Theonella deliqua Hall & Ekins & Hooper 2014, n. sp.

Theonella deliqua n. sp.

Figs 1–4

Material examined. Holotype: QM G329195 (=SBD520375), Australia, Great Barrier Reef, inter-reef sea floor, south of Wreck Island Reef, 23.775°S 15.005°E, 41.3 m (depth), coll. CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Gwendoline May, 13.Apr.2004, epibenthic sled. Paratype: QM G325567 (=SBD518107), Australia, Great Barrier Reef, inter-reef sea floor, south of Wreck Island Reef, 23.375°S 151.975°E, 43.5 m (depth), coll. CSIRO Great Barrier Reef Seabed Biodiversity Project on RV Gwendoline May, 22.Apr.2004, epibenthic sled.

Description. based on examination of holotype and paratype; both specimens post-fixed in ethanol (70%) after initial frozen storage.

Growth form and gross morphology: sponge consists of very thin sheets, thickness ~ 50 µm; sheets encrust exclusively over single species of Tenagodus Guettard, 1770 (Gastropoda, Caenogastropoda, Siliquariidae); sponge forms mass with snails, cements Tenagodus shells, incorporates small amounts of algae, detritus and debris; Tenagodus shells in interior of mass appear non-live, shells at perimeter of mass sometimes contain live (at time of fixation) snails; mass incorporates Tenagodus of various ages, some tiny (<1 mm diameter), others mature (> 5 mm diameter); holotype mass measures ~ 5 × 7.5 × 3 cm (total mass, including shells) (Figs 1A, 2A–D).

Colour: unknown in life; bright orange portions of sponge mixed with green algae and cream snail shells when frozen; colour retained in ethanol; stains ethanol pale golden yellow; yellow pigment greasy.

Oscules: unobserved macroscopically in frozen and fixed material; visible microscopically, few, inconspicuous, shallow, discrete, elliptical, ~ 100–200 µm (length), distributed sparsely (Fig 3A).

Texture: difficult to determine due to inclusion of large volume of snail shells; sponge very soft, 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, forming dense carpet; collagen homogenous; occasional foreign megascleres (oxeas, regular triacts) incorporated into mesohyl (Figs 2D, 3A–C).

Megascleres: nil.

Microscleres: single category of microrhabd; microrhabds as highly spined microxeas, small, isodiametric, slender, fine, slightly curved, curvature irregular, tips sharply hastate, rhabd covered with numerous, fine, narrow, conical spines; spines as long or longer than rhabd width, project prominently from spicule shaft, arise perpendicular to axis; shaft straight, lacks torsion; dimensions 7.2–21.6 (14.6) × 2.5–3.4 (3.0) µm (Fig 3D).

Etymology. The specific epithet deliqua derives from the Latin deliquus (adjective), meaning lacking or wanting, and refers to the absence of desmas in this species.

DNA sequence data. 1 COI barcode sequence was obtained for the holotype (GenBank Accession: KJ494355; see Table 1); this sequence was 709 bp in length (including primers).

Ecology and distribution. Specimens of T. deliqua have, to date, been recovered only from the seabed of the inter-reef region of the Great Barrier Reef. Both specimens that we have examined have formed close associations with specimens of a single species of Tenagodus (Siliquariidae). Species of Tenagodus are known to occur only in obligate relationships with sponges (Bieler 2004), although species-specificity (between sponge and snail) of this obligate relationship has not been established (Pansini et al. 1999).

Remarks. During examination of the holotype of Theonella deliqua n. sp., a dense mass of regular triactinal spicules (calthrops) was found; many of these calthrops were damaged and had broken rays (Fig 2D). This mass of spicules was found lying in a valley between two Tenagodus shells and incorporated broken oxeas and other spicules (from the Family Didemnidae Giard, 1872 (Class Ascidiacea) and some possibly of holothurian origin). Another similar region, containing an accumulation of monactinal spicules, was found in the broken mouth of an empty Tenagodus shell (Fig 2C). These regions overlie the thin sheets of T. deliqua, but are not incorporated intimately into the mesohyl of the sponge. The localisation of the spicule masses, in conjunction with their varied composition, indicates clearly that they are of foreign origin, and are not innate components. Further, T. deliqua itself encrusts closely over the surface of the Tenagodus shells, cementing only the shells together; detritus and debris appears to amass in rafts at low points where two shells are joined by the sponge.

The microrhabds of the holotype and paratype of T. deliqua are of similar proportion, averaging 14.6 µm in length, and spanning a range from 7.1 to 21.6 µm. The range of spicule measurements was normally distributed (Fig. 4), although one spicule was detected which lay outside of this normal range, measuring only 6.7 µm. Although the range of microrhabd length is quite large, the majority of spicules ranges between 12 and 17 µm in length, and this size may be interpreted as “typical” for specimens of T. deliqua.

Comments. Specimens of T. deliqua are readily distinguished from the type-species for Theonella, T. swinhoei, (and all other currently known species), by the absence of tetractinal megascleres. No desmas and no triaenes (phyllotrianes nor dichotriaenes) were observed in either specimen of T. deliqua that we examined. The spicule complement of T. deliqua comprises only microrhabds; this condition has not been observed to date in any recorded species of Theonella. Despite the lack of obvious morphological homologies with T. swinhoei and the other members of Theonella, membership of this new species to Theonella can be asserted confidently. The microrhabds of T. deliqua have a similar morphology to those observed in T. swinhoei and other species of Theonella. Although they are not noted directly in the original description by Gray (1868), we have examined material in the QM Porifera collection which is attributed to T. swinhoei, and observed that the microrhabds of T. swinhoei, like those in T. deliqua, are generally straight; although the rhabd may be bent, the central axis is free completely of any torsion, with fine, conical spines projecting perpendicularly from the spicule shaft. The lack of torsion is significant and shared between the microscleres of T. swinhoei and T. deliqua. The straightness of the rods is in contrast to the morphology seen in the streptasters of other astrophorids; this straight morphology justifies our use of the term “microrhabd”, rather than sanidaster or streptaster, to describe these microscleres. Further, and perhaps more significantly, the combination of the corroborating molecular analyses (see below) and the presence of shared chemotaxonomic characters (see below) offers strong support to the attribution of this new species to Theonella.