Leptotyphlinae

Grebennikov, Vasily V. & Newton, Alfred F., 2008, Minute larvae of Leptotyphlinae (Coleoptera: Staphylinidae): description of three genera with discussion on the monophyly and phylogenetic position of the subfamily as inferred from larval morphology, Zootaxa 1817, pp. 49-58 : 51-52

Larvae of Leptotyphlinae

Diagnosis. Larvae of Leptotyphlinae can be separated from those of most Staphylinoidea by their small size (body length 1–2 mm in the oldest instar). From the larvae of other small staphylinoids ( Ptiliidae , Leiodidae , Hydraenidae , Scydmaenidae , Aleocharinae , Pselaphinae and some others) larvae of Leptotyphlinae can be distinguished using the following combination of characters: stemmata absent ( Figs. 8, 9 , 12, 13 , 18, 23 ); head prognathous, with long coronal suture (about 40% of head length), lyriform dorsal ecdysial lines ( Figs. 8 , 12 , 18, 23 ) and parallel ventral ecdysial lines along the ventral mid-line of the head ( Fig. 13 ); antennae shorter than one third of the head length ( Figs. 12 , 18 ), with elongate sensorium ( Fig. 20 ); maxilla with articulated mala bearing elongate process at apex ( Fig. 22 ); mandibles non-serrate, with single large mesal pre-apical tooth ( Figs. 12, 13 , 18, 19, 23 ); tibiotarsi swollen at middle with two large ventral spines ( Figs. 14 , 28 ); separate abdominal laterotergites absent and apparently fused with terga thus completely encircling spiracles ( Figs. 15, 17 ); and urogomphi indistinctly articulated to tergite IX, short and stout ( Figs. 15–17 , 29, 30 ). Larvae of some Euaesthetinae with reduced number of stemmata might resemble those of Leptotyphlinae ; but the mandibles of known euaesthetine larvae lack a pre-apical tooth.

Description. Habitus. Larvae small, normally about 1mm in body length. Frayed setae absent; trichobothria absent; each side of epicrania and all thoracic and abdominal terga with one large pore-like opening dorsally.

Head. Stemmata absent; coronal suture about half length of head capsule; constricted neck region absent; occipital foramen wide, about 0.7–0.8X as wide as maximum head width; dorsal ecdysial lines lyriform; nuchal carina apparently absent; ventral wall of head capsule on each side of the prementum without anteriorly directed large sclerotized tooth; posterior tentorial pits short, 2– 3 X as long as wide; posterior tentorial arms thread-like and more than 20X longer than wide; tentorial bridge originates from posterior tentorial arms, narrow; attachment of anterior tentorial arms to dorsum of head capsule rounded, not transverse; ventral ecdysial lines present, linear, extending from base of head to near posterior tentorial pits; oblique hypostomal ridge on ventral surface of head capsule near maxillary foramina long, about twice as long as length of cardo; labrum fused to clypeus forming nasale; lateral sclerites on each side of labrum near fusion to clypeus absent; anterior edge of nasale serrate or not, if serrate, then without median tooth; tormae absent.

Antennae. Basal antennomere at its middle not constricted or interrupted by membrane; antennae 3-segmented; antennae shorter than 1/3 of length of head capsule; main sensory appendage on antenna elongate and narrow, parallel-sided along much of length, located antero-mesally on penultimate antennomere, longer than the width of penultimate antennomere; ultimate antennomere of regular shape or slightly shortened, length to width ratio 1–2.5; membrane connecting basal antennomere with head capsule absent or short, not longer than membrane between antennomere 2 and 3; first (basal) antennomere without setae; second (penultimate) and third (ultimate) antennomeres each with three long setae in apical half.

Mandibles. Mola absent; each mandible without mesal serration, with preapical tooth directed dorsomesad; mandibles not asymmetrical, almost straight or slightly curved, apices directed anteriorly and partly mesad.

Maxillae articulated with ventral wall of head through condyle, membranous maxillary articulation highly reduced; cardo as wide as base of stipes, or 1.2X wider, without transverse ridge; stipes not narrowed apicad, lateral edges without obvious constriction; maxillary palpomere 2 straight; maxillary palpomere 3 not flexible, about 4 times as long as wide; galea and lacinia completely fused forming finger-shaped subparallel mala articulated to stipes; mala subequal in length to apical width of stipes, attached to mesal surface of stipes, protruding mesally; first (basal) maxillary palpomere (immediately apicad of maxillary palpifer) without setae; second (penultimate) maxillary palpomere with two setae; third (apical) maxillary palpomere entire, without setae and with one digitiform sensillum; submentum and mentum free, not incorporated in the ventral head wall; mentum with triangular or subquadrate sclerite bearing two pairs of setae; maxillary foramina open anteriorly and mesally; ligula present, not sclerotized or digitiform, as wide as, or narrower than basal labial palpomere, at apex straight, pointed or rounded, not bilobed; about as long as width of basal labial palpomere; labial palpomere 2 rigid and about 5X as long as its basal width; ligula without long membranous and microsetose anterior projection; apical labial palpomere and ventral sclerite of prementum entire, not subdivided by membrane.

Thorax. Pro-, meso- and metatergum without anterior and posterior carinae; cervicosternum transverse, anterior to proepisterna; longest seta on trochanter not more than 1.5X as long as width of trochanter; leg’s longest seta located on trochanter; tibiotarsus stout, not styliform; tibiotarsus at middle wider than at distal or proximal end; setae at apex of tibiotarsus short, as long as, or shorter than, claw width at base.

Abdomen. Terga and sterna longitudinally not divided by membrane; abdominal segment IX without elongate and latero-posteriorly directed tube-like process on each side; openings of abdominal (and thoracic) spiracles not or slightly elevated above body surface; laterotergites absent and apparently fused with terga, completely encircling spiracles; urogomphi present, each with apical seta about as long as urogomphus; urogomphi one-segmented, about as long as tergum IX, indistinctly articulated to abdominal segment IX but probably immobile.

Figures

FIGURES 2 – 11. Leptotyphlinae, larval morphology of the undescribed genus from Australia. 2 — habitus, ventral view (head inserted; ventral view); 3 — habitus, lateral view (head inserted, dorsal view); 4 — anterior part of head showing right antenna with elongate and slightly curved sensorium, dorsal view; 5 — base of stipes, cardo, labial palpi, prementum, mentum, free triangular submentum, and oblique hypostomal ridge, ventral view; 6 — abdominal segments VIII, IX (bearing 1 - segmented urogomphi indistinctly attached to tergum) and X, lateral view; 7 — abdominal segments VI – X, dorsal view; 8 — head, dorsal view; 9 — head, ventral view; 10 — right maxilla, ventral view; 11 — thorax and abdominal segments I – IV, lateral view. Scale bar 0.05 mm.

FIGURES 12 – 17. Leptotyphlinae, larval morphology of the undescribed genus from Australia. 12, 13 — head (left mandible, right antenna and maxilla omitted), dorsal (12) and ventral (13); 14 — right foreleg; 15, 16, 17 — abdominal segments VIII, IX (with urogomphi) and X, dorsal (15), ventral (16) and lateral (17).

FIGURES 18 – 24. Leptotyphlinae, larval morphology of the undescribed genus from Mexico (18 – 22) and undescribed genus from Chile (23, 24). 18, 19, 23, 24 — head, dorsal (18, 23, 24) and ventral (19) (left antenna and right mandible omitted); 20 — right antenna, dorsal; 21 — nasale, dorsal; 22 — left maxilla, dorsal.

FIGURES 25 – 31. Leptotyphlinae, larval (25 – 30) and adult (31) morphology of the undescribed genus from Mexico. 25, 26 — abdominal segment VI, dorsal (25) and ventral (26); 27 — pro-, meso-, and metathorax, left lateral (legs omitted); 28 — left fore tibiotarsus and claw, posterior; 29, 30 — abdominal segments IX (with indistinctly articulated short urogomphi) and X, ventral (29) and dorsal (30); 31 — aedeagus.