Archetype

Homology Weekly: Tentorial Pits

The anterior tentorial pits (arrows) in a Tetraponera aethiops worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

The head of an ant in frontal view has a couple of holes usually located in the area between the mouth and the place where the antennae are inserted. These holes look intriguing from the outside– Are they part of a sensing organ? Do they secrete a special chemical signal or defense substance through them? Are they use for breeding? The answer is more mundane than that. As I mentioned in an earlier post, most of what one sees in the outer surface of the arthropod’s exoskeleton does not have an external function, but is rather a symptom of the inside working in these wonderful machines. These particular holes mark the places where the cuticle invaginates to form the internal skeleton of the insect cranium known as the tentorium. The external holes produced by these invaginations are thus termed the tentorial pits.

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Tags: Acropyga, Discothyrea testacea, Leptanilloides, Tentorial Pits, Tentorium, Tetraponera aethiops, Tetraponera attenuata

Homology Weekly: Clypeus

Tetraponera aethiops worker showing the location of the clypeus in green (Scanning Electron Micrograph, Roberto Keller/AMNH)

When looking at an arthropod from our vertebrate perspective it is easy to forget that we are looking right at the animal’s skeleton. While our own vertebrate skeleton consists of a series of internal compact pieces with sponge-like cores that support an external layer of muscles and entrails (all nicely wrapped in skin), the reverse is true for arthropods. The arthropod skeleton consists of a series of external plates and hollow tubes that form enclosed spaces within which the internal musculature system attaches¹. One consequence of this peculiar body architecture is that most of what we see on the outer surface of this exoskeleton is but a reflection of what is going on on the inside– minute external pits correspond to places where the cuticle folds in to form internal pillars, and innocent looking shallow furrows on the surface are large internal walls where powerful muscles originate. A simple examination of the exoskeleton, therefore, can tell us a lot about particular functions and consequently about an insect’s behavior. › Continue reading

Tags: Acanthoponera, Cibarium, Clypeus, Exoskeleton, Formica fusca, Labrum, Onychomyrmex, Tetraponera aethiops

Homology Weekly: Stridulatory Organ

Pars stridens (in yellow) on the fourth abdominal tergite in a Pachycondyla villosa worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

Many insects produce chirping sounds by rubbing body parts against each other in a behavior know as stridulation. The structures involved have modifications specialized for this purpose thus forming a stridulatory organ.

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Tags: Nothomyrmecia macrops, Pachycondyla villosa, pars stridens, plectrum, Rhytidoponera, Stridulation, Stridulatory Organ, Tetraponera aethiops