Mystrium maren Bihn & Verhaagh

Bihn, Jochen H. & Verhaagh, Manfred, 2007, A review of the genus Mystrium (Hymenoptera: Formicidae) in the Indo-Australian region, Zootaxa 1642, pp. 1-12 : 7-11

Mystrium maren Bihn & Verhaagh , new species

Fig. 7–9 , 12, 15

Type material. HOLOTYPE: Worker. INDONESIA: West Papua Province, Waigeo Island, near Urbinasopen, Gunung Susu, 0°22'45'' S, 131°15'10'' E, 350–450m a.s.l., January 2001 (leg. A. Riedel), deposited at MZB. PARATYPE: worker from the same collection as holotype, deposited at SMNK.

Measurements and indices. Holotype worker: HL 2.46, HW 2.72, CI 111, SL 1.84, SI 68, ML 2,81, WL 2.73, PW 1.37; Paratype worker: HL 2.34, HW 2.64, CI 113, SL 1.71, SI 65, ML 2.81, WL 2.62, PW 1.35.

Diagnosis (worker). The following character combination differentiates M. maren from all its congeners: the outer and inner margins of mandibles in dorsal view parallel and sinuate; the apex of each mandible only slightly expanded and subtruncate; outer face of labrum with a bilateral-symmetric rugoreticulum; maxillary palps 4-segmented; the second segment of the maxillary palp longer than the basal (first) segment; antennal segment III at least twice as long as broad; each anterolateral corner of the head produced into a long and pointed spine; dorsum of head with rugose-reticulate cuticular sculpture and spatulate to clavate hairs; minute compound eyes.

Description (worker). General morphology of the worker as shown in figures 7–9. Head wider than long; posterior margin of head in full-face view deeply and roundly emarginate. Each anterolateral corner of the head produced into a forward directed, long and curved spine. Mandibles long and slender; the outer and inner margins of each mandible in dorsal view parallel and distinctly sinuate; the inner margin with two staggered, longitudinal rows of hamulus-like teeth, each row with 12–14 teeth; teeth of the lower row larger than those of the upper row; the apex of each mandible only slightly expanded and subtruncate; the medioventral corner of the apex with an additional tooth; distal 2/3 on the dorsal face and distal half on the ventral face of each mandible with a longitudinal carina.

Labrum (fig. 15) about twice as wide as long; its distal margin convex with a median emargination; outer (ventral) face of labrum entirely foveolate-reticulate, and overlaid by a peculiar pattern of rugae: one ruga running between basolateral corners in an arc which is parallel to the distal margin and divides the outer surface of the labrum into distal and basal areas; additional rugae delimiting symmetrically two roughly rectangular fields on the median portion of the distal area.

Maxillary palps 4-segmented (fig. 12); the basal (first) segment roughly cone-shaped, shorter and much broader than the second. Labial palps 3-segmented.

Anterior clypeal margin convex with 9 truncated teeth; the teeth evenly spaced along the clypeal margin, without a median toothless gap. Antennal scape (antennal segment I) in dorsal view (as in fig. 7) curved only weakly and broadened in its distal part, in frontal view (perpendicular to dorsal view) strongly curved, with its predistal part ventrally broadened; apex of scape bends only weakly dorsad in this view. Each of antennal segments II–VI longer than broad; antennal segment III at least twice as long as broad; antennal segments IX–XII (the four distal segments) forming a weak club. Compound eyes minute, consisting of 7–10 ommatidia, situated near the midpoint of the sides of the head.

In lateral view, the dorsal outline of the mesosoma almost flat; promesonotal suture wide and deeply depressed; metanotal groove distinct but shallower and narrower than promesonotal suture. Mesosoma in dorsal view distinctly constricted between pronotum and propodeum. Propodeal spiracle directed laterad. Hind tarsus, when five tarsal segments combined, only slightly longer than hind tibia. Petiolar node in dorsal view about twice as broad as long. Subpetiolar process expanded anteroventrally and forming a rounded apex. Gastral segment I in dorsal view less than twice as broad as long, nearly as broad as the segment II.

Head and dorsa of mesosoma, petiolar node and gastral segment I rugose-reticulate; anterodorsal part of head between scape insertion and lateral spine with longitudinal rugae; lateral face of each mandible with evenly spaced, oblique rugae; coxae with strong rugae; dorsa of gastral segments I and II with longitudinal rugae, which are sparsely interconnected by transverse ridges; rugae finer on gastral segment II than on I; helcium and girdling constriction of gastral segment II scrobiculate; intervals between rugae with fine foveolatereticulate microsculpture; strength of microsculpture varies greatly among body parts: distinct on anterodorsal and mediodorsal faces of head, on lateral faces of mesosoma, in promesonotal depression, on posterior face of propodeum, on anterior face of petiole, on all gastral segments including the presclerites and on legs; microsculpture on posteriodorsal and ventral faces of head, and on dorsa of mesosoma and petiolar node very shallow and obscure, i.e. the areas nearly smooth (the less-microsculptured areas were mostly hidden under soil particles, that stuck on the integument [or possibly a mixture of soil particles and integumental secretion], and became visible only after cleaning).

Dorsum of head, antennal scape, antennal segments II–VII, mesosoma, petiole and dorsum of gaster with decumbent to suberect, bluntly pointed, narrowly spatulate or clavate setae; posterodorsal margin of gastral segments I–IV with a row of subdecumbent, longer and narrower spatulate setae; pygidium with both spatulate and simple hairs; setae on ventrum of head appressed and simple; hairs on ventrum of gaster subdecumbent and simple; antennal segment IX–XII densely covered with decumbent, simple hairs and a few simple, erect hairs.

Most body parts dark brown to black, except for anterior part of head, mandibles, antennae and gaster which are of a variable lighter, rusty brown color; coloration of legs changing gradually from dark brown coxae to yellow brown apical tarsal segments; integument mostly dull, but the less-microsculptured areas somewhat shining.

Queen and male unknown.

Etymology. Named in dedication to Dr. Maren Scheidhauer, friend of the first author and as beautiful — though of low overall resemblance — as this ant. The specific name is an arbitrary combination, to be treated as a noun in apposition.

Distribution. The two known specimens were extracted from a leaf litter sample taken in an old growth rainforest near the summit of Gunung Susu.

Comments. As in M. leonie we cannot determine which reproductive strategy M. maren follows. But we conclude that the described specimen is a worker because wingless reproductives in Mystrium have reduced mandibles which are inappropriate for hunting. This is clearly not the case for the holotype of M. maren .

The holotype and paratype of M. maren show similar camouflage tendencies as described for M. leonie .

Figures

FIGURES 7 – 9. Mystrium maren (holotype, worker): 7 — head, frontal view, 8 — dorsal view, 9 — lateral view.

FIGURES 10 – 15. 10 – 12. Maxillary palpus (right side): 10 — M. camillae (specimen from W-Malaysia: Lake Kenyir), 11 — M. leonie (holotype), 12 — M. maren (paratype). 13 – 15. Labrum (ventral side, distal margin at bottom): 13 — M. camillae (specimen from W-Malaysia: Lake Kenyir), 14 — M. leonie (holotype), 15 — M. maren (holotype).