Archetype

Homology Weekly: Arolium

Foot of a Oecophylla smaragdina worker. Pretarsal claws and manubrium in red; arolium in yellow; tarsi in green (Scanning Electron Micrograph, Roberto Keller/AMNH)

This orchid-looking thing is really the foot of an ant. The large unfolded structure in between the powerful pair of claws is the adhesive organ of the foot called arolium (pl. arolia). It is basically a soft membranous bag folded into a suction cup that allows the ant to walk on vertical or upside down smooth surfaces.

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Tags: Arolia, Arolium, Ectatomma tuberculatum, Oecophylla smaragdina, Probolomyrmex guineensis, Procryptocerus, Tetraponera attenuata

Homology Weekly: Gaster

The five segmented gaster (in yellow, arabic numeral) in a Cerapachys nitidulus worker. Roman numerals refer to abdominal segments (Scanning Electron Micrograph, Roberto Keller/AMNH)

Gaster is a morphological term that is very useful and yet imprecise for the purpose of comparative anatomy as it is currently used in ants. It comes from the Greek for “belly” and it refers to the collection of segments in the metasoma that remain after the pedicel of ants and wasps. It is the bulbous part of the body that hosts the insect viscera.

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Tags: Cerapachys nitidulus, Cybertaxonomy, Gaster, Manica rubida, Plazi

Homology Weekly: Propodeum

Abdomen of a Manica rubida worker. Roman numerals correspond to external abdominal segments. Propodeum shown in blue (Scanning Electron Micrograph, Roberto Keller/AMNH)

The propodeum is the subversive segment of the apocritan abdomen. As explained in a previous post, at some point during the evolution of Hymenoptera this first abdominal segment decided to part ways with its serial homologues and fuse with the thorax, forming a secondary tagma we call mesosoma. It is the Texas of the body’s segments so to speak.

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Tags: Acanthoponera minor, Aculeata, Apocrita, epinotum, Lasius (Acanthomyops) occidentalis, Manica rubida, Mesosoma, Propodeum, wasp waist

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

Homology Weekly: Tagmata

Profile view of a Ponera pennsylvanica worker showing primary tagmosis. Red: head; yellow: thorax; blue: abdomen (Scanning Electron Micrograph, Roberto Keller/AMNH)

When a group of successive segments along the arthropod body form a distinct section (by fusion, for example), the division is called a tagma (pl. tagmata). In the case of hexapods (= insects plus their primitively wingless cousins) the body segments are arranged into the three familiar tagmata: head, thorax and abdomen. › Continue reading

Tags: Abdomen, Alitrunk, Apocrita, Head, Mesosoma, Metasoma, Ponera, Tagma, Tagmata, Thorax

Homology Weekly: Dentiform Clypeal Setae

Anterior part of the head of an Australian Onychomyrmex doddi worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

Among the many interesting features found in members of the subfamily Amblyoponinae is the presence of unique teeth-like structures at the anterior margin of the ant’s cranium. They are arranged in one or two parallel rows, right above the opening of the oral cavity, in a plate called clypeus. › Continue reading

Tags: Amblyopone, Amblyoponinae, Clypeus, Concoctio, Gerontoformica, Onychomyrmex, Setae

Homology Weekly: Sensillae Trichoidea

Detail of the antennal apex of a Dorylus helvolus worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

This image shows the surface of the tip of the antenna in the African driver ant Dorylus helvolus. The tongue-shaped structures are one of the many types of hair-like sensory organs called sensillae trichoidea (Latin for, well, hair-like sensory organs). These organs are basically composed of a central piece of cuticle in the shape of a long filament or short paddle inserted into a socket and kept in place by a membranous ring. The central piece, thus, can freely move in all direction allowed by the socket. › Continue reading

Tags: Antenna, Dorylus, Sensillae trichoidea

Homology Weekly: Hypopygium

Last week’s post featured the acidopore: a modification of the ventral plate in the last visible segment of the abdomen in females, as it occurs in the formicine subfamily of ants (e.g., wood ants, carpenter ants, weaver ants). Counting from front to back, this ventral plate is part of the seventh abdominal segment and is denoted by a special term in insects: hypopygium (pl. hypopygia). It is colored in red in the images below.

Abdomen of a Leptogenys sp worker from Nepal, profile view (Scanning Electron Micrograph, Roberto Keller/AMNH)

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Tags: Abdomen, Hypopygium, Leptogenys, Morphology

Homology Weekly: Acidopore

Acidopore of a Formica fusca worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

It is popular knowledge that ants secrete formic acid. What most people don’t know is that only a well-defined subgroup of species have this capacity. Female ants in the subfamily Formicinae have an acid producing gland that sprays its content through a special opening at the rear end of their abdomens, aptly called the acidopore. › Continue reading

Tags: Acidopore, Ants, Formic Acid, Formica, Morphology