Laccomimus Toledo & Michat, 2015, gen. n.
Creators: name: Toledo, Mario
name: Michat, Mariano C.
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Dytiscidae
Laccomimus

description: Laccomimus gen. n.
Type species: Laccophilus pumilio LeConte, 1878, here designated.
Description. Habitus (Figs 1; 3–4). Small Laccophilini (TL: 1.8–2.5 mm; MW: 0.9–1.3 mm), oval or oblong-oval, teardrop-shaped, outline between head, pronotum and elytra continuously curved. Maximum width at about proximal 1/5 of elytra. Elytral tip pointed, gradually to abruptly narrowed. Colouration testaceous or reddishyellow, darker on elytra, which often bear pale markings; in one species elytra marmorate. Body surface smooth, without strongly impressed punctures. Elytra with characteristic iridescence, also occurring (although sometimes less evident) on pronotum, ventral surface, and metatarsi.
Head. Broad, smooth, shiny, never iridescent, with fine and poorly impressed microreticulation, sometimes with few, scattered and shallow punctures.
Pronotum. Short, with angled projection at middle of base (Figs 5–6), lateral margins not bordered, hind angles always rounded (Fig. 7). Surface smooth, with fine microreticulation; often with a subtle iridescence. Punctures mostly along lateral sides, hind and fore margins, arranged in more or less regular series.
Elytra. Elongate, apically attenuate and often strongly narrowed. Sutural line between elytron and epipleuron not visible in dorsal view, therefore sides of elytra apparently not bordered. Surface smooth, iridescent, with fine microreticulation of elongate cells (Figs 14–17). Small and superficial punctures visible in most species, sparse and/or arranged in irregular, longitudinal series. Epipleuron broad to metacoxae/first abdominal ventrite, then strongly narrowed, distinctly attenuate just before elytral tip (Figs 10–13).
Underside. (Figs 8–13) Smooth, more or less iridescent, with microreticulation as on elytra (Figs 18; 19), usually more impressed, especially in females. Lateral expansions of metaventrite (“metasternal wings”) thin and arched. Prosternum and head separated by a more or less pronounced step, (Figs 20–31). Prosternal process more or less blunt (Figs 20–31), in lateral view keeled to saddle shaped, depending on species; in ventral view broadly lanceolate to cordiform, bordered, ending in short, pointed to broadly rounded tip, reaching or barely reaching metaventrite. Metacoxal lines sinuate, strongly convergent anteriorly (Figs 32–41); fore laminae of metacoxal processes divided by deep V-shaped incision, either broadly rounded to angulate or ending in sharp spine. Abdominal ventrites lacking curved scratchlike sculpture. Last ventrite as long as rest of abdomen, or almost so (Fig. 42), with large spiculiferous punctures at about distal 2/3.
Legs. Pro- and mesothoracic legs short, tarsomeres with width greater than length except for fifth almost the length of third and fourth together. Pro- and mesotarsal claws as long as or slightly longer than fifth tarsomere. Spurs of mesotibiae very long, almost as long as entire mesotarsus (Figs 52; 53). Swimming setae on mesotibiae present only apically. Posterior surface of mesofemora always with a series of 3–4 long, stiff setae (Figs 8; 12; 52). Spurs of metatibiae simple, not bifid (Figs 54–55). Metatarsi with iridescence as on elytra; segments 1–4 with short posterolateral lobes and small combs of flat spines. Last metatarsomere with inner claw smaller, outer claw more developed, spur shaped.
Males. Last abdominal ventrite tectiform, distally slightly sinuate to almost straight at sides, ending in more or less pointed medial tip (Fig. 42). Pro- and mesotarsomeres 1–3 weakly but visibly dilated, each one bearing a pair of stalked suction palettes (Figs 44–51). In all but one species, outer claw of forelegs modified, scimitar-shaped (Figs 49; 70–76), in some cases with few small denticles on ventral margin. Aedeagus (Figs 84–115) asymmetrical as in other genera of Laccophilini; median lobe elongate, generally divided into three parts, variable in shape and proportions depending on species: i) with a thicker base, ii) with distal portion gradually narrowed to apex, or iii) ending in apical expansion (Fig. 91). Left paramere long and thin, arched, either sinuate or straight, reaching half or more than half length of median lobe; right paramere smaller, subtriangular or oval. Both parameres with single long seta at tip.
Females. Often duller than males due to more impressed reticulation; iridescence on elytra, pronotum and metacoxae more intense than in males in most cases. Last abdominal ventrite triangular, with almost pointed to almost truncate apex (Fig. 43). Female genitalia (Figs 116–120): distal segments of gonocoxae blade-shaped, sharply acute at tip, with small median tooth-like process; an additional subapical denticle present in two species. Ramus short, with more or less densely dentate “saw”, depending on species, and lateroproximal processes rudimentary.
In general, the species of Laccomimus are hard to identify without examination of male sexual characters. External features are often homogeneous or very variable and difficult to evaluate.
Distribution and ecology. A mainly Neotropical genus, widespread in Central and South America. Three species reach Argentina, and another one reaches Florida in the US. Little ecological information is known for this genus. A large portion of the studied material was collected at light. Available field data (see Figs 130–138) suggest a preference for lentic or stagnant waters that are rich in debris and vegetation. Apparently, a few species live in running waters or have a wider ecological range. Young (1954) gave a quite detailed description of the habitat of L.
pumilio in Florida (Alachua County), where specimens were collected from the heavily shaded edges of a large, permanent woodland pond near Gainesville, in association with Hydrophilidae (Helocombus bifidus (LeConte, 1855) and Enochrus spp.) and Dytiscidae (Desmopachria granum -complex, listed by Young (1954) as " grana - complex"). The occurrence of adults of this genus is reported to be very seasonal (see Young 1954).
Etymology. Laccomimus is derived from the words lacco, meaning “lake”, and mimus, meaning “actor”. Maybe “water actor” for their animated and aquatic habits. Name given in litteris by Frank N. Young and Paul J. Spangler. The gender of the name is masculine.
Phylogenetic relationships of Laccomimus. The phylogenetic analysis included the following characters:
Character 0. Prosternum + head: (0) divided by a shallow step; (1) divided by a deep step; (2) prosternum protruding anteriorly. In Laccomimus the anterior side of the prosternum, just posterior to the head, is quite thick. Pronotum and head are therefore separated by a kind of step (character 0.1; Figs 20–22; 29–31), which is particularly visible in those species with a protruding prosternum (character 0.2; Figs 24–27). In other genera such as Laccodytes, Neptosternus or Laccophilus, the anterior rim of the prosternum is thin (character 0.0).
Character 1. Base of pronotum: (0) with median angular projection; (1) straight or almost so. In most genera of Laccophilini, including Laccomimus and the L. phalacroides -group of Laccodytes, a median, posterior lobe of the hind margin of the pronotum projects between the elytra covering the scutellum (character 1.0; Figs 5; 6). In some genera (e.g. Neptosternus, the L. apalodes- group of Laccodytes) the hind margin of the pronotum is straight, lacking a visible projection, although the scutellum remains concealed (character 1.1).
Character 2. Posterior angles of pronotum: (0) rounded or angulate; (1) ending in a spiniform process. In Neptosternus and in the L. apalodes -group of Laccodytes (Toledo et al. 2010), the posterior angles of the pronotum end in a spiniform process, projected backward (character 2.1; see fig. 26 in Toledo et al. 2010). In the remaining Laccophilini genera (including Laccomimus) and in the L. phalacroides -group of Laccodytes, the posterior angles of the pronotum are rounded or slightly angulate (character 2.0; Fig. 7 and see fig. 27 in Toledo et al. 2010).
Character 3. Prosternal process (ventral view): (0) elongate, reaching mesocoxae but not extending beyond their hind margins; (1) very long, extending beyond hind margins of mesocoxae; (2) broad, not or barely reaching mesocoxae. In Laccophilus, the phalacroides -group of Laccodytes (Toledo et al. 2010), and some other Laccophilini genera, the prosternal process is elongate, narrow, with its apex extending between the mesocoxae (at most extending a little over the hind margins of the mesocoxae as in some species of Laccophilus) (character 3.0; see figs 6, 8 in Toledo et al. 2010 and figs 101–103 in Brancucci 1983b). In the L. apalodes -group of Laccodytes and in Neptosternus, the prosternal process ends in a long, almost needle-like apex, visibly going beyond the hind margins of the mesocoxae (character 3.1; see figs 4, 7 in Toledo et al. 2010). Finally, in Laccosternus and Laccomimus the prosternal process is short and broad, with its apex not or barely reaching the mesocoxae (character 3.2; Figs 23–31); the only exception occurs in Laccomimus distinctus, in which the prosternal process is almost similar to that of Laccophilus (Figs 20–22).
Character 4. Prosternal process (ventral view): (0) simple; (1) trifid. Members of the genus Neptosternus bear a peculiar three pointed prosternal process, resembling a fork (character 4.1). In the remaining Laccophilini genera the prosternal process is single pointed (character 4.0).
Character 5. Prosternal process (lateral view): (0) elevated or carinate, visibly reaching and positioned on same plane as metaventrite; (1) elevated or carinate, barely reaching and positioned on same plane as metaventrite; (2) saddle-shaped, barely reaching and positioned below metaventrite. In most genera of Laccophilini the prosternal process in lateral view is elevated or even carinate, and its apex clearly reaches the metaventrite between the mesocoxae. It is also positioned on the same frontal plane as the mesocoxae (character 5.0). In Laccosternus and in most species of Laccomimus the situation is similar but the apex barely reaches the metaventrite (character 5.1; Figs 23; 28; 29–31), with the exception of Laccomimus distinctus in which the prosternal process in lateral view looks more like that described for character 5.0 (Figs 20–22). In a few species of Laccomimus (L. amazonas, L.
spinosus, L. variegatus), the prosternal process can be thought as saddle-shaped, i.e. the outline of the process is strongly sinuate in lateral view and the apex is bent upward, not or barely reaching the metaventrite (character 5.2; Fig. 27).
Character 6. Strong and sparse punctures on elytra: (0) absent; (1) present. Both species of Laccosternus (more evident in L. grouvellei (Régimbart, 1895)) share a strong punctation of sparsely distributed punctures on the whole elytral surface (character 6.1). A strong and diffuse punctation on the elytra was not observed in other Laccophilini, with the exception of the longitudinal series of punctures (more or less clearly impressed, and usually less regular and somewhat sparse in posterior half) commonly present in all species (character 6.0).
Character 7. Epipleural carina: (0) not visible dorsally; (1) visible dorsally. In Neptosternus, Laccodytes and Napodytes the carina between the elytron and epipleuron is visible in dorsal view. This gives the appearance of a border running along the lateral side of each elytron (character 7.1). In all other genera of Laccophilini, including Laccomimus, this carina is not visible and the elytra do not appear laterally bordered in dorsal view (character 7.0).
Character 8. Silky sheen, mainly on elytra and metatarsi: (0) absent; (1) present. Members of Laccomimus are unique within the Laccophilini genera studied in the presence of a characteristic silky sheen which is more evident on the elytra and metatarsi (character 8.1). This sheen is absent in other genera of Laccophilini (character 8.0).
Character 9. Metacoxal lines: (0) sinuate, converging anteriorly; (1) straight, subparallel. In some genera of Laccophilini, including Neptosternus and Laccodytes, the metacoxal lines are straight and parallel, or almost so (character 9.1; see figs 9–11 in Toledo et al. 2010). In other genera the metacoxal lines are sinuate and converge anteriorly at the level of the suture separating the metacoxae and the metaventrite (character 9.0; Figs 8–13; 32– 41).
Character 10. Lobes of metacoxal processes: (0) separated by a deep notch; (1) notch almost absent. In most genera of Laccophilini, including Laccomimus, the lobes of the metacoxal processes are separated by a more or less deep notch (character 10.0; Figs 32–41). In Laccophilus and Philodytes these lobes are very close to each other (character 10.1; see figs 105, 107, 108 in Brancucci 1983b).
Character 11. Lobes of metacoxal processes: (0) rounded to slightly angulate; (1) strongly angulate to acuminate; (2) truncate. Within the studied genera of Laccophilini, Laccosternus and most species of Laccomimus share rounded or slightly angulate lobes of the metacoxal processes (character 11.0; Figs 37; 39–41). In some species of Laccomimus the lobes end in a sharp spine in both sexes or in a sort of spine in males and in a more or less marked angulation in females (character 11.1; Figs 32; 33–36; 38). In Laccophilus and Philodytes the lobes are distally truncate (character 11.2; see figs 105, 107, 108 in Brancucci 1983b).
Character 12. Larger mesotibial spur: (0) not longer than first two tarsomeres; (1) almost as long as whole mesotarsus. In Laccomimus the mesotibial spurs are very long, the larger one is almost as long as the whole mesotarsus, excluding the claws (character 12.1; Figs 52; 53). In all other genera of Laccophilini studied, including Laccosternus, the mesotibial spurs are shorter, reaching at most the second mesotarsomere (character 12.0).
Character 13. Apex of metatibial spurs: (0) simple; (1) bifid. The apically bifid condition of the metatibial spurs (character 13.1) is typical of all known species of Laccophilus except one (see key to genera of Laccophilini, below). In all other genera of Laccophilini, including Philodytes, the apices of the metatibial spurs are acute (character 13.0).
Character 14. Claws of male protarsus: (0) equal in shape, unmodified; (1) different in shape, outer claw scimitarshaped. In all species of Laccomimus, except L. distinctus, the outer protarsal claws of males are modified, typically in the shape of a scimitar, different from the inner claw which has a normal sabre shape (character 14.1; Figs 47; 49–50). In all other genera of Laccophilini, both male anterior claws are unmodified (character 14.0).
Character 15. Median lobe of aedeagus: (0) without a lateral membranous expansion; (1) with a lateral membranous expansion. A lateral membranous expansion is present on the median lobe of the aedeagus of species of the L. apalodes -group of Laccodytes (character 15.1; see figs 44, 45 in Toledo et al. 2010). No other Laccophilini studied exhibits this feature (character 15.0).
Character 16. Left paramere: (0) short and broad, shorter than half of length of median lobe; (1) elongate, at least half length of median lobe. In Laccomimus the left paramere is elongate and very long, at least as long as half the length of the median lobe, usually longer (character 16.1; Figs 84–98; 101–105). The right paramere is, instead, very small. In all other genera of Laccophilini, the left paramere is at most as long as half of the length of the median lobe, usually shorter although generally broad; the right paramere is normally shorter then the left paramere, but the difference is not marked (character 16.0).
Character 17. Gonocoxal blades: (0) with two denticles; (1) smooth or with one denticle. In Laccosternus and Laccomimus (with the exception of L. distinctus and L. malkini), the gonocoxal blades are smooth or at most exhibit a single small rounded tooth at about half the length on the dorsal side (character 17.1; Figs 118–119); In all other genera of Laccophilini studied and in two species of Laccomimus, the gonocoxal blades bear a subapical, sharp tooth on dorsal side, together with the median tooth described before (character 17.0; Figs 116–117).
Character 18. Lateral proximal processes of ramus: (0) well developed; (1) short, almost rudimentary. In females of Laccosternus and Laccomimus the lateral proximal process of the female ramus is very short, almost rudimentary (character 18.1; Figs 116–120). In Laccophilus and in all other studied genera, the lateral proximal processes of the ramus are long and well developed (character 18.0).
The final data matrix includes 20 taxa and 19 characters (15 binary and four multistate) (Table 1). The analysis with TNT yielded a single most parsimonious tree of 26 steps (CI = 0.92; RI = 0.97), which supports the monophyly of Laccomimus and the paraphyly of Laccodytes as presently defined. It also demonstrated weak support for the internal nodes of Laccomimus, with the exception of a robustly supported clade formed by L. variegatus, L. spinosus and L. amazonas (Fig. 121).
Among the New World genera of Laccophilini, Laccomimus has been confounded with Laccodytes. The confusion may have arisen from the small size of members of both genera and the scarce knowledge of Laccodytes until recently. In spite of this, Laccodytes and Laccomimus are very different morphologically. They have different body shapes, very flat with short to truncate elytral tips and lateral sides of the elytra finely bordered in dorsal view in Laccodytes (character 7.1, Fig. 2), less flat, with strongly attenuate elytral tip and elytra not bordered in dorsal view in Laccomimus (character 7.0). In Laccodytes the metacoxal lines are straight and subparallel (character 9.1), whereas in Laccomimus they are sinuate and strongly converging anteriorly (character 9.0). In Laccodytes the pro- and mesothoracic legs are long and slender, whereas in Laccomimus they are short and robust. The distant relationship of Laccodytes and Laccomimus suggested by our analysis (Fig. 121) is supported by previous results of and analysis by Ribera et al. (2008). In fact, the specimens identified as " Laccodytes sp1" and “ Laccophilini ” in fig. 3 of that paper actually belong to Laccomimus, whereas the specimen identified as " Laccodytes sp2" is actually Laccodytes (Ignacio Ribera, 2015, personal communication). Laccomimus is therefore related to Africophilus Guignot, 1948 based on results by Ribera et al. (2008), with a rather isolated position within Laccophilinae, and more distantly related to Laccodytes.
Apomorphies of Laccomimus are: i) the prosternum and head divided by a deep step (character 0) (this is particularly marked in species with a protruding prosternum); ii) prosternal process short and blunt, cordiform or almost so, not or barely reaching mesocoxae (character 3); iii) aedeagus with very long left paramere, normally longer than half the length of the median lobe (character 16); iv) larger mesotibial spur almost as long as mesotarsus (character 12); v) surface of body, especially of elytra and metatarsi, with a characteristic silky sheen (character 8); vi) male outer claw of protarsi modified (except in one species) (character 14); vii) gonocoxae with one tooth (with two teeth in two species) (character 17); viii) lateral proximal process of ramus short, almost rudimentary (character 18). None of these character states occurs in Laccodytes in its current concept (Toledo et al. 2010). On the other hand, all species of Laccodytes are stream dwellers as may be indicated by the variegate dorsal colour patterns, a colouration generally exhibited by reophilic Laccophilini (Balke et al. 2000). Laccomimus, instead, apparently inhabits mainly stagnant or slowly flowing waters, although two or three species appear to be found mainly in running waters. The third genus of American Laccophilini, Napodytes, is morphologically very close to Laccodytes, and apparently also similar in ecology, differing only in few, very specialised characters. Laccomimus is a quite homogeneous genus, although some species groups are distinctive.
Species Character Laccodytes is presently divided into two very distinct groups: the L. apalodes -group, including two species that appear similar to Neptosternus, and the L. phalacroides -group, including the remaining species (Toledo et al. 2010). Characters 1, 2, 3 and 15 define these two groups, with all the derived conditions present in the L. apalodes - group, and the primitive states present in the L. phalacroides -group (Table 1). The strong differentiation of these two groups, supported by our phylogenetic results (Fig. 121), suggests that Laccodytes in its current form is not monophyletic. Since this study is focused on Laccomimus, however, we prefer not to make changes to Laccodytes at this stage.
Laccodytes and Napodytes are grouped together with the Oriental and Afrotropical reophilic genus Neptosternus based on a clearly visible suture between the elytron and epipleuron in dorsal view (= “lateral side of elytron bordered”) (Ribera et al. 2008; Toledo et al. 2010). Laccomimus, on the other hand, is closer to other Laccophilinae genera such as the poorly known, Oriental genus Laccosternus, with which it shares the following features: the prosternal process more or less cordiform (depending on the species in Laccomimus), previously regarded as an apomorphy of Laccosternus (character 3); the metacoxal lines sinuate and strongly converging anteriorly (character 9), with the lobes of the metacoxal processes rounded and divided by an evident notch (character 10); similarly small size and elongate body, attenuate caudally; females with the gonocoxae with one tooth (character 17) and with a short and rudimentary lateroproximal process of the ramus (character 18). The mesotibial spurs, however, are short in Laccosternus, similar to those found in Laccophilus (character 12). After the recent discovery of Laccosternus krausi Brancucci & Vongsana, 2013, the second known species of Laccosternus and the first description of a male of this genus, it is clear that male characters differ from those of Laccomimus, Laccosternus have parameres that are more similar to Laccophilus (character 16). This confirms that Laccosternus and Laccomimus are two separate genera, although closely related, and may be sister groups depending on where the phylogeny presented here is rooted (Fig. 121). With Neptosternus as outgroup (a procedure supported by the distant relationship of this genus with Laccomimus, see Ribera et al. 2008) the result supports a sister relationship of these two genera. The strongly scattered punctation on the elytra described for Laccosternus grouvellei is also visible (although less marked) in L. krausi, suggesting that a diffuse elytral punctation (character 6) might be another character state defining Laccosternus. Male features of L. grouvellei are still unknown since this species is at present only known from three females collected in Sumatra, Laos, and Malaysia (Toledo et al. 2002).
description: Published as part of Toledo, Mario & Michat, Mariano C., 2015, Description of Laccomimus gen. n. and eleven new species from the Neotropical region (Coleoptera, Dytiscidae, Laccophilinae), pp. 301-354 in Zootaxa 3990 (3) on pages 303-308, DOI: 10.11646/zootaxa.3990.3.1, http://zenodo.org/record/244301