Definition

1. Noun:
   • A simple eye, or an eye with a single lens: In zoology, an ocellus is a type of simple visual organ found in many invertebrates, such as insects and some other arthropods. It is distinct from a compound eye.
   • An eyelike spot or marking: In biology, an ocellus is a circular, often colorful marking that resembles an eye, commonly found on the wings of butterflies, moths, or the bodies of other animals.

Examples of Usage

• Noun (Simple Eye):

  • The insect's head bears two compound eyes and three ocelli.
  • Ocelli are sensitive to light intensity but do not form detailed images.

• Noun (Eyelike Marking):

  • The butterfly's wings have prominent ocelli to scare away predators.
  • The peacock feather is famous for its beautiful ocelli.

Advanced Usage

• In Entomology: The term is used precisely to describe the simple eyes located on the heads of insects, arachnids, and myriapods.

  • The dorsal ocelli of the dragonfly are thought to aid in flight stabilization.

• In Lepidopterology (Study of Butterflies and Moths): Refers specifically to the eye-spot patterns.

  • The number and arrangement of ocelli are key identification features for some moth species.

Variants and Related Words

• Ocellar (adjective): Pertaining to an ocellus.

  • The ocellar region of the insect's head was examined.

• Ocellated (adjective): Having ocelli or eyelike spots.

  • The ocellated lizard gets its name from the blue spots along its body.

Synonyms

• Simple eye: For the visual organ sense.
• Eyespot: For the marking sense.
• Stemmata (plural): A term sometimes used for the simple eyes of insect larvae.

Notes on Meaning

• The two primary meanings are distinct but related through the concept of an "eye-like" structure—one is a functional sensory organ, and the other is a decorative or defensive marking that mimics an eye.
• The plural form is ocelli (pronounced /oʊˈsɛlaɪ/ or /əˈsɛli/).

Noun

1. an eyelike marking (as on the wings of some butterflies); usually a spot of color inside a ring of another color
2. an eye having a single lens