The sponge I have obtained from the UQ Lab Aquarium for this species project is a hard-bodied sponge in the genus of Tethya sponges, within the class Demospongiae. Demosponges have a spongin skeleton, with or without siliceous spicules. The specimen also belongs to the order Hadromerida; those demospongiae with radially patterned monactinal (single-ended ray) spicules (Vacelet & Boury-Esnault, 2013; Lévi, 1998). It belongs to the Phylum Porifera, within Kingdom Animalia and family Tethyidae (Heim et al., 2007. The specific species, I have classified as Tethya robusta, on account of its distinguishing physical characteristics; spherical shape, cortical spiculation, distribution and spicule types (Sarà, 1992).

Tethya sponges are well known for their globular-to-spherical body morphs and are generally divided into two morphofunctional groups; hard-bodied and soft-bodied. Tethya robusta is a hard-bodied sponge, with a compact and tough external cortex that is typically yellowish, pale orange or pale brown (Sarà & Sarà, 2004; Sarà, 1990). Sarà et Sarà (2004) characterises T.robusta as notably spherical and spiculated, with very distinct rounded tubercles (~2-4mm, Sarà 1990). Flattened papillae and externally protruding spicules also define the species (Sarà & Sarà, 2004). The internal medulla is usually ochraceous yellow, or ‘apple’ to olive-green (Sarà, 1992). The cortex of my collected specimen was a pale orange and the medulla, a bright, potentially ‘apple’ green (see Figure 1). An extracted portion of the specimen analysed under dissection (x10) and compound microscope (x40-60), indicates a well-defined cortex-medulla boundary and prominent cortical spiculation, as described for T.robusta (Figures 1-4, Sarà, 1992).  

Within T.robusta’s globose spongin form, silaceous spicules called strongyloxeas (Figure 3), spherasters (Figure 3) and micrasters (figure 6) were found, as expected for most Tethya species (Sara, 2002). Strongyloxeas (Figure 1-4 & 5A) are stylote (elongated) megascleres that radiate outwards from the choanosomal core, as visible to the naked eye (Figure 1, Sarà, 2002). Specifically, strongyloxeas are short and apically rounded in some areas for this species (Figure 4 & 5A) with dense packing of longer, less-rounded strongyloxeas extending outward from the central region of the medulla (Figure 1-4, Sarà, 1990).

Megascleres and microscleres:

Strongyloxeas provide the majority of structural support within T.robusta, while the spherasters and micrasters, known as microscleres, have a lesser known auxiliary function; maintaining inhalant pores on the sponge surface and surrounding inhalant and exhalant canals within body tissue (Bavestrello et al., 2000; Sarà & Manara, 1991; Ribeiro & Muricy, 2011). The following scanning electron micrographs (SEM's) in figure 6 (below) identify the spherasters and micrasters observed within the medulla canals of my collected specimen.

Architectural skeleton:

Different Tethya species have different megasclere and microsclere shapes and distributions within the cortex and medulla (Sarà, 1992; Sarà, 1990; Sarà & Gaino, 1987). The distribution for T.robusta observed by Sarà (1992) at Laing island in Papua New Guinea (figure 7), shows radial divisions of stongyloxeas as the main category of spicules, with spherasters (~20-80μm) in the medulla being smaller than those in the cortex, and cortical and medulla micraster forms being different (Figure 8, Sarà, 1992). Micraster forms are defined primarily by the 'sharpness' of their ray tips, from tylasters (most sharp) to chiasters (intermediate) and oxyasters (blunt, Van Soest et al., 2012). According to Sarà (1992) cortical micrasters include; oxyasters, chiasters and tylasters (8-12μm), and medulla micrasters include; oxyasters-chiasters (12-16μm). This is compared with the scanning electron microscope (SEM) images of the medulla and cortex for the collected specimen (Figure 8, Sarà, 1992). Notable size variation of megasters (spherasters) within T.robusta is expected between populations in Papua-New Guinea, the Maldives and Australia, with Australian T.robusta having generally larger megasters (Sarà, 1993). Unlike T.boeroi, no medulla-nucleus is found in T.robusta, as would be signified by transverse strongyloxeas in figure 9 (Sarà, 1992). The cortical layer is well developed with spicule layering, and small sub-dermal lacunes are observed below (Sarà, 1990), as shown in Figure 1.  

Sara (1992), describes the morpho-functional differences observed between soft-bodied and hard-bodied Tethya at Laing Island, regarding ecological niche. Soft-bodied Tethya, T.viridis and T.microstella, appear to coexist in a majority of habitats with hard-bodied T.robusta; whereby soft-bodied species are found in sheltered areas, and the hard-bodied T.robusta, in exposed regions (Sarà, 1992, figure 10). A similar dynamic is also observed on a north Australian reef, where T.robusta again occupies exposed areas of the habitat, while T.orphei and T.microstella occupy the sheltered niche (Sarà 1990). Another potential example of this co-existence is seen in Mediterranean reefs, between T.citrina (soft-bodied) and T.aurantium (hard-bodied) (Corriero et al., 1989). Sarà (1990) suggests that within soft-bodied Tethya species, flattening seems to be an adaptation to inhabiting tight interstitial areas. Clear differences in the skeletal architecture and aquiferous systems present questions about the resource partitioning between similar species on the same reef and how differences in feeding modalities and locomotion between soft-bodied and hard-bodied Tethya may facilitate sympatry (Sarà, 1992). Additionally, the tank that my T.robusta specimen was collected from also possessed two other Tethya species (figure 11) that were soft-bodied, although obvious differences between reef-habitat and tank-habitat should be noted.   

Sexual Reproduction:
Tethya are oviparous sponges which produce ooctyes with a true primary envelope, a common feature to all of Eumetazoa (Ereskovsky, 2010) and released eggs have peripheral vacuoles to facilitate the attachment to the substrate and protect the egg (Ereskovsky, 2010). The synthesis of a collagen capsule by the lophocytes of the mesohyl is seen in Tethya citrina, and this is hypothesized to be a prototype of the Metazoan vitellaine membrane (Ereskovsky, 2010). Oocytes can be found throughout the choanosomal tissue of Tethya sp. Sexual reproduction includes; gametogenesis, fertilization, embryonic development and sexual differentiation. In the study of Corriero et al. (1996) on T.citrina & T.aurantium, no males were found in collection. This is either because of a short season of spermatogenesis or simply because males are scarce in these populations (Corriero et al. 1996). Scalera Liaci et al. (1971) only found 6 males in a population of 863 T.aurantium. More information is needed about the reproductive cycles of T.robusta. Unfortunately, no ooctyes were found in my specimen.

Sexual Strategies:

T.aurantium and T.citrina are two Tethya species that live sympatrically in the Mediterranean. Both are gonochoristic and partially coincide in oocyte production during the Summer months (Corriero et al., 1996). In the summer, T.citrina produces more ooctyes than T.aurantium. However, in the winter months when both bud asexually, T.aurantium produces many more asexual buds (Corriero et al., 1996). T.citrina is also adapted to colder, more northern waters and sexually reproduces earlier, perhaps suggesting that it outcompetes T.aurantium in sexual reproduction (Corriero et al., 1996). It is hypothesised by (Corriero et al., 1996) that these differences can be explained by differential reproductive resource allocation. 

Asexual Reproduction:
Asexual budding, provides an alternate method of self-replication, well-described in sponges. Bud shape and size within Tethya can be highly variable, for example, T.norvegica is a deep-water species that has notably fast budding, with buds that produce secondary budding (Corriero et al., 1996). According to Sarà (1992), T.robsuta has stolons to anchor its buds. According to observation of Tethya budding, stalks progressively constrict until the propagule breaks off and moves to grow on the substrate further away (Vacelet, 1959, Sánchez, 1984; Teixidó et al., 2006). Unfortunately, no stolons or asexual buds were observed in my collected specimen.

Methods: In the interest of recording T.robusta locomotion, I used three Tethya found in a tank of UQ Lab Aquarium as subjects in an experiment, positioning each Tethya in the centre of their own container lined on one side with blue cellophane and the other with red (see figure 12A). The initial position of the sponge was recorded on the bottom of the container with permanent marker and recorded again the following week (t=7 days), over a period of two weeks (figure 12B). One of the sponges (T.robusta) was sacrificed from the experiment in the second week for dissection analysis (n=5). My experiment was based upon a previous experiment on Tethya sp., that used light and dark sides of a container to test for phototaxis (Star, 2015). The Tethya were fed with microalgal solution at the start of the second week and water was changed. Containers were rotated clockwise and swapped to another container position anti-clockwise to reduce environmental bias with randomization.

Aim: The experiment aimed to test for a bias in movement away from the blue-light side, because blue-light sensitive cryptochrome has been proposed as the major photoreceptive system for other demosponges such as Suberites domuncula (Müller et al.2010) and Amphimedon queenslandica (Rivera et al., 2012).
The key assumption of this experiment -that Tethya sensing blue-light will evade it in order to seek sheltered habitat -is perhaps flawed, because as noted in the literature (Sara, 1992), hard sponges, including T.robusta have been known to occupy open habitat (See Ecology: Sympatry & Ecological Niche, above).

Results: Minimal movement (<1cm) was observed for one of the sponges, with no obvious bias toward either side (figure 12B). Considering that the Tethya species were not removed from the rubble, as in Star (2015), there is the possibility that they might be less inclined to seek sheltered habitat. However, this experiment, low replication (n=5) and potential pseudoreplication aside, did not find evidence of blue-light sensitive negative-phototaxis, or a bias towards red light. 

With more Tethya subjects (n>10) of the same soft-bodied, sheltered-niche seeking species (T.viridis or T.microstella, for example; Sarà, 1992) this experiment could perhaps give more valuable insight into the presence of blue-light sensitive cryptochrome within demosponges, as a precursor to more complex photoreception (Gehring and Seimiya, 2010).

The aquiferous system within Tethya species, as observed in T.wilhelma, consists of the following components, following the current of water through the sponge (figure 13):

ostia -> incurrent canals -> prosopyls -> choanocyte chambers -> apopyles -> excurrent canals -> oscules

Tethya, as a genera within demospongiae, have leucon-typecanal systems with complex canal regions and choanocyte chambers (Hammel & Nickel, 2014). The ostia, in T.robusta, are generally reduced compared to other species (Sarà, 1990). Microscopic sub-dermal lacunae act as incurrent openings to the incurrent canals (Sarà, 1990). From there, water is flushed between the prosopyle (incurrent opening of the choanocyte chamber) and apopyle (excurrent opening), through the choanocyte chambers where water velocity changes due to pressure drop (Figure 14 ). Small to large variations in apertures of the canal system contribute significantly to the pressure drop that occurs to optimize nutrient uptake and gas exchange within the system (Hammel & Nickel, 2014). While choanocyte chambers are necessary displacement pumps that create differentials in the aquiferous system, resistance is also necessary to increase particle rate capture, as can be seen in figure 14 (Hammer & Nickel, 2014). 

As mostly, sessile filter feeders they are highly dependent on their aquiferous systems for fundamental physiological function (Hammel & Nickel, 2014). Therefore, the morphological and architectural complexities within the aquiferous system must reflect hydrodynamic constraints and fluid dynamics (Hammel & Nickel, 2014). The key effectors of contractions are endopinacocytes (Nickel et al., 2011). These cells cause changes in the diameters of canals, to increase resistance in the system (Nickel et al., 2011). Contractile waves, such as those observed in T.wilhelma, have also been shown to affect perfusion rates (Nickel et al, 2011). Interestingly, Hammer & Nickel (2014) discovered that choanocyte chambers in T.wilhelma have ‘reticuloapoplyoctyes’ which are involved in the regulation of water flow within choanocyte chambers. This cell type, as shown in figure 15 (4), is highly fenestrated to allow for the gradual influx of water through the apopylar opening, increasing the gauge inflation and resistance, without risk of self-inflicted damage (Hammer & Nickel, 2014). The number of choanocytes within a chamber was found to be dependent on the chamber and individual size of the Tethya (Hammer & Nickel, 2014). I was not able to find the choanocyte chambers in SEM, though one can observe similarities in the lacunae of T.robusta (figure 1 & 13). While T.wilhelma gives a good reference for T.robusta, more investigation of species-specific anatomy is needed within the Tethya genus.

Sponges are a critically important part of benthic ecosystems in polar, temperate and tropical seas.  In these settings, they provide important ecosystem services that range from the bio-erosion of calcium carbonate structures, formation of habitat for many other species and production and consolidation of sediments (Bell et al. 2008).  Demospongiasuch as Tethya sp. also provide important roles in cycling of silicon, which may be of global significance (Bell, 2008). One study on Caribbean coral reefs includes that sponges provide several, very crucial functional roles; primary production, nitrification, calcification, cementation, bioerosion, water filtering and chemical exhalatant properties (metabolites), among others (Diaz & Rützler,2001). Thus, losses of location-specific species are likely to have large-scale impacts on respective ecosystems.

While sponges, as a group, are not considered threatened in many parts of the world (Bell et al. 2015) the destruction of habitat in tropical regions from activities such as seabed mining and declining water quality threaten many of the habitats that sponges depend on (Bell et al., 2015). A lack of data exists about how most species are affected by anthropomorphic activity and there is no comprehensive assessment of sponge conservation status, though efforts in the Mediterranean have received attention for threats resulting from the overharvesting of specific sponge species (Bell et al., 2015). Importantly, the impacts of ocean acidification and climate change need to be considered, as well. Warming related mass mortality (80-90%) in Mediterranean sponges was observed in 2011 (Cebrian et al., 2011).

Interestingly, there are species of Tethya, such as T.orphei, which are externally black or dark violet due to the filamentous cyanobacteria found in the outer layers of the cortex (Sarà,1990). Research also finds evidence that various microbes associated with sponges, including T.berquistae and C.nucula, produce a multitude of secondary metabolites (Mehbub et al., 2014); Nickel, 2006) that can be used for medicinal drug treatments (Anjum et al., 2016). In my observation under compound microscope of T.robusta's cortex, I found what could potentially be black cyanobacteria (figure 19).

 Research into nucleosides, such as ‘spongouridine’ in T.crypta, have been used for the synthesis of the anti-viral drug, ara-A, as well as the anticancer agent, ara-C (Anjum et al., 2016; Proksch et al., 2002), which is used to treat lymphoma and leukaemia. Derivatives are also being used for other cancers (Anjum et al., 2016). These examples among several others in the literature demonstrate the drug discovery potential associated with sponges, in particular, Tethya sp, such as T. robusta.