Compass jellyfish (Chrysaora hysoscella)
|Size||Bell diameter: up to 300 mm (2)|
Common and widespread (2).
The compass jellyfish has a saucer-shaped bell, with 32 semi-circular lobes around the fringe, each one with a brown spot (2). On the upper surface of the bell, 16 brown V-shaped marks radiate outwards from a dark central spot. The mouth, the only opening to the exterior, is located on the centre of the underside of the bell, and is surrounded by 4 arms. There are also 24 tentacles around the edge of the bell, grouped in threes. The colour of this jellyfish varies, with a variable level of brown pigment (2).
Although it has been recorded from around all of the coasts of Britain, it is more frequently found in the south and west (2).
Inhabits inshore waters (2).
Jellyfish are propelled through the water by means of pulsations of the bell. They often become washed ashore by wind and storms, where they die. This jellyfish catches its food with its tentacles, which can be extended and retracted. A range of planktonic animals are caught in this way before being transferred to the central arms around the mouth.
Adults are hermaphrodites, and function initially as males before becoming functional females. Sperm is released from the mouth of a functional male, and drawn into a female, also through the mouth (the mouth being the only external opening). Fertilisation then takes place inside the female. Free-swimming larvae (planulae) are released from the female during summer or autumn. They remain in the plankton for just a few days before settling as a polyp known as a scyphistoma. During the following spring, the scyphistoma produces tiny jellyfish (ephyrae) by a form of asexual reproduction. These tiny jellyfish detach, and quickly develop into mature jellyfish by summer. The compass jellyfish lives for around one year (2).
This species is not currently threatened.
Conservation action has not been targeted at this common and widespread species.
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- Asexual reproduction: reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by fission (or in plants ‘vegetative reproduction’); part of the organism breaks away and develops into a separate individual. Some animals, including vertebrates can develop from unfertilised eggs, this process, known as parthenogenesis gives rise to offspring that are genetically identical to the parent.
- Hermaphrodites: possessing both male and female sex organs.
- Larvae: 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.
- Planktonic: aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
- Polyp: typically sedentary soft-bodied component of cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.
- National Biodiversity Network Species Dictionary (August 2002): http://www.nhm.ac.uk/nbn/
- Fish, J. D. and Fish, S. (1989) A student's guide to the seashore. 2nd Edition. Cambridge University press, Cambridge.