Kinorhynchs: Kinorhyncha

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KINORHYNCHS: Kinorhyncha

NO COMMON NAME (Echinoderes sensibilis): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

Kinorhynchs (KIH-nuh-rinks) are tiny, spiny worms that live in the sea. Adult kinorhynchs are 0.008 to 0.05 inch (200 micrometers to 1.2 millimeters) long. Most kinorhynchs are clear, but some are yellowish or reddish. Kinorhynchs have 13 body segments: a head, a neck, and 11 trunk segments. The head is spherical, can be drawn into the trunk, and has 5 to 7 rings and as many as 91 spines that face backward. The mouth, which is at the tip of the head, contains sharp teeth and is surrounded by bristles. There are more bristles inside the mouth. The head is joined to the trunk by a neck that has plates that close over the head when it is pulled back into the trunk. The trunk is covered by armor and spines and contains glands that release mucus.

GEOGRAPHIC RANGE

Kinorhynchs live all over the world.

HABITAT

Kinorhynchs live in all seas from polar to tropical and at all depths. Most live in mud or mud mixed with sand.

DIET

Kinorhynchs eat diatoms, waste material, and bacteria. Diatoms (DYE-uh-tahms) are a type of algae that have a shell. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves.

BEHAVIOR AND REPRODUCTION

Kinorhynchs move by contracting the muscles on the top and bottom of their body. The contraction increases pressure on the fluid in the trunk. This process plows the spines into the sand or mud and pushes the worm forward, at the same time forcing its head out of the trunk. When the worm relaxes its muscles, the head is pulled back into the trunk.

Kinorhynchs collect diatoms by using their rigid bristles as tweezers to pinch an end of the diatom's shell, manipulate the diatom into their mouth, and break the shell. Then they suck out the insides.

Kinorhynchs have separate sexes. A male places a bag of sperm in a female, where fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place. The female then attaches the egg sac to sand grains. In about ten days the young kinorhynchs tear open the egg sac by straightening their bodies and thrusting out their heads. Young kinorhynchs shed their outer layer five or six times before reaching adult size.

KINORHYNCHS AND PEOPLE

Kinorhynchs have no known importance to people.

CONSERVATION STATUS

Kinorhynchs are not considered threatened or endangered.

NO COMMON NAME (Echinoderes sensibilis): SPECIES ACCOUNT

Physical characteristics: The trunk of Echinoderes sensibilis kinorhynchs is 0.012 to 0.014 inch (320 to 350 micrometers) long and yellowish. The head has 91 spines arranged in seven circles. There are hairlike fibers on some trunk segments.

Geographic range: Echinoderes sensibilis (abbreviated as E. sensibilis) kinorhynchs live on the Pacific coast of Japan.

Habitat: E. sensibilis kinorhynchs live in saltwater pools in areas that are exposed at low tide.

Diet: E. sensibilis kinorhynchs eat diatoms.

Behavior and reproduction: Scientists do not know how E. sensibilis kinorhynchs behave. The young shed six times as they grow into adults.

Echinoderes sensibilis and people: E. sensibilis kinorhynchs have no known importance to people.

Conservation status: E. sensibilis kinorhynchs are not considered threatened or endangered. ∎