Laccodytes Régimbart

Toledo, Mario, Spangler, Paul J. & Balke, Michael, 2010, Taxonomic revision of the Neotropical diving beetles genus Laccodytes Régimbart, 1895 (Coleoptera: Dytiscidae), Zootaxa 2347, pp. 37-58 : 38-42

Genus Laccodytes Régimbart

Laccodytes Régimbart (1895: 345) ; Peschet (1919: 146); Zimmermann (1919: 119; 1920: 29); Guignot (1937: 138); Balfour-Browne (1939: 104); Young (1954: 48); Steiner (1981: 257, 258); Brancucci (1983a: 253); Nilsson et al. (1989: 299); Pederzani (1995: 43, 73); Nilsson (2001: 239).

Type species. Laccodytes phalacroides Régimbart, 1895 , by subsequent designation ( Guignot 1937), see Nilsson et al. (1989).

Diagnosis. Small beetles, TL 1.6–2.4 mm. Habitus ( Figs 1–2 ) oval, dorsoventrally flattened. Usually without angle between pronotum and elytra.

Pronotum with base medially produced caudad, or almost straight. Hind angle either rounded or projected backwards to form a needle-shaped, acute tip. Surface with simple MR, without coarser punctation. Prosternal process broadly carinate, with a needle or thorn-like apical projection. Prosternum and head separated by a shallow step, therefore gula and medial line of prosternum apparently on the same level. Metacoxal process with hind lobes straight or slightly rounded, often separated by a more or less deep V-shaped notch. Elytra apically oval or truncate; narrowly bordered laterally. Epipleuron in both sexes broad, up to caudal margin of sternite 6 or 7, not enlarged apically. MR of dorsal and ventral side usually of polygonal meshes, their orientation often slightly to distinctly horizontal, especially so on elytra and metacoxae.

Fore and middle legs long and slender, tarsomeres 1–3 shorter than 4–5 together. Hind legs with tarsi less broadened than in Laccophilus but slightly more so than in Neptosternus , with a antero-lateral expansion, more or less developed, on tarsomere 1–4. Metatibial spurs short, tip acuminate (truncate in L. olibroides ).

Male with pro- and mesotarsus hardly or not dilated at all, bearing three pairs of stalked suction palettes ventrally: one pair on each of the 1st–3rd tarsomere ( Fig. 3 ). Foreclaws in both sexes subequal in length and shape. Sternite 7 caudad rounded or tectiform; or slightly ( L. americanus ), or deeply concave ( L. olibroides ), or V-shaped ( L. androginus ) like in females. Aedeagus asymmetrical; parameres short.

Female with sternite 7 caudally with a central U- or V-shaped incision, more or less developed. Ovipositor serrate, but the “saw” consists of but a few teeth ( Figs 15–16 ).

Distribution and ecology. Laccodytes is only known from tropical South America. Most of the species have been collected in and around the lands southern of the Orinoco basin, between the Guyana, northern Brazil and southern Venezuela ( Fig. 61 ). Two species are known from southeastern Brazil and one from central-western Brazil. At present most of the known species come from the range of the Guyana Shield, in Venezuela and Guyana. The mountain ranges of south-eastern Brazil (related to the Planalto Central) might represent another hot spot for this genus. The available ecological data suggest that Laccodytes inhabit streams, often encountered among layers of decaying leafs and debris. We found specimens e.g. in moss on a boulder in strong current, in a water depth of about 50 cm ( Venezuela: Tobogan de la Selva). Sometimes, several species occur syntopically.

Taxonomic history. After Laccophilus Leach, 1815 and Neptosternus Sharp, 1882 , this was the third genus of the Laccophilinae to be described ( Pederzani 1995). Since the original description, only two more species were added ( Peschet 1919; Guignot 1955), and while the genus was occasionally mentioned in keys or catalogues, little has been published on Laccodytes otherwise and confusion occurred related to the definition of this genus ( Young 1954). However, in a paper describing the genus Napodytes from Equador, Steiner (1981) suggested that Laccodytes and Napodytes are sister-groups.

Phylogeny and Classification. The small size, emarginate caudal margin of female sternite 7, the short segments 1–3 of pro and mesotarsus and the peculiar shape of the prosternal process are potential apomorphies for Laccodytes . However, all of these characters also occur in Napodytes Steiner (1981) . For that reason, Steiner suggested that Laccodytes + Napodytes are sister taxa. Steiner (1981) characterized Napodytes based on two apomorphies, which are in fact autapomorphies for the only species of the genus, N. boki Steiner, 1981 : (1) some male antennomeres enlarged, and (2) hind tibia in both sexes with only one apical spur.

On the other hand, Laccodytes and Napodytes appear externally similar to Neptosternus , with which they share: border of lateral sides of elytra visible in dorsal view, metatarsi poorly broadened, and long and slender fore and middle legs. This may suggest a closer relationship between these three genera. In a molecular phylogenetic analysis of the Dytiscidae , Laccodytes grouped with the Australian Australphilus , and both are in a clade with the other strictly running water Laccophilini , Philaccolilus , Philaccolus and Neptosternus ( Ribera et al. 2008) . (Note: in that paper, Laccodytes sp.2 is in fact Laccodytes bassignanii , and what was named Laccodytes sp. 1 belongs to a new genus of small Laccophilini , which are however stagnant water species).

Laccodytes can easily be grouped in two species-groups. The L. apalodes -group with L. apalodes and L. rondonia is characterized by a long needle-like prosternal process extended caudally past the mesocoxae for a third of its length ( Figs 4, 7 ), the acute posterior pronotal angles ( Fig. 26 ), a membranous expansion on the median lobe of the aedeagus ( Figs 44, 45 ) and the slightly dilated male pro- and mesotarsomeres 1–3. The L. phalacroides -group includes all other species. Its members have a shorter tip of prosternal process not going beyond mesocoxae or very hardly so ( Figs 5, 6, 8 , 40, 41, 43 ), rounded posterior angles of pronotum ( Fig. 27 ), no membranous expansions on the median lobe of the aedeagus and male pro- and mesotarsi not dilated. These character states, except for the latter, might in all cases represent the plesiomorphic state as they are generally present in other Laccophilini .

Figures

FIGURES 1 – 2. Habitus of: 1) Laccodytes rondonia sp. n.; 2) L. bassignanii sp. n.

FIGURES 3 – 16. SEMs of some Laccodytes species structures: 3) segments 1 - 3 in male protarsus of L. americanus; 4) prosternal process of L. apalodes; 5) idem, L. americanus; 6) idem, L. neblinae; 7) metaventrite of L. apalodes, the arrow indicates the groove in which the tip of prosternal process fits; 8) idem, L. neblinae; 9) metacoxal process of L. apalodes; 10) idem, L. americanus; 11) idem, L. neblinae; 12) hind tarsus of L. apalodes (male); 13) idem, L. americanus (male); 14) idem, L. neblinae (female); 15) ovipositor of L. apalodes; 16) idem, L. americanus.

FIGURES 54 – 61. Last abdominal segment (left male; right female) in Laccodytes species: 54) L. apalodes; 55) L. rondonia; 56) L. americanus; 57) L. phalacroides; 58) L. takutuanus; 59) L. neblinae; 60) L. bassignanii; 61) Laccodytes sp. 1 female.

FIGURES 26 – 27. Hind angle of pronotum of: 26) Laccodytes rondonia; 27) L. bassignanii.

FIGURES 44 – 47. Male genitals in Laccodytes species: 44) L. apalodes: a) median lobe of aedeagus in lateral view, b – c) right and left parameres; 45) L. rondonia: idem; 46) L. americanus: idem; 47) L. phalacroides: a) apical half of median lobe of aedeagus in dorsal view, b) median lobe in lateral view, c – d) right and left parameres;

FIGURES 40 – 43. Line drawings of prosternal process: 40) Laccodytes takutuanus; 41) L. phalacroides; 42) L. rondonia; 43) L. olibroides.