Acoels: Acoela

views updated

ACOELS: Acoela

NO COMMON NAME (Convolutriloba longifissura): SPECIES ACCOUNT


Acoels (AY-seels) are tiny wormlike sea animals. They are the simplest animals with bilateral symmetry (bye-LAT-er-uhl SIH-muh-tree), meaning the right and left halves of the body match each other. Most acoels are no longer than about one-sixteenth of an inch (2 millimeters), although one species can reach a length of about five-eighths inch (15 millimeters). The bodies of acoels are flat ovals.

Acoels have either a simple mouth or none at all. The mouth is on the bottom of the animal. Acoels have no digestive tract, no system for eliminating waste or balancing salt content in their cells, and no reproductive organs. The nervous system is a loose net of fibers strung throughout the body. Most acoels have simple eyes. Almost all acoels have an organ for balance and for adjusting themselves to their surroundings.


Acoels live in all the oceans of the world.


Acoels live in shallow coastal seawater. Some drift or swim in open water, and others live among sand grains on the sea bottom. A few species live on other invertebrates (in-VER-teh-brehts), or animals without a backbone. Some acoels live on Antarctic ice floes.


Acoels eat algae, plankton, and waste material. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves. Plankton is microscopic plants and animals drifting in water.


Acoels move by using tiny hairlike fibers that cover the entire outside of their bodies. Acoels use sexual reproduction, although some species also use asexual reproduction by splitting in two, by breaking off part of the female's body, or by budding. Asexual (ay-SEK-shuh-wuhl) means without and sexual means with the uniting of egg and sperm for the transfer of DNA from two parents. In budding a bump develops on the animal, grows to full size, and then breaks off to live as a new individual. Acoels have no distinct reproductive organs. Eggs and sperm form directly in the middle tissue layer.


Acoels have no known importance to people.


Acoels are not threatened or endangered.

NO COMMON NAME (Convolutriloba longifissura): SPECIES ACCOUNT

Physical characteristics: Convolutriloba longifissura (abbreviated as C. longifissura) is a species of oval wormlike animals colored green by the presence of algae in their tissues. C. longifissura has hooks on its back that are used for defense and capturing prey.

Geographic range: C. longifissura lives all over the world.

Habitat: C. longifissura lives in sand beds in shallow seawater.

Diet: C. longifissura eats animals that are smaller than it is. It sometimes eats the algae that live in it.

Behavior and reproduction: Scientists do not know how C. longifissura behaves. It reproduces by mating between males and females. Eggs and sperm unite inside the female's body, and the fertilized (FUR-teh-lyzed) eggs are released. C. longifissura also reproduces asexually. The hindmost fourth of a female separates from the body and drops away. The fragment divides, and the new individuals form eyes and mouths over a period of two or three days. Meanwhile, the female regrows the lost section and repeats the breaking process, launching a new group of offspring every four days.

Convolutriloba longifissura and people: C. longifissura has no known importance to people.

Conservation status: C. longifissura is not threatened or endangered. ∎



Brusca, Richard C., Gary J. Brusca, and Nancy Haver. Invertebrates. 2nd ed. Sunderland, MA: Sinauer, 2002.

Web sites:

Seifarth, Wolfgang. Marine Flatworms of the World. (accessed on January 29, 2005).

"When We Were Worms." BBC Online Network. (accessed on January 29, 2005).