Myrmhopla

This is currently a subgenus of Polyrhachis. Please see Polyrhachis for further information.

Species Groups
Kohout (2010) - Myrmhopla was established by Forel (1915) as a subgenus of Polyrhachis  Fr. Smith, 1857, with Formica armata (Le Guillou, 1842) as the type species. Forel did not define his new subgenus but Emery (1925) later delimited Myrmhopla  as follows (translation): “Worker. - Dorsum of thorax rounded, that is to say not marginate, except in some species (groups cryptoceroides and viehmeyeri); pronotal spines shorter than propodeal, sometimes absent; metanotal groove variable. Petiole variable amongst the groups and species; body of petiole in form of an elongate node, angled anterodorsally in profile or, to the contrary, forming a thick scale, higher than long, angular or rounded in front; generally bearing single pair of spines very variable in form, size and direction; rarely the spines are hook-like; in many species where they form a gaster embracing arc, there is between spines also a pair of teeth or small vertical spines. First gastral segment large. Female. - Very similar to the worker, with spines usually stronger and shorter.”

When Emery published his diagnosis of Myrmhopla, the subgenus already included some 140 species and subspecific forms. In an attempt to partition the high degree of diversity within such a large subgenus, he subdivided Myrmhopla into six species-groups. Dorow (1995) divided the subgenus further, recognising 16 species-groups, the six proposed by Emery and ten that he established as new. Five of these groups are relevant to the Australian fauna; the bicolor, dives , mucronata, sexspinosa and viehmeyeri-groups.

However, as mentioned by previous authors (Bolton, 1975; Dorow, 1995), the large degree of morphological diversity within Myrmhopla presents problems with maintaining the subgenus as it was originally perceived. Virtually none of the characters originally used by Emery (1925) to define Myrmhopla consistently apply to the species currently placed within the subgenus and some characters vary within a single species-group. The concept of the subgenus has widely been criticised (Hung, 1967) and the formation of numerous species-groups within Myrmhopla has only partially alleviated the problem.

Considerable morphological differences between various species-groups are evident throughout the subgenus Myrmhopla, but nowhere as markedly as in relation to the P. viehmeyeri-group. For example, a marginate mesosoma is a particularly significant character separating species of the viehmeyeri-group from the rest of Myrmhopla, except perhaps some species of the extralimital P. cryptoceroides-group (e.g. Polyrhachis cryptoceroides) (Kohout, 2006a). In some respects, viehmeyeri-group species resemble members of the subgenus Hedomyrma as they share a spinose and marginate mesosoma and a petiole featuring a more-or-less flat dorsum. However the characteristic vermiculate sculpturation, bristle-like pilosity and distinct reddish-brown colouration of species of the viehmeyeri-group clearly separate them from Hedomyrma species. The most remarkable feature of viehmeyeri-group species is their subterranean nesting habit combined with a sophisticated parasitic relationship with certain groups of ectatommine and poneroid ants (Maschwitz et al., 2003). The morphological and behavioural distinctness of the viehmeyeri-group is further supported by a preliminary molecular phylogeny of Polyrhachis (S.K.A. Robson, pers. comm.) that places the viehmeyeri -group (i.e. P. loweryi) closest to species of the subgenus Chariomyrma (Polyrhachis lata and Polyrhachis sokolova) and rather distant from representatives of other Myrmhopla species-groups. Considering these facts, I believe that the viehmeyeri-group should be removed from the subgenus Myrmhopla and a new subgenus Hirtomyrma is proposed to incorporate its constituent species.

Kohout's ideas regarding the lack of monophyly is supported by Mezger and Moreau (2015).

Regardless of the lack of clear evidence to support all of the species within these grouping, the following species groups do contain species that have been evaluated and discussed in the context of having affinities with other species and to stand apart from other groups' species. Clearly further work is needed to clarify species boundaries, species groups, and the delimitation of appropriate heirarchies and the associated nomenclature.

bicolor species group
Kohout (2010):

The Polyrhachis bicolor species-group was established by Dorow (1995) who subdivided the former P. dives -group (as delimited by Emery, 1925) and transferred many of its original constituents into three, earlier established groups (P. armata -, sexspinosa - and viehmeyeri-groups), or into five groups he newly proposed (P. arachne -, bicolor-, cephalotes-, hector- and mucronata-groups). As presently defined, the bicolor-group includes only four species. However, about 11 infraspecific forms are currently associated with the name-bearing species, P. bicolor. Many of these forms apparently represent valid species and, in addition, at least twice as many closely related new species are in collections awaiting description. This relatively small, but widespread and complicated group is in great need of revision.

Worker
(modified from Dorow, 1995) Mostly small to medium-sized ants (HL 1.15-1.85) with general characteristics of the genus. Mandibles smooth or very finely, longitudinally striate, rather polished with small piliferous pits towards bases. Anterior clypeal margin with shallow, central, medially emarginate flange, laterally flanked by teeth or acute angles. Head semicircular in side view, oval in frontal view; genae immarginate. Eyes moderately to strongly convex, clearly exceeding lateral cephalic outline in full face view. Mesosoma totally immarginate, armed with rather slender spines. Petiole nodiform with a pair of lateral spines usually embracing first gastral segment, without intercalary spines or teeth. Antennal scapes and tibiae slender and long, spider-like. Sculpturation of head, mesosoma and petiole mostly a fine punctation, usually obscured by rich pubescence, producing a matt appearance. Gaster shagreened or finely reticulate-punctate, opaque. All body surfaces with abundant, relatively long, erect hairs and silvery to golden, appressed or suberect pubescence. Body bicoloured, mostly black with gaster and appendages light reddish-brown or amber-coloured (as in P. bicolor), or virtually unicoloured with body black and gaster, including appendages, black or very dark reddish-brown (as in Polyrhachis longipes).

Queen
Apart from sexual characters, very similar to worker. Armament of pronotum, propodeum and petiole distinctly reduced with spines shorter and stronger. Sculpturation, pilosity and colour virtually identical to worker.

Distribution and biology. Polyrhachis bicolor-group species are distributed throughout south-east Asia, including Myanmar, India, Thailand, Malaysia, Singapore, Vietnam and the Philippines, extending south to Indonesia, New Guinea and northern Australia. Members of the bicolor-group are arboreal nesters, building polydomous nests of silk and vegetation debris among the leaves of mostly rainforest trees and shrubs (Robson & Kohout, 2007).

dives species group
Kohout (2010):

The Polyrhachis dives species-group was originally delimited by Emery (1925) and has previously contained as many as 77 species and subspecies. Dorow (1995) redefined the group and transferred a number of species into the earlier established armata-, sexspinosa- and viehmeyeri-groups (all Emery, 1925), or into his newly proposed arachne-, bicolor-, cephalotes-, hector- and mucronata-groups. The P. dives-group, as presently defined, includes about 14 species and subspecies with only one Australian species, P. dives .

Worker
(modified from Dorow, 1995) Mostly medium-sized ants (HL 1.40-2.00), some species exhibiting slight polymorphism. Mandibles rather densely longitudinally striate or rugose with numerous piliferous pits. Anterior clypeal margin with central, medially emarginate flange, laterally flanked by acute teeth. Head semicircular in side view, almost circular in frontal view. Genae immarginate or with a short carina running about half way from occipital margin towards mandibular bases (as in some extralimital species, e.g. Polyrhachis lacteipennis). Eyes rather flat or only moderately convex, in full face view not or only marginally exceeding lateral cephalic outline. Mesosoma totally immarginate. Pronotum armed with rather short or only moderately long spines (except in P. dives belli, where pronotal spines are slender and relatively long); propodeal spines slender and elevated with their tips curved outwards. Petiole with lateral spines, that in most species conform to shape of gaster, and a pair of distinct intercalary teeth. Body rather distinctly, more-or-less regularly, reticulate-punctate (as in P. dives), moderately rugose (as in P. lacteipennis) or coarsely foveolate (as in Polyrhachis menelas). Gaster shagreened or closely punctate. Body with only a few, short, erect hairs; closely appressed, mostly silvery or pale golden pubescence rather sparse over head and body (as in P. dives) or virtually lacking (as in P. lacteipennis). Gaster with somewhat longer, silvery or golden pubescence, that is virtually lacking in several extralimital species. Body and appendages mostly black with gaster black or very dark reddish-brown.



Queen
Queen in several species (e.g. P. dives) distinctly larger than worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. Spines distinctly shorter with pronotal spines reduced to acute angles. Propodeal spines modified into blunt, horizontal, posteriorly directed and somewhat dorso-ventrally compressed stubs; petiolar spines very short, only weakly curved, almost straight. Body sculpturation, pilosity and colour identical to that in worker.

Distribution and biology. The Polyrhachis dives species-group is the most widespread species-group within Myrmhopla. It stretches from Guam Island in the Pacific, throughout east and south-east Asia (e.g. China, Japan, Taiwan, Philippines, Malaysia, Thailand, Myanmar, Nepal, India, Sri Lanka), the Middle East and Arabian Peninsula (e.g. Pakistan, Iran, Iraq, Israel, Saudi Arabia, Oman, Yemen) and reaches as far west as Morocco in northern Africa. From southern Asia it extends southwards to Indonesia, New Guinea and northern Australia. Members of this group are mostly arboreal, building nests upon the leaves and branches of trees and shrubs, preferably in open habitats, such as grassy woodlands, open forests and swamps (see image). However, some extralimital species (e.g. P. lacteipennis) were observed to be lignicolous or subterranean nesters. The incorporation of silk and occasionally carton occurs in all arboreal nests. These nests can be either mono- or polydomous. Single and multiple queen colonies have been documented in P. dives (see Robson & Kohout, 2007).

flavoflagellata species group
Kohout (2008) species-group worker diagnosis:

Worker. Mostly small to medium-sized ants (HL 1.15-1.85) with general characteristics of the genus. Anterior clypeal margin arcuate and entire, or medially truncate, or with a deeply emarginate median flange. Head disproportionally large compared to rest of body with eyes relatively flat, situated close to posterolateral corners. Mesosoma rather flat, laterally immarginate, humeri armed with short, triangular teeth. Propodeal spines relatively short, more-or-less horizontal, or distinctly elevated. Petiole with a pair of lateral spines that are either acute and posteriorly directed (as in e.g. P. flavoflagellata), or reduced to obtuse, laterally directed stumps (as in P. stylifera). Dorsum of petiole with a pair of short but distinct, acute intercalary spines (as in P. flavoflagellata and P. muara) or blunt tuberculae (as in P. stylifera) or smoothly rounded (as in P. storki). Head and body closely and finely punctate; gaster very finely shagreened. Hairs virtually absent from most of body, except a few, rather short, erect hairs on front of head and around gastral apex. Closely appressed, silvery or golden pubescence present in various densities over most dorsal surfaces. Mostly black, with only base of gaster and appendages sometimes light to dark reddish brown.

key to flavoflagellata species group
Key to workers of the flavoflagellata group (Kohout, 2008)

1.
Lateral petiolar spines reduced to blunt, stumplike, lateral projections (Cambodia).....stylifera Karavaiev

Lateral petiolar spines relatively long, acute, dorsoposteriorly diverging..... 2

2.
Anterior clypeal margin with deeply emarginate median flange; dorsum of petiole without intercalary teeth or spines.....storki Kohout

Anterior clypeal margin entire or simplytruncate with a shallow median emargination; dorsum of petiole with a pair of distinct intercalary spines..... 3

3.
Propodeal spines distinctly dorsoposteriorly elevated from their bases (Fig. 2); bicoloured, body black, base of gaster and appendages mostly light reddish-brown.....flavoflagellata Karavaiev

Propodeal spines more-or-less horizontal (Fig. 4); virtually unicoloured, body black, appendages black or very dark reddish-brown.....muara Kohout

mucronata species group
Kohout (2010):

The Polyrhachis mucronata species-group of the subgenus Myrmhopla was delimited by Dorow (1995) who subdivided the earlier established P. dives-group (Emery, 1925). Dorow listed 36 species and subspecies within the group, however, the status of several subspecific forms still remains unresolved. Two new species were recently described from Sulawesi (Kohout, 2008) and one species is considered a junior synonym (see below). Only a single species of the group, Polyrhachis mucronata, is relevant to the Australian fauna.

Worker
(modified from Dorow, 1995) Small to medium-sized ants (HL 1.25-2.10) with general characteristics of the genus. Mandibles mostly longitudinally striate or finely rugose with numerous piliferous pits. Anterior clypeal margin with shallow, median flange (as in P. mucronata), or shallowly truncate (as in Polyrhachis retrorsa). Head usually semicircular in side view, oval in frontal view; genae immarginate. Eyes moderately to strongly convex, clearly exceeding lateral cephalic outline in full face view. Mesosoma totally immarginate, usually highly convex and relatively short (as in P. mucronata), but also somewhat elongated and distinctly less convex (as in Polyrhachis tristis). Pronotum armed with acute teeth (as in P. mucronata), or rarely with long slender spines (as in Polyrhachis amana), or simply rounded (as in Polyrhachis moeschi). Propodeal spines relatively long and strong in most species, however, also short (as in Polyrhachis orpheus). Petiole columnar with a pair of lateral spines usually embracing first gastral segment; spines mostly slender, but also remarkably massive (as in Polyrhachis lucidula)] and [[Polyrhachis ridleyi). Dorsum of petiole with a pair of more-or-less distinct intercalary teeth, except in some species (e.g. P. amana and P. orpheus). Sculpturation of head, mesosoma and petiole ranging from rather smooth and highly polished (as in P. emmae) to closely punctate (as in Polyrhachis oedacantha). Gaster usually more finely sculptured, shagreened and polished, only rarely closely punctate, opaque (as in Polyrhachis tristis). Body pilosity and pubescence virtually lacking in most species, however, in Polyrhachis mitrata and P. retrorsa whole body covered with rather diluted, whitish pubescence. Body mostly black, rarely with purple metallic reflections (as in P. oedacantha and Polyrhachis phalerata). Gaster black or reddish-brown with appendages ranging from orange or light reddish-brown to black.



Queen
Queen very similar to worker with usual differences indicating caste, including three ocelli, complete thoracic structure and wings. Body armature, notably propodeal and petiolar spines distinctly shorter and stronger. Sculpturation, pilosity and colour essentially as in worker.

Distribution and biology. The Polyrhachis mucronata species-group is distributed throughout east and south-east Asia (China, Philippines, Laos, Malaysia, Thailand, Myanmar, India, Sri Lanka), extending south to Indonesia (Sumatra, Java, Sulawesi) and New Guinea (including Bismarck Archipelago), reaching the southern limit of its distribution in northern Queensland. The known members of this group are arboreal nesters, building nests of silk and vegetation debris upon the leaves of rainforest trees and shrubs, mostly in the lower arboreal zone (see image).

sexspinosa species group
Dorow (1995):

EMERY (1925) described the workers as: "petiole long, anteriorly with an elevated angle in profile, spines inserting distally, spines relatively short and only little diverging; head long, distally narrowing; sculpture rugose; large species" (own translation). Additional data of this group are: Large slender species (TL: 8-13 mm) with an immarginate thorax. Long slender spines are present on prothorax, propodeum and petiole, only in Polyrhachis calypso the petiolar spines are curved hook-like. The head is elongately oval in frontal view. The long and spider-like legs and the antennae are round in transection, the genae are immarginate. only the neck might wear a "frill". The mat body is usually sculptured rugosely, the shiny gaster is often only finely punctate. Polyrhachis melpomene in contrast has a striate body sculpture except on the gaster. Erect hairs and appressed pubescence are usually numerous. The body colour is black, brownish or reddish.

These species arc polydomous weaver ants of the shrub and tree layer.

This group, which was established by Emery (1925), today comprises 17 species. Polyrhachis melpomene, which was placed by EMERY (1925) into the Polyrhachis-dives-group, and Polyrhachis olybrius (=Polyrhachis olybria), which he could not associate, also belong to this species-group. Bolton(1975) and Kohout (1987) (for the Philippines) revised this group.

Distribution: Australia. India. Indonesia. Malaysia, New Guinea. New Caledonia, Philippines. Solomons. Singapore. Thailand (new). This group has evolutionary centers in New Guinea and in the Philippines.

Kohout (2010):

The Polyrhachis sexspinosa species-group of the subgenus Myrmhopla Forel, 1915 was established by Emery (1925), who included 12 species and subspecies from New Guinea and south-east Asia. Bolton (1975) revised the world fauna of the group and recognised 12 valid species with all of the included infraspecific taxa considered synonyms. Three new species from the Philippines were later added, one subspecies (Polyrhachis sexspinosa reclinata) raised to specific status (Kohout, 1987) and one species (Polyrhachis barnardi) synonymised (Kohout & Taylor (1990), raising the number of valid species of the group to 15. Dorow (1995) recognised 17 species as constituents of the group, including Polyrhachis melpomene and Polyrhachis olybria. However, these two species were later transferred to different subgenera (P. melpomene and its junior synonym Polyrhachis dolichocephala to subgenus Hedomyrma and Polyrhachis olybria to the nominal subgenus Polyrhachis), and two former subspecies (Polyrhachis arcuspinosa waigeuensis and Polyrhachia sexspinosa esuriens) were raised to specific status by Kohout (1998). At present the P. sexspinosa species-group comprises 19 valid species, including one (P. spinosa) recently elevated to its original specific status (Kohout, 2008) and one described below as new (Polyrhachis dispar). Four species of the group are relevant to the Australian fauna with two (P. dispar and Polyrhachis glabrinotum) considered endemic. They appear to be derived from common ancestral stock, such as the New Guinea-based species Polyrhachis aureovestita and Polyrhachis bubastes Fr. Smith, 1863 (Bolton, 1975) and speciated after loosing connection with the maternal New Guinean populations following the sinking of the continental bridge between New Guinea and Australia. On the other hand, the more robust populations of the relatively common P. sexspinosa (Latreille, 1802) and P. reclinata maintained most of their original characteristics, with specimens from Cape York Peninsula indistinguishable from their New Guinean counterparts.

Worker
Relatively large ants (HL >2.0), except for the rather small, extralimital Polyrhachis nofra (HL 1.52-1.53), with general characteristics of the genus. Mandibles smooth and polished apart from small piliferous pits towards bases. Anterior clypeal margin arcuate, often obtusely truncate medially or with shallow median emargination. Head contracted posteriorly, distinctly narrower behind than in front of eyes. Eyes with short, erect hairs; strongly convex or protuberant, clearly exceeding lateral cephalic outline in full face view. Occipital margin with more-or-less developed lateral angular prominences which are usually visible with the head in full face view (except in P. dispar and P. glabrinota). Mesosoma immarginate; pronotum strongly convex, humeri armed with rather strong, mostly forward curved spines. Promesonotal suture strongly impressed. Mesonotum flat or weakly convex in profile; mesopleural process present as a simple lobe (as in P. dispar and P. sexspinosa) or a dentiform structure, that can be acute or obtuse (as in P. glabrinota and P. reclinata); metanotal groove usually replaced by a minutely raised ridge. Propodeum armed with a pair of spines that are either vertical or inclined forwards (as in P. sexspinosa), or posteriorly reclined and often curved (as in P. dispar, P. glabrinota and P. reclinata). Petiole nodiform with a pair of lateral spines, without intercalary spines or teeth. Gaster, when contracted, broadly ovate. Sculpturation of head, mesosoma and petiole ranging from weak to rather heavy, gaster usually finely shagreened. All body surfaces, including appendages, with relatively long, erect hairs. Pubescence mostly appressed or suberect, somewhat radiating, present in various densities but usually not completely hiding underlying sculpturation. Pubescence on gastral dorsum organised in a characteristic midline pattern in virtually all species (except P. nofra) or almost completely absent (P. exotica Kohout, 1987). Body mostly black, or partly reddish-brown (as in P. glabrinota), with appendages usually lighter, reddish-brown.

Queen
Very similar to worker with usual characters of full sexuality, including three ocelli, complete thoracic structure and wings. Armament of pronotum, propodeum and petiole somewhat reduced with spines shorter, less curved and usually more stubby. Sculpturation, pilosity, pubescence and colour virtually as in worker.

Distribution and biology. Polyrhachis sexspinosa-group species are distributed throughout the Indo-Australian region, with only a few species known from the Oriental region and one from the Solomon Islands. In Australia, the group is limited to the northern part of Cape York Peninsula in Queensland, north of the 14°S parallel. Members of the sexspinosa-group are mostly arboreal nesters, building nests of silk and vegetation debris between the foliage of rainforest trees and shrubs. However, some species deviate from this behaviour and have their own characteristic methods of nesting. Colonies of P. sexspinosa invariably build pocket-like nests of silk, vegetation debris and bark fragments against the trunks of rainforest trees (see figure). In contrast, colonies of P. dispar, P. glabrinota and P. reclinata at Iron Range National Park were frequently found nesting within the hollow internodes of a bamboo, Bambusa forbesii. Only one colony of P. reclinata was located under the bark of a living tree, while most nests of P. glabrinota were constructed between leaves, usually in the lower arboreal zone, about 2-3 m above the ground.

Nomenclature

 *  MYRMHOPLA [subgenus of Polyrhachis]
 * Myrmhopla Forel, 1915b: 107 [as subgenus of Polyrhachis]. Type-species: Formica armata, by original designation.
 * Myrmhopla senior synonym of Cephalomyrma, Florencea: Hung, 1967b: 402.
 * CEPHALOMYRMA [junior synonym of Myrmhopla]
 * Cephalomyrma Karavaiev, 1935a: 115 [as subgenus of Polyrhachis]. Type-species: Polyrhachis (Cephalomyrma) stylifera, by monotypy.
 * Cephalomyrma junior synonym of Myrmhopla: Hung, 1967b: 402.
 * FLORENCEA [junior synonym of Myrmhopla]
 * Florencea Donisthorpe, 1937a: 624 [as subgenus of Polyrhachis]. Type-species: Polyrhachis (Florencea) kirkae (junior synonym of Polyrhachis nigriceps), by original designation.
 * Florencea junior synonym of Myrmhopla: Hung, 1967b: 402.