OP
OP
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How to identify a Sponge?
Yesterday I found a really odd-looking thing on the glass of my tank:
(Odd thingy captured with a macro lens)
The shape was so weird that I had no idea what I was looking at, so the obviously took a closer look under the microscope. It quickly became clear that I was dealing with a sponge, since I saw spicules similar to the ones from post 68 on page 4. (Star-shaped spicules alone could also come from colonial sea squirts, but together with the needle-like ones below they point to a sponge)
What I was seeing were "Monaxons", meaning spicules that don't branch in multiple directions and are simply "needle-like". They still come in quite a few different shapes though:
(Names of various Monaxons)
The best match for the spicules I was seeing was "Strongyle", as they didn't change much in thickness and had blunt, rounded ends without being knobbed. A more precise description would probably be "Strongyloxeas" or "Anisostrongyles", but there are so many different types that roughly knowing the group they belong to is already helpful.
However, this alone isn't enough to identify a sponge. So besides these "Megascleres" (large spicules), I also took a close look at the "Microscleres" (small spicules). This specimen had two or three different kinds of those, referred to as Megasters (large asters) and Micrasters (small asters).
(Megasters: "star-shaped" asters called Euasters, or in this case Spherasters or Oxyspherasters)
| Spherasters | Tylospheraster | Strongylospheraster | Oxyspheraster |
|---|---|---|---|
| Ray Tips/Ends | Knobbed | Blunt | Pointy |
(Micrasters: also "star-shaped", but with longer rays. These are called Tylasters, Strongylasters or Oxyasters)
| Asters | Tylaster | Strongylaster | Oxyaster |
|---|---|---|---|
| Ray Tips/Ends | Knobbed | Blunt | Pointy |
Combined, these different spicules help quite a lot with the identification. The combination matches the family definition of Tethyidae, and after searching through possible species, I found Tethya gracilis, Known in German as the "Wandering Sponge" (freely translated)
The original species description comes from German aquaria and also covers Tethya wilhelma and Tethya minuta, but so far T. gracilis is the best match. To confirm it, I would still need to check the sponge's choanosome (the inner region of the sponge) for Oxyasters, since the images I took are only from the Cortex (outer layer), and measure the Oxyspherasters, as their size, shape and number of rays are what set T. gracilis apart from the other two species.
With measurements and maybe a "fully grown" specimen, it might have been possible to pin down the exact species with reasonable certainty. But I've already done a bunch of reading to get this far, so I think I'll leave it at the family, and maybe genus level for now.
I hope explaining at least a tiny bit of the process I go through when trying to identify sponges was interesting to you all 
Resources
- Łukowiak M., 2020. Utilizing sponge spicules in taxonomic, ecological and environmental reconstructions: a review.
- Łukowiak et al. 2022. The terminology of sponge spicules.
- Spicules.org. free illustrated spicule database based on Łukowiak et al. 2022.
- Marine Conservation Society. Sponges of the British Isles ("Sponge V"), glossary of spicule terms.
- Sarà 2002. Family Tethyidae Gray, 1848. In: Systema Porifera.
- Sarà et al. 2001. Three New Species of Tethya (Porifera: Demospongiae) from German Aquaria.
- Santodomingo et al. 2024. Integrative taxonomy of Tethya: description of four new species based on morphology, phylogeny and microbiome diversity.
- WoRMS. Tethya gracilis Sarà, Sarà, Nickel & Brümmer, 2001.
