what is unique about hydrozoans

Full Answer

What makes Hydrozoa unique?

They are distinguished from other groups by their complex life cycle, by the growth of medusae from buds rather than strobilae or from metamorphosis, by the presence of a velum inside the bell of the medusa, and by the production of gametes from ectodermal, rather than endodermal, tissue.

How are hydrozoans different from other cnidarians?

Unlike some other cnidarian groups, the lining of the central cavity lacks stinging nematocysts, which are found only on the tentacles and outer surface. All colonial hydrozoans also include some polyps specialized for reproduction.

What characteristic sets hydrozoans apart from all other cnidarians?

One defining characteristic shared by the hydrozoans is that their gonads are derived from epidermal tissue, whereas in all other cnidarians they are derived from gastrodermal tissue.

What are two characteristics of the class Hydrozoa?

Main attributes:Internal space for digestion is the gastrovascular cavity.Gastrovascular cavity has one opening, the mouth.Exoskeleton of chitin.Are almoust entirely marine and predators.Sexual reproduction produces the planula larvae.Two body forms, a polyp and medusea.Presence of stinging cells called Cnidocytes.More items...

How do hydrozoans differ from Cubozoans?

Cubozoans live as box-shaped medusae while Hydrozoans are true polymorphs and can be found as colonial or solitary organisms.

What is the difference between Hydrozoa and Scyphozoa?

The difference between most hydrozoans and most scyphozoans is that in hydrozoans, the polyp stage usually predominates, with the medusa small or sometimes absent. Often, the medusa never breaks away from the parent polyp, and remains in a state of arrested development, although its gametes function.

What are the unique features of cnidarians?

The five main characteristics of cnidarians are:Radial symmetry.Diploblastic animals.Tissue level of organisation.Presence of cnidoblasts with stinging nematocysts on the tentacles.Polymorphism and have two body forms, i.e. polyp and medusa.

What is unique about the cnidarians?

Cnidarians have a unique feature: stinging cells called cnidocytes (NID-uh-sites). Each cnidocyte cell has a long, coiled, tubular harpoon-like structure, called a nematocyst (Greek root word nema meaning thread; Greek root word cyst meaning bag).

Are Hydrozoa carnivores?

Hydrozoa are carnivorous, feeding mostly on small crustaceans, fish eggs and larva. Cnidaria are characterized by a life cycle that includes the presence of planula larva, defined as “a free-swimming cylindrical larva bearing numerous cilia” by The Encyclopedia Britannica.

What makes a Hydrozoa a Hydrozoa?

The Hydrozoa is a class of Cnidaria. They are characterized by having a life-cycle involving sexual and asexual reproduction. Most hydrozoans have a benthic, colonial polyp stage, which reproduces asexually by budding.

What is polymorphism Hydrozoa?

The occurrence of more than one type of structurally and functionally different individuals within a population is called polymorphism. The class Hydrozoa of phylum Coelenterata includes a large number of colonial species that contain more than one form of individuals which are called zooids.

Why is Hydra atypical of the class Hydrozoa?

So, although a common laboratory animal Hydra is an atypical hydrozoan, because it only has a polyp stage and lives in fresh water. In other fresh water forms the medusa dominates. Craspedacusta sowerbyi, only common freshwater jellyfish.

How do members of the class Scyphozoa differ from other cnidarians?

Scyphozoans exhibit the main characteristics of cnidarians. They have radial symmetry and are diploblastic, meaning that their body wall consists of the outer epidermis (ectoderm) and the inner gastrodermis (endoderm), which are separated by mesoglea.

What is difference between polyp and medusa?

In the phylum Cnidaria, which includes jellyfish and sea anemones, polyp and medusa are two different stages of the life cycle....Difference Between Medusa and PolypPolypMedusaPolyps are sessileMedusae are mobileShapePolyps possess a tubular shapeMedusa has a bell-shaped body13 more rows•Sep 29, 2020

What are the characteristics of anthozoa?

Major Attributes:Tropical marine habitat.Mouth surrounded by tentacles with nematocysts.Partioned gastrovascular cavity.Secretes nonliving substance around outside of body to support and protect soft body tissues.Reproduces sexually by producing a free-swimming larva (planula) or asexually by budding or fission.More items...

Are Hydrozoa carnivores?

Hydrozoa are carnivorous, feeding mostly on small crustaceans, fish eggs and larva. Cnidaria are characterized by a life cycle that includes the presence of planula larva, defined as “a free-swimming cylindrical larva bearing numerous cilia” by The Encyclopedia Britannica.

What are the names of the hydrozoa?

Leptothecata. Siphonophorae. Trachylinae. Actinulida. Limnomedusae. Narcomedusae. Tatalidoae. 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.

What phylum do hydrozoans belong to?

A few genera within this class live in fresh water. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria .

What is the colonial phase of 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".

How big is a hydrozoan medusae?

The medusae of hydrozoans are smaller than those of typical jellyfish, ranging from 0.5 to 6 cm (0.20 to 2.36 in) in diameter. Although most hydrozoans have a medusoid stage, this is not always free-living, and in many species, exists solely as a sexually reproducing bud on the surface of the hydroid colony.

What is the name of the class of animals that live in salt water?

Hydrozoa. 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. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive ...

How many tentacles does a hydrozoan have?

A tube-like structure hangs down from the centre of the umbrella, and includes the mouth at its tip. Most hydrozoan medusae have just four tentacles, although a number of exceptions exist. Stinging cells are found on the tentacles and around the mouth. The mouth leads into a central stomach cavity.

What is the form of a hydroid?

The hydroid form is usually colonial, with multiple polyps connected by tubelike hydrocauli. The hollow cavity in the middle of the polyp extends into the associated hydrocaulus, so that all the individuals of the colony are intimately connected.

What is the classification of hydrozoans?

Actinulide. Chondrophora. Trachylina. Siphonophora. References. The hydrozoans (Hydrozoa) are animals that belong to an order of the phylum Cnidaria that includes almost entirely colonial organisms. These can be fixed to the substrate, or moving freely through the waters.

What domain is hydrozoa?

Taking into account that hydrozoa belong to the Eukarya domain, all the cells that comprise them are of the eukaryotic type. This means that its DNA is enclosed in an organelle called the cell nucleus, delimited by the nuclear membrane.

What are hydropolyps?

They are known as hydropolyps, and in most cases they establish large colonies. Only a few species like the hydra are solitary. As with the polyps of other species of cninadria, the polyps of hydrozoans are fixed to the substrate through a structure known as hydrorriza, which closely resembles the roots of land plants.

How many species of hydrozoans have been discovered?

Hydrozoans were described for the first time in the year 1843 and since then a total of approximately 3000 species have been discovered, which are distributed in the five orders that make up the group.

What are the two types of cycles in hydrozoans?

Regarding their biological cycle, in hydrozoans two types of cycles can be seen: metagenetic, which is the one with alternation of generations (polyp and jellyfish); and the hypogenetic in which only one form is observed (polyp or jellyfish).

What order are hydrozoans in?

The hydrozoan (Hydrozoa) are animal that belong to an order of the phylum Cnidaria that include almot entirely colonial organim. Thee can be fixed to the ubtrate, or moving freely through the water.Hy.

Is a hydrozoan a multicellular organism?

Due to this it can be affirmed that hydrozoans are multicellular organisms. Likewise, they are characterized by having the shape of polyps and jellyfish, although there are species that only have polyps and others that only have the shape of a jellyfish.

What are some examples of hydrozoans?

Polyps bud and branch, the exact form being specific. Colonies may be quite large and members may be specialized and unable to survive alone. Examples of hydrozoans include the freshwater Hydra species and the marine Portuguese man o’ war ( Physalia physalis ), both of which have specialized stinging structures called nematocysts.

Where are hydroids found in Argentina?

The coast near Mar del Plata, Argentina, is characterized by outcroppings of quartzitic rocky blocks extending from the intertidal several kilometers out to sea.The blocks provide settlement areas for many benthic invertebrates, including hydrozoans. Starting in November 2000, Genzano et al. (2002) collected 11 approximately monthly samples of hydroids along a 10-m line transect on one block, Banco del Medio, 18-20 m below the surface. They laid a 10-m chain with 2-cm links arranged in 1-m segments on the rock and identified and counted hydroid clumps in contact with the chain in each segment to estimate cover. Of the 13 species of hydroid recorded, the most common were Amphisbetia operculata, Sertularella mediterranea, and Plumularia setacea. The average coverage and SD of these species are given in their Table 3.

What order are hydra and cordylophora?

Hydra and Cordylophora belong to the order Hydroida of the class Hydrozoa. Craspedacusta, Limnocnida, and Calposoma are classified as members of the order Limnomedusae. The parasitic Polypodium has been assigned to the order Trachylina of the same class (cf. Hyman, 1940 ). The fact that the other three orders of the class Hydrozoa (Actinulida, Siphonophora, and Hydrocorallina) and the other three classes of coelenterates (Scyphozoa, Cubozoa, and Anthozoa) are not represented outside of the sea is curious. There is not even any serious speculation as to why freshwater invasion by coelenterates has been so severely limited. There is no special osmoregulatory organ in the phylum, but this is not an explanation since its absence has not stopped the successful invaders. Because of their small size, soft bodies, and often sessile habits, freshwater Cnidaria are either not collected or not well preserved in most routine collecting procedures. They are, however, widely distributed and can be found in most ponds and streams when a specific search is made. When they are abundant, they can be major predators of small invertebrates and even of tiny fish. In turn, Hydra is fed upon by flatworms, and crayfish eat Craspedacusta. Probably, other animals prey on freshwater Cnidaria, but this has not been carefully studied.

How many genera are there in cnidarians?

Cnidarians, or coelenterates, have been relatively unsuccessful in adapting to freshwater, being represented only by one class (Hydrozoa) with four or five pure ly freshwater genera: the common hydras (brown Hydra and green Chlorohydra, or H. viridissima) and the rare medusoid Craspedacusta and polypoid Calposoma and Polypodium ( Fig. 3 ). Cordylophora, a mostly estuarine taxon, occasionally penetrates relatively freshwaters, where it lives in a colonial, sessile form. Despite their low diversity, cnidarians—or at least hydras—are routinely present on almost any reasonably hard substrate in permanent ponds and lakes and in streams ranging from headwater streams to large rivers.

What class is Cnidaria?

The freshwater representatives of Cnidaria are small animals belonging to the class Hydrozoa, with relatively few species and somewhat monotonous anatomy. They consist of the following taxa:

What are the members of the Cnidaria phylum?

The Cnidaria phylum includes sea anemones, Hydra (sessile solitary species), corals, sea fans, sea whips (colonial species) and jellyfish (free-swimming species) that live in aquatic (mostly marine) environments ( Ruppert et al., 2003 ). Cnidarians appear to have diverse morphologies, but all members of this phylum universally possess stinging cells called cnidoblasts. Cnidoblasts are unique to the animals of this phylum and are used to define the phylum. The bodies of individuals in the Cnidaria phylum exhibit radial or biradial symmetry, and almost all tissues have a basic structure composed of two cellular layers, the epidermis (outside) and the gastrodermis (inside). A gelatinous-like substance called the mesoglea is present between the two layers of the tissues and maintains the integrity of the tissues and the body. In addition, cnidarian bodies are relatively simple, and well-organized organs or systems that are found in vertebrates are not present in cnidarians, such as vascular and central nervous systems. Cnidarians only have a passive transport system that depends on diffusion; a simple nerve net; some functionally defined tissues such as tentacles for predation, attack and defense mechanisms; and a sac-like gastrovascular cavity used for digestion and absorption.

Is the taxonomy of hydrozoa marine?

The taxonomy of Hydrozoa is under frequent revision, last in 2009. My major sources on taxonomy all have different ways to classify hydrozoans. They seem to agree that most species are marine. All species presented here are, according to WORMS, classified as member of the subclass Hydroidolina. Three important groups or orders, dominate the Norwegian marine fauna:

Do hydroids have holsters?

Athecate hydroids, Anthoathecata, do not have a protective holster around their polyps or hydranths.

What is the body of a zooid?

Each zooid consists of a tubular body that has two layers separated by a thin jellylike mesoglea (layer of connective tissue), a terminal mouth, and surrounding circlet (s) of tentacles. The zooids are joined basally to a common living tube called the stolon that runs the length of the colony.

How long is a hydroids life cycle?

Hydroids have three basic life-cycle stages: (1) a tiny free-swimming ciliated planula larva about 1 mm (0.04 inch) long, which settles and metamorphoses into (2) a sessile (attached), usually colonial polyp stage, which in turn liberates (3) a gamete-producing male or female medusa (“jellyfish”).

What is a hydrid?

Hydroid, any member of the invertebrate class Hydrozoa (phylum Cnidaria). Most hydroids inhabit marine environments, but some hydroids have invaded freshwater habitats. Hydroids may be either solitary or colonial, and there are about 3,700 known species.

Do hydroids have medusa?

Many hydroids have, through evolution, suppressed the medusa by retaining it on the sessile hydroid colony. Hydra, a well-known freshwater genus that has the distinction of being solitary rather than colonial, lacks a medusa stage.

How many species are in Hydrozoa?

7 orders consisting of 2700 species. Description: Hydrozoa consist of several marine organisms existinting in all three layers of the marine habitat. Some Hydrozoans live on the the surface (velella and Physalia) floating with large sail like structures above water for locomotion and long tentacles with nematocytes or stinging cells below ...

What is the digestive system of hydrozoans?

Though these organisms feed on smaller organisms, their digestive system is a simple gastrovascular cacity lined with flagellated cells that circulate food in with the filtering of water. The use of Cnidocytes enable the Hydrozoans to paralyze prey as well as ward off predators.

Which order of organisms can grow very large covering mass amounts of ocean substrate?

These Hydrozoans are the orders Milleporina and Stylasterina which are corals and form an internal, epidermal skeleton of calcareous. These organisms can grow very large covering mass amounts of ocean substrate. Another sessile Hydrozoa is the Hydra which is truely unique among the Hydrozoans.

Do hydrozoans have tentacles?

The Hydra is solitary, lacks a medusoid phase and feeds with long tentacles that extend from around the mouth. Some Interesting Facts: Hydrozoans have many cell types, but form only two tissue types for their bodies, epidermus and gastrodermis.

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Systematics and evolution

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