Cycreon Orchymont, 1919

Arriaga-Varela, Emmanuel, Wong, Sin Yeng, Kirejtshuk, Alexander & Fikacek, Martin, 2018, Review of the flower-inhabiting water scavenger beetle genus Cycreon (Coleoptera, Hydrophilidae), with descriptions of new species and comments on its biology, Deutsche Entomologische Zeitschrift 65 (1), pp. 99-115 : 99-103

Cycreon Orchymont, 1919

Cycreon Orchymont, 1919: 119.

Types species.

Cycreon sculpturatus Orchymont, 1919 (by original designation).

Diagnosis.

(1) antennal grooves on prosternum small and marked by a weak ridge close to the lateral margins of prosternum (Fig. 2 C–D); (2) mentum deeply excised anteromesally (Figs 1J, 2B, 5B, E, H, L, P); (3) mesoventral medial elevation reduced to a narrow carina (Fig. 2 E–F); (4) grooves for reception of procoxae absent (Fig. 2 E–F); (5) metaventrite without abdominal lines or demarcated anterolateral angles (Fig. 2E), (6) abdominal ventrite 1 not carinate medially (Fig. 2G); (7) aedeagus with the median lobe not fused to the bases of parameres, reaching into the phallobase; (8) median portion of male sternite 9 tongue-like (Fig. 3D, H, M).

Note.

Orchymont (1919) mentioned the absence of antennal grooves, which were supposed by Hansen (1991) who did not have the chance to study specimens of this genus. Shatrovskiy (2017) revealed that antennal grooves are present although very small, and weakly marked by a faint ridge.

Differential diagnosis.

Cycreon is distinct among Megasternini in lacking the median carina of abdominal ventrite 1 (Fig. 2G); in this character it only corresponds to the Megasternini genera Pyretus Balfour-Browne and Acaryon Hebauer. From Pyretus , Cycreon is easily diagnosed by the narrowly laminate elevation (in contrast to widely pentagonal and widely contacting metaventrite in Pyretus ), simply carinate median portion of prosternum (forming an elevated prosternal plate in Pyretus ), and small antennal grooves (antennal grooves are large and reaching lateral pronotal margin in Pyretus ). The genus Acaryon from Madagascar is similar to Cycreon in many characters, including the relatively large eyes, simply carinate prosternum, antennal grooves not reaching pronotal margin, narrowly carinate elevation on mesoventrite, metaventrite without additional ridges, and dorsal punctation (with semicircular to circular punctures in Cycreon , and circular setiferous punctures intermixed with usual punctation in Acaryon ). However, Cycreon can be distinguished from Acaryon by the shape of the mentum (deeply emarginate anteromedially in Cycreon , weakly sinuate on anterior margin in Acycreon ), presence of the grooves for reception of procoxae at sides of the mesoventral elevation (absent in Cycreon , present in Acaryon ) and the dorsal colouration (unicoloured or bicoloured in Cycreon , unicoloured yellow with dark central pronotal spot in Acaryon ).

Description.

Body (Fig. 1 A–D) 2.2-3.4 mm long, elongate-oval, weakly convex. Colouration more or less reddish-brown, pronotum and underside usually somewhat paler (yellowish-brown), elytra usually darker.

Head. Clypeus with anterior margin with very fine bead, anteromedian margin slightly to strongly emarginate medially (Figs 1E, 5A, D, G, K, O), anterolateral angles rounded, antennal bases exposed; frontoclypeal suture distinct laterally, reduced in medial third; transverse ridges absent. Median portion of frons and clypeus not elevated above remaining surface. Dorsal surface glabrous, with dense punctation composed of shallow circular impressions (incomplete in some species), with a small puncture at anterior margin; interstices between punctures without visible microsculpture (Fig. 4A, D, G). Eyes moderately large, with dorsally visible portion slightly smaller than ventral one, separated by 4.9 –5.5× the width of one eye in dorsal view. Labrum (Fig. 1I) ca. 0.4 × as wide as head, membranous, largely retracted under clypeus, very weakly bisinuate at anterior margin, moderately densely pubescent dorsally, setae becoming longer on lateral portions. Mandible (Fig. 1 F–H) with apex deeply bifid (teeth may be partially abraded in some specimens; compare Fig. 1F, G), curved; its external margin very weekly crenulate at basal half; prostheca with anterior third covered by long thin setae, distal group of these setae facing ventrally and proximal group of them facing mesally (Fig. 1H); mola with fine lamellae having poriferous structure. Maxilla of male with sucking disc on galea (Fig. 2B); maxillary palps with basal palpomere minute, palpomere 2 large, widened at apical half, 1.2 × as long as palpomere 3, palpomere 3 slightly shorter than palpomere 4, slightly widening apicad, palpomere 4 fusiform, without digitiform sensilla. Mentum (Figs 1J, 2B, 5B, E, H, L, P) transverse, about twice as wide as long, lateral margins with few sparse setae, anterior margin very deeply emarginate; labial palps trimerous, palpomere 1 transverse, palpomere 2 subequal in width but slightly longer than palpomere 1 and with few long setae, palpomere 3 narrow, slightly longer than palpomere 2. Submentum with moderately dense setiferous punctures, gular sutures vaguely developed, rather widely separated from each other, tentorial pits small, almost rounded. Antenna with 9 antennomeres; scape (antennomere 1) long, cylindrical, constricted medially; pedicel (antennomere 2) rather short, bulbous basally; antennomeres 3-5 short, subequal in length, antennomere 5 much wider than preceding ones; cupule slightly asymmetrical, as long as antennomere 5; antennomeres 7-9 forming an elongate pubescent club (2.2 × longer than wide), antennomeres 7-8 subequal in length, antennomere 9 slightly longer, roundly subacuminate at apex; sensorial antennal fields absent. Genal ridge absent.

Prothorax. Pronotum transverse, moderately convex, about as wide as bases of elytra combined; lateral margins minutely bordered; anterior and posterior angles rounded (Fig. 1E); punctation dense, composed of shallow circular impressions with one small puncture at posterior margin, circular impression sometimes incomplete (Fig. 4B, E, H). Prosternum (Fig. 2C) weakly raised medially, with faint longitudinal carina; prosternal process short, almost reaching midlenght of procoxal cavities, not bifurcate; precoxal part short. Procoxal cavities large, open posteriorly. Notosternal suture distinct. Antennal grooves present, very short, vaguely defined by thin ridge parallel to lateral notosternal suture, vanishing posteriad (Fig. 2 C–D).

Mesothorax. Mesoventrite completely fused with anepisternum; anterior collar of mesothorax narrow. Median portion of mesoventrite simply tectiform, elevation forming a ridge shortly overlapping anterior margin of metaventrite. Grooves for reception of procoxae absent (Fig. 2 E–F). Mesepimeron moderately narrow, very weakly widening laterad. Mesocoxal cavities narrowly separated. Scutellar shield small, triangular, 1.1 × as long as wide. Elytra weakly convex, weakly bordered laterally, each elytron bearing 10 series, series 1-9 consisting of foveate impressions (punctures) with a setiferous puncture on anterior margin (Fig. 4C, F, I); serial punctures situated in longitudinal sulci; series 1-4 and 9 reaching apex, series 5 and 8 enclosing series 6-7 subapically, series 9 and 10 fainter, series 10 reduced both anteriorly and posteriorly; epipleuron almost horizontal, gradually narrowing posteriad, vanishing behind level of posterior margin of metaventrite, bearing moderately dense short setae (Fig. 2E).

Metathorax. Metaventrite (Fig. 2E) with postcoxal line closely following posterior edge of mesocoxa and slightly deviating only in anterolateral angles; mesal elevate area flat and pentagonal, rather narrow, about as long as wide; lateral portions densely covered with short setae. Femoral lines and anterolateral ridges absent. Metanepisternum ca. 4.5 × as long as wide, with anterior oblique ridge, metepimeron with minute ventral portion. Metafurca well developed. Hind wings (Fig. 1L) well developed, with transverse vein r4 arising from basal portion of radial cell, RP rather long, reaching ca. halfway to wing base, basal cubito-anal cell small, closed; wedge cell absent; transverse vein mp-cua joining to MP3+4+CuA1+2; anal lobe not defined.

Legs. Procoxae large, subglobular, transverse, with long setae, junction with trochanter; meso- and metacoxae wide, transverse. Tronchatero-femoral junction straight. Femora flattened, comparatively long, with very short setae; profemur without impressed parts; metafemur 1.1 × as long as mesofemur (Fig. 1 M–O). Tibiae rather long, triangular, flattened, straight or curved, especially on external margin, with short lateral and mesal spines. Tarsi pentamerous (Fig. 1 N–O), tarsomeres densely covered by short stiff setae; metatarsomere 1 longer than metatarsomere 2 and 3 combined, metatarsomeres 2-4 continuously getting shorter, metatarsomere 5 about 0.4 × than metatarsomere 1. Claws simple, arcuate; empodium bisetose.

Abdomen with five ventrites. Ventrite 1 without median carina (Fig. 1G), about as long as ventrites 2-4 together. Male sternite IX with tongue-like median projection with round to roundly acuminate anterior margin and rounded posterior margin, lateral struts almost reaching base of median projection (Fig. 3D, H, M). Aedeagus (Fig. 3A, E, J–K) simple; median lobe subparallel-sided to moderately sinuate, in C. floricola sp. n. enlarged basally and connected to phallobase by strong muscles; phallobase short, symmetrical to slightly asymmetrical, manubrium present, short; parameres simple. Female genitalia as in Kanala (see Fikáček 2010).

Key to the species of Cycreon

Species accounts