The Ulster Museum - Object Of The Month

Hymedesmia (a new species)

April

This was one of 28 new species discovered by Ulster Museum researchers during a project on the Sponges of Rathlin Island. It will be named after Rathlin Island. It has a very distinctive appearance, bright yellow in colour with raised holes (oscules) surrounded by intake sieves to take in water for feeding, so unlike many other sponge species can be identified by its living appearance. Each individual sponge is about 1cm in width and can be up to 4cm in length. Since its discovery on Rathlin the museum team have also found it on the Maidens, a small cluster of rocks on Northern Ireland's east coast.

Several specimens of this species were collected by SCUBA diving, from depths of between 20 and 50 metres. The researchers took photos of the sponges using cameras in underwater housings before cutting a small piece of the sponge and collecting it in a plastic bag. Once at the surface the sponges are preserved in alcohol and stored in the museum's collections.

Sponges are identified by tiny skeletal structures termed "spicules". Many species look similar when living so examining these structures is the only way they can be accurately identified. Each species has a different combination of spicule sizes and shapes. This species has spiny spicules with unusual conical spines. To identify it the museum researchers had to examine these using a scanning electron microscope, enabling them to see them at over 10,000 times life size. Most species of this genus have been described from Scandinavia so as part of their research they visited sponge collections held in Copenhagen to make sure the species hadn't already been described. The material of this species and the other new Rathlin species held by the museum will become "type specimens" when they are given names. If researchers in other areas think they have found these species in the future they can compare their material with the type specimens to check they are a good match.

Habitas: more information on sponges

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