A review of the alderfly genus Leptosialis Esben-Petersen (Megaloptera, Sialidae) with description of a new species from South Africa

Abstract The monotypic South African alderfly genus Leptosialis Esben-Petersen, 1920 is reviewed and Leptosialis africana Esben-Petersen, 1920 is redescribed. In the process a new species of alderfly Leptosialis necopinata sp. n. from the Eastern Cape and KwaZulu-Natal provinces of South Africa is recognised and described. Within Sialidae the new species most closely resembles Leptosialis africana. A key to the two species of Leptosialis using both adult and larval characters is provided.


introduction
The Afrotropical Megaloptera fauna have historically received very little attention and only four species of alderfly (Sialidae) are currently recognised: Sialis vanderweelei Aspöck & Aspöck, 1983 (Egypt), Protosialis afra Navás, 1936 andP. madegassa Navás, 1927 (Madagascar), and Leptosialis africana Esben-Petersen, 1920 (South Africa). Leptosialis Esben-Petersen was established from adult specimens collected in the Cedarberg Mountains of the Western Cape Province. Additional localities and illustrations were provided by Barnard (1931Barnard ( , 1940. Crass's (1949) description of putative larvae of L. africana used specimens collected in the Eastern Cape and KwaZulu-Natal provinces, approximately 1000 km from the type locality.
With very few specimens in museum collections, it is clear that these African alderflies are rarely encountered insects. The adults have historically been collected in summer amongst riparian vegetation associated with the still reaches of slow-flowing streams, and the larvae inhabit slow flowing streams with clay or silt substrates (Crass 1949, Mansell 2003. While examining the Iziko South African Museum and Albany Museum collections, two distinct phenotypes of putative L. africana adults were found, corresponding to the two disjunct regions from which they have been recorded. The specimens from the Eastern Cape and KwaZulu-Natal provinces are distinct enough from Western Cape L. africana to warrant recognition as a new species. Crass's (1949) larval material from the Eastern Cape and KwaZulu-Natal correspond to the new species.

Materials and methods
The specimens included in the present study are deposited in three collections: the Albany Museum, Grahamstown (AMGS), the Natural History Museum, London (NHM), and the Iziko South African Museum, Cape Town (SAMC). Label data for the specimens are presented in quotation marks; information from different labels is separated by a virgule (/), and information on different lines of a label is separated by commas. Information in square brackets clarifies or augments the often cryptic text on the specimen label(s) and provides their geographic coordinates.
Terminalia preparations were made by clearing the distal half of the abdomen in a cold, saturated potassium hydroxide (KOH) solution for 8-10 h. After neutralising the KOH with acetic acid and water, the distal half of the abdomen was transferred to glycerine for further dissection and examination. Following examination, the cleared terminalia was placed in a microvial containing glycerine and pinned beneath the specimen. The terminologies of venation and terminalia follow Wootton (1979) and Aspöck and Aspöck (2008), respectively. Wing and body measurements were made from photographs of whole specimens with reference to the photographed scale bar. Diagnosis. The adults of Leptosialis are characterized by the following morphological traits: the narrowly elongated forewing, which is about 3.0-4.0 times longer than wide; the distally branched Rs; the MA either unbranched, bifurcated or trifurcated; the MP distally branched or with one or both main branches bifurcated; the male 9 th tergum with a pair of posterolateral, digitiform processes; the paired ectoproct; the 11 th gonocoxite in caudal view ventrally with a pair of acute, hook-like processes. At present no characters can be used to distinguish the larvae of the genus Leptosialis from other alderfly genera, many of which currently lack larval description. Description. Adults (Figs 1-4). Forewing length ~8-11 mm in males; ~11-12 mm in females. Body: generally brown or blackish-brown. Head: antenna pilose approximately half the length of the forewing; ocelli absent, or represented by three very small tubercles on vertex; labrum ~4.0-5.0 times wider than long, lateral margins rounded, front margin slightly emarginated. Prothorax > two times wider than long. Legs: yellow or dark brown, bearing dense setae; tarsal claws reddish brown. Wings: Forewing 3.0-4.0 times longer than wide, minutely hirsute, margins pilose; costal area broadened basally; subcostal area with five to eight distinct costal crossveins proximally; sc-r absent; Rs distally branched, MA either unbranched, bifurcated or trifurcated, MP distally branched or with one or both main branches bifurcated, CuA bifurcated; three or four crossveins between R and Rs. Hindwing as broad or slightly broader than forewing, about 3.0 to 3.5 times as long as wide; two or three distinct costal crossveins proximally; venation similar to forewing, with three crossveins between R and Rs. Male genitalia: 9 th tergum transversely arched, with a pair of posterolateral, digitiform processes; ectoproct paired, small, roundly inflated ventrad; 11 th gonocoxite in caudal view ventrally with a pair of acute, hook-like processes. Female genitalia: 7 th sternum broad, posterior margin distinctly produced; 9 th gonocoxite broad, apex bearing small, stout gonostylus.
Larvae . Head: yellow to reddish brown. Thorax: pro-, meso-and metathorax orange to reddish brown, with distinct reticulated patterns of yellowish marks. Legs: pale yellow, bearing dense setae; tarsal claws reddish brown; Abdomen: dark purplish or blackish brown dorsally with paired, pale, submedian, comma-shaped marks on each segment; anal prolegs and hooked claws absent; elongated caudal filamentous appendage present; 7 pairs of pale yellow lateral abdominal gills present.
Remarks. The genus Leptosialis is the only representative of the Sialidae in South Africa. Because wing venation is quite different between the two Leptosialis species, it is difficult to find a stable morphological diagnosis for this genus. The male ninth tergum with a pair of digitiform processes could be the most important character to distinguish Leptosialis from its closely related genera, Stenosialis and Austrosialis. The two species may be distinguished using the following key.

Key to Leptosialis
1 Adults: (Figs 1, 2) Forewing narrowly rounded with MA and both branches of MP simple (Barnard 1931: fig. 12). Male: terminalia with 11 th gonocoxite broadly triangular dorsoventrally, with a pair of short, simple hook-like processes ventrally, visible in caudal view. Female: (Fig. 15) 8 th gonocoxite small, subtriangular. Larvae: (Fig. 22 Barnard / 1930-131" (NHM); 2 larvae (in alcohol), South Africa: Western Cape: Diagnosis. The adults of L. africana may be easily distinguished from adults of L. necopinata sp. n. by the shape and venation of the forewing, where the wings of L. africana are narrowly rounded compared to being broadly rounded to truncated in L. necopinata sp. n. In addition, the wings of L. africana show MA and both branches of MP all simple, while L. necopinata sp. n. has MA and one or both branches of MP all bearing additional forks. The larvae of L. africana may be distinguished by the reddish brown head and thorax dorsally with distinct yellowish marks that are lacking in L. necopinata sp. n.
Description. Adult male (Fig. 2). Forewing length 8.1 mm, hindwing length 7.0 mm (n = 1). Head (Fig. 5): pale to dark brown, frons and clypeus black; vertex with a pair of raised black vittae medially and several small, raised, black protrusions laterally. Compound eyes blackish brown, strongly produced. Antennae dark brown, pilose, approximately half the length of the forewing. Mouthparts yellowish brown, diminutive. Thorax (Fig. 5): entirely blackish brown. Legs yellow, bearing dense yellowish setae; coxae blackish brown; femora pale brown; 1 st -3 rd tarsomeres distally pale brown; 4 th and 5 th tarsomeres brown; tarsal claws reddish brown. Wings narrowly rounded, brown, slightly darker proximally; veins brown. Forewing nearly 4.0 times as long as wide; five to eight distinct costal crossveins proximally; sc-r absent; Rs distally branched, MA unbranched, MP distally branched, and CuA bifurcated; three or four crossveins between R and Rs. Hindwing slightly broader than forewing, about 3.5 times as long as wide; two or three distinct costal crossveins proximally; venation similar to forewing, with three crossveins between R and Rs. Abdomen: blackish brown. Terminalia (Figs 10-13) with 9 th tergum transversely arched, with a pair of digitiform processes posterolaterally that curve slightly ventromedially; anterior and posterior margins slightly concave arcuately in dorsal view; 9 th sternum slightly longer than 9 th tergum; posterior margin moderately produced; 9 th gonocoxite in lateral view nearly elliptical; ectoproct paired, small, roundly inflated ventrad; 11 th gonocoxite broadly triangular dorsoventrally, dorsal margin slightly sinuous in dorsal view, with a pair of short and acutely hook-like processes ventrally in caudal view.
Remarks. The type specimen was noted by Esben-Petersen in his description as male, but its abdomen and genitalia are now lost. This species of alderfly shows sexual dimorphism, with females being larger than males. Although it lacks an abdomen, the holotype is probably a female, based on comparison with confirmed male and female specimens, and contrary to the original description. Etymology. The specific epithet 'necopinata' is a feminine adjective in the second declension which refers to the Latin for unexpected or unforeseen, following the discovery of the adults strikingly different from L. africana and relating to the unforeseen occurrence of this second species in the relatively well-sampled waters of South Africa.

Leptosialis necopinata
Diagnosis. The adults of L. necopinata sp. n. may be easily distinguished from adults of L. africana in having broadly rounded to truncated wings compared to narrowly rounded wings in the latter species. In addition the forewing venation of L. necopinata sp. n. has MA and one or both branches of MP all forked distally, whereas those of L. africana are fused into three simple veins. The larvae of L. necopinata sp. n. can be distinguished from L. africana by the paler colouration of head and thorax, which lack distinct marks on the vertex and pronotum.
Description. Adult male (Fig. 3). Forewing length 10.6 mm, hindwing length 9.8 mm (n = 2). Head (Fig. 7) black, slightly pale brown surrounding posterior margin of compound eyes; vertex with a pair of raised black vittae medially, and several small raised black protrusions laterally Compound eyes blackish brown, strongly produced. Antennae blackish brown, pilose, approximately half the length of the forewing. Mouthparts blackish brown. Thorax (Fig. 8) entirely black. Legs dark brown throughout, bearing dense brown setae; tarsal claws reddish brown. Wings (Fig. 9) distally broadly rounded to truncate, brown, slightly darker proximally; veins brown. Forewing approximately 3.0 times as long as wide; proximally with five to eight distinct costal crossveins; sc-r absent; RS distally branched, MA bifurcated or trifurcated, MP with one or both main branches bifurcated, and CuA bifurcated, three or four crossveins between R and Rs. Hindwing as broad as forewing, about 3.0 times as long as wide; with two or three distinct costal crossveins proximally; venation similar to forewing, with three crossveins between R and Rs. Abdomen blackish brown. Terminalia (Figs 16-19) with 9 th tergum transversely arched, with a pair of digitiform processes posterolaterally that curve slightly ventromedially; anterior and posterior margins slightly arcuately concave in dorsal view; 9 th sternum slightly longer than 9 th tergum, posterior margin moderately produced; 9 th gonocoxite in lateral view nearly elliptical; ectoproct paired, small, roundly inflated ventrad; 11 th gonocoxite broadly triangular dorsoventrally, dorsal margin slightly sinuous in dorsal view, ventrally with a pair of acute hook-like processes in caudal view, in lateral view ventral processes with an anteriorly directed, hook-shaped accessory protuberance one third along its length.
Remarks. The larvae of L. necopinata sp. n. have been described in detail by Crass (1949).

Discussion
At first glance L. necopinata sp. n. appears to belong to the Australian endemic genus Stenosialis (Liu et al. 2008). However, the male genitalia of L. necopinata sp. n. are generally similar in structure to those of L. africana, confirming the taxonomic status of the new species within the genus Leptosialis. Although the forewing venation of L. necopinata sp. n. is similar to that of Stenosialis and Austrosialis based on the two-branched Rs, 2 or 3-branched MA, and 4-branched MP, the hindwing of L. necopinata sp. n. also has a four-branched MP, which is different from the always three-branched MP in both Australian genera (Liu et al. 2008). The diagnosis of the venation in L. necopinata sp. n. does not provide synapomorphies for Leptosialis because it may be a plesiomorphic ground plan of sialid venation, which is very similar to the earliest alderfly fossil, Dobbertinia reticulata Handlirsch, from the Lower Jurassic of Germany (Ansorge 2001). The venation of Sialidae genera is very conserved and indicative of symplesiomorphies (Flint 1973). A world revision of the genera using genitalic differences is needed to confirm placement of the genera and species. The possible synapomorphic character of Leptosialis might be the male 9 th tergum with a pair of digitiform posterior projections, although this character is also present in an extinct alderfly species Protosialis herrlingi Wichard (2002) from the Eocene Baltic amber. Further clarification on the phylogenetic status of Leptosialis awaits a rigorous study of the phylogeny of the world Sialidae.