Cychrus, Fabricius, 1794

Busato, Enrico, 2012, semigranosus Palliardi, 1825, with a key to the larvae of the European Cychrus species (Coleoptera: Carabidae), Zootaxa 3361, pp. 1-17 : 15

Key for the identification of larvae of European species of the genus Cychrus :

1. Frontoclypeolabrum with very prominent lateral lobes outside and forwards, which are markedly distinct from the median lobe; in the lateral view it is flattened in the proximal area, and markedly thickened in the distal area. Approximately along the middle of its length, it forms a convexity that gently slopes down distally and laterally, finally forming two distinctly slanted folds in the insertion areas of the lateral lobes, at the sides of the median lobe. The latter, in the lateral view, is prominent and almost of the same thickness as the median convexity ( Fig. 31).................................................. 2

—. Frontoclypeolabrum with non-prominent lateral lobes, flattened, scarcely distinguishable from the median lobe. In the lateral view the three lobes almost lie on the same level and almost form a single level, obliquely oriented towards the proximal area of the frontoclypeolabrum. In the lateral view the proximal area shows a marked convexity, which is the thickest point of the frontoclypeolabrum. It gently slopes down towards the distal area, forming a fold approximately perpendicular to the longitudinal axis of the frontoclypeolabrum, in the proximal area of the median lobe and at the points where the lateral lobes fit ( Fig. 32)................................................................................................. 5

2. Sternal area of segments I–III made up of five sclerites. Median and inner sternites fused into a single central sclerite. The central sclerite and the outer sternites fuse together, starting from segment IV and forming a new central sclerite with a clear median fusion line. In segment IX they are completely merged together and only two central sclerites are fused in the visible median line. General appearance is extremely squat ( Fig. 33)................................. ( spinicollis group) 6

—. Sternal area of segments II–VI made up of eight sclerites. Sometimes, in the first four segments, the inner sternite is formed by two distinct sclerites. The median sternite, which is narrow and long and much larger than the others, is placed horizontally on the inner sternite, which is almost of the same size. In segment VII the median and the inner sternites merge together to form a single central sclerite that also includes the outer sternites, showing the median fusion line. In urite VIII, the hypopleurites are merged with the central sclerite and the total number of abdominal sclerites is reduced to three. In segment IX the merging of all abdominal sclerites is complete ( Fig. 34)................................................................. 3

3. Head large, subquadrate. Frontoclypeolabrum is as large as it is long, or slightly longer than it is large. Metathoracic legs with short tibiae and short tarsi (ratio t/C: 0.38–0.42; ratio ta/C: 0.54–0.61). General appearance is extremely squat...............................................................................................( caraboides group) 7

—. Head subrectangular. Frontoclypeolabrum clearly longer than it is wide, subrectangular. Metathoracic legs with moderately long tibiae and long tarsi (ratio t/C: 0.45–0.58; ratio ta/C: 0.59–0.83). General appearance is slim..................... 4

4. Median lobe of the frontoclypeolabrum is rounded and barely sketched, flattened in the dorsal view, at the same level of the lateral lobes or slightly lower ( Fig. 31). In the first instar larvae the ruptor ovi is formed by two spinulae, on each side of the frontoclypeolabrum, vertically arranged, one anteriorly the other. Metathoracic legs with very long tarsi (ratio ta/C: 0.73–0.83)............................................................................ ( cordicollis group: C. cordicollis )

—. Median lobe of the frontoclypeolabrum is prominent, as wide as the lateral lobes, and is slightly more prominent in the dorsal view than the lateral lobes ( Fig. 35). In the first instar larvae the ruptor ovi is formed by a single spinula on each side of the frontoclypeolabrum. Metathoracic legs with moderately long tarsi (ratio: ta/C: 0.59–0.63).......... ( attenuatus group) 8

5. External margin of tergites has four to five long setae that give the larva a hairy appearance ( Figs. 1, 2, 13–15). The urogomphi have moderately short setae ( Fig. 15)............................................ ( schmidti group: C. schmidti )

—. External margins of tergites without long setae. The urogomphi have very short setae. [Body shape markedly weak and stretched with the first thoracic segment much longer than usual. Lateral lobes of frontoclypeolabrum with back margins almost parallel to the longitudinal axis of the head ( Fig. 36)]....................... ( angustatus group: C. cylindricollis )

6. Mandibular internal margin all finely indented ( Fig. 37)............................................. C. spinicollis

—. Mandibular internal margin smooth................................................................ C. dufouri

7. Frontoclypeolabrum slightly longer than large, bulging in the proximal area, has a maximum width both next to the lateral lobes of the anterior margin and at the middle of its length. Median lobe prominent, conical with a beveled tip, a little bit wider than a lateral lobe ( Fig. 38).................................................................... C. caraboides

—. Frontoclypeolabrum as large as it is long, with its maximum width next to the lateral lobes of the anterior margin. Median lobe much wider than a lateral lobe ( Fig. 39)............................................................. C. italicus

8. Mandibular internal margin smooth.............................................................. C. attenuatus

—. Mandibular internal margin denticulate, lying at around 1/3 the length of the mandible ( Fig. 19)............ C. semigranosu