Contribution to the knowledge of psammophylous representatives of Procloeon Bengtsson 1915—Psammonella Glazaczow 1987 and Pseudocentroptiloides Jacob 1987 (Ephemeroptera: Baetidae)

The taxon Procloeon Bengtsson 1915, which is treated here at a genus rank, is characterized by one greatly enlarged denticle on the posterior margin of each cercomere in the distal part of the cercus. For the first time, this character is illustrated for Procloeon (Pseudocentroptiloides) shadini (Kazlauskas 1964), Procloeon macronyx (Kluge & Novikova 1992), P. heterophyllum (Kluge & Novikova 1992), P. pulchrum (Eaton 1885), P. albisternum (Novikova in Tshernova et al. 1986), P. pennulatum (Eaton 1870), P. chinensis (You & Gui 1995) and P. maritimum (Kluge 1983). Certain representatives of Procloeon and one species of a non-related genus Cheleocloeon Wuillot & Gillies 1993 have similar modifications of larval claws and mouth parts, which independently evolved as adaptation to inhabitance of stream bottoms mostly consisting of clean sand. Among Procloeon, such psammophylous specialization is characteristic for the subgenera Securiops Jacobus et al. 2006, Psammonella Glazaczow 1987 and Pseudocentroptiloides Jacob 1987; selected features of this specialization occur in some species formally placed in the subgenus Procloeon s. str., such as Procloeon macronyx (Kluge & Novikova 1992). Procloeon (Securiops) primasia (Kaltenbach et al. 2023) is reported here from the river Mekong in Laos for the first time. The subgenus Psammonella is characterized not only by loss of hind wings (as reported in its original description), but also by a unique modification of maxillae. Besides two formally known species of Psammonella, 4 new species are described here. Procloeon (Psammonella) magnificum sp. nov. is described from Sri Lanka based on larvae, reared subimagines and imagines of both sexes and eggs. Procloeon (Psammonella) diplofolium sp. nov. is described from Thailand based on larvae and reared female subimagines. Procloeon (Psammonella) mekongiense sp. nov. is described from Laos based on larvae and a female subimago extracted from larva. Procloeon (Psammonella) flavonigrum sp. nov. is described from India based on larvae and a male subimago extracted from larva. A new species Procloeon (subgen. ?) furcalabrum sp. nov. is described based on a single larva from Thailand; its labrum and hypopharynx resemble those of Psammonella and Pseudocentroptiloides, but maxillae and labium retain plesiomorphic structure. The older species names proposed for Procloeon macronyx (Kluge & Novikova 1992) and Procloeon (Pseudocentroptiloides) shadini (Kazlauskas 1964) are discussed. It is proposed not to use the names originally published as Centroptilum romanicum Bogoescu 1949 and Centroptilum nana Bogoescu 1951, regarding them instead as nomina dubia, because they were originally based on doubtfully associated sets of individuals; no holotypes were designated; and the specimens used by Bogoescu are not preserved.