Specimen of the Week: Week Forty-One
By Emma-Louise Nicholls, on 23 July 2012
Have you ever looked at something you’ve not seen before and thought “What on earth is THAT?” I pride myself on my zoological knowledge, but no matter how much you know, every day is a school day. When I first started at the Grant Museum I was busy putting a thousand specimens on the floor in the middle of the museum, when I came across something quite unfamiliar. I could tell from its structure roughly what group of animal it was, but had never seen this particular thing before. It was beautiful, fragile and… dirty. (Some building work going on next door had been shaking dust down on to some of our specimens, tsk.) I am happy to say it is now beautiful, fragile and clean. This week’s Specimen of the Week is…
**!!!The Glass Rope Sponge!!!**
1) The glass rope sponge is a marine species that cannot survive in brackish- or fresh-water. Although there are currently no known specimens of glass rope sponges from the fossil record, it could be that we just have not found them yet. As my ex-MSc supervisor liked to say ‘absence of evidence is not evidence of absence’. Quite right.
2) The glass rope sponge is part of the class of sponges called Hexactinellida, meaning that part of their silicious skeleton radiates in a six-fold pattern. The silicious skeleton in the case of the glass rope sponge, is what gives it its name. If you imagine a small rugby ball with a rope coming out of it, that somehow stands erect in water, and is see-through-glass-coloured, you are more or less looking at a glass rope sponge.
3) The ‘stem’ is composed of siliceous fibres that have evolved into long, thin strands. The silica portion of the sponge is transparent and in the case of our glass rope sponge; Hyalonema sieboldii, also known as the Japanese glass rope sponge; these long, elegant strands have long been used as ornaments.
4) Glass rope sponges are found in southeast Asia in areas of the Andaman Sea, Indian Ocean, Pacific Ocean and South China Sea. Their distribution includes offshore waters belonging to the Philippines, Indonesia and Japan. They are a benthic species of sponge and have a sessile life habit. This means that they are attached by the base to the seafloor substrate and are subsequently unable to move freely. As with most, but not all species of sponge, this species is totally harmless to humans.
5) The specimen of glass rope sponge held at the Grant Museum came in a ‘buy one get numerous encrusting zoanthids for free’ deal. On the stem of the glass rope sponge are around 200 small animals that belong in the group Cnidaria, which includes corals, sea anemones and jellyfish. Each of the tubes seen in the image on the left would have contained an individual animal, or polyps. Much like the sponge they have grown attached to, they are not free-moving and need a substrate for a base. They have therefore colonised the glass rope sponge and would have survived by filter-feeding detritus material out of the water column using tiny tentacles.