Sea gooseberry  (Pleurobrachia pileus)

Not threatened (2).

Members of the phylum Ctenophora are known as sea-gooseberries or comb-jellies, and are startlingly beautiful marine invertebrates. They are commonly mistaken for jellyfish, but belong to their own group that is totaally unrelated to jellyfish (3). Pleurobrachia pileus has a transparent spherical body bearing two feathery tentacles, which can be completely drawn back into special pouches. The name comb-jelly refers to the eight rows of hair-like cilia present on the body, which are known as comb-rows. The rhythmic beating of these cilia enables the animal to swim, and also refracts light, creating a multi-coloured shimmer (2).

This sea-gooseberry has an almost cosmopolitan distribution, being found widely around the world (2). It is common in the waters surrounding Britain (4).

This species is pelagic. It may be found in rock pools when stranded by low tides, especially in summer (4).

Despite their delicate, almost ghostly appearance, sea-gooseberries are voracious predators, feeding on fish eggs and larvae, molluscs, copepod crustaceans, and even other sea-gooseberries (5). Prey is caught by the long tentacles, which act as a net and bear adhesive cells known as colloblasts. The tentacles are then ‘reeled in’ and the prey is passed to the mouth (2).

This species is hermaphroditic. Breeding occurs from spring to autumn; the eggs and sperm are released into the water and fertilisation therefore occurs externally. The larva, known as a ‘cydippid larva’ is free-swimming. Most individuals die following spawning. This species may be preyed upon by fish and other sea-gooseberries (2).

This species is not threatened.

Conservation action is not required for this common species.

For more information on the sea gooseberry see:

Fish, J.D. and Fish, S. (1989) A Student’s Guide to the Seashore. Unwin Hyman Ltd., London.

For further information on comb-jellies see:

Microscopy UK: Comb-jellies:
www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay98/comb.html

• Copepod: Large and diverse group of minute marine and freshwater crustaceans belonging to the subclass Copepoda. They usually have an elongated body and a forked tail.
• Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
• Hermaphroditic: possessing both male and female sex organs.
• Larva: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Pelagic: inhabits the open oceans.

1. National Biodiversity Network Species Dictionary (September, 2003)
   http://www.nhm.ac.uk/nbn/
2. Fish, J.D. and Fish, S. (1989) A student’s guide to the seashore. Unwin Hyman Ltd, London.
3. Microscopy UK: Comb-jellies (November, 2003)
   http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay98/comb.html
4. Gibson, R., Hextall, B. and Rogers, A. (2001) Photographic Guide to the Sea and Shore Life of Britain and North-west Europe. Oxford University Press, Oxford.
5. University of Bangor. The Distribution and Abundance of Ctenophores in the Menai Straits and Eastern Irish Sea in Comparison to the Distribution and Abundance of Their Copepod Prey (November, 2003)
   http://www.sos.bangor.ac.uk/marine/mb/O3B32_Field_Course_II/K_Clarke_02.htm