Symbiocloeon Müller-Liebenau 1979

Kluge, Nikita J., Vishnevskaya, Maria S. & Palatov, Dmitry M., 2025, Winged stages of Symbiocloeon laoense Palatov 2023 (Ephemeroptera: Baetidae) and systematic position of larvae developing inside mantle cavities of bivalve mollusks, Zootaxa 5728 (2), pp. 287-320 : 289

Genus Symbiocloeon Müller-Liebenau 1979

( Figs 1–60 , 65 , 67–70 )

Symbiocloeon Müller-Liebenau (in Müller-Liebenau & Heard) 1979: 58 (larva).

Type species: Symbiocloeon heardi Müller-Liebenau (in Müller-Liebenau & Heard) 1979 .

Larva. Able for inhabitancy in mantle cavities of freshwater bivalve mollusks.

Both mandibles with prostheca stick-like, with setae between prostheca and mola ( Figs 1–4 ). Maxilla of « Cloeon - type » ( sensu Kluge 2017: 94), i.e. with distal dentiseta bent in same direction as canines and two other dentisetae ( Figs 5–6 ). Labial palp 2-segented, i.e. lacking boundary between initial 2nd and 3rd segments and lacking muscle going from 2nd segment to base of 3rd segment ( Figs 7–9 ).

Legs lacking long setae; two-channel setae of longitudinal row on outer-dorsal side of femur either very short ( Fig. 22 ), or absent; other setae not longer or absent. Femoral patch absent. Apex of femur with incision on anterior side, caused by the fact that anterior-outer projection is shortened and not reaching anterior-inner projection ( Fig. 25 ). Claws lacking denticles on proximal part; either without denticles, or with two rows of denticles in distal part only ( Figs 23, 24 , 68 ).

Scales on surface of abdominal terga either absent, or with opercula-bearing sockets (i.e., each socket with two operculae) ( Fig. 68 ). Caudalii with primary swimming setae, without secondary swimming setae.

Winged stages. Hind wings absent. Other characters of winged stages known for S. laoense only (see below).

Distribution and species composition. Includes 4 described species distributed in the Oriental Region: Symbiocloeon madhyasthai Subramanian & Sivaramakrishnan 2009 (known from Southern India), S. heardi Müller-Liebenau (in Müller-Liebenau & Heard) 1979 and S. corbiculinum Palatov (in Bespalaya et al.) 2023 (both known from Thailand) and S. laoense Palatov (in Bespalaya et al.) 2023 (known from Laos). Larvae of all these species develop in mantle cavities of freshwater clams (Malacozoa, Bivalvia). Among them, larvae of S. madhyasthai and S. heardi inhabit large clams belonging to the family Unionidae , and S. corbiculinum and S. laoense inhabit small clams Corbicula fluminea .

Figures

FIGURES 1–6. 1–2, left and right mandibles of Symbiocloeon corbiculinum (paratype); 3–6, Symbiocloeon laoense: 3–4, left and right mandibles; 5, maxilla; 6, apex of maxilla in pressed and broken condition, to show all canines and dentisetae. Abbreviations: can, 3 maxillary canines; ds1, ds2, ds3, dentisetae.

FIGURES 7–9. Symbiocloeon laoense: labium. 7, with focus on dorsal side; 8, with focus on ventral side; 9, view from dorsal side (hidden margins and muscles shown by interrupted lines).

FIGURES 10–13. Symbiocloeon laoense: larvae.

FIGURES 14–18. Symbiocloeon laoense: exuviae of last instar male larva. 14, abdominal terga; 15, abdominal sterna; 16, thoracic sterna and pleura with left legs; 17, head; 18, right half of pronotum and mesonotum.

FIGURES 19–22. Symbiocloeon laoense: larval legs. 19–21, fore, middle and hind legs (exuviae in dry condition, to show relief); 22, two-channel setae on anterior side of femur near outer margin (shown by arrow on Fig. 21).

FIGURES 23–25. Symbiocloeon laoense: larval legs. 23–24, claw; 25, apex of femur, view from anterior side.

FIGURES 26–29. Symbiocloeon laoense: subimaginal exuviae. 26, right half of mesonotum; 27, mesopleura; 28, abdominal terga and sterna; 29, fragment of abdominal tergum V.

FIGURES 30–35. Symbiocloeon laoense: subimaginal of legs. 30–31, fore leg of male; 32–33, fore leg of female; 34, hind leg; 35, tarsus of hind leg. Abbreviations: a.pt, apex of patella-tibial suture; pt, patella-tibial suture visible as stripe lacking microtrichia.

FIGURES 36–42. Symbiocloeon laoense: male imagines. 36–38, male imago reared from larva extracted from mollusk; 39–42, male imago reared from subimago collected at light; 40, abdomen; 41, fore leg; 42, middle leg.

FIGURES 43–47. Symbiocloeon laoense: male genitalia. 43–45, of male imago reared from subimago collected at light: 43, with focus on ventral side; 44, with focus on penis; 45, view in alcohol; 46, of male imago reared from larva extracted from mollusk, with focus on ventral side; 47, crumpled subimaginal gonostyli extracted from larva ready to molt. Abbreviations: gv, gonovectis; ms, median sclerite of styliger; m.sg, styligeral muscle; pb, penial bridge.

FIGURES 48–50. Symbiocloeon laoense: male genitalia. 48, imago; 49, subimago; 50, crumpled subimaginal gonostyli extracted from larva ready to molt. Abbreviations: g31, gs2, gs3, segments of gonostylus; gv, gonovectis; ms, median sclerite of styliger; m.sg, styligeral muscle; pb, penial bridge, us, unistyliger.

FIGURES 51–54. Symbiocloeon laoense: female imago. 51, ventral view; 52, dorsal view; 53, fore leg; 54, fore wing.

FIGURES 55–60. Symbiocloeon laoense: eggs. 55, general view; 56, papillae on chorion; 57–58, view from widest side; 59–60, view from stretched side.

FIGURES 63–66. Mollusk Corbicula fluminea. 63–64, young larva moving in mantle cavity; 65, last instar larva in mantle cavity; 66, mollusks in cage with running natural water, some individuals with opened siphons.

FIGURES 67–70. 67–69, larva of Symbiocloeon sp. 2 from Russian Far East: 67, claw; 68, abdominal tergum VII; 69, labium; 70, the same of Symbiocloeon sp. 1 from Myanmar.