Brown venus, fish parasite and jewelbox sighted

March 18th, 2008

Photo: Dave Jarvis

The bivalve Callista chione, also known as the brown venus, was found stranded on a beach in Hayle, Cornwall. Callista chione is an uncommon species in Britain although it is found in South-West England and the Channel Islands. It is a large oval shell that can grow up ton 9cm in length. The outer shell is a reddish-brown colour with darker streaks and the inner shell is an off white colour.

Photo: Steve Trewhella

This isopod, Gnathia maxillaris was also found this month. Gnathia maxillaris is a small isopod; up to 5mm in length and male, female and juvenile Gnathia maxillaris are significantly different in their appearance. The one pictured is a Juvenile. They can usually be found in crevices, empty barnacle shells and Laminaria holdfasts. Around 100 embryos develop inside the body of the female before being released as larvae or Zupheae where they become fish parasites. The usually attach to the bodies of; the Shanny (Lipophrys pholis), the Long-spined Sea Scorpion (Taurulus bubalis) and the Corkwing Wrasse (Symphodus melops). They leave the fish host after a blood meal, their thoracic region expanded and become Pranizae larvae. Not much is known about the adult Gnathia maxillaris but it is believed that they do not feed.

Photo: Steve Trewhella

Found in a fish box in Chesil was the shell Pseudochama gryphina, known as a jewelbox. The first of this species recorded in the UK.

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Discoveries in January

January 22nd, 2008

January brought some unusual, interesting and lesser known species. A Tentacled Lagoon Worm was found in Devon. A Gribble and an interesting parasite were both found on Dorset beaches.

The tentacled lagoon worm (Alkmaria romijni) was found on the Dart estuary in Devon. This is a nationally scarce species. Alkmaria romijni is a small worm, up to 5mm long with eight tentacles which are thread-like and slimy. This species is protected under the Wildlife and Countryside Act 1981 due to it scarcity.

Also found was a gribble (Limnoria lignorum)  boring into wood on a Dorset beach. Gribbles are small wood borers, about 3.5-4mm long.

An interesting find was this whale louse, an ectoparasite found on a dolphin washed up on a beach, again in Dorset.

All Photos: Steve Trewhella

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‘Pearls’ from the common mussel

October 26th, 2007

Mussels containing inclusions or ‘pearls’ were found in Loch Long in Scotland. Mytilus edulis, known as the common mussel, is a bivalve; 80-100mm in length and dark blue to purple and sometimes brown in colour. It attaches firmly to rocks and stones etc. by byssus threads. The pearls found in these mussels are formed around parasitic worm larvae that infect the mussels. The parasite is usually the flatworm Gymnophallus bursicola, which enters as larvae and lodges itself in the mantle of the mussel. In order to protect itself, the mussel forms layers of a shell-like nacreous (iridescent) material over the worm to form a pearl. Mytilus edulis, alongside other bivalves, can also be infected by the pea crab (Pinnotheres pisum) which commonly inhabits the mantle cavity of the mussel.

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