Dryopoidea, Billberg, 1820

Tihelka, Erik, Jäch, Manfred A., Kundrata, Robin, Li, Yan-Da, Engel, Michael S., Lozano-Fernandez, Jesus, Huang, Diying & Cai, Chenyang, 2022, Mastigocoleidae fam. nov., a New Mesozoic Beetle Family and the Early Evolution of Dryopoidea (Coleoptera), Insect Systematics and Diversity 6 (3), pp. 1-18 : 13-14

Dryopoidea

The monophyly of Mastigocoleidae is supported by the following conspicuous characters: 1) antennae with 11 antennomeres, not pectinate or clubbed, with basal antennomere distinctly broadest, antennomere II shortest, and antennomeres II–XI more or less distinctly gradually, but noticeably, tapering toward the apex (more distinct in Mastigocoleus , less so in Cretaceocoleus ); 2) apical maxillary palpomere not expanded apically and distinctly diagonally truncate; 3) compound eyes with interfacetal setae; 4) head without subantennal grooves; 5) anterior edge of prosternum forming a chin-piece; 6) prosternal process curved and tapering apically, much shorter than the prosternal distance; and 7) mesocoxae longitudinally oriented, separated by less than their width. These characters are further elaborated on below.

(1) The shape of antennae seen in Mastigocoleidae , with antennomere I widest and longest, and the remaining antennomeres not modified and gradually tapering apically, is unique within Dryopoidea and likely within the whole of?oleoptera. Accordingly, it represents the most distinctive putative apomorphy of the group. The most similar antennal morphology to the one observed in Mastigocoleidae is present in some members of the small dryopoid family?helonariidae. However, the chelonariid genera Chelonarium Fabricius, 1801 and Pseudochelonarium Pic, 1916 have their basal antennomeres dilated and the remainder of the antennomeres of subequal width, which differs from Mastigocoleidae where antennomeres taper toward the apex gradually. The new fossil family also differs from?helonariidae in not having enlarged antennomeres III and IV that fit into a cavity of the mesoventrite. However, the enlargement of the basal antennomeres is notably present in Dryopidae and Lutrochidae . Antennomere I or antennomeres I and II are enlarged in Dryopidae , while in Lutrochidae both antennomeres I and II are always enlarged. However, both Dryopidae and Lutrochidae usually have the remaining antennomeres, forming a serrate club, which is certainly not the case in Mastigocoleidae . Unlike Dryopidae and Lutrochidae , Mastigocoleidae have antennomere II shortest of all antennomeres, and the antennae are long, extending well beyond the posterior pronotal margin.

(2) Another notable diagnostic character of the family is the shape of the fourth maxillary palpomere. While it is cylindrical, subulate, or slightly expanded and truncate apically in most species of Dryopoidea ( Lawrence 1982) , mastigocoleids have the apical palpomere roughly subcylindrical but obliquely truncate apically. Within Dryopoidea , this condition is most similar to that in Lutrochidae , where palpomere IV is slightly expanded and truncate to subtriangular apically. In Dryopidae , the terminal palpomere is always cylindrical to fusiform.

(3) Within Dryopoidea , the presence of interfacetal setae is restricted to Dryopidae , Lutrochidae , and Mastigocoleidae . All other dryopoid families lack setose compound eyes, at least in their groundplan. the antennae, contrary to what can be observed in Lutrochidae and Dryopidae , where such grooves are at least faintly present. The presence of antennal grooves may be associated with the shortening of antennae observed in aquatic dryopoids, which is not the case in Mastigocoleidae .

(5) All three families share a distinctly produced anterior edge of the prosternum forming achin-piece, which is otherwise rare in Dryopoidea and occurs only in some Psephenidae (some Eubriinae ), Elmidae , Protelmidae , Limnichidae , and Heteroceridae ( Lawrence et al. 1999) .

(6) The prosternal process of mastigocoleids is elongate, extending well beyond the procoxae and fitting into a mesoventral cavity. The prosternal process is equally wide throughout but becomes less ventrally protruding toward the apex and curves dorsad. This condition is distinct from Lutrochidae where the prosternal process is about as wide as long and beaded laterally. The prosternal process is more variable in Dryopidae , but the process is always shorter than the precoxal prosternal distance. In Mastigocoleidae , the prosternal proces is much shorter than the precoxal prosternal distance.

(7) Mesocoxae are always transverse in Dryopidae , they are circular to slightly transverse in Lutrochidae . The mesocoxae of Mastigocoleus and Cretaceocoleus are longer than wide. Although the degree of mesocoxal separation differs in the two mastigocoleid genera, it never exceeds two thirds of the mesocoxal width. Mesocoxae are always widely separated in Lutrochidae , while in Dryopidae , they are narrowly to moderately separated.