Symbiocloeon, Muller-Liebenau & Heard, 1979
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publication ID |
https://doi.org/10.11646/zootaxa.5728.2.3 |
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publication LSID |
lsid:zoobank.org:pub:DEDCEEF6-772A-44F1-B314-A7C466EDED33 |
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persistent identifier |
https://treatment.plazi.org/id/03CD87BD-3D74-FF95-A4FF-FB7BBD65F884 |
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treatment provided by |
Plazi |
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scientific name |
Symbiocloeon |
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Position of Symbiocloeon View in CoL View at ENA within Baetungulata
Difference between Symbiocloeon and Baetofemorata. The taxon Baetofemorata Kluge & Novikova 2011 comprises most part of Baetungulata; it has the following characters: (1) Femoral patch is always present (the same in some Labiobaetini ). (2) Inner margin of both mandibles between prostheca and mola always lacks setae. (3) If larval abdominal terga and other body parts bear wide scales, sockets of these scales are semicircular, lacking side operculae. (4) On all legs of subimago each tarsal segment is covered mainly by blunt microlepides; only in distal parts of segments pointed microlepides can be present ( Kluge 2022). (5) In mature larva ready to molt to subimago, developing subimaginal gonostyli are folded under larval cuticle either by the « Baetis - type », or the « Acentrellatype » (see above); in these cases both 2nd and 3rd segments of gonostylus are directed medially.
No one of these characters occurs in Symbiocloeon : (1) In all known species of Symbiocloeon femoral patch is absent. (2) Both mandibles bear setae between prostheca and mola ( Figs 1–4 View FIGURES 1–6 ). (3) In that species of Symbiocloeon , which abdominal terga retain scales, sockets of these scales have well-developed side operculae ( Fig. 68 View FIGURES 67–70 ). In S. corbiculinum and S. laoense these scales and their sockets are completely lost. (4) In the single species with known subimago ( S. laoense ), the last tarsomere is entirely covered with pointed microlepides ( Fig. 35 View FIGURES 30–35 ). (5) In the single species, which development of subimaginal gonostyli is known ( S. laoense ), the gonostyli are folded by the « Nigrobaetis - type », i.e. with apices of 2nd segments directed laterally ( Figs 47 View FIGURES 43–47 , 50 View FIGURES 48–50 ).
Difference between Symbiocloeon and Labiobaetini . The large tribe Labiobaetini Kluge & Novikova 2016 belongs to Baetungulata and has the following characters: (1) In male imago sterno-styligeral muscle is completely lost. (2) In mature larva ready to molt to subimago, developing subimaginal gonostyli are folded under larval cuticle either by the « Labiobaetis - type », or the « Acentrella- type » (see above); in these cases both 2nd and 3rd segments of gonostylus are directed medially.
No one of these characters occurs in Symbiocloeon : (1) In the single species with known male imago ( S. laoense ), the sterno-styligeral muscle is retained ( Fig. 43 View FIGURES 43–47 ). (2) In the single species, which development of subimaginal gonostyli is known ( S. laoense ), the gonostyli are folded by the « Nigrobaetis - type », i.e. with apices of 2nd segments directed laterally ( Fig. 47 View FIGURES 43–47 , 50 View FIGURES 48–50 ).
Difference between Symbiocloeon and Indobaetis . The small Oriental genus Indobaetis Müller-Liebenau & Morihara 1982 has the following characters ( Kluge & Novikova 2014): (1) On fore leg of female subimago and imago 1st tarsomere is completely fused with 2nd tarsomere, so the tarsus is 4-segmented, like tarsi of middle and hind legs. (2) In mature larva ready to molt to subimago, developing subimaginal gonostyli are folded under larval cuticle by the « Labiobaetis - type », with 2nd and 3rd segments of gonostylus directed medially.
No one of these characters occurs in Symbiocloeon : (1) In the single species, which female subimago and imago are known ( S. laoense ), tarsus of fore leg is 5-segmented ( Figs 32 View FIGURES 30–35 , 53 View FIGURES 51–54 ), as on fore leg of male ( Fig. 30 View FIGURES 30–35 ), and in contrast to middle and hind legs ( Fig. 34 View FIGURES 30–35 ). (2) In the single species, which development of subimaginal gonostyli is known ( S. laoense ), the gonostyli are folded by the « Nigrobaetis - type », i.e. with apices of 2nd segments directed laterally ( Figs 47–50 View FIGURES 43–47 View FIGURES 48–50 ).
Comparison of Symbiocloeon and Nigrobaetis . The Arctogean genus Nigrobaetis Kazlauskas (in Novikova & Kluge) 1987 is distributed in Holarctic, Oriental and Afrotropical Regions. Its larvae differ from most other Baetidae and most other mayflies by characteristic shape of head, with antennae bases brought together and the frons forming elevated longitudinal carina between them (Kluge & Novikova 1987: figs 1. 14, 1. 16). The same feature is found in Indobaetis and some Neotropical taxa.
Larvae of Symbiocloeon do not have this character: their frons is not carinate, and antennal bases are widely separated ( Bespalaya et al. 2023: figs 6B, 12A). Other characters of Symbiocloeon are either in agreement with that of Nigrobaetis , or represent apomorphies which can be derived from the structures belonging to Nigrobaetis . Possibly, shape of larval head was secondarily changed in Symbiocloeon , in connection with general flattening of the body adopted for inhabitance in mantle cavity of mollusks.
The genus Nigrobaetis is divided into subgenera Nigrobaetis s.str., Takobia Novikova & Kluge 1987 (= Alainites Waltz & McCafferty (in Waltz, McCafferty & Thomas) 1994 and Margobaetis Kang & Yang (in Kang, Chang & Yang) 1994 (see below).
Comparison of Symbiocloeon and Margobaetis . The subgenus Margobaetis is distributed mostly in the Oriental and Afrotropical Regions with a few species in southern Palaearctic; it is characterized by a peculiar structure of eggs, which have one side stretched cone-shapely ( Figs 73–74 View FIGURES 71–74 ) ( Kluge et al. 2024). The same egg structure occurs in the single examined species of Symbiocloeon , S. laoense ( Figs 55–60 View FIGURES 55–60 ; 71–72 View FIGURES 71–74 ).
Comparison with Nigrobaetis ( Margobaetis) minutus . The Oriental species Nigrobaetis ( Margobaetis) minutus ( Müller-Liebenau 1984) , has special similarity with Symbiocloeon laoense in egg structure ( Figs 71–74 View FIGURES 71–74 ; compare also Figs 55–60 View FIGURES 55–60 with Kluge et al. 2024: figs 39–43).
These two species have also similarity in structure of male imaginal genitalia (compare Figs 43–46 View FIGURES 43–47 with Kluge et al. 2024: figs 35–37). This similarity is caused by similar shape of the gonovectes, similar shape of the gonostyli with elongate terminal segment, similar median sclerotized projection of the penial bridge, and similar median styligeral sclerite located between the unistyligers. Among these features, the sharp bent of gonovectes is characteristic for Baetovectata, and their shape is usual among Baetovectata; the elongate distal segments of gonostyli is usual for Nigrobaetis and some other taxa; the median projection of penial bridge and the presence of median styligeral sclerite are species-specific characters. Similar median projection of penial bridge is well known as a species-specific character of some non-related baetid species belonging to various genera.
The median styligeral sclerite is less known. One of autapomorphies of Baetidae is reduction of median part of male imaginal styliger, so that the styliger is transformed into a pair of unistyligers with incision between them; the unpaired median sterno-styligeral muscle is terminated on integument of this incision ( Kluge & Novikova 2011: p. 5, fig. 3). In some baetids, the incision between unistyligers bears a distinctly outlined, sclerotized and pigmented median styligeral sclerite, on which the unpaired median sterno-styligeral muscle is terminated. This sclerite is present in various representatives of the plesiomorphon Protopatellata (Kluge 2018: fig. 46, 49, 51) and in a few Anteropatellata.Among Anteropatellata, the median styligeral sclerite is present in Cheleocloeon truncifolium Kluge 2016 ( Kluge 2016a: fig. 110), but absent in other species of the genus Cheleocloeon ; it is present in Centroptella ornatipes Kluge 2021 ( Kluge 2021: figs 149–150), but absent in other species of the genus Centroptella ; it is present in Nigrobaetis ( Margobaetis) minutus ( Müller-Liebenau 1984) ( Kluge et al. 2024: figs 35, 37), but absent in other species of the genus Nigrobaetis . The median styligeral sclerite is present also in Symbiocloeon laoense ( Figs 43 View FIGURES 43–47 , 48 View FIGURES 48–50 ).
All features of larvae and imagines other than the egg structure and the structure of male imaginal genitalia, are quite different in Nigrobaetis ( Margobaetis) minutus (see Kluge et al. 2024) and Symbiocloeon laoense (see above and Bespalaya et al. 2023).
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