Everything about Antenna Biology totally explained
Antennae (singular
antenna) are paired
appendages connected to the front-most
segments of
arthropods. In
crustaceans, they're
biramous and present on the first two segments of the head, with the smaller pair known as
antennules. All other arthropod groups, except
chelicerates and
proturans which have none, have a single,
uniramous pair of antennae.
Antennae are jointed, at least at the base, and generally extend forward from the head. They are
sensory organs, although the exact nature of what they sense and how they sense it isn't the same in all groups, nor always clear. Functions may variously include sensing
touch, air motion, heat, vibration (sound), and especially
olfaction (smell) or
gustation (taste).
Insects
In
insects,
olfactory receptors on the antennae bind to
odour molecules, including
pheromones. The
neurons that possess these receptors signal this binding by sending
action potentials down their
axons to the
antennal lobe in the
brain. From there, neurons in the antennal lobes connect to
mushroom bodies that identify the odour. The sum of the electrical potentials of the antenna to a given odor can be measured using an
electroantenogram.
The three basic segments of the typical insect antenna are the
scape (base), the
pedicel (stem), and finally the
flagellum, which often comprises many units known as
flagellomeres. Muscles are only present in the two first segments, the scape and pedicel. The scape is surrounded by a membranous region of the head. It pivots on a single marginal point called the
antennifer, allowing it to move in any direction. The number of flagellomeres can vary greatly, and is often of diagnostic importance. True flagellomeres have a membranous articulation between them, but in many insects, especially the more primitive groups, the flagellum is entirely or partially composed of a flexible series of small
annuli, which are not true flagellomeres. In many
beetles and in the
chalcidoid wasps, the apical flagellomeres form a
club, and the collective term for the segments between the club and the antennal base is the
funicle (or
funiculus); for traditional reasons, in beetles it's the segments between the club and the scape, but in wasps, it's the segments between the club and the pedicel. In the groups with more uniform antennae (for example:
Diplopoda), all segments are called
antennomeres. Some groups have a simple or variously modified apical or subapical bristle called an
arista (this may be especially well-developed in various
Diptera).
Crustaceans
Crustaceans bear two pairs of antennae. The first pair are
uniramous and are often referred to an
antennules, while the second pair are
biramous, meaning that each antenna is composed of two parts, joined at their base . In most adults, the antenna are sensory organs, but they're used by the
nauplius larva for both feeding and swimming. In some groups of crustaceans, such as the
spiny lobsters and
slipper lobsters, the second antennae are enlarged, while in others, such as
crabs, the antennae are reduced in size.
Image:PanulirusJaponicus .jpg|A spiny lobster, showing the enlarged second antennae
Image:Scyllarides latus.jpg|The large flattened plates in front of the eyes of a slipper lobster are the modified second antennae
Image:Boi.crab1.jpg|The crab Cancer pagurus, showing its reduced antennae
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