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Ants of the subfamily Pseudomyrmecinae: Use Of Morphometric Measurements

The identification of pseudomyrmecine ants requires careful, accurate measurements of various body structures in the workers, queens, and males. The list below contains the principal metrics that are cited in the keys and species descriptions. Additional details on measurement procedures are given in Ward (1989, 1993). When the head is placed in a full-face, frontal (i.e., dorsal) view, it is positioned in such a way that the posterior margin of the head and the anterolateral margins, above the mandibular insertions, lie in the same plane of view.

Metric Measurements

For the first eleven items listed below (HW to EL), the head is positioned in a full-face, frontal view.

HW Head width: maximum width of head, including the eyes (see Figure 1 below).
VW Vertex width: width of the posterior portion of the head (vertex), measured along a line drawn through the lateral ocelli (Figure 1)
HL Head length: midline length of head proper, from the posterior margin (or, if the posterior margin is concave, from the midpoint of a line drawn across the margin) to the anterior extremity of the clypeal margin (Figure 1)
N1, N2, N3, N4, N5
A series of cumulative measurements taken during the measurement of HL, starting from the midpoint of a line drawn across the posterior margin of the head. N1: distance to the midpoint of a line drawn between the lateral ocelli; N2: distance to the middle of the median ocellus; N3: distance to a line drawn across the posterior margins of the compound eyes; N4: distance to a line drawn across the anterior margins of the compound eyes; N5: distance to a line drawn across the anterior margins of the antennal sclerites (toruli).
OD Ocellar distance: distance from the middle of the median ocellus to the midpoint of a line drawn between the lateral ocelli; this is calculated as N2-N1 (see also Figure 1).
OOD Oculo-ocellar distance: distance from the middle of the median ocellus to the midpoint of a line drawn across the posterior margins of the compound eyes; this distance is calculated as N3-N2, and it is negative in value if the posterior margin of the compound eye exceeds the median ocellus (see also Figure 1).
EL Eye length: length of compound eye, calculated as N4-N3 (see also Figure 1).
PFC Maximum frontal carinal distance: maximum distance between the frontal carinae, posterior to their fusion with, or approximation to, the antennal sclerites; this measurement is used in those species where the frontal carinae diverge posteriorly (e.g., Ward, 1989, figure 40).
MFC Minimum frontal carinal distance: minimum distance between the frontal carinae, posterior to their fusion with, or approximation to, the antennal sclerites (Figure 2).
ASD Antennal sclerite distance: maximum distance between the lateral margins of the median lobes of the antennal sclerites, measured in full-face, dorsal view of the head (Figure 2).
ASM Antennal sclerite distance, inner margins: minimum distance between the inner margins of the antennal sclerites, anterior to ASD (Figure 2).
ASO Antennal sclerite distance, outer margins: maximum distance between the outer, lateral margins of the antennal sclerites (Figure 2).
CLW Width of median clypeal lobe, measured between the anterolateral angles (measured only in species where the median clypeal lobe is laterally angulate; e.g., Pseudomyrmex satanicus and P. spinicola in Ward 1993, figures 10, 11).
MD1, MD2, MD4, MD5, MD8, MD9
A series of mandibular measurements (see Figure 3). MD1: basal width of the mandible; MD2: width of mandible, taken parallel to MD1, at the level of the apicobasal tooth; MD4: distance along the basal margin of the mandible from the base to the mesial basal tooth; MD5: length of the basal margin; MD8: distance along the masticatory margin from the apex to the fourth tooth, counting from the apex; MD9: length of the masticatory margin.
EW Eye width: maximum width of compound eye, measured along its short axis in an oblique dorso-lateral view of the head.
SC Scape length: length of the first antennal segment, excluding the radicle.
LF1 Length of first funicular segment: maximum measurable length of the first funicular segment (pedicel), including its basal articulation in workers and queens but excluding the basal articulation in males (where it is variably exposed).
LF2 Length of second funicular segment: maximum measurable length of the second funicular segment.
LF3 Length of third funicular segment: maximum measurable length of the third funicular segment.
WF2 Width of second funicular segment.
DPL Diagonal length of the propodeum: length of the propodeum, measured in lateral view along a diagonal line drawn from the metanotal groove to the propodeal (often called “metapleural”) lobe (see Figure 4).
BF Length of the dorsal (often called “basal”) face of the propodeum, measured in lateral view from the metanotal groove to the point on the surface of the propodeum which is maximally distant from the diagonal propodeal line (Figure 4).
DF Length of the declivitous face of the propodeum, measured in lateral view from the propodeal lobe to the point on the surface of the propodeum which is maximally distant from the diagonal propodeal line (Figure 4).
PDH Propodeum height: height of the propodeum, measured in lateral view, from the base of the metapleuron to the maximum height of the propodeum, along a line orthogonal to the lower metapleural margin (see Ward, 2001, figure 3).
MTW Metapleural width: maximum distance between the metapleura, measured in dorsal view (see Ward, 2001, figure 4).
MP Depth of metanotal groove (“mesopropodeal impression”), measured in lateral view from the bottom of the metanotal groove to a line drawn across the dorsal surface of the mesonotum and propodeum.
FL Profemur length: length of the profemur, measured along its long axis in posterior view (Figure 5).
FW Profemur width: maximum measurable width of the profemur, measured from the same view as FL, at right angles to the line of measurement of FL (Figure 5).
LHT Length of the metatibia, excluding the proximomedial part of the articulation which is received into the distal end of the metafemur (Figure 6).
PL Petiole length: length of the petiole, measured in lateral view from the lateral flanges of the anterior peduncle to the posterior margin of the petiole (Figure 7).
PND Petiolar node distance: distance from the lateral flanges of the anterior petiolar peduncle to the maximum height of the node, measured from the same view as PL and along the same line of measurement (Figure 7).
PH Petiole height: maximum height of the petiole, measured in lateral view at right angles to PL, but excluding the anteroventral process (if present) (Figure 7).
PPL Postpetiole length: length of the postpetiole, measured in lateral view, from the anterior peduncle of the postpetiole to the point of contact with the fourth abdominal tergum, excluding the pretergite (Figure 7).
DPW Dorsal petiolar width: maximum width of the petiole, measured in dorsal view.
MPW Minimum petiolar width: minimum width of the petiole, measured in dorsal view, anterior to DPW.
PPW Dorsal postpetiolar width: maximum width of the postpetiole, measure in dorsal view.

Illustrations of selected measurements

Figure 1. Full-face view of worker head Figure 2. Measurements associated with the frontoclypeal complex
Figure 3. Worker, right mandible Figure 4. Worker, lateral view of propodeum

Figure 5. Worker, profemur
Figure 6. Worker, metatibia
Figure 7. Worker, lateral view of petiole and postpetiole

Indices

Indices calculated from the preceding measurements include the following ratios (the unnecessary practice of multiplying such ratios by 100 has not been observed).

CI Cephalic index: HW/HL
OI Ocular index: EW/EL
REL Relative eye length: EL/HL
REL2 Relative eye length, using HW: EL/HW
OOI Oculo-ocellar index: OOD/OD
VI Vertex width index: VW/HW
FCI Frontal carinal index: MFC/HW
FCI2 Frontal carinal index, using ASD: MFC/ASD
ASI Antennal sclerite index: ASD/ASO
ASI2 Antennal sclerite index, using ASM: ASM/ASD
SI Scape index: SL/HW
SI2 Scape index, using EL: SL/EL
SI3 Scape index, using LF2: SL/LF2
FLI Funicular length index: (LF2 + LF3)/WF2
FI Profemur index: FW/FL
PDI Propodeal index: BF/DF
PDI2 Propodeal index (alternate): PDH/MTW
MPI Metanotal index: MP/HW
NI Petiole node index: PND/PL
PLI Petiole length index: PH/PL
PLI2 Petiole length index, using PPL: PPL/PL
PHI Petiole height index, using PPL: PH/PPL
PWI Petiole width index: DPW/PL
PWI2 Petiole width index, using PPW: DPW/PPW
PWI3 Petiole width index, using MPW: MPW/DPW
PWI4 Petiole width index, using LHT: DPW/LHT
PPWI Postpetiole width index: PPW/PPL
PPWI Postpetiole width index, using HW: PPW/HW

Setal Counts

CSC Cephalic setal count: number of standing hairs, i.e., those forming an angle of 45° or more with the cuticular surface (Wilson, 1955), visible on the posterior half of the dorsum of the head, as seen in lateral and posterior views
MSC Mesosoma setal count: number of standing hairs visible in outline on the dorsal surface of the mesosoma.
HTC Metatibial setal count: number of standing hairs visible in outline on the outer (extensor) surface of the metatibia, with the line of view orthogonal to the plane of tibial flexion. This count excludes small apical tufts of hair.
MTC Mesotibial setal count: equivalent count for the mesotibia.

Literature Cited

  • Ward, P.S. 1989. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaestiones Entomologicae 25:393-468.
  • Ward, P. S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae). Journal of Hymenoptera Research 2:117-168
  • Ward, P. S. 2001. Taxonomy, phylogeny and biogeography of the ant genus Tetraponera (Hymenoptera: Formicidae) in the Oriental and Australian regions. Invertebrate Taxonomy 15:589-665.
  • Wilson, E. O. 1955. A monographic revision of the ant genus Lasius. Bulletin of the Museum of Comparative Zoology 113:1-201.

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