Anisopleura furcata Selys, 1891

Description of the larva of Anisopleura furcata Selys, 1891 View in CoL

Material examined. THAILAND, 1 ♁ F-1, 1 ♀ F-1, 19/III/2003, Doi Suthep , small shallow rocky stream, (unavailable coordinate data; elevation 1,100 m), Chiang Mai province, A.G. Orr leg. ; 1 ♁ F-1, 21/III/2003, Mae Ton Luang village (18° 56' 40.0" N, 99° 22' 03.4" E; elevation 1,130 m), Chiang Mai province, A.G. Orr leg. GoogleMaps ; 2 exuviae (last stadium larvae at collecting, then reared in laboratory): 1 ♁, 1 ♀, 13/VI/2023, Huay Pha Samran at Doi Inthanon National Park, (18° 31' 38.9" N, 98° 27' 14.7" E; elevation 1,028 m), Chiang Mai province, T.S. Keetapithchayakul leg. GoogleMaps ; 4 last stadium larvae: 2 ♁♁ F-0, 1 ♀ F-0, 1 ♀ F-1, 13/VI/2023, Huay Pha Samran at Doi Inthanon National Park , (18° 31' 38.9" N, 98° 27' 14.7" E; elevation 1,028 m), Chiang Mai province, T.S. Keetapithchayakul, K. Wongkamheang & N. Makbun leg. GoogleMaps ; 4 last stadium larvae: 2 ♁♁ F-1, 2 ♀♀ F-0, 13/VI/2023, Huay Pha Tang at Doi Inthanon National Park , (18° 31' 15.7" N, 98° 31' 19.1" E; elevation 1,302 m), Chiang Mai province, T.S. Keetapithchayakul, K. Wongkamheang & N. Makbun leg. GoogleMaps

Description of larva. Habitus elongate with long robust legs with broad flattened femora, abdomen semi– cylindrical, tapered caudad, with seven pairs of ventral gills, anal gills saccoid, elongate and gradually tapering; coloration variable, yellowish-brown to brownish-black; front of head with conspicuous tubercles ( Fig. 2 View FIGURE 2 ).

Head: roughly squashed pentagon in outline, breadth circa 1.56 times length; hind margin produced sharply backward to meet occipital margin, forming clearly angulated corners, with postocular margin shallowly convex then sinuous posteriorly ( Figs. 2 View FIGURE 2 , 3B View FIGURE 3 ). Antennae ( Fig. 3A View FIGURE 3 ), 8–segmented, with A3 longest, relative length of antennomeres 0.75: 0.98: 1 (0.41 mm): 0.61: 0.80: 0.48: 0.39: 0.28, A1–A8 with scattered small SS, and A1 with apical circlet of CVS ( Fig. 3B, D View FIGURE 3 ). Total length antenna shorter than head measured from occipital margin to base of labrum. Labrum ( Fig. 3B, C View FIGURE 3 ) fringed with long SS distally on basal half, 4–5 elongate tubercles on either side, the longest distinctly curved; clypeus globular, antefrons scattered small SS and TWS, with 1 pair of elongated tubercles ( Fig. 3B View FIGURE 3 ); postfrons with 3 prominent ocelli; compound eyes broad and rounded, protruding to anterolaterally side; occiput with dense TWS and scattered SS; postocular lobes with TWS, scattered CVS and SPS near compound eyes, posterior margin with tubercle and TWS intermingled with CVS; genae ( Fig. 3E View FIGURE 3 ) with row of 4 (right) or 3 (left) moderately long stout spines (ca one third width of corresponding point of eye viewed ventrally or longer) arranged in a comb below eye margin; interspersed among the dominant spines are smaller SS and CVS; regular row of spiniform setae and CVS along ventral margin of compound eyes. Articulation of labial prementum and postmentum reaching level of middle of foreleg; prementum ( Fig. 4A View FIGURE 4 ) wedge-shaped with distinctly sinuous lateral margins bearing fine denticulations for most of their length ( Fig. 4C View FIGURE 4 ); distally wider than 0.80 length, with a pair of SS on middle of ventro–posterior side in ventral view; distal 1/3 heavily infuscated; ligula (median lobe) ( Fig. 4D View FIGURE 4 ) produced moderately with rounded profile and finely serrate margin; median cleft very short, extending to a pigmented elongate-spatulate trace that probably represents the sealing of a longer cleft during development; pair of small tubercles and, scattered small SS. Labial palp ( Fig. 4B View FIGURE 4 ) 0.33 length of prementum, outer margin with row of spines (each spine bearing small SS) from near base to midpoint, inner margin with narrow flange transversely grooved and weakly crenate in distal 2/3; apex with 3 lobes and movable hook; outer lobe moderately long smooth, uncinate tooth, middle lobe longer and thicker, terminally rounded weakly uncinate tooth overlapping outer lobe slightly in dorsal view; inner lobe a tiny rounded tooth, appressed to mid-lobe; movable hook strong and short about 0.58 × as long as labial palp, rapidly tapered to acuminate apex, curving weakly inwards. Mandible ( Fig. 5 View FIGURE 5 ) with mandibular formula: L 1+1’234 y a(m 0)b / R 1+1’234 0 a(m 1,2,3,4)b, asymmetrical, robust with well-developed long teeth on each incisor lobe, with molar crest; left mandible with 5 incisor teeth, molar crest with 2 teeth (a>b), with an additional tooth; right mandible with 5 incisor teeth, molar crest with 6 teeth (a>1=2=3>4<b). Outer margin of mandible with two strong spurs partly fused to form bifid process, easily visible in dorsal and ventral view in the intact animal ( Fig 5A, C View FIGURE 5 ). Maxilla ( Fig. 6A, B View FIGURE 6 ) galeolacinia with 7 teeth, 4 dorsal teeth of approximately the same size, apical teeth largest, 3 ventral teeth of small size.

Thorax: narrower than the head, with scattered TWS intermingled with CVS and SLS. Prothorax saddle-shaped, anterior margin reaching postocular lobe, fitted into occipital margin of head; posterior margin rounded, with row of CVS; lateral margin anteriorly with 4–5 elongate tubercular processes protruding laterally and posteriorly pronounced bifid supracoxal spurs ( Fig. 6C View FIGURE 6 ); wing pads pale brown to dark brown, with 2–3 rows of CVS from proximal to distal part, parallel, fore- and hindwing pads reaching base of S6 and midpoint of S6 respectively. Legs broad, robust with femora especially broad and flattened, covered with dense SS, intermingled with SLS and CVS, forelegs with 2 coxal spurs ( Fig. 6C View FIGURE 6 ); tibial comb ( Fig. 6D, E View FIGURE 6 ) with numerous SS intermingled with SLS and CVS in dorsal view, with numerous SS and 4–6 SLS locating distal margin end in ventral view; tarsi with 2 rows of SS and scattered long simple setae, tarsi formula: 3–3–3; 2 simple claws.

Abdomen: narrowing caudally, scattered SLS, intermingled with CVS and SS; abdominal terga, with a row of SLS and simple setae on posterior margin, abdominal terga S2–S9 with a cluster of SLS intermingled with SS on the middle of posterior margin; abdominal pleura scattered SLS; abdominal sterna smooth, with a pale network of tracheoles, seven pairs of tapered abdominal gills on S2–S8 becoming progressively shorter and more slender posteriorly, abdominal pleura S9 with row of SLS on distal margin. Male gonapophyses ( Fig. 7A, B View FIGURE 7 ) well developed, slender, almost semicircular in lateral view with serrate ventral margin formed by acute, broad-based, raised triangular plates with CVS, tip blunt, parallel in ventral view, reaching middle of abdominal sternite S10; gonopore small, embossed O-shaped with central fissure; female gonapophyses ( Fig. 7C, D View FIGURE 7 ) comprising 2 pairs of long valves, with lateral valves slightly arching from anterior margin of abdominal sternite S8, with acute, broad-based, raised triangular plates with CVS on the ventral side and with TWS on base; tips rounded, extending well beyond abdominal sternite S10; central valves smooth, slender, apically rounded, and slightly shorter than lateral valves. Male cerci, stout, blunt tip, slightly curved, convergent, with scattered SLS and SS; female cerci slender, blunt tip, concave ventrally with scattered long SLS and SS. Caudal gills ( Fig. 8 View FIGURE 8 ) saccoid tapering almost evenly caudad, median and lateral gills similar; brownish-black with yellowish-white long stout terminal filament, with dense SS on anterior part covered with SLS and long SS.

Measurements. (in mm; n = 10 (5 F-0, 3 F-1 alcohol preserved specimens and 2 exuviae); Minimum–Maximum [mean]: total length of body without caudal gills = 13.59–18.68 [16.72]; length of caudal gills (median: lateral) = 9.09–9.95 [9.48]: 7.96–9.74 [8.93]; width and length of head = 2.785 –3.165 [2.99] and 3.15–3.36 [3.27]; length of antenna = 1.76–2.09 [1.96]; maximum width and length of prementum = 2.59–3.06 [2.87] and 3.33–3.5 [3.39]; length of movable hook = 0.82–0.90 [0.87]; length of inner and outer wing pads = 5.7–6.63 [6.28] and 5.41–6.16 [5.89]; length of femora (fore: mid: hind) = 2.15–3.06 [2.83]: 3.45–3.66 [3.56]: 4.4–4.75 [4.59]; length of tibiae (fore: mid: hind) = 2.6–3.88 [3.26]: 2.55–4.07 [3.41]: 3.26–4.52 [4.07].

Biological notes

The larvae of A. furcata inhabit small clear streams in open habitats surrounded by trees, herbs, and shrubs and also in dense primary forest. The composition of the habitat on Doi Inthanon was as follows: pebble/gravel/sand/silt (45%), small stones (30%), leaf litter (10%), aquatic plants (5%), large rocks (4%), and large boulders (1%) ( Fig. 8 View FIGURE 8 ). The habitats where AGO collected his specimens were both smaller clear streams with a mainly rocky substrate, and gently flowing riffles; the larvae were located under mossy rocks and stones 20–30 cm diameter. Doi Suthep was heavily forested, and very close to the source of the stream; Mae Tong Luang was downstream a little from the source in a shaded area where the riparian flora was still largely intact, despite extensive clearing upstream and in the surrounds.

They cling to the substrate, often upside down, under stones and pebbles in riffles ( Fig. 9 View FIGURE 9 ) and may be found together with larvae of the genus Euphaea Selys, 1840 . Some specimens had chironomid larva attached in their abdominal gills in a phoretic association ( Boonsoong 2016).

Discussion

Besides the larva of A. furcata , another three larvae of the genus Anisopleura have been illustrated and/or described. Needham (1911) briefly described A. comes illustrating the larval habitus, and the labial palp; A. subplatystyla was illustrated only by the larval habitus and prementum with sketchy labial palps ( Fraser 1929) and A. lestoides was described in some detail by Kumar & Prasad (1977). It should be noted that while Fraser unaccountably stated that the larva bore no abdominal gills, the illustrations he provided were probably quite accurate.

The larva of A. furcata can be separated from the other three species by a combination of characteristics, especially the profusion of elongated tubercles on the labrum and antefrons (short tubercles are probably present to some extent in A. comes , and unidentified specimens examined by AGO from the Himalayas suggest they are probably present but very much shorter in A. lestoides and A. subplatystyla ), the presence of a bifid spur on the outer margin of the mandibles (single spur: A. lestoides , single spur suggested: A. comes and A. subplatystyla ), presence of row of CVS on distal end of A1 (probably absent: A. lestoides , no information: A. comes and A. subplatystyla ), inner lobe of labial palps forming tiny truncate tooth (tiny truncate tooth: A. comes ; short but well defined tooth: A. lestoides , no information: A. subplatystyla ). There exists an anonymous photograph of another Anisopleura species, taken in southern Vietnam and viewed by AGO, that based on location is most probably A. bipungio Hämäläinen & Karube, 2013 (M. Hämäläinen pers comm.). This larva is very like that of A. furcata with which it is closely related (M. Hämäläinen pers comm.). It also has long tubercles on the frons and labrum but three spurs on the outer mandible and the antennae are 7-segmented.

Superficially, A. furcata is immediately separated from any known congeners by virtue of the elongated tubercles on labrum and antefrons. Although previous descriptions and illustrations of other Anisopleura species were lacking in fine detail from A. lestoides and A. subplatystyla , at least, A. comes shows smaller tubercles in the habitus drawing. It seems inconceivable that such a prominent character could have passed unnoticed by any of these authors, but low or sparse button-like tubercles would not have been recorded.

All Anisopleura larvae bear a resemblance to the known larvae of other genera within the family Euphaeidae , including Bayadera Selys, 1853 , and Euphaea with which they may co-occur. These genera all have the definitive synapomorphy for the family, the presence of abdominal gills on S2–S8, and also share characters such as saccoid gills, stout build and, usually, a subocular row of spines on the genae, all of which, however, also occur in other ‘calopterygoid’ families, sensu Bybee et al. (2021). A less obvious, possible synapomorphy for Euphaeidae may be the presence of claviform setae, first noted by Needham & Gyger (1939) in Euphaea refulgens Hagen in Selys, 1853, which they surmised had a sensory function.

The diagnostic characteristics of Anisopleura distinguishing it from the genera Bayadera and Euphaea are as follows: 1) very shallow posterior lobes with sinuous posterior margin where it meets the rear margin of the occiput forming a sharp posterior angle (deep without sinous margin: Bayadera / Euphaea ), 2) antenna shorter than head from rear margin of occiput to base of labrum (at least as long as or longer in Bayadera / Euphaea ) and 3) well developed but acute male gonapophyses (poorly developed: Euphaea ; large and sausage shaped Bayadera ) ( Kumar & Prasad 1977; Wu et al. 2019; Keetapithchayakul et al. 2020, Yang & Orr 2024). Information on larval characters in the family Euphaeidae is at present not well resolved. In some cases, specimens are available, but identity is not confirmed. Many previous descriptions have mostly been done on an ad hoc basis, without proper reference to congeners or other genera, often simply because this information did not exist, and older (and recent) literature is either lacking in detail or inaccurate, or both, leading to some confusion regarding the significance of diagnostic characters ( Keetapithchayakul et al. 2020). There is a range of potential diagnostic characters such as the shape of the postocular lobe, gonapophyses, perhaps the arrangement of subocular spines along margin of the genae, armature of postocular lobe, and the shape of the caudal gills. The presence/absence and arrangement of setae in various situations and the presence of prothoracic coxal spines and supracoxal armature may also be significant.

To characterise the larvae of the family Euphaeidae a concentrated effort to thoroughly assess these features is needed in order to assess their diagnostic status in each species or genus. For this, good series of verified specimens are needed. At present the larvae for three genera in the family ( Cyclophaea Ris, 1930 , Schmidtiphaea Asahina, 1978 , and Cryptophaea Hämäläinen, 2003 ) are completely unknown. Therefore, further study should be aimed at concentrated fieldwork to obtain the much needed specimens, as well as rearing and/or DNA matching with adults to ensure reliable determinations, rather than supposition. With habitats contracting at an alarming rate, and already members of the family judged as endangered, the need for this basic groundwork has never been so pressing.