Structures of the Lepidopteran head
A possibly helpful oversimplification is to consider the insect head as being derived from the first few segments of a primitive centipede-like athropod with each segment having paired appendages. Starting out as leg-like these appendages have become much modified in the course of evolution. Starting anteriorly:
ANTENNAE: Paired, many-segmented, usually partly scaled.
COMPOUND EYES: Paired, large rounded. Often with erect hairs between the facets
Ocelli: (singular: ocellus) Paired, small simple eyes, one above each compound eye. Present in some Lepidopteran families, absent in others.
Chaetosemata: Paired structures of unknown function on top of head between compound eye and ocellus in Family Zygaenidae only.
In the primitive arthropod, the anterior border of the mouth is formed by the labrum which articulates with the clypeus and the clypeus with the frons.
In Lepidoptera these structures are not separately identifiable being fused to form the front of the head or "face".
MANDIBLES: Present (but difficult to see) in Families Micropterigidae and Eriocraniidae only; absent in all other Lepidopteran familes.
In the primitive arthropod the mandibles articulate with the genae, paired plates that form the sides of the head and bordered antero-inferiorly by the frons, antero-superiorly by the compound eye, superiorly by the vertex, postero-inferiorly by the postgena, postero-superiorly by the occiput.
MAXILLAE:
LABIUM: This forms the posterior border to the mouth and is reduced to a small plate in Lepidoptera. The LABIAL PALPS are usually 3-segmented and scaled. They are well-developed in all but the most primitive Lepidopteran families.
Whether the head is rough-haired or smooth-scaled and whether the scales on the vertex are broader or narrower than the antennal shaft are useful features in the identification of some families.
ANTENNAE: Paired, many-segmented, usually partly scaled.
- SCAPE: First antennal segment. May be simple, tufted, have an anterior PECTEN of stiff hair-like scales or have scales expanded into a concave EYECAP
- Pedicel: Second antennal segment (of little use in taxonomy or identification of Lepidoptera)
- FLAGELLUM: (or shaft) All remaining antennal segments together. Usually more specialised in male than female. May be moniliform (like a string of beads), filiform (thread-like), ciliate, clavate (clubbed), dentate (toothed), serrate (saw-like), lamellate (like a stack of plates) or pectinate (comb-like)
COMPOUND EYES: Paired, large rounded. Often with erect hairs between the facets
Ocelli: (singular: ocellus) Paired, small simple eyes, one above each compound eye. Present in some Lepidopteran families, absent in others.
Chaetosemata: Paired structures of unknown function on top of head between compound eye and ocellus in Family Zygaenidae only.
In the primitive arthropod, the anterior border of the mouth is formed by the labrum which articulates with the clypeus and the clypeus with the frons.
In Lepidoptera these structures are not separately identifiable being fused to form the front of the head or "face".
MANDIBLES: Present (but difficult to see) in Families Micropterigidae and Eriocraniidae only; absent in all other Lepidopteran familes.
In the primitive arthropod the mandibles articulate with the genae, paired plates that form the sides of the head and bordered antero-inferiorly by the frons, antero-superiorly by the compound eye, superiorly by the vertex, postero-inferiorly by the postgena, postero-superiorly by the occiput.
MAXILLAE:
- Laciniae: present only in Families Micropterigidae and Eriocraniidae. Absent or rudimentary in all other families.
- Galeae: greatly elongated, internally grooved, fastened together with interlocking hooks and spines to form a tubular PROBOSCIS which is coiled at rest - present in all Lepidopteran families except Micropterigidae.
- Maxillary palps: present, scaled, 5 or 6-segmented and folded at rest in the more primitive families; reduced or absent in more advanced families
LABIUM: This forms the posterior border to the mouth and is reduced to a small plate in Lepidoptera. The LABIAL PALPS are usually 3-segmented and scaled. They are well-developed in all but the most primitive Lepidopteran families.
Whether the head is rough-haired or smooth-scaled and whether the scales on the vertex are broader or narrower than the antennal shaft are useful features in the identification of some families.
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