Showing posts with label Gastrotricha. Show all posts
Showing posts with label Gastrotricha. Show all posts

Gastrotricha

.
Gastrotrich, group of microscopic wormlike animals that are common in aquatic environments worldwide. The gastrotrich lives in bottom sediments and on the surface of submerged vegetation and debris. Its head is divided into lobes and its body is generally flat, transparent, and unsegmented. Its back and sides are spiny, bristly, or scaly. The flattened bottom surface bears small hairs, or cilia, in characteristic patterns that are helpful in classifying species. Along the sides of the body are adhesive tubes that are used for clinging to vegetation.

Gastrotrichs range in length from 0.05 to 4.0 mm (0.002 to 0.16 in). Marine gastrotrichs, those living in the ocean, are abundant on the surfaces of corals and in shallow sandy areas, while freshwater species prefer standing water such as puddles, marshes, and wet bogs. They may be present in habitats where there is much decay and they can withstand low levels of dissolved oxygen for short periods. The gastrotrich feeds as it moves, ingesting bacteria, algae, small protozoans, and organic debris from the substrate. Waving cilia on the head create currents that push food particles to the mouth.

Marine gastrotrichs are hermaphroditic (having both male and female sex organs) and individuals alternately produce eggs and sperm. Most freshwater species are entirely female and reproduce through parthenogenesis (egg development without fertilization). A female will produce one to five very large eggs in its lifetime. The eggs are of two types: thin-walled eggs that develop as soon as they are laid, and thick-walled eggs that require exposure to harsh conditions such as drying, freezing, or high temperatures before they develop. Gastrotrichs have no larval stages. On emergence from the egg, the gastrotrich is already about 25 percent of its adult size. It grows rapidly and some species reach sexual maturity in only three days. The lifespans of gastrotrichs in nature are unknown, but individuals in laboratory cultures live 3 to 22 days. Gastrotrichs are important as food for many organisms in aquatic food webs.

Scientific classification: Gastrotrichs make up the phylum Gastrotricha, which contains two orders. Animals in the order Macrodasyida are strictly marine, and those in the order Chaetonotida are primarily freshwater.

Types of Invertebrates

.
Ctenophora -> Jellyfish-like marine animals distinguished by eight rows of cilia that propel the body in swimming. They feed on other invertebrates using two retractable sticky tentacles to capture prey. All ctenophores are hermaphroditic and reproduce sexually. Many are luminescent. – Examples: Sea walnuts, comb jellies

Platyhelminthes -> Structurally simple worms with no anus or circulatory system. Known as flatworms, their flattened bodies enable internal tissues to be near the skin surface, permitting gas and nutrient exchange with the environment. A muscular layer just beneath the skin layer aids in locomotion. Flatworms are hermaphrodites and reproduce sexually. They typically have a life cycle involving a parasitic larval stage. Many types of flatworms are parasites of vertebrates. – Examples: Flatworms, flukes, tapeworms

Mesozoa -> Minute parasitic animals of invertebrates, particularly squids and octopuses. These worms have a simple, elongated, ciliated body. They reproduce sexually and have a complex life cycle involving more than one larval form. – Exmaple: Rhopalura granosa

Nemertea or Rhynchocoela -> Animals characterized by a proboscis, a long, muscular tube used in capturing invertebrate food. Nemerteans have elongated, flattened bodies and they lack an internal body cavity. They have a mouth opening for food ingestion and an anal opening for wastes. The blood of some nermerteans contains oxygen-carrying hemoglobin. Nemerteans reproduce sexually. – Examples: Nemertine worms, ribbon worms

Gastrotricha -> Microscopic multicellular animals that inhabit both freshwater and marine water. An external layer, the cuticle, encasing these animals contains cilia that aid in locomotion. Adhesive tubes found on the sides or at the posterior end aid in surface attachment. Freshwater species have a forked tail. These animals feed on dead or living bacteria, diatoms, or small protozoa. Marine species are hermaphroditic, while most fresh water species are female, reproducing by parthenogenesis. – Examples: Turbanella cornuta, Chaetonotus anomalus

Rotifera or Rotatoria -> Microscopic aquatic animals characterized by a corona, a wheel-shaped organ on the head used in feeding and swimming. The rapid beating of the cilia on the corona draws nutrient-containing water into the mouth. A protective cuticle covers the elongated, cylindrical body. Reproduction is sexual during brief periods of the year and throughout the rest of the year females reproduce via parthenogenesis. – Examples: Synchaeta oblonga, Phylodina roseola

< Next Page >

Popular Posts