Strumigenys schulzi group

AntWiki: The Ants --- Online
Jump to navigation Jump to search

Strumigenys schulzi group Bolton (2000)

Species

Nearctic

Neotropical

Worker Diagnosis

Mandibles in full-face view and at full closure triangular, with serially dentate masticatory margins that engage throughout their exposed lengths. In ventral view outer margin of mandible without a prebasal inflected angle. MI 10-24.

Dentition. Basally with a row of 5 teeth followed by 2 smaller teeth and 4 denticles, or with 5 teeth and 4 denticles only; terminating in a slightly enlarged apical tooth, giving a total dental count of 10 or 12. Usually no diastema between basal lamella and basal tooth, only rarely otherwise. [Dental rows are variously specialised in different species; see discussion below.]

Basal lamella lobate to rounded-triangular, as high as long or somewhat higher; less commonly low and elongate-rectangular, longer than high. Lamella of about equal height to the tallest teeth or slightly lower. In full-face view at least the anterior margin of the lamella usually visible when mandibles fully closed.

Labrum terminates in a pair of elongate narrowly triangular to conical lobes.

Clypeus with anterior margin very shallowly concave, transverse or evenly shallowly convex. Lateral margins straight to shallowly convex and weakly divergent posteriorly. Outer margins of fully closed mandibles intersect anterior clypeal margin at about the anterolateral angles, or continue just outside the lateral margins in full-face view (1 species).

In ventral view the lateral clypeal margins usually extend slightly beyond the outer margins of the mandibles.

Clypeus dorsally with decumbent to appressed short spatulate to squamate hairs that are directed anteriorly (minute elevated hairs occur in some species). Lateral margins of clypeus fringed by a row of freely projecting spatulate hairs that are curved anteriorly.

Preocular carinae visible in full-face view.

Ventrolateral margin of head angulate to marginate between eye and mandibular insertion.

Postbuccal impression narrow and shallow.

Cuticle of side of head within scrobe reticulate-punctate.

Scape short to moderate, SI 50-82, very feebly to markedly dorsoventrally flattened, dorsum and ventre converging anteriorly to a sharp leading edge that may extend into a flange or even a thin lamella. Ventral surface of scape flat to shallowly transversely concave.

Leading edge of scape with a row of freely projecting spatulate to spoon-shaped hairs, one or more of which curve toward the base of the scape (in three species all hairs spoon-shaped, at right-angles to long axis of scape or inclined toward apex of scape and slightly down-curved).

Propodeum armed with a pair of triangular teeth subtended by lamellae, the latter sometimes very narrow and cariniform.

Spongiform strip or curtain usually absent from ventral surface of petiole (present but narrow in two species); a low non-spongiform cuticular crest may occur. Lateral spongiform lobe of petiole node small, sometimes vestigial or even absent. Lateral and ventral spongiform lobes of postpetiole present but may be very reduced. Base of first gastral sternite in profile with a narrow spongiform pad or strip (vestigial to absent in a few species).

Pilosity. Pronotal humeral hair either absent, or straight to curved and simple to somewhat thickened apically, or large and spoon-shaped, but never flagellate. Apicoscrobal hair absent, or curved and stout; never flagellate. Dorsum of head in profile usually with a transverse row of 4-6 standing hairs between highest point of vertex and occipital margin, these hairs distinctly longer and more erect that any other component of the cephalic pilosity (absent in some species). Dorsal (outer) surfaces of middle and hind tibiae with decumbent to appressed short spatulate hairs only, or with abundant short stubbly erect hairs (l species).

Sculpture. Dorsum of head behind clypeus and dorsal alitrunk with fine dense reticulate-punctate sculpture; rarely part or all of pleurae smooth but this area usually also entirely sculptured. Postpetiole usually densely sculptured, rarely smooth.

Notes

The diagnosis indicates that this group is probably not monophyletic; a few species show exceptions in one or two of the features listed above, though none exhibits all the noted exceptions. However, I currently consider these to represent secondary modifications from a common basic theme in agreement with Brown's (1953a) conclusion, and therefore propose to leave the group as a unit, though admittedly weakly defined, for the present.

The structure of the mandibles, clypeus, labrum, preocular carinae and scapes is encountered widely in the genus, being expressed in species groups from all over the tropics that earlier formed the core of genus Smithistruma, now abandoned (Bolton, 1999). Within this larger aggregation of groups the schulzi-group is characterised by the following in combination.

1 Pilosity of lateral clypeal margins and leading edge of scape is consistent (although not confined to this group), but flagellate hairs are always entirely absent.

2 Sculpture of the head (including scrobe), dorsal and lateral alitrunk and disc of postpetiole tends to be of uniform dense reticulate-punctation.

3 Ventral spongiform appendage of petiole is vestigial or absent.

Beside this, many species in the group have relatively large and conspicuous eyes (5 or more ommatidia in the longest row) and tend to be associated with plants rather than being denizens of rotten wood, the leaf litter or topsoil. Several species have been recorded from plant cavities or from epiphytes (Brown, 1953a; Brown, 1964).

The varying dental arrangements seen in the group are derived from a common pattern, one that occurs frequently in the genus. This pattern consists of 5 sharp teeth basally (that may vary in size) following the basal lamella with or without a diastema. These are followed by 2 smaller teeth (teeth 6 and 7), 4 minute denticles and a small apical tooth, to give a total count of 12. In Strumigenys cassicuspis, Strumigenys castanea, Strumigenys metrix, Strumigenys microthrix, Strumigenys necopina, Strumigenys orchibia, Strumigenys schulzi, Strumigenys stauroma and Strumigenys umboceps teeth 1 (basal) - 3 are longer than 4 and 5 but all are acute. In Strumigenys epinotalis and Strumigenys pholidota tooth 3 from the base is the longest, longer than 1-2 or 4-5, all of which are about of equal length and acute. In margaritae teeth 1, 3, and 5 are acute and higher than 2 and 4; teeth 2 and 4 are blunt apically. The sequence is continued in this species with tooth 6 blunt and 7 acute. Strumigenys depressiceps is specialised by the loss of two teeth (apparently 6 and 7) and great elongation of the basal lamella. In this species teeth 1 and 2 are shorter than 3-5, though all are acute. Tooth 5 is immediately followed by 4 minute denticles and a small apical tooth, giving a total dental count of 10. Brown's (1953a: 136, fig. 18) drawing of the mandible of depressiceps shows teeth 4 and 5 very short, but in specimens that I have dissected they are as long as tooth 3. I suspect they are broken off in Brown's figure. The most derived dentitions known in the group so far are exhibited by Strumigenys emiliae, Strumigenys urrhobia and Strumigenys dapsilis. In emiliae and urrhobia there is no diastema, teeth 1 (basal) and 3 are acute; tooth 2 is slightly lower and more blunt apically; tooth 4 is broadly rounded and plate-like; teeth 5-11 share a common fused base. Teeth 6-10 are very small and form a palisade between the distal margin of the larger tooth 5 and the proximal margin of tooth 11, the latter also enlarged and almost as tall as 5. Distal to tooth 11 is a deep cleft in the margin, beyond which is an elevated broad flat plateau that terminates apically in a small curved point, the whole of which appears to represent a much enlarged and modified apical tooth 12. A diastema is conspicuous in dapsilis between the basal lamella and the reduced basal tooth, the only known species in the group to exhibit such a development. The diastema is plainly visible in full-face view even when the mandibles are fully closed. Distal of the diastema the basal tooth is very small, reduced to a mere denticle. Teeth 2 and 4 are much larger, triangular and acute, but teeth 3 and 5 are low broadly rounded plates. Distal to these tooth 6 is acute but smaller than 2 or 4. Dentition beyond tooth 6 is difficult to discern in the two specimen s available as the mandibles are tightly closed, but appears to consist of 4 or 5 minute denticles and a small apical tooth.

References