An oral arm is an
anatomical
Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
structure of "true"
sea jellies
Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella ...
(or Scyphozoans), which belong to the class
Scyphozoa
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies").
The class name Scyphozoa comes from the Greek word ''skyphos'' (), denoting a kind of drinking cup and alluding to the ...
. Oral arms characterize
Semaeostomeae
Semaeostomeae (literally "flag mouths") is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbra ...
, an order of large jellyfish.
The oral arms (of which there are usually four) are located around the mouth and hold the stinging cells, or
cnidocyst
A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...
s, which are used to inject potential prey (or potential predators) with venom.
Functions
These four long oral arms, hang from the center of the underside, where the mouth of the jellyfish is located. In most cases, 24 other, thinner extensile
tentacles
In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
hang from the rim of the bell. Jellyfish reproduce sexually. Males release sperm through their mouth into the water column and this is received into the female's mouth, where
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
occurs. Development has to occur pretty quickly, as the lifespan of a jellyfish is only a few months. The eggs develop either inside the female, or in brood pouches located on the oral arms. They also aid in the capture and ingestion of food, and may contain stinging cells.
See also
*
Jellyfish
Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
*
Scyphozoan
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies").
The class name Scyphozoa comes from the Greek word ''skyphos'' (), denoting a kind of drinking cup and alluding to the ...
*
Semaeostomeae
Semaeostomeae (literally "flag mouths") is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbra ...
References
* Ben Waggoner, Brian Speer, and David Smith.
Life History and Ecology and
" ''Scyphozoa''.
Cnidarian anatomy
Scyphozoa
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