Obelia colony. Difference Between Obelia and Aurelia 2023-01-02
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Obelia is a colonial hydrozoan, a type of aquatic invertebrate that belongs to the phylum Cnidaria. It is found in both freshwater and marine environments and is commonly found in shallow waters along the coast. Obelia colonies are composed of a series of interconnected tubes and can range in size from a few centimeters to several meters in length.
Obelia colonies are made up of many individual polyps, which are small, tube-like structures that are connected to one another. Each polyp has a central digestive cavity, called a gastrovascular cavity, which is used for both digestion and circulation. The polyps also have tentacles, which are used for capturing and consuming prey.
Obelia colonies have a simple life cycle, alternating between a sexually reproducing medusa stage and asexually reproducing polyp stage. In the medusa stage, the colony produces free-swimming medusae, which are the sexually reproducing forms of the organism. These medusae then give rise to new polyp colonies through a process called budding.
Obelia colonies are important members of the aquatic ecosystem, serving as both predators and prey. They are known to feed on small plankton and other small organisms, and in turn, they are preyed upon by larger animals such as fish and birds.
Obelia colonies are also important indicators of the health of aquatic environments. Changes in the abundance and distribution of Obelia colonies can be used to monitor the health of the ecosystem and detect any changes that may be occurring.
In conclusion, Obelia is a colonial hydrozoan that is found in both freshwater and marine environments. It has a simple life cycle and plays an important role in the aquatic ecosystem as both a predator and prey. Obelia colonies are also important indicators of the health of aquatic environments and can be used to monitor changes in the ecosystem.
Life Cycle of Obelia
ADVERTISEMENTS: The mouth is situated at the terminal end of the manubrium. Because medusa is a motile form, it serves two key purposes for the colony: reproduction and gamete dispersal. The enteron has a fluid and its lining is flagellated. Plant and Animal Biology, Volume 1. The compound name of this type is due to its dual functioning capacities, protection and the power of contraction. The outer layer of the body is composed of ciliated ectodermal cells and the inner layer is made of endodermal cells. The tip of the manubrium is perforated by the mouth which leads through a gullet into the coelenteron of the medusa.
Obelia (Sea Fur): Structure, Movement and Respiration
One phase is completely engaged in the growth of the colony, the asexual phase or polyp with diploid 2n genetic composition, while the other phase is engaged in producing gametes the sexual phase or medusae, which is also diploid 2n in genetic composition and produce haploid n gametes Fig. The other end of the planula develops a mouth and becomes the first founding hydranth polyp or zooid of the hydroid colony. Near the bulbs the ectoderm has pigment granules and nerve cells, they are often called ocelli and it is claimed that the ocelli are sensory to light, but more probably there are no ocelli, the pigment granules are accumulated excretory matter. In hydroid colonies, the tentacled feeding zooids or hydranths are usually white, pink or violet white in Obelia and in Obelia the chitinous outer covering or perisarc often gives the colonies a yellowish colour. The cleavage is holoblastic and equal.
Obelia colony, vegetative and reproductive polyps, WM Microscope slide
They may be either in the form of pits or closed vesicles but in both cases, the walls contain sensory cells with bristles projecting into the lumen. Each is covered by a transparent gonotheca, thus forming a cylindrical gonangium which has no mouth or tentacles. Obelia Colony — A Gross Structure: Each colony of Obelia consists of a horizontal thread-like root called hydrorhiza which is attached to a weed or any substratum. The medusa also possesses a similar double network, but also has two nerve rings, one either side of the radial canal - an outer nerve ring and an inner nerve ring. Each of them resembles a Hydra in appearance, having about twenty solid tentacles. The coelenteron is greatly reduced.
Obelia are usually found no deeper than 200 metres 660ft from the water's surface, growing in intertidal rock pools and at the extreme low water of spring tides. The tentacles of Obelia are solid and contain endoderm cells at its core. Endodermal cells throughout the colony phagocytose the food particles and complete digestion intracellularly. Instead of secreting a horny case, as in Hydra, the ectoderm becomes ciliated and a planula larva is formed, which freely swims about in water. Medusoid Phase : Medusa develops as hollow offshoot of the blastostyle. The gonotheca opens at its distal end by a gonopore, through which the medusae escape. Hydrorhiza is a branched structure and gives only mechanical anchorage to the whole colony.
The mode of sexual reproduction provides wide dispersal of the species due to its free swimming habit. Biological Traits Information Catalogue. Polyps asexually produce medusae, while medusae sexually produce polyps. When mature the medusa reproduces sexually. The manubrium consists precisely the same layers — ectoderm, mesoglea and endoderm. In the sub-umbrella, the muscle processes of the ectoderm are so large in proportion to the epithelial part that they almost form muscles only.
Small organisms like aquatic crustaceans, nematodes and other worms are caught by the tentacles, armed with nematocysts. Obelia has only one kind of nematocysts called basitrichous isorhizas in which the capsule is oval, butt is absent, the thread is open at the tip and has spines on its base. Gonads lie on radial canals externally and the gametes are ectodermal. Both the male and female gonads are similar externally. Water is used for fertilisation. Velum is characteristic of hydrozoan medusae but it is insignificant in Obelia. The lateral wall of the body gives off small lateral buds called the medusa-buds.
This zooid and medusa are carnivorous, feeding upon small aquatic crustaceans, nematodes and other worms. ADVERTISEMENTS: The hydranths are more numerous and constitute the feeding zooids. In addition to the above two zooids, the lateral branches also bear short club-like structures which are either primordial or developing gastro-zooids or blastostyles. The outer ends fuse and gives rise to a continuous cuticle along the entire length of the body. Respiration, Circulation and Excretion. Blastostyle or Gonozooid or Reproductive-zooid: These types of zooids are few in number in comparison to the number of gastro-zooids.
Velum is absent but the velarium containing endodermal canal is present. A dilatation occurs near the open or distal end. It is a branched filament like structure and remains attached with the substratum. The medusae derived from the polyp are independent units, living apart, and feeding themselves. The terminal bud apical bud is a developing hydranth.
The cavity of the blastostyle pushes the coenosarc out to form a small protuberance or bud. This cell type has a prominent nucleus and several small vacuoles. The coelenteron of the hydranth communicates with the cavity of the hydrocaulus and thus the absorbed food is distributed to the entire colony. On the sub-umbrella, the gonads ovaries or testis appear as knobs beneath the radial canals. Muscle strands are derived only from the epidermis.
