We say that these sentences are written in the present perfect form of the past tense. On closer inspection, the first three sentences have events and actions that started in the past, but are either still happening now or are in some way connected to the present. At first glance, they all appear to be written in the past tense with ‘- ed’ ending verbs signalling that events and actions have already taken place. 15: 212-214.Read the six scintillating sentences opposite. On a new species of Cassiopea from Jamaica.

^ 'These jellyfish can sting without touching you, thanks to 'mucus grenades'' at the National Geographic website.

'Degrading mangrove leaves of Rhizophora mangle Linne provide a natural cue for settlement and metamorphosis of the upside down jellyfish Cassiopea xamachana Bigelow'. Journal of Experimental Marine Biology and Ecology. 'The role of temperature in survival of the polyp stage of the tropical rhizostome jellyfish Cassiopea xamachana'.

^ Ohdera et al: Upside-Down but Headed in the Right Direction: Review of the Highly Versatile Cassiopea xamachana System.

'Upside-down Jellyfish: Cassiopea xamachana'. Bigelow collected the specimen in a lagoon near The specific epithet, xamachana, was chosen by Bigelow to honor the indigenous name of the island of Jamaica, the type location of the species. Cassiopeia was punished by Poseidon, ruling god of the sea, for being a bad mother. In Greek mythology, Cassiopeia was the mother of Andromeda.

The cassiophores allow the jellyfish to kill or stun its prey at a distance, and are responsible for the stinging sensation experienced by swimmers, divers and aquarists who get too close to the jellyfish. The jellyfish surround themselves with a layer of mucus containing cassiosomes, independent bodies consisting of a layer of stinging cells surrounding a piece of jelly between sixty and a hundred cilia enable the cassiophore to swim independently of the jellyfish's body. This is the reverse of the usual situation of rhizostome jellyfish, in more temperate locations, where the scyphistomae are temperature-tolerant and the medusae are cold-sensitive. In Florida, the medusae are found all the year round but the scyphistomae are only present in late summer and fall. In due course, when they have acquired zooxanthellae and the temperature exceeds 20 ☌ (68 ☏), these strobilate (split) and new medusae are formed. Under favorable conditions these bud and form further scyphistomae. Having settled, the larvae undergo metamorphosis into the hydroid stage of the lifecycle, forming tiny sessile polyps called scyphistomae. Decomposing red mangrove ( Rhizophora mangle) give off a substance which attracts the larvae to settle. Gametes are released by the medusae into the water and the fertilized eggs hatch into planula larvae, which attach to the sea bed or some other suitable substrate. The life cycle of Cassiopea xamachana alternates between a polyp phase and the medusa phase. This species has become an important model system to study the molecular basis of cnidarian-algal symbiosis. Having paralysed the prey, it digests them on the oral surfaces and the resulting fragments are ingested through the oral openings. For its further needs, as well as being able to absorb nutrients dissolved in the water, it can also catch small prey using the cnidocytes with which its tentacles are armed.

Biology Ĭassiopea xamachana obtains part of its nutritional needs from the symbiotic zooxanthellae it harbors in its tissues these use energy from the sunlight to produce carbohydrates by photosynthesis. If disturbed the jellyfish may pulsate their bells and rise in the water, soon flopping back onto the seabed. It is normally found in large aggregations on the muddy seabed of inshore bays and shallow lagoons. Distribution and habitat Ĭassiopea xamachana is found in warm parts of the western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. The mesogloea, the jelly-like tissue, contains symbiotic zooxanthellae, single-celled protists, which are photosynthetic and give the jellyfish its variable color, often bluish-grey or bluish-green. Instead of a central mouth, there are numerous oral openings in the tentacles which connect via channels to the stomach. The four pairs of much-branched tentacles are on the upperside. Compared to most species of jellyfish it is upside-down, that is to say the bell, which is saucer-shaped, is underneath and acts like a suction cup to stabilise the jellyfish on the seabed. The medusa phase of Cassiopea xamachana can grow to a diameter of about 25 cm (10 in).

Cassiopeia jelly fish