Platystictidae

Orr, Albert G. & Dow, Rory A., 2015, Description of two final stadium platystictid larvae from Borneo, including that of Drepanosticta? attala Lieftinck, identified using DNA barcoding (Odonata: Zygoptera: Platystictidae), Zootaxa 3985 (4), pp. 565-574 : 571-572

Platystictidae sp. A

Figs 4, 3 b, f, h.

Material. One F larva, ♂, Brunei, Kuala Belalong Field Studies Centre, 4°32'46’9"N ”15°09'30’1"E,” 60 m a.s.l., leaf pack in main stream, 1.ix.1995, leg. A.G. Orr.

Description. In general appearance rather similar to D. attala but head relatively shorter and narrower anteriorly and eyes only moderately large and without setae. Legs and abdomen proportionally a little shorter. Caudal lamellae similar but median and lateral lamellae more nearly equal ( Fig. 4). Coloration overall brown ochre. Most parts of body bearing fine setae, but these generally a little shorter and sparser than in D. attala .

Head in dorsal view broad and strongly prognathous, shorter and more contracted anteriorly than in D. attala , posterior margin concave, thus producing a strong cardioid outline to the head overall, Compound eyes large. Anteclypeus fairly narrow and labrum basally narrow, strongly expanded at its anterior margin and bearing a dense fringe of strong, moderately long setae. Mandibles clearly apparent in dorsal view but labial palps concealed or almost so. In ventral view ( Fig. 3 h) mandibles with four well-defined teeth on incisor lobe; molar lobe of right mandible with minute thorn-like process only near inner margin; molar lobe of left mandible with single long, strong, fairly narrow tooth with a moderate sub-basal shoulder; left mandible with only three fully developed teeth on the incisor, the dorsal fourth being vestigial. Seen in ventral view ( Fig. 3 f) galeolacinea of maxilla with three long outer (ventral) spines, one longer terminal spine and three inner spines; maxillary palp narrow, curved and bearing long dense, fine setae. Articulation of mask reaching posterior margin of procoxae when retracted. Prementum ( Fig. 3 b) flat ventrally, only slightly concave dorsally and overall smooth; moderately broad (length: maximum breadth ratio 1.47); laterally moderately convex with margins bearing sparse fringe of fine setae; anterior margin (ligula) moderately produced to form a convex flap, with margins rounded, thus describing a quarter circle; terminal cleft sealed; margins bearing 26–28 short, thick peg-like setae terminating in a crown of spines as in D. attala ; tuft of long fine setae on either side of ligula. Labial palp short and stout (length palp: length prementum 0.31), terminating in a smooth, simple broad shallow hook, with slight serrations on its inner margin; outer margin basally bearing sparse long setae; movable hook stout, short and only slightly curved. Antennae as in D. attala . Legs slightly shorter than in D. attala ; femora stout and somewhat angular, bearing sparse fine setae; tibiae thin, bearing long, fine setae. Wing pads separate and divergent, surpassing hind margin of S5. Abdomen rather shorter than in D. attala , gradually tapered posteriorly, generally bearing short fine setae. Caudal lamellae partially inflated but clearly dorso-ventrally flattened with distinct dorsal and ventral crease; median lamella clearly less than half as long as abdomen including a well-developed terminal filament bearing long fine setae; lateral lamellae about four-fifths length of median, with well developed terminal filaments; cerci short, slightly incurved, clavate; in ventral view margin of S10 not strongly produced medially. Male gonapophyses absent.

Measurements (mm): Total length (without caudal lamellae) 12.4; maximum width of head 2.8; hind femur 3.0; cercus 0.17; right lamella 2.5; median lamella with filament 3.1.

Remarks. This species differs clearly from D. attala in the shape of its head and body, by having smaller eyes, a more elongate mask with less convex sides to the prementum, more rounded ligula, narrower mandibles lacking any central molar process on the right side, reduction in teeth on incisor of right mandible, longer ventral spines on the galeolacinea, and by having generally less dense and shorter setae. The body pattern is well developed in D. attala and absent in this species, a difference that may be significant.

The collection site was the main stream characterized in Orr (2001, 2006), in a leaf pack collected in a shallow riffle about midstream. Chemical properties of the water are given in Cranbrook and Edwards (1994: p 312). In this situation the RH drops below 80% at times during the day. This species might potentially belong to the genera Drepanosticta , Protosticta or Telosticta , all of which occur within an area of ca 5 ha. Nevertheless its presence in the open stream points to it possibly being the larva of D. rufostigma (Selys, 1886) . This is not only by far the commonest species in the area (often a poor indicator of larval identity!) but it also appears, apart from D. attala , to be the species most tolerant of sunlight and lower humidity experienced in more open situations. Drepanosticta attala has also been recorded from larger, open canopy, forest streams, see Dow & Orr (2012: 290) and Dow & Ngiam (2014: 25).

Figures

FIGURE 3. Details of Drepanosticta? attala: (a) mask, dorsal view; (c) dorsal detail of crown-like setae on margin of ligula; (d) ventral detail of caudal appendages; (e) Ight maxilla, ventral view; (g) mandibles ventral view; (i) right antenna, and Platystictidae sp.: (b) mask, dorsal view; (f) right maxilla, ventral view; (h) mandibles ventral view.