Acentrella glareosa, Sroka, Pavel & Arnekleiv, Jo Vegar, 2010

Sroka, Pavel & Arnekleiv, Jo Vegar, 2010, Two new species of Acentrella Bengtsson, 1912 (Ephemeroptera, Baetidae) from Kazakhstan with notes on the Palaearctic fauna, Zootaxa 2693, pp. 1-20 : 2-12

Acentrella glareosa sp. nov.

Figs. 1–24

Mature larva (preserved in 75% EtOH) General coloration yellowish brown. Body length 4–5 mm.

Head yellowish with darker pattern consisting of small irregular spots, arranged in two rows. This pattern not apparent in mature male larvae because of presence of turbinate eyes in middle head portion. Head surface with hairs and tube scales, mainly on genae and clypeus. Genae highly developed and its size comparable with eyes ( Fig. 5 ). Antennae ca. 1.7 × length of head capsule. Inner margin of scape projected apicomedially, with numerous tube scales occurring on surface of this projected part. Similar scales present also on inner margin of pedicel. Incisors of right mandible ( Fig. 9 ) with seven bluntly pointed teeth. Outer margin with minor subapical tooth on ventral side. Right prostheca extended apically, with numerous sharp teeth. Left mandible incisors ( Fig. 8 ) with six major bluntly pointed teeth. Left prostheca apically extended, with mostly short blunt teeth and several pointed teeth on inner side. Maxillary palp ( Fig. 10 ) two-segmented, distal segment slightly longer than proximal one. Articulation between segments distinctly narrow. Proximal segment of maxillary palp enlarged apicomedially. Surface of maxillary palp with occasional hairs, distal segment with one apical scale, distinguishable with difficulty. Labrum ( Fig. 7 ) approximately 1.7 × wider than long, with 1+3–4 long submarginal setae. Only very sparse hairs occurring on dorsal side. One regular row of fringed setae, arranged in pairs, situated along anterior margin ( Fig. 13 ). Labial palp ( Figs. 11, 12 ) three-segmented, articulation between second and third segment indistinct. Second segment almost without apparent apicomedial projection. Shape of third segment regular, rounded. Ventral surface of labial palp covered with sparse hairs (first and second segment) and stout setae accompanied with hairs (third segment). Dorsal surface of labial palp with a group of 2–3 long setae on second segment. Paraglossae approximately 2 × wider than glossae. Apical part of paraglossae with 3 irregular rows of long, serrated setae.

Prothorax approximately 2.5 × wider than long, pale brown, with indistinct darker smudges laterally. Mesothorax of same basic color as prothorax, with several darker spots mainly frontally and medially. Forewing pads significantly extended sidewards. Both prothorax and mesothorax with occasional occurrence of hairs and tube scales. On mesosternum and metasternum presence of bluntly pointed appendages near bases of coxae. Hind wing pads ( Fig. 2 ) reduced to small posterolateral appendages of metathorax.

Legs ( Fig. 4 ) brownish, with darker coloration at proximal and distal parts of femora and tibiae. Tarsi and tarsal claws also darker brownish. Femora with one regular row of bilateraly ciliate bristles approximately as long as femur width along femoral posterior margin ( Figs. 4 , 14 ). Ciliae relatively long and dense ( Fig. 15 ). Dorsal surface of femora densely covered with hairs and tube scales in area near anterior margin (highest occurrence of tube scales near femur base, Fig. 20 ). Femoral villopore present, formed by flattened setae ( Fig. 16 ). Tibiae with two (dorsal and ventral) rows of ciliate bristles ( Figs. 4 , 17 ). Bristles of dorsal row approximately 1.6 × (forelegs and middle legs) and 2 × (hind legs) longer than tibia width. Bristles of ventral row shorter, aproximately 0.75 × (forelegs and middle legs) and 0.9 × (hind legs) as long as tibia width. Ventral row less regular than dorsal row, most developed in hind legs. Bristles of both tibial rows similar to femoral bristles, bilateraly ciliate with long and dense ciliae. Moreover, surface of tibia covered with sparse hairs (fringed and simple). Tarsi with one regular row of ciliate bristles (approximately 2 × longer than tarsal width) on outer margin ( Figs. 4 , 18 ). Structure of tarsal bristles same as tibial and femoral bristles. Surface of tarsus covered with sparse individual setae of two types (fringed and simple; Fig. 19 ). Tarsal claw with 7–8 denticles, diminishing proximally. One pair of vestigial subapical bristles present ( Figs. 21, 22 ).

Abdomen ventrally flattened (semicircular in cross section), terga approximately 1.3–1.4 × wider than respective sterna. Basic coloration of terga pale brown, with various darker patterns ( Fig. 1 ). Terga I–III pale, with only indistinct darkening in central part. On tergum IV, such darkening is situated along anterior margin only. Tergum V darker, with large pale spot centrally. On terga VI–VIII darker coloration prevails, although two lateral pale spots occur on each of these terga. Tergum IX rather pale, with darker stripe along anterior margin, tergum X darker. Two minor dark dots apparent on central part of terga II–V and VII–VIII. Surface of terga ( Figs. 23, 24 ) smooth, with sparse minute setae, tube scales missing. Posterior margin of terga ( Fig. 24 ) with tiny irregular multidentate projections accompanied with sparse hairs. Tracheal gills ( Fig. 6 .) always longer than corresponding segment (up to 2 × in gill pairs IV and V). 7 gill pairs present, individual gill plates white, without apparent tracheization, without serrated margins. Shape of individual gill plates oval, rather elongated. Sternal friction pads ( Fig. 3 ) well developed, consisting of numerous non-articulated multidentate scales. These scales arranged in two oblique elongated fields in the middle of surface on sterna II–IX. Further paired fields located along posterior margin of sterna IV–IX, size of these fields larger in more posterior segments. Paraproct surface also covered with non-articulated multidentate scales. Enlarged scales forming two or three irregular rows on posterior half of paraproct inner margin. Length of cerci unknown (broken in specimens studied), individual articulations accompanied with up to 4 rows of wide scales and several hairs. Row of hairs along inner margin present. Paracercus vestigial, one-segmented.

Type material. Holotype: mature male larva, Kazakhstan, Dzhungaria Region, River Borokhudzir, Arnekleiv leg.; paratypes (partly mounted on slides): 15 mature and 37 immature larvae.

Material is deposited in the Institute of Natural History, Museum of Natural History and Archaeology, Trondheim, Norway, (holotype, 26 paratypes) and in the collection of the Institute of Entomology, Academy of Sciences of the Czech Republic, České Budĕjovice (26 paratypes).

Description of the type locality. The larvae were found in the Borokhudzir River in Dzhungaria, southeastern Kazakhstan in August 1994. The locality is situated some 25 km north of the town of Kocktahl at an altitude of about 1200 m. The larvae were sampled from a riffle stretch with substrate mainly consisting of gravel (2–15 cm diameter) and stones (15–30 cm diameter). The river was about 20–40 cm deep at the location and 8–10 m wide. The stones were partially covered by attached green algae. Water temperature was 15.8 °C at the sampling time, pH ≥ 7.6 and the water conductivity was rather high (K25= 242 μS/cm).

Etymology. The name of the species points to the substrate of its habitat in the river–glarea/glareosus (Latin) means “gravel”.

Differential diagnosis. Acentrella glareosa sp. nov. lacks functional hind wing pads, thus it can be easily differentiated from all species with well-developed hind wing pads and functional hind wings in the adult stage.

Among the Central Asian species most resemblances can be found in A. sibirica ( Kazlauskas, 1963) . This species shares with A. glareosa sp. nov. mainly the shape of labium, arrangement of posterior margins of terga and the presence of vestigial paracercus. A. glareosa sp. nov. can be distinguished from A. sibirica by the different shape of maxillary palp (in A. sibirica without the medioapical protuberance on the first segment) and the arrangement of bristles on it’s legs (presence of the second ventral row of tibial bristles in A. glareosa sp. nov.; absence of ciliation on legs bristles in A. sibirica ). These characters are rather unique and also clearly differentiate the new species also from all other Acentrella species known so far.

Combination of the morphological characters distinguishing the larvae of Acentrella glareosa sp. nov. from the other representatives of the genus is summarized in Table 1 .

Mature larva (preserved in 75% EtOH).

Body length 4.5–6 mm.

Head yellowish with darker pattern consisting of small irregular spots, arranged in two rows. This pattern not apparent in mature male larvae because of presence of turbinate eyes in middle head portion. Surface of head with dense areas of tube scales (mainly on clypeus, genae and around eyes). Highly developed genae. Antennae ca. 1.5 × length of head capsule. Inner margin of scape slightly projected apicomedially, with numerous tube scales occurring on surface of this projected part. Similar scales present also on inner margin of pedicel. Labrum ( Fig. 29 ) approximately 1.5 × wider than long, with 1+5–7 long submarginal setae and regular row of fringed setae along anterior margin. Numerous tube scales in posterior half of dorsal surface. Both mandibles ( Figs. 30, 31 ) with incisors divided into seven bluntly pointed teeth. Right prostheca apically with numerous thin pointed teeth, apex of left prostheca with approximately four blunt teeth accompanied with several longer pointed projections. Maxillary palp ( Fig. 32 ) two-segmented, distal segment slightly longer than proximal segment. Articulation between segments not distinctly strangled. Both segments symmetric, cylindrical. Surface of maxillary palp with occasional hairs, distal segment without spines apically. Labial palp ( Figs. 33, 34 ) three-segmented, articulation between second and third segment indistinct. Second segment with only slightly developed apicomedial projection. Third segment asymmetric, conical. Ventral surface of labial palp covered with sparse hairs (first and second segment) and stout setae accompanied by hairs (third segment). Dorsal surface of labial palp entirely without hairs, only row of 3–4 setae on second segment present. Paraglossae approximately 2 × wider than glossae ( Fig. 34 ). Apical part of paraglossae with three irregular rows of long serrated setae.

Prothorax pale brown, with darker pattern laterally. Mesothorax of same basic color as prothorax, with several elongated darker spots situated mainly frontally and medially. Surface of prothorax and mesothorax densely covered with tube scales, mainly in areas of darker coloration ( Fig. 35 ). On mesosternum and metasternum presence of bluntly pointed appendages near bases of coxae. Hind wing pads fully developed ( Fig. 27 ).

Legs ( Fig. 26 ) brownish, with darker coloration at proximal and distal parts of femora and tibiae. Tarsi and tarsal claws also darker brownish. Femora in all leg pairs with one regular row of bilateraly ciliate bristles along posterior margin, approximately 0.5–0.6 × as long as femur width ( Figs. 41, 42 ). Dorsal surface of femora with large area of non-articulated multidentate scales in central part. Surface very densely covered with tube scales and hairs, mainly near anterior margin ( Fig. 44 ). Fermoral villopore present, formed by flattened setae ( Fig. 36 ). Tibiae with one (dorsal) regular row of long ciliate bristles. Bristles of this row 0.75 × (forelegs), 1 × (middle legs and hind legs) as long as tibia width. Moreover, surface of tibia covered with many tube scales and hairs ( Fig. 37 ). Outer margin of tarsus without regular row of bristles. Surface of tarsus covered with numerous tube scales and hairs ( Fig. 38 ). Tarsal claw with approximately 11 denticles of same shape, diminishing proximally. One pair of minute subapical bristles present.

Abdomen ventrally flattened (semicircular in cross section), terga approximately 1.7–1.8 × wider than respective sterna. Basic coloration pale brown with darker patterns ( Fig. 25 ). All terga with darker coloration situated along all its margins. Anterior and posterior darker stripes can extend in the middle and fuse, dividing central pale area into two lateral spots (terga I, II, VI, VII, VIII). A thin pale stripe can occur in the middle of such central darkening (terga VII, VIII). Tergum IX colored rather exceptionally, with darker stripe along anterior margin only. Two minor dark dots apparent on central part of terga V–VIII. Surface of terga covered with small, pointed, non-articulated projections and huge number of tube scales ( Figs. 39, 40 ). Posterior margin of terga ( Fig. 43 ) with row of tiny irregular multidentate projections. Tracheal gills ( Fig. 28 ) always longer than corresponding segment (up to 1.5 × in gill pairs IV and V). Seven gill pairs present, individual gill plates white, without apparent tracheization, without serrated margins. Shape of individual gill plates oval, approximately 1.5 × longer than wide. Sternal friction pads, consisting of numerous non-articulated multidentate scales covering whole surface of sterna. Paraproct with all surface covered with similar scales, inner margin without distinct teeth. Length of cerci 3–3.5 mm (2/3 of body length). Individual articulations accompanied with rows of scales and occasional hairs. Row of hairs along inner margin present. Paracercus vestigial, one-segmented.

Type material. Holotype: mature male larva, Kazakhstan, Dzhungaria Region, tributary of Borokhudzir River, Arnekleiv leg.; paratypes (partly mounted on slides): 4 mature and 1 immature larvae.

Material is deposited in the Institute of Natural History, Museum of Natural History and Archaeology, Trondheim, Norway (holotype, 3 paratypes) and in the collection of the Institute of Entomology, Academy of Sciences of the Czech Republic, České Budĕjovice (2 paratypes).

Description of the type locality. The larvae were found in a small tributary brook to the Borokhudzir River in Dzhungaria, southeastern Kazakhstan in June 1995. The locality is situated on the northern slopes of the Borokhudzir River valley at an altitude of about 1800 m. The surroundings were mostly grazing land and the location was about 1 km from the confluence to River Borochudzir. The brook was spring-fed, about 10– 20 cm deep and had a water velocity of 10–30 cm /s at the sample location. The brook was 0.5–1.5 m wide and the subtratum consisted of gravel (2–10 cm diameter) and small stones (10–20 cm diameter). The stones were very slippery according to a film of brownish-green attached algae. The water chemistry was probably influenced by runoff from the cattle-grazed surroundings, but unfortunately we do not have any water chemistry data from this brook. A more detailed description of the area is given in Dolmen et al. (1997).

Etymology. The name of the species refers to the nature of its habitat– charadra (Greek) means “mountain stream, torrent”.

Differential diagnosis. Acentrella charadra sp. nov. posses developed hind wing pads and can be easily recognized from all species with vestigial or absent hind wing pads (and therefore missing hind wings in the adult stage).

Acentrella charadra sp. nov. shows unique characters differentiating the species from all other representatives of the genus with developed hind wing pads. The most obvious morphological characters distinguishing the larvae of A. charadra sp. nov. are the presence of subapical bristles on tarsal claws, the shape of leg bristles (bilateraly ciliate on femora and tibiae, row of tarsal bristles missing) and vestigial paracercus. A. charadra also shows a unique arrangement of labial palp, elongated in comparison with other Acentrella species, with an apparent (although still relatively poorly developed in comparison with many Baetis species) apicomedial projection on the second segment.

All other important diagnostic characters are summarized in the Table 1 .

Figures

FIGURES 1 – 6. Acentrella glareosa sp. nov., larva: 1, color pattern of the body; 2, hind wing pad; 3, sternal friction pads extent; 4, hind leg; 5, head; 6, gill plates I – VII.

FIGURES 7 – 12. Acentrella glareosa sp. nov., larva: 7, labrum; 8, left mandible incisors; 9, right mandible incisors; 10, maxillary palp; 11, labium, ventral view; 12, labial palp, dorsal view.

FIGURES 13 – 18. Acentrella glareosa sp. nov., larva (SEM photographs): 13, anterior margin of labrum; 14, posterior margin of femur; 15, detail of ciliation of femoral bristles; 16, femoral villopore; 17, rows of tibial ciliate bristles; 18, row of tarsal ciliate bristles.

FIGURES 19 – 24. Acentrella glareosa sp. nov., larva (SEM photographs): 19, surface of tarsus; 20, tube scales on dorsal surface of femur; 21, apical part of tarsal claw; 22, detail of vestigial subapical bristles; 23, surface of terga; 24, posterior margin of terga.

FIGURES 25 – 34. Acentrella charadra sp. nov., larva: 25, color pattern of the body; 26, hind leg (tube scales not depicted); 27, hind wing pad; 28, gill plates I – VII; 29, labrum; 30, left mandible incisors; 31, right mandible incisors; 32, maxillary palp; 33, labial palp, dorsal view; 34, labium, ventral view.

FIGURES 35 – 40. Acentrella charadra sp. nov., larva (SEM photographs): 35, surface of prothorax; 36, femoral villopore; 37, surface of tibia; 38, surface of tarsus; 39, surface of terga; 40, surface of terga, detail.

FIGURES 41 – 44. Acentrella charadra sp. nov., larva (SEM photographs): 41, posterior margin of femur; 42, detail of ciliation of femoral bristles; 43, posterior margin of terga; 44, tube scales on femur.

Tables

TABLE 1. Summary of morphological diagnostic characters of Acentrella glareosa sp. nov. and Acentrella charadra sp. nov. For detailed description of individual characters see text.

Character	Acentrella glareosa sp. nov.	Acentrella charadra sp. nov.
1. labrum–number of long submarginal setae	1+3–4	1+5–7
2. labrum length/width ratio	1.7	1.5
3. maxillar palp–apicomedial enlargement of first segment	present	absent
4. labial palp–apicomedial projection of second segment	nearly absent	slightly developed
5. labial palp–shape of third segment	symmetric, rounded	asymmetric, conical
6. labial palp–number of setae on dorsal side of second segment	2–3	3–4
7. number of rows of bristles on paraglossa	3	3
8. leg bristles ciliation	bilateraly ciliate	bilateraly ciliate
9. femoral bristles	present, as long as femur width	present, 0.5–0.6 × as long as femur width
10. tibial bristles–dorsal row	present, 1.6 × (forelegs and middle legs) and 2 × (hind legs) longer than tibia width	present, 0.75 × (forelegs), 1 × (middle legs and hind legs) as long as tibia width
11. tibial bristles–ventral row	present, 0.75 × (forelegs and middle legs) and 0.9 × (hind legs) as long as tibia width	absent
12. tarsal bristles	present, 1.5 × longer than tarsus width	absent
13. subapical bristles on tarsal claw	vestigial	present
14. number of denticles on tarsal claw	7–8	11
15. hind wing pads	vestigial	functional
16. surface of terga	smooth, with sparse minute setae, tube scales missing	covered with small, pointed, non- articulated projections and huge number of tube scales
17. posterior margin of terga	multidentate projections	multidentate projections
18. sternal friction pads	small, distinctly bordered	covering all sternal surface
19. number of gill pairs	7	7
20. marginal teeth on paraproct	absent	absent
21. paracercus	vestigial, one-segmented	vestigial, one-segmented
Acentrella charadra sp. nov. Figs. 25–44