What are Marine hydrozoans?
Hydrozoa (hydrozoans, from ancient Greek ὕδωρ, hydōr, “water” and ζῷον, zōion, “animal”) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most living in salt water. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
What is the difference between hydrozoans and Scyphozoans?
Differences between a Scyphozoan & Hydrozoan medusae? Schyphozoans – More ‘jelly & 4 oral arms. Hydrozoans – No oral arms. Have a velum ring & less jelly (fold up when preserved).
What is the polyp form of a jellyfish?
medusa
Jellyfish have a stalked (polyp) phase, when they are attached to coastal reefs, and a jellyfish (medusa) phase, when they float among the plankton. The medusa is the reproductive stage; their eggs are fertilised internally and develop into free-swimming planula larvae.
Is Coral medusa or polyp?
Classes. In the class Anthozoa, comprising the sea anemones and corals, the individual is always a polyp; in the class Hydrozoa, however, the individual may be either a polyp or a medusa, with most species undergoing a life cycle with both a polyp stage and a medusa stage.
Are hydrozoans polyps?
Like many cnidarians, hydrozoans have both polyp and medusa stages in their life cycle. Most hydrozoans form colonies of asexual polyps and free-swimming sexual medusae. Colonies are usually benthic, but some, notably the siphonophores, are pelagic floaters.
How do hydrozoans move?
The body of a hydrozoan medusa has a dome-like umbrella shape and it is ringed by tentacles. Most have only four tentacles with nematocysts on them and around the mouth. The rim of the bell contains muscle fibres which allow the animal to move along by contracting then relaxing its body.
How do hydrozoans reproduce?
Most hydrozoans have a benthic, colonial polyp stage, which reproduces asexually by budding. Many have free swimming, sexually reproducing medusae (see Introduction to Ctenophores (and Cnidarian medusae)). Others have attached gonophores, which will produce eggs or sperm.
What is a marine polyp?
Coral polyps are tiny, soft-bodied organisms related to sea anemones and jellyfish. At their base is a hard, protective limestone skeleton called a calicle, which forms the structure of coral reefs. Reefs begin when a polyp attaches itself to a rock on the sea floor, then divides, or buds, into thousands of clones.
Are Hydrozoans polyps?
What is unique about hydrozoans?
Like all cnidarians, hydrozoans have special ectodermal cells called cnidocytes, each containing a single intracellular structure called a cnida (aka nematocyst). Cnidae are unique to the Cnidaria. Each cnida, when triggered by a mechanical or chemical stimulus, shoots out a tiny hollow tube at high speed.
Are scyphozoa medusae or polyps?
Scyphomedusae are the “jellyfish” with which most people are familiar. Scyphozoan polyps and medusae exhibit no cephalization and contain no brain, but in some species, light-sensitive eyespots are located along the bell margin of the medusa. Scyphozoan medusae differ from those of hydrozoans in lacking a velum.
Why are coral polyps important?
They help the coral survive by providing it with food resulting from photosynthesis. In turn, the coral polyps provide the cells with a protected environment and the nutrients they need to carry out photosynthesis.
What is the function of colonial polyps in Hydrozoa?
Colonial polyps often have some division of function, with certain polyps specialized for defense, feeding, or reproduction. Most hydrozoans are predators or filter-feeders, though a few have symbiotic algae (zooxanthellae), in the same way that other other groups of cnidarians do.
What are the characteristics of colonized Hydrozoa?
Colonial hydrozoans include siphonophore colonies, Hydractinia, Obelia, and many others. In hydrozoan species with both polyp and medusa generations, the medusa stage is the sexually reproductive phase. Medusae of these species of Hydrozoa are known as “hydromedusae”. Most hydromedusae have shorter lifespans than the larger scyphozoan jellyfish.
Which Hydrozoa have both a polypoid and medusoid stage?
Most hydrozoan species include both a polypoid and a medusoid stage in their lifecycles, although a number of them have only one or the other. For example, Hydra has no medusoid stage, while Liriope lacks the hydroid stage.
How do hydrozoans affect marine ecosystems?
Hydrozoans are both predators and prey for many marine organisms, and large seasonal blooms of medusae may strongly affect local fish and zooplankton populations. Some species of polyps are hosts for symbiotic algae, and many large pelagic forms have symbiotic hyperiid amphipods living on or in them.
