Ancyronyx schillhammeri Jaech , 1994

Freitag, Hendrik, 2013, Ancyronyx Erichson, 1847 (Coleoptera, Elmidae) from Mindoro, Philippines, with description of the larvae and two new species using DNA sequences for the assignment of the developmental stages, ZooKeys 321, pp. 35-64 : 55-58

Ancyronyx schillhammeri Jaech, 1994 Figs 8, 9, 15 A–H

Ancyronyx schillhammeri Jäch, 1994: 617-619 (adult description), Freitag and Pangantihon 2010: 133-137 (faunistic records).

Material examined.

1 ♀ [FR029], 1 L (0.61 [FR030]) (ZSM) "PHIL.: Mindoro, San Teodoro, Tukuran Riv.; small lowld.riv.; riffle & run; woodlitter, gravel; sec.veget.; c. 30m asl., 13°25'34"N, 120°58'37"E 23.4.1994, leg. Freitag (303a) M’’; 3 ♂♂, 1 ♀ (PNM) "PHIL.: Mindoro Oriental, Bongabong, Brgy. Formon, Pastuhan, Tangisan Falls; deep mountain valley, sec. forest, submerged wood, riffle, c. 200 m asl., c. 12°43'N, 121°23'E; 27.10.2011 leg. Freitag (318a)M"; 3 ♂♂ (CFM) "PHIL: Or. Mindoro, Roxas, Bagumbayan, polluted Magugo River; sec.veget.; submerges wood, run; 6m asl., c. 12°35'27"N, 121°31'00"E; 05.6.2000 leg. Freitag & Pangantihon (329c)M"; 1 ♂, 4 ♀♀ (CFM) "PHIL: Or. Mindoro, Roxas, Brgy. San Vicente, Baroc River; subm. wood; gravel flood plains; c. 12°37'07"N, 121°24'06"E, 90m asl; leg. Freitag 1 Apr.2013 (BRf)M"; 4 ♂♂, 7 ♀♀ (CFM) "PHIL: Or. Mindoro, Roxas, Brgy. San Vicente proper, Taugad River; subm. wood; sec.veget.; c. 12°37'06"N, 121°23'49"E, 100m asl; leg. Freitag 2 Apr.2013 (TR1f)M"; 5 ♂♂, 1 ♀ (SMTD, ZSM) "PHIL: Or. Mindoro, Roxas, Brgy. San Vicente, Tauga River; subm. wood, run; sec.veget.; c. 12°37'18"N, 121°22'58"E, c. 140m asl; leg. Freitag 28.Nov.2011 (TR2f)M"; 1 ♂, 3 ♀♀ (ZMUC) "PHIL: Or. Mindoro, Roxas, Brgy. San Vicente, Sitio Tauga Diit, Baroc River tributary Tauga Daka; subm. wood in run; sec.veget.; c. 12°38'05"N, 121°19'33"E, c. 530m asl; leg. Pangantihon, 23 Jan. 2013 (TDR3f)M"; 1 ♀ (CFM) "PHIL: Or. Mindoro, Roxas, Brgy. San Vicente, Sitio Quirao, Baroc River tributary Hinundugan River; subm. wood; c. 12 °36'23"N, 121°23'29"E, c. 118m asl; leg. Pangantihon, 22 Jan.2013 (HR1f)M"; 1 ♀ (CFM) "PHIL: Oc. Mindoro, San Jose, Brgy. “Central” Purok Tunnel, Busuanga River; rural, cogon gras roots, riffle & run, c. 73 m asl., c. 12°27'51"N, 121°02'08"E; 07.VI.2012 leg. Freitag & Pangantihon (330b)M".

Larval diagnosis

(based on a single presumably sixth instar specimen). Colour in last instar larva predominantly brown as in Fig. 9; dorsal head darkest to almost black at pronotal disc; lateral head, antennae, anterior and lateral pronotal margins, legs (except for tip of claw), lateral abdominal segment margins and conical projections, posterior abdominal tip and areas around the sagittal line (especially thoracic area) distinctly paler, yellowish to pale brown. Ventral side entirely pale except for pale brown gula, maxillae and labium; ventral part of genae conspicuously dark brown.

HW c. 0.60 mm; entirely c. 3.8 mm long.

Body shape of the Ancyronyx variegatus group type, generally very similar to that of Ancyronyx procerus (comp. Freitag and Balke 2011: 72-75) in the external habitus, except for the following: Posterolateral projections (Figs 9, 15A, B) of abdominal segments IV–VIII slightly broader and stouter; spiracles distinctly larger, very prominent; entire lateral margin with distinct long trichoid setae; tubercles much more prominent (especially at dorsal side).

Head (Figs 15 C–F) distinctly widest basally, slightly conical anteriad; without median pointed projection at frons; the pair of sublateral anterior projections between antenna and clypeus rather shallow (Fig. 15C). Frons moderately densely and equally covered with prominent setiferous tubercles; setae very short. Genae rugose, with irregular depressions, ridges, and scattered tubercles (Fig. 15D); lateral glabrous area with stemmata elongately subtriangular (Fig. 15D). Antenna (Fig. 15E) less than half as long as head. Scape short, slightly longer than wide, with subapical fringe of stout sensilla; pedicel cylindrical less than three times as long as scape and c. three times as long as wide, with few apical sensilla; flagellum and sensorium as in Ancyronyx procerus . Ventral side (Fig. 15F) with well-developed longitudinal crests bordering the stipes. Labrum broad, c. 3.5 times as wide as long; lateroapical edges rounded; entire visible dorsal surface with small setiferous tubercles. Maxilla (Fig. 15E, F) almost as in Ancyronyx procerus . Labium (Figs 15E, F) with mentum widest in apical half; pair of moderately long trichoid setae inserted sublaterally at anterior 0.3; some additional trichoid setae present at lateral margin in apical half; pair of apicolateral teeth inserted at a distinct subapical crenation; submentum straight, without conspicuous median ridge, apically broadly concave.

Prothorax (Fig. 15G, H) slightly wider than long; tergum with irregularly shaped and round signa in posterior half; median and submedian pairs clearly defined by bordering tubercles, not fused (Fig. 15G). Venter of prothorax (Fig. 15H) similar to that in Ancyronyx procerus , but anterior sclerites distinctly shorter, oblique, not subtriangular; anterior margin with conspicuous setiferous tubercles; anterior and lateral sclerites partly fused near anterior prothorax margin; transverse sutures dividing the lateral sclerites distinctly ending before lateral margin. Venter of meso- and metathorax (Fig. 15H) with more conspicuous setiferous tubercles particularly at posterior margins of anterior sclerites.

Legs (Figs 15H, J) proportioned as in Ancyronyx procerus , but tubercles and setae larger and more distinct. Subbasal tooth of claws long and trichoid, overreaching tip of claw.

Abdominal terga (Figs 9, 15A, B, I) with slightly depressed groove along sagittal line at least from 1st up to 4th segment; posterior terga margins with rim of squamose setae. Posterior venter margins with rim of trichoid setae. Segment IX (Fig. 15I) dorsally with shallow sagittal crest formed by densely arranged tubercles bearing large trichoid setae; apex widely rounded to slightly truncate; ventral side rugose, not glabrous. Operculum without longitudinal ridges, entirely rugose and covered with conspicuous scattered setae.

Larval differential diagnosis.

The larvae of Ancyronyx schillhammeri are easily distinguishable from all other known Ancyronyx larvae of Mindoro by their larger size, the somewhat dorsoventrally depressed habitus, the much larger and protruding posterolateral appendages, as typical for the Ancyronyx variegates species group. Among this species group, it resembles the larva of Ancyronyx procerus in colour, but can be clearly distinguished by the absence of the pointed projections at median frons, the more shallow projections between antenna and clypeus, the larger and more protruding spiracles, the conical head shape, and the surfaces of head, thorax, and abdomen that are densely covered with larger tubercles bearing long conspicuous setae. From Ancyronyx helgeschneideri itis easily distinguishable by the darker colour, the pale dorsosagittal stripe, the dark dorsal abdominal segment IX and the broader and conical head.

Distribution.

Only known from Oriental Mindoro and one locality of Occidental Mindoro near San Jose.

Ecology.

Ancyronyx schillhammeri occurs exclusively on submerged wood. Decaying pale light woods appear to be preferred by the species. At the sites of the Baroc River catchment, which were sampled regularly throughout the year, the abundance of this species was found to increase distinctly towards the end of the dry season (February to April) and declines rapidly with the beginning rainy season, presumably due to wash out. It is found in both habitat types: clean, cool and torrent rhithral creeks and rivers as well as warm, mesosaprobic lowland streams. This suggests less specific ecological requirements in terms of stream hydraulics, water temperature, and water quality.