Meladema Laporte, 1835

Bilton, David T. & Ribera, Ignacio, 2017, A revision of Meladema diving beetles (Coleoptera, Dytiscidae), with the description of a new species from the central Mediterranean based on molecules and morphology, ZooKeys 702, pp. 45-112 : 48-50

Meladema Laporte, 1835

Meladema Laporte, 1835:98, gender feminine; type species: Meladema coriacea Laporte, 1835:98, by monotypy; conserved in ICZN Opinion 1725 ( ICZN 1993). Scutopterus Dejean, 1833:54, unavailable name, rejected in Opinion 1725 ( ICZN 1993).

Diagnosis.

Adults can be recognised within the Colymbetinae on the following combination of characters: pronotal beading absent; protibiae only weakly emarginate basoventrally; prosternal process medially rounded; anterior margin of metaventrite deeply incised for reception of prosternal process; metatarsomeres I-IV distinctly sinuate apically, with apicolateral lobes and metatarsal claws subequal in length, outer approximately two-thirds length of inner ( Miller and Bergsten 2016). The sculpture of the elytra referred to by Miller and Bergsten (2016) is not a constant generic character of Meladema (see below). Larvae of two species ( M. coriacea and M. lanio ) have been described to date ( Bertrand 1928, 1932a, 1932b, Falkenström 1938, Nilsson and Hilsenhoff 1991, Alarie and Hughes 2006). First instar larvae of Meladema can be distinguished from most other genera of Colymbetinae on: Additional setae present on dorsal margin of femur; short, spine-like mesofemoral seta FE5; additional setae on both ventral and dorsal margins of tibiae and relatively large size ( Alarie and Hughes 2006). They can be separated from Bunites Spangler, 1972 on details of the setation of the coxae and abdominal segment 8 ( Michat 2005). Third instar larvae are characterized by: relatively large size (head length> 4.40 mm cf. <3.50 mm in other described Colymbetinae); urogomphus more elongate (> 1.7 × dorsal length of last abdominal segment cf. <1.5 ×); large number of secondary setae on legs and the presence of predominantly short and spine-like setae on outer and elongate setae with hair-like secondary setae along inner margin of urogomphus (see Alarie and Hughes 2006).

Description.

Compound eyes large, rounded, laterally somewhat protruding (Figure 3); anterior margin distinctly emarginate. Antennae long, slender, all segments elongate; segment 2 least so, 2.5 × longer than broad; all other segments> 3 × longer than broad; all segments broadening distally. Antennal insertions invisible dorsally, adjacent to anterior margins of compound eyes, below lateral margins of frons. Anterior margin of clypeus arcuate; anterior angles obtuse, weakly rounded. Clypeus with strongly trans verse anterolateral foveae, each occupying approximately 0.25 × length of anterior margin. Foveae shallow posteriorly, deep and abrupt anteriorly; furnished with stiff whitish or golden-yellow setae. Anterior margin of labrum with broad, semicircular emargination; central 0.4 furnished with stiff, close-set setae. Labium transverse, broadest anteriorly; anterior margin with brush of fine, close, elongate setae; lateral setae approximately 2 × length of those at centre. Labial palpomeres elongate, particularly palpomere 2. Palpomere 3 with raised medial and apical tubercles ventrally, furnished with stout setae. Palpomere 3 expanded to apex, curved, convex ventrally and concave dorsally. Maxillary palpomere 1 slightly elongate; palpomeres 2-4 increasingly so. Palpomere 4 swollen, inner face almost straight, outer strongly curved; with setae on internal and ventral faces towards apex. Mentum setose anterolaterally; excavated in centre, with longitudinal ridges laterally. Pronotum strongly transverse, somewhat thickened laterally; without distinct lateral bead (Figure 3). Anterior angles acute, furnished with bunch of stiff, golden setae; posterior angles obtusely rounded. Anterior margin broadly arcuate around centre; posterior margin sinuate laterally or almost straight (Figure 3). Elytra elongate, broadest close to or behind middle (Figures 3, 4), with strong lateral bead; apices conjointly rounded. Each elytron with three rows of serial punctures (Figure 3). Each puncture of rows bearing 1-5 stout, recumbent to erect setae (e.g. Figures 3, 9, 10). Elytra of at least some individuals of all species with transverse, crescentic striolae (e.g. Figures 5, 6, 25, 26). Prosternum arched to tectiform; prosternal process lanceolate, bordered laterally, apex acuminately rounded. Metaventrite projecting anteriorly between mesocoxae; projection with elongate median groove to receive prosternal process; groove with marked central ridge, widening anteriorly. Discrimen and metacoxal suture strong, deep. Metacoxal lines strongly marked; metacoxal processes broadly rounded. Abdominal pleurite 2 without transverse ridges. Abdominal ventrites 2-6 with semicircular foveae laterally. Abdominal ventrite 6 with curved lateral wrinkles (Figures 11, 15).

Male. Foretarsi (Figure 12) with segments 1-3 strongly expanded and transverse, bearing four distinct rows of large articulo-setae ventrally; two on segment 1, one each on segments 2-3. Articulo-setal field bordered by dense, stiff, elongate, curved, hooked, golden setae. Segment 4 transverse; approximately 0.6-0.8 width of segment 3; with fields of stout, elongate setae of varying size laterally, inner setae curved anteriorly. Segment 5 elongate, with stout, elongate spines of varying size ventrally, close to lateral margins; basal spines curved interiorly. Foretarsal claws (Figures 12, 13) elongate, subequal, curved. Mesotarsi (Figure 12) with segments 1-3 expanded, transverse, bearing four distinct rows of large articulo-setae ventrally; two on segment 1, one each on segments 2-3. Articulo-setal field bordered by dense, stiff, elongate, curved, hooked, golden setae. Segment 4 elongate, with two rows of short, stout, stiff curved spines. Segment 5 strongly elongate, with two rows of stout spines ventrally, close to lateral margins. Mesotarsal claws elongate, subequal, curved. Abdominal ventrite 6 with weakly emarginated apex (Figure 11). Median lobe of aedeagus (Figure 14) elongate, strongly curved dorsally, with narrowly acuminate apex; lateral margins with transverse wrinkles in basal half; sinuate laterally towards apex in ventral view. Parameres (Figure 14) elongate, with dense setal fringe along internal margin, continued around apex, with scattered setae along external margin.

Female. Fore and mesotarsi simple, with ambulatory spines and setae only. Abdominal ventrite 6 (Figure 15) with bluntly pointed apex. Reproductive tract (Figure 16) with large, sclerotised bursa, with transverse corrugations and an elongate bursal gland; gland reddish in fresh material. Spermatheca elongate, fertilization and spermathecal ducts closely aligned, both relatively short. Gonocoxae (Figure 16) stout, elongate, with dense setation over entire surface and distinct apical penicil of setae. Laterotergites (Figure 16) elongate, with medial articulation. Gonocoxosternites (Figure 16) with bluntly pointed, setose apices. Female tract and genital structures do not appear to differ significantly between species and are not discussed further.

Remarks.

Both molecular and morphological data suggest a close relationship between Meladema and the Nearctic Hoperius Fall, 1927 and Neoscutopterus J. Balfour-Browne, 1943 ( Morinière et al. 2015, 2016, Miller and Bergsten 2014). Female genital tract anatomy, here described for the first time, is similar to that described and figured for Neoscutopterus ( Miller 2001).