jellyfish Class Scyphozoa

In the large jellyfishes or Scyphozoa the medusoid phase is dominant, the polyp, known as the hydra tuba or scyphistoma, being a small tubular organism resembling Hydra. The class comprises five orders as follows: Semaeostomeae, Rhizostomeae, Coronatae. Cubomedusae and Stauromedusae The most noticeable external feature of the class is its four-rayed symmetry. The bell of … Read more

Hydrozoa Sea firs (hydroids), hydras and siphonophores

Sea firs (hydroids), hydras and siphonophores (Class Hydrozoa) The class Hydrozoa comprises over 2,700 species and is subdivided into seven orders: Athecata, Thecata, Limnomedusae, Trachymedusae, Narco medusae, Siphonophora and Hydrocorallinae. Both polyp and medusa are generally present, but the latter may be reduced and then does not always leave the parent colony. Many members of … Read more

Cnidarians Reproduction

Reproduction and development in Cnidarians Cnidarians are usually dioecious, that is, the sexes are separate, but may be hermaphrodite. Gametes are usually shed into the seawater, where fertilisation occurs. In general, medusae produce gametes, but in instances where only the polyp occurs, (e.g. in anthozoans) gonads are borne on the projecting internal septa or (e.g. … Read more

Cnidaria structure

Cnidaria structure Musculo-epithelial cells in Cnidarians The major cell types of the Cnidaria are the musculo epithelial cells, nerve cells, and nematoblasts which produce nematocysts. The ‘body’ is composed mainly of musculo-epithelial cells. These cells, found only in the cnidarians, are a means of producing an epithelium combined with a contractile system. Each cell consists … Read more

Phylum Cnidaria | Cnidarians Examples

The phylum Cnidaria is predominantly marine and contains many common shore animals such as sea anemones and sea firs (hydroids), as well as deeper water forms such as the Portuguese Man o’ War. Freshwater forms are less common, but one group, the hydras, is probably the best-known member of the phylum. Classes of Cnidaria There … Read more

Sub orders of Class Nuda in Sponges

Class Nuda These are sponges that lack intercellular jelly. In other words, the star-shaped cells and the amoeba cytes form a network through which water percolates, and there are no inhalant or exhalant canals. Glass sponges (Order Hexactinellida) Sponges of this order are characterized by siliceous spicules based on a hexaradiate or six-rayed plan. Suborder … Read more