Strumigenys lujae group

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Strumigenys lujae group Bolton (2000)

Species

Afrotropical-West Palaeartic

S. ludovici and S. simoni also occur in the Malagasy region

Worker Diagnosis

Mandibles in full-face view and at full closure stoutly elongate-triangular to very long narrow-triangular, serially serrate or minutely denticulate, engaging throughout their length or slightly separated basally. In profile mandible shallowly curved and only its extreme base overlapped dorsally by the clypeus. In ventral view outer margin of mandible without a prebasal inflected angle. MI 26-50.

Dentition. Apical (masticatory) margin of mandible serially minutely multidenticulate or serrate, with a continuous row of well over 25 tiny denticles or a continuous finely saw-like edge on each mandible. In some species the basal most 4-8 denticles are larger than those situated more distally.

Basal lamella of mandible apparently absent (see below), rarely vestigial; usually the denticle row extends to the basal angle without interruption but occasionally a lamellar vestige present basally.

Labrum terminates in a pair of triangular to conical narrow lobes.

Clypeus with a lower (secondary) anterior margin that is convex and thinly lamellate, difficult to see; close behind this and slightly higher is the true (primary) margin, which is broader and more conspicuous, and from which anteriorly directed hairs arise. Lateral margins very short and convergent anteriorly. Outer margins of mandibles intersect anterior clypeal margin at or very near the anterolateral clypeal angles.

Clypeus with true anterior margin bearing a row of narrowly spatulate hairs that are weakly downcurved and project forward over the lamellate lower (secondary) clypeal margin and extreme bases of the mandibles in full-face view. Lateral margins of clypeus with a few similar anteriorly curved hairs.

Preocular carina conspicuous in full-face view.

Ventrolateral margin of head between eye and mandibular insertion broadly convex, the side rounding evenly into the ventral surface. Postbuccal impression vestigial to absent.

Cuticle of side of head within scrobe reticulate-punctate.

Scape slender, short to very long, SI 65-127, cylindrical, subcylindrical or slightly dorsoventrally flattened.

Leading edge of scape with a row of freely projecting curved hairs that are narrowly to broadly spatulate or narrowly spoon-shaped. Some of these hairs are usually (but not always) curved toward the base of the scape.

Spongiform appendages of petiole and postpetiole moderately developed to vestigial. Base of first gastral stemite without a pad or crest of dense spongiform tissue.

Pilosity. Extremely variable through the group; humerus of pronotum with or without a specialised projecting hair.

Sculpture. Very variable but dorsum of head behind clypeus always reticulate-punctate.

Notes

The very distinctive structure of the mandibles and anterior clypeus renders the lujae-group easily identifiable. A similar development of the clypeus, so that it has two apparent margins, occurs in some members of the Nearctic clypeata-group. The origin and development of this bimargination are discussed there.

At first glance most species of this group appear to lack any trace of a basal lamella on the mandible but it remains visible basally in Strumigenys sulumana. Closer examination reveals that the basal lamella is present but has been elongated distally and pressed into service as part of the masticatory margin, becoming denticulate or serrate along its inner margin and displacing the original 12 denticles toward the apex. In many populations of lujae slightly enlarged teeth occur in the apical third that are apparently remnants of the original principal dental series as it is expressed in most other “short-mandibulate” species-groups of Pyramica.

Species of the lujae-group are by far the commonest dacetines encountered in the Afrotropical region, and two species have also invaded the Malagasy region. The serially minutely denticulate mandibles characteristic of the group have been paralleled by two Malesian species belonging to the capitata group (Strumigenys serraformis, Strumigenys serradens) and by the Neotropical Strumigenys mirabilis, but in all of these a mandibular basal lamella remains fully developed, the anterior clypeus lacks the specialisation of the lujae-group, the base of the first gastral stemite has a spongiform pad and in the capitata-group species the preapical mandibular tooth is enlarged.

The previously described species of this group formerly constituted the genus Serrastruma, now abandoned (Bolton, 1999). The species were initially revised by Brown (1952b) and have been fully described in Bolton (1983). The species notes that follow only document significant changes to the taxonomy, minimal diagnoses and additions to distributions discovered subsequent to these publications.

References

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