Ancyronyx procerus Jaech , 1994

Freitag, Hendrik & Balke, Michael, 2011, Larvae and a new species of Ancyronyx Erichson, 1847 (Insecta, Coleoptera, Elmidae) from Palawan, Philippines, using DNA sequences for the assignment of the developmental stages, ZooKeys 136, pp. 47-82 : 69-72

Ancyronyx procerus Jaech, 1994 Figs 918 A–J

Ancyronyx procerus Jäch, 1994: 611-613 (adult description); Jäch, 2003: 259 (new records).

Material examined.

1 L (0.61) (ZSM [FR014]) "PHIL.: Busuanga, Coron; Guadelupe, Balolo R./Brdg. Nat.Rd. km 14; lowld. creek; sec.veget.; run, gravel, CPOM, c.10m asl, 12°01'43"N, 120°06'48"E 03.2.1995, leg. Freitag (169)M"; 1L (0.63) (NMW) "MALAYSIA, Sarawak, Mulu NP, Long Iman 4.3.1993 leg. M. Jäch (20)".

Larval description (based on 6th instar).

Colour (Fig. 9) predominantly brown; head distinctly darker to almost black dorsally; lateral head, antennal scape, anterior pronotal collar and legs whitish or yellowish pale. Entire ventral side (except for parts of genae), antennal pedicel, anterior margin of pronotum, claws, lateral abdominal projections, small medioposterior areas or entire posterior margin of thoracic and abdominal segments and a median middle portion of abdominal segment IX pale brown to yellowish.

HW c. 0.62 mm, entirely c. 3.7 mm long. Body flattened dorsoventrally, moderately vaulted dorsally, almost flat ventrally, with sagittal line (longitudinal groove from prothorax at least up to 5th abdominal segment). Dorsal side moderately densely covered with setiferous tubercles (Fig. 18A). Ventral side smoother, with scattered setae and few setiferous tubercles (Fig. 18B). Retractable portions of body segments and pronotal collar without setae and tubercles (Fig. 18A). Lateral margins of abdominal segments I–VIII produced laterad forming posterolateral-directed conical projections (Fig. 18C). Projections increasing in size caudad, those of segment VIII c. 3.5 times as long as such on segment I. Rather inconspicuous spiracles present laterally on mesothorax and abdominal segments I–VIII.

Head (Figs 18A, D–F) subquadrate, partly retractable, distinctly prognathous, with three anterior-dorsad directed, pointed projections, one each side between antenna and clypeus and one at median frons (Fig. 18A). Frons rather glabrous, only with small and scattered setiferous tubercles. Stemmata arranged as single lateral spot in a glabrous area, slightly exposed. One irregular rim of moderately long setae at ventrolateral head margin (not visible in dorsal view). Frontal suture broadly V-shaped. Frontoclypeal suture uneven, but somewhat straight. Clypeus distally microreticulate, with protuberant anterior seam; without subbasal fringe of setae or tubercles. Ventral side (Fig. 18D) with few scattered setae and an obvious longitudinal crest each side lateral of gula and maxillae. Genae rugose, with asperities and scattered tubercles. Gula with rather inconspicuous asperities. Maxilla (Figs 18D, E) moderately broad; cardo stout, undivided; lateral portion with one median acuminate seta; stipes subrectangular, glabrous, with few short and one long latero-subapical trichoid setae; maxillary palpus (Fig. 18E) four-segmented, approx. as long as stipes broad, distal segment smallest, cylindrical with several apical sensilla of various shape; predistal segment with lateroapical trichoid seta; galea and lacinia subequal in length and shape, approx. as long as palpus, apically with sensilla. Labium (Figs 18D, E) with broad (about 1.7 times of stipes) mentum (postmentum), broadest at basal half, with median groove most depressed posteriorly, with one pair of moderately long trichoid setae sublaterally at anterior 0.25, one subbasal pair each of spinose and trichoid setae and one pair of short apical lateral teeth. Submentum (prementum) short, transverse, apically convex, with sagittal ridge and one laterobasal pair of setae; ligula inconspicuous with various setae and pegs; labial palpi short, with short and stout palpifer; apical segment similar to that of maxillary palpi, preapical segment with lateral tuft (Fig. 18E). Mandibles not examined. Labrum c. 3 times as wide as long, anterior margin distinctly convex, with a subapical fringe of ramose setae and scattered trichoid and truncate (sensory) setae, proximal portion glabrous. Antenna (Fig. 18F) three-segmented, c. 1/2 as long as head. Peduncle short, about as long as broad, without (visible) dorsolateral fringe of branched trichoid setae; scape cylindrical, longer than pedicel and c. twice as long as broad, with few apical trichoid setae; pedicel cylindrically elongate, comparably short, only slightly longer than scape; flagellum and sensorium (broken off in figured specimen) subequal in length, slender, cylindrically elongate, c. five times as long as broad; apex of flagellum with inconspicuous elongate sensillum.

Prothorax subquadrate, almost as long as broad, with round signa (glabrous areas) in posterior half and near depressed sagittal line. Meso- and metathorax subtrapezoidal, distinctly broader than long, distinctly shorter than prothorax (Fig. 9); medial longitudinal groove and lateral rims distinctly produced posterolaterad. Venter of prothorax (Fig. 18G) with five sclerites: two oblique anterior, two lateral, and one posteromedial sclerite. Anterior sclerites subtriangular; procoxal cavity closed posteriorly; lateral sclerites posteriorly extend mesad, anteriorly appearing divided by an oblique incomplete suture. Entire anterior and lateral prothoracic venter glabrous, few setiferous tubercles in posterior portions. Venter of meso- and metathorax (Fig. 18G) with six sclerites: two oblique anterior, two subquadrate sclerites anterolateral, two elongate meso-posterolateral sclerites; coxal cavities open posteriad; setiferous tubercles sparse on lateral portion; medial portions almost glabrous. Membrane connecting pro- and mesothoracic venter largely extended medially, appearing almost as a separate sclerite (like a prosternal process in adults). Posterior margin of anterior sclerites with fringe of setiferous tubercles.

Legs (Figs 18G, H) stout (compared to larvae of the previous species and adults), similar in shape and length, with scattered trichoid sensilla mainly at femora and tibiae. Coxae large, subtrapezoidal; trochanter shorter, elongately subtrapezoidal, rather slender; femora subtrapezoidal, short; tibiae subcylindrical, broadest basal, distinctly narrower than femur, longer than other segments. Claws elongate, moderately bent, with one subbasal presumably trichoid tooth (broken or invisible in specimen examined).

Abdomen (Figs 9; 18B, I, J). Segments I–VIII similar in shape, broadly subrectangular in dorsal view; terga with depressed sagittal line at least from 1st up to 5th segment. Retractable anterior portion with squamose asperities; posterior terga margins with a rim of squamose setae. Remaining median portions of terga more or less equally covered with setiferous tubercles. Ventral sclerites of segments I–VIII subrectangular, extendingly fused with pleural sclerites from 1st to 8th segment; posterior venter margins with a rim of squamous setae. Segment IX (Figs 18I, J) elongate, subconical (broadest subbasally), subtriangular in cross-section; apex broadly rounded, not emarginate; dorsal and lateral portions densely covered with setiferous tubercles; ventral side with scattered short trichoid setae and some long filiform setae sublaterally (most broken off in specimen figured in Fig. 18J). Operculum (Fig. 18I) subtrapezoidal to subtriangular, less than double as long as broad, medially depressed, rugose. Basal half with small longitudinal ridges and scattered sensilla; apical half with squamose asperities and a lateral rim of trichoid setae; the internally inserted pair of hooks rather small. Gill chamber with long, ramose gill tufts overreaching the opercular margin.

Variation between larval instars.

The two final instar specimens available do not allow to draw conclusions about variations between the instars.

Larval differential diagnosis.

The species resembles the previous ones only in very general characters, such as the presence of posterolateral appendages and the distribution of spiracles. This larva is, however, not torpedo-like elongate and subsemicircular in cross section, but dorsoventrally somewhat depressed, only slightly vaulted dorsally. By this it rather resembles the species Ancyronyx variegatus from North-America than those of the Ancyronyx patrolus group (Freitag & Jäch, 2007, p. 58).

Distribution.

Known from Busuanga, Philippines (recent study; Fig. 20), Malaysia, Brunei and Vietnam ( Jäch 1994)