM G329978, detail of accumulation of microrhabds in situ; scale bar = 30 µm. D. QM G329978, single microrhabd; scale bar = 10 µm.