The Surrounding Sea - Gower - page 125

snail on Oxwich beach. Over 200 individuals were collected, including a related species, J. exigua . These
'purple sea snails' are pelagic molluscs that float on a 'bubble-raft'.
FIG 66. By-the-wind-sailor, a common pelagic species often found stranded on the beaches. (Margaret Hodge)
Several sightings of large sunfish have been made near Worms Head, and a specimen weighing 18
kilogramswascaughtin1983;evenlargerspecimenssometimesoccur.Onesunfishcaughtonthesurface
in Caswell Bay on 28 August 1851 was 1.8 metres long and said to weigh around 500 kilograms. The
most recent sighting is from 2002. The fish's unusual rounded shape is reflected in its scientific name, as
Mola is Latin for millstone. In 1843 the rare oblong sunfish M. oblongus was caught in Swansea Bay, but
it has not been recorded since.
The large dustbin-lid jellyfish Rhizostoma octopus is sporadic in occurrence from year to year, but
when present it occurs in large 'swarms' in the summer and autumn. Enormous numbers are often found
in Rhossili Bay. Naturalists have struggled for more than half a century to record the distribution and
abundance of dustbin-lid jellyfish in British and Irish waters. Today, low-flying aircraft are being used to
survey wide areas and this method has revealed huge numbers of these jellyfish (roughly one per square
metre) in Carmarthen Bay between April and November. What causes these jellyfish to aggregate in the
bay is unknown, but they also occur in similar numbers in Tremadoc Bay, near Criccieth on the Lleyn
peninsula. It is generally a species of coastal waters and can be found stranded on the shore, or in rock
pools, by receding tides, but it is believed that some specimens probably live in deep water during winter.
The animal has a solid appearance and varies in colour from whitish pale or yellow to shades of green,
blue, pink or brown. Unlike some jellyfish there are no marginal tentacles and there are four pairs of very
large oral arms on its under surface, hence the specific name octopus . The small amphipod crustacean
Hyperia galba can be found throughout the body and more usually in its gastric or gonad pouches, where
they are sought by some species of fish.
Another jellyfish, the blue jellyfish Cyanea lamarckii , which occurs in astonishing shades of blue and
violet and can sting people, has also been found washed up on Gower beaches. It is a pelagic species that