Scyphozoa
Scyphozoa Temporal range:
| |
---|---|
Cephea cephea | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Cnidaria |
Subphylum: | Medusozoa |
Class: | Scyphozoa Götte, 1887 |
Subgroups | |
The Scyphozoa are an exclusively marine class of the phylum Cnidaria,[2] referred to as the true jellyfish (or "true jellies").
The class name Scyphozoa comes from the Greek word skyphos (σκύφος), denoting a kind of drinking cup and alluding to the cup shape of the organism.[3]
Scyphozoans have existed from the earliest Cambrian to the present.[1]
Biology
Most species of Scyphozoa have two life-history phases, including the planktonic
As medusae, they eat a variety of crustaceans and fish, which they capture using stinging cells called
Anatomy
Scyphozoans usually display a four-part symmetry and have an internal gelatinous material called mesoglea, which provides the same structural integrity as a skeleton. The mesoglea includes mobile amoeboid cells originating from the epidermis.
Scyphozoans have no durable hard parts, including no head, no skeleton, and no specialized organs for respiration or excretion.[6][7] Marine jellyfish can consist of as much as 98% water, so are rarely found in fossil form.
Unlike the
The mouth opens into a central stomach, from which four interconnected diverticula radiate outwards. In many species, this is further elaborated by a system of radial canals, with or without an additional ring canal towards the edge of the dome. Some genera, such as Cassiopea, even have additional, smaller mouths in the oral arms. The lining of the digestive system includes further stinging nematocysts, along with cells that secrete digestive enzymes.[5]
The nervous system usually consists of a distributed net of cells, although some species possess more organised nerve rings. In species lacking nerve rings, the nerve cells are instead concentrated into small structures called
Reproduction
Most species appear to be
Growth and development
The fertilized egg produces a planular larva which, in most species, quickly attaches itself to the sea bottom. The larva develops into the hydroid stage of the lifecycle, a tiny sessile polyp called a scyphistoma. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa, or budding several medusae off from its upper surface via a process called strobilation. The medusae are initially microscopic and may take years to reach sexual maturity.[5]
Commercial importance
Scyphozoa include the moon jelly
The jellyfish fished commercially for food are Scyphomedusae in the order Rhizostomeae.[10] Most rhizostome jellyfish live in warm water.[4]
Taxonomy
Although the Scyphozoa were formerly considered to include the animals now referred to as the classes
Class Scyphozoa
- Subclass Coronamedusae
- Order Coronatae
- Family Atollidae
- Family Atorellidae
- Family Linuchidae
- Family Nausithoidae
- Family Paraphyllinidae
- Family Periphyllidae
- Family
- Order
- Subclass Discomedusae
- Order Rhizostomeae
- Suborder Daktyliophorae
- Family Catostylidae
- Family Lobonematidae
- Family Lychnorhizidae
- Family Rhizostomatidae
- Family Stomolophidae
- Suborder Kolpophorae
- Family Cassiopeidae
- Family Cepheidae
- Family Mastigiidae
- Family Thysanostomatidae
- Family Versurigidae
- Family
- Order Semaeostomeae
- Family Cyaneidae
- Family Drymonematidae[13]
- Family Pelagiidae
- Family Phacellophoridae
- Family Ulmaridae
References
- ^ .
- ^ Dawson, Michael N. "The Scyphozoan". Retrieved 2008-08-11.
- ISBN 978-0030139192.
- ^ .
- ^ ISBN 978-0-03-056747-6.
- ^ Cartwright, P., Halgedahl, S.L., Hendriks, J.R., Jarrad, R.D., Marques, A.C., Collins, A.G., and Lieberman, B.S., 2007, Exceptionally preserved jellyfishes from the Middle Cambrian. PLOSONE Issue 10: e1121, p.1-7.
- ^ Richards, H.G., 1947, Preservation of fossil jellyfish: Bulletin of the Geological Society of America, v. 58, p. 1221.
- ^ Morris, M., and Fautin, D., 2001, Animal Diversity Web: University of Michigan Museum of Zoology, "Scyphozoa., Accessed: September 28, 2008.
- PMID 17486542.
- S2CID 6518460.
- ^ a b Daly, Brugler, Cartwright, Collins, Dawson, Fautin, France, McFadden, Opresko, Rodriguez, Romano & Stake (2007). The phylum Cnidaria: A review of phylogenetic patterns and diversity 300 years after Linnaeus. Zootaxa 1668: 127–182
- ^ "Scyphozoa". WoRMS. World Register of Marine Species. Retrieved 30 July 2012.
- ^ Bayha, K. M., and M. N. Dawson (2010). New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa, Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton. The Biological Bulletin 219(3): 249–267
External links
- The Classification and Distribution of the Class Scyphozoa
- Encyclopædia Britannica (11th ed.). 1911. .