AskDefine | Define sessile

Dictionary Definition

sessile adj
1 permanently attached to a substrate; not free to move about; "an attached oyster"; "sessile marine animals and plants" [syn: attached] [ant: vagile]
2 attached directly by the base; not having an intervening stalk; "sessile flowers"; "the shell of a sessile barnacle is attached directly to a substrate" [syn: stalkless] [ant: pedunculate]

User Contributed Dictionary

English

Etymology

From Neo-Latin sessilis, literally sitting, from sessus, perfect passive participle of verb sedēre, sit, + adjective suffix -ilis.

Adjective

  1. permanently attached to a substrate; not free to move about; "an attached oyster"
  2. attached directly by the base; not having an intervening stalk; "a sessile leaf"

Italian

Adjective

  1. sessile

Extensive Definition

Sessile is a term in biology with two distinct meanings:

In botany and medicine

In botany, sessile means "without a stalk", as in flowers (pedicel) or leaves (petiole) that grow directly from the stem or Peduncle; however, in limnology, sessile vegetation are any organisms anchored to the benthic environment. The term is also used in medicine to describe tumors and polyps that lack a stalk, as opposed to those that are pedunculated.

In zoology

In zoology sessile animals are those which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a rock, or the hull of a ship in the case of barnacles. Corals lay down their own substrate.
Sessile animals typically have a motile phase in their development. Sponges have a motile larval stage, which becomes sessile at maturity. In contrast, many jellyfish develop as sessile polyps early in their life cycle. Many sessile animals, including sponges, corals, and hydra, are capable of asexual reproduction in situ by a process of budding.

Sessile animals

Sponges

Most of the 2000 species of sponges are marine animals; only about 50 species live in fresh water. Sponges are sessile animals that come in a wide variety of sizes and shapes and are adapted to different movement patterns of water. Sponges reproduce both sexually and asexually. In most species, a single individual produces both egg and sperm, but individuals do not self-fertilize. Water currents carry sperm from one individual to another. Asexual reproduction is by budding and fragmentation.
Clumping is a behavior in an animal, usually sessile, in which individuals of a particular species group close to one another for beneficial purposes.

See also

sessile in German: Sessile Tiere
sessile in Italian: Sessilità
sessile in Simple English: Sessile
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