Metallactus hamifer , Suffrian 1866
Creators: name: Sassi, Davide
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Metallactus
Metallactus hamifer

description: Metallactus hamifer species-group
List of the species belonging to Metallactus hamifer group:
Metallactus abditus sp. nov. (Figs 1; 18)
Metallactus agonista Suffrian, 1866 (Figs 2; 19)
Metallactus albivittis Suffrian, 1866 (Figs 3; 20)
Metallactus albopictus Suffrian, 1866 (Figs 4; 21)
Metallactus bivitticollis (Jacoby, 1907) (Figs 5; 22)
Metallactus chamorroi sp. nov. (Figs 6; 23)
Metallactus crassicollis Suffrian, 1866 (Figs 7; 24)
Metallactus dicaprioi sp. nov. (Figs 8; 25)
Metallactus hamifer Suffrian, 1866 (Figs 9; 26)
Metallactus luniger Suffrian, 1866 (Figs 10; 27)
Metallactus madefactus sp. nov. (Figs 11; 28)
Metallactus octoguttatus (Burmeister, 1877) comb. nov. (Figs 12; 29)
Metallactus pollinctor Suffrian, 1866 (Figs 13; 30)
Metallactus praetorius sp. nov. (Figs 14; 31)
Metallactus sekerkai Sassi 2015 (Figs 15; 32)
Metallactus tarsalis Suffrian, 1866 (Figs 16; 33)
Metallactus viator sp. nov. (Figs 17; 34)
General characters of the species-group. The overall outline is typical of genus Metallactus, namely, cylindrical, with scarce tendency of elytral lateral margins to converge towards apex. Pronotal /elytral length ratio (greater than 0.5) and lateral margin of elytron (weakly excised) are typical of Metallactus as well (Chamorro-Lacayo, 2013).
Frons is generally wide, flat, with feeble to moderate punctation and apparent mid-cranial suture. Ocular lines generally poorly defined, only in M. chamorroi marked by an irregular line of punctures so that ocular line can somehow be distinguished down to the canthus. Frontoclypeal suture scarcely detectable. Eyes large, reniform with moderately deep canthus, scarcely bulging (in most of Pachybrachis species eyes are characteristically more protruding laterally when observed from above; in this regard the shape of eyes of Metallactus in general is more similar to Griburius). As usual in genus Metallactus, eyes never meet or almost meet dorsally on the head, and the interocular distance is not particularly different comparing male and female of the same species, as it is the case in several species of the related genus Griburius. Conversely, such distance is comparable to the one of most Pachybrachis species, both Palaearctic and American.
The antennae do not reveal any tendency in the development and shape of the antennomeres which therefore are quite uniform in the comparison between the different species. The antennal length shows some differences between sexes, but not always at the same level. For instance, antennomeres are equally shaped and lengthtened in both sexes of M. luniger, while they appear slightly stout and shorter in females of M. hamifer and M. albopictus. Preserved apical antennomeres in male lectotype of M. bivitticollis are broadened, but in the single female available for study they look similar to the ones of externally similar species like M. praetorius and M. chamorroi. In the holotype (female) of M. viator antennae are decidedly stubby and shortened.
Posterolateral pronotal impressions are almost always only faintly marked, only in M. madefactus and in M. luniger they look moderately pronounced (in Pachybrachis pronotal impressions are very poorly marked to completely obliterated, whereas they are visible in several species of Griburius). Pronotal lateral margins are narrow, regularly and moderately arched so that pronotal maximum width is generally just behind midline (on average, pronotal margins tend to be straighter in M. kollari species-group).
Elytral are almost parellel-sided (fairly curved on sides only in M. viator), with narrow margins and humera moderately raised. Elytral punctation moderately impressed, at least partially arranged in irregular rows. Elytral epipleuron is smooth, slightly convex, impunctate (in Pachybrachis an irregular row of punctures is almost always detectable).
Pygidium often bears two hollow impressions near lateral margins.
Legs are constantly normally shaped, without particular differences between sexes.
The morphology of the endophallus sclerites shows, as usual, a number of interesting peculiarities which often proved to be a species-specific resource in the delimitation of the taxa. As a whole, the most important traits of endophallus seem to be focused on the shape of sclerite III (which ranges from slender and regularly tapered to quite squat and vaguely looking like a grebe head), on the shape of the branches of sclerite IV (whose apex ranges from almost regularly tapered to fairly broadened to saddle-like arranged) and on the shape and dimension of the dorsal spicules (from erected, thorn-like to almost or totally obliterated). In addition, sclerite I in at least one species (M. agonista) tends to be widened, linked with the controlateral one and devoid of the denticle.
Contrary to the morphology of male genitalia, female genital structures currently provide information only partially useful in species discrimination. In fact, both the spermatheca and the rectal apparatus reveal a degree of intraspecific variation basically at the same order of magnitude as it is in the interspecific comparison. Only a careful analysis of a much higher number of specimens than the one available for the present study will allow to define the real effectiveness of female genitalia in the diagnosis of the species.
As in other groups of Metallactus species, the ductus of the spermateca is long, thin and delicate. It is coiled to form a long spiral whose coils have more or less tight windings, to some extent depending on species. The thickness and length of the ductus might have some diagnostic interest as well. Moreover, in all species the ductus tends to form a tangle about halfway along the length, outside or close to the vasculum. The size, shape, and compactness of this tangle might prove to have importance in the discrimination of the different species, but at the present state of knowledge it is difficult to assess the intraspecific variability. The last section of the ductus (“distal not coiled portion of duct”), just before the insertion on the bursa copulatrix, is basically rectilinear in some species (or has few rather loose windings), conversely, in the others, the ductus is substantially wrapped in coils also in this terminal section. The apex of vasculum, while also showing variability in some degree between individuals of the same species, seems however to have two substantial morphological patterns: either rather stocky and shortly pointed, or more lengthened and sharper. Interesting differences are evident in the morphology of the spermatheca in comparison with other genera of South American Pachybrachina. At the current state of knowledge, it is not possible to provide a reliable framework, so it is not considered appropriate to go into details or provide drawings that could later be misleading. However, as regard the few species considered so far, it can be said that in Ambrotodes the spermatheca is thin, and in some cases twisted into an S-shape, the ductus is very long, slender, curled up to form a sort of a tangle, but has no coils. In Griburius the vasculum does not show great differences with Metallactus, but the ductus is short, rather rigid, not coiled, with only a few bends along its proximal section. Furthermore, the insertion on the bursa copulatrix is not particularly swollen nor pigmented. In Mylassa the vasculum is slender, sickle-shaped as it is usual in Pachybrachina, but the ampulla is unusually lengthened, the ductus is very short and coiled and its insertion on bursa copulatrix massive and thickened. In Pachybrachis spermatheca is similar to the one of Metallactus, but again the ductus is remarkably shorter and not coiled (very similar to Palaearctic Pachybrachis species hitherto observed).
Several comparisons were made among species belonging to the group object of this study, and belonging to other species-groups as well, but it does not seem possible to indicate any particular trait worthy of note in the structure of the female rectal apparatus so far. The variability found within the species seems in fact to be of the same order of magnitude of the variability observed at the interspecific level. For this reason, and to avoid pointing out differences potentially misleading, because they might be due to simple individual variability, the structure of the rectal apparatus was not illustrated in this publication.
Distribution: M. sekerkai has hitherto been reported only from Bolivia. Two further species (M. agonista and M. hamifer) have been found in Bolivia as well, but their distribution is wider. The remaining species are from Argentina, Brazil, Paraguay and Uruguay. The overall pattern of distribution (with the exception of the “Bolivian” species) is basically identical to the one of M. kollari species-group (Sassi, 2018). This confirms the great closeness between the two complexes.
description: Published as part of Sassi, Davide, 2019, Revision of the Metallactus hamifer species-group (Coleoptera: Chrysomelidae: Cryptocephalinae), pp. 201-245 in Zootaxa 4657 (2) on pages 204-206, DOI: 10.11646/zootaxa.4657.2.1, http://zenodo.org/record/3763876