A , One of the featherduster worms called a Christmas-tree worm , Spirobranchus giganteus, has a double crown of radioles and lives in a calcareous tube. B , Sabellid polychaetes, Bispira brunnea, live in leathery tubes. Figure Nereis virens , an errant polychaete. A , Anterior end, with pharynx everted. B , External structure. C , Posterior end. D , Generalized transverse section through region of the intestine.
Figure Amphitrite , which builds its tubes in mud or sand, extends long grooved tentacles out over the mud to pick up bits of organic matter. The smallest particles are moved along food grooves by cilia, larger particles by peristaltic movement. With around 10, known species, the Oligochaeta make up about half of the phylum Annelida. These worms usually have few setae chaetae or "bristles" on their outer body surfaces, and lack parapodia , unlike polychaeta.
Polychaetes are a diverse and abundant group of segmented worms. They are commonly known as bristle worms because of their characteristic hairs called 'chaetae'. Polychaetes are mainly found in the marine environment, from shallow waters down to the depths of deep-sea trenches. Annelid setae are stiff bristles present on the body. They help, for example, earthworms to attach to the surface and prevent backsliding during peristaltic motion.
These hairs make it difficult to pull a worm straight from the ground. The atoke is a single metal bell and looks like a large pea-pod. The sound is produced by holding the bell in the palm of the hand the palm functions as the resonator and striking it with a metal rod. Oligochaetes feed on dead and decaying material, which helps take it out of the environment.
They replace it with 'new' material that is nutrient rich and ready for use again by other organisms like plants. The digestive tract is a simple tube, usually with a stomach part way along. The smallest species, and those adapted to burrowing, lack gills, breathing only through their body surfaces.
Most other species have external gills, often associated with the parapodia. Their nutrition comes from things in soil, such as decaying roots and leaves. Animal manures are an important food source for earthworms. They eat living organisms such as nematodes, protozoans, rotifers, bacteria, fungi in soil. Worms will also feed on the decomposing remains of other animals. What are parapodia , chaetae or setae.
The setae of some polychaetes, e. These brittle setae are easily broken off and contain a toxin that produces a painful reaction in humans. In the scaleworms, a series of overlapping scales form a covering over the animal's upper surface. In the sea mouse these scales are completely covered by long, slender, feltlike setae projecting from the parapodia. Sedentary polychaetes are usually adapted to living permanently in tubes or burrows; some attach themselves to rocks or piers. Many sedentary polychaetes, like the lugworm, Arenicola, live in burrows in sand or mud.
The majority, however, are tube builders. Tubes of different species vary greatly in their composition and structure. They may be composed of sand, shell, or other particles held together with mucus, or made entirely of organic substances secreted by the worm that harden on contact with water.
The tubes may be straight, branched, spiraled, or U-shaped. Most are permanently attached to a substrate, and the worm seldom or never ventures outside; however, the tube worm Cistenides moves about the seafloor, dragging along its delicate tube of sand grains. Sedentary polychaetes have greatly modified head regions for specialized feeding habits. Many are adapted for feeding on organic matter deposited on the ocean floor. For example, the lugworms have a simple, thin-walled, jawless proboscis, which is used to draw sand into the gut, where organic matter is removed.
The food is brought by beating of cilia in a groove running along each filament. Order Errantia and Sedentaria Polychaetes can be separated into two large orders, Errantia and Sedentaria , based on the development of the anterior appendages and life habits. Sedentary Polychaete. Errant Polychaete The jaw of Glyceridae. Hong Kong Sedentary Polychaetes Since the 's, about species of sedentary polychaetes have been reported from Hong Kong Shin Sedentary Polychaetes: Tube Dwellers Spionidae.
Sandy Tube of Pectinariidae. Errant Polychaete. Errant Polychaetes.
0コメント