The Sea Gooseberry

Pleurobranchia pileus

The Sea Gooseberry (Pleurobranchia pileus) is a neretic Ctenophore that is common to the waters around Ireland. Its body is clear and 2-3 cm in diameter. This bears eight rows of equally spaced comb plates, each made of rows of long, fused cilia which it beats to move through the water. P. pileus is a non-selective carnivore, using 15 cm soild, highly extensile tentacles to lasso animals which are brought up to the mouth. This leads to a long, narrow pharnyx, which opens to the stomach (Kotpal, 2009 Modern Text Book of Zoology: Invertebrates pp. 318-319). It posses a sense organ called a statocyst at its aboral end and it has been shown that P. pileus can sense the presence of predators and move away accordingly, away from the sediment, reducing predation risk (Esser et al., 2004 Marine Biology 145 pp. 595-601).

Pleurobranchia pileus

P. pileus is at its most abundant in Irish seas in October to November, however a summer peak in numbers is often common (Fraser, 1970 Journal du Conseil 33 pp. 149-168). Populations can reach high densities during these periods (>10 individuals per cubic meter). Mills (2001, Hydrobiologia 451 pp. 55-68) has suggested that P. pileus numbers are increasing globally, along with other Ctenophores and Scyphozoa in response to changing ocean conditions. This could have serious consequences for fishery yields, and marine ecosystems as a whole, worldwide as both these organisms are both competitors and predators of young fish.