Thereotricha BLAGODEROV & GRIMALDI 2004, new genus
Creators: name: BLAGODEROV, VLADIMIR
name: GRIMALDI, DAVID
Publisher: name: Zenodo
Year: 2004
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Diadocidiidae
Thereotricha

description: Thereotricha, new genus
DIAGNOSIS: Eyes forming incomplete eye bridge, facets large, round. Ocelli three. Flagellomeres barrel­shaped, length no more than 1.5Χ the width. Antepronotum and proepisternum subequal, setose. Proepimeron touches episternum at the episternal suture. Anepisternum smaller than katepisternum. Anepisternal cleft distinct, narrow. Midpleural pit present. Metepisternum setose. Anterior parapsidal suture distinct. Insertion of abdomen wide. Wing membrane with or without macrotrichia. Sc short, ends free. Rs base, r­m, base of M 3+4, and CuA fork very basal. Section M2 connects r­m and base of M 3+4 and CuA fork. M 3+4 reduced.
TYPE SPECIES: Thereotricha sibirica, n.sp.
ETYMOLOGY: The genus name is a feminine anagram of Heterotricha. The name is feminine.
COMMENTS: The new genus is close to the Heterotricha group of genera, which have been included in the Sciaridae or Diadocidiidae. Recently, Chandler (2002) reviewed known taxa of the group and described seven more genera from all zoogeographic regions except Nearctic. These taxa seem to represent a stem group of Recent families of Sciaroidea, but monophyly of the group is not apparent. The new genus differs from all taxa of the Heterotricha group in having eyes with large facets, that form an eye bridge, short antennae, the scape and pedicel not differing from flagellomeres in length, palpi very short, anepisternite and katepisternite subequal, the base of RS in basal position, and r­m and the section of M2 subequal, where eyes and palpi demonstrate an apomorphic condition. The new genus resembles Sciaropota Chandler in the porrect antenna with short flagellomeres, an absence of a clearly differentiated series of scutellar bristles, large katepisternum, mesepimepon broader below, but it differs by the short Sc, long stem of M 1+2, and reduced M 3+4.
Distinct synapomorphies separate the group from other Mesozoic Sciaroidea: M1 section completely reduced; M2 section fused with tb in one vein meeting the base of M 3+4, and that oblique vein is shifted distad. The same structure of the basal veins is observed in advanced representatives of the Mesozoic family Mesosciophilidae, which are thought to represent a sister group to Mycetophilidae (Kalugina and Kovalev, 1985; Blagoderov, 1993). Similar conditions occur in the peculiar Mesozoic family Archizelmiridae (Grimaldi et al., 2003), but Archizelmiridae have crossvein r­m aligned with M2 + tb and the basal portion of M 3+4, forming one horizontal vein and the base of RS is shifted distad. Diadocidiidae s.str. (Diadocidia and Docidiadia n.gen.) also have these veins aligned (r­m through the base of M 3+4), but they form a vertical vein. In Mycetophilidae the combined vein M2 + tb lost contact with the base of M 3+4 and meets the base of CuA or MA (arculus) (see Shcherbakov et al., 1995). Some Mycetophilidae (Drepanocercus, Ectrepesthoneura, Cretaceous Paradzickia, Drepanorzeckia, Ekhiritus, Zazicia) have the fork of M 3+4 and CuA sessile or short­stalked, but the base of the fork is situated more basally that in Mesozoic Sciaroidea and the Heterotricha group. Moreover, at least in Ectrepesthoneura the sessile fork of M 3+4 and CuA is secondary (see Analyses below and fig. 78). Obviously, reduction of M1 and fusion of M2 with tb might have originated several times in the history of Sciaroidea. Although monophyly of the group combining Recent Heterotricha ­ like taxa and Cretaceous Thereotricha is not proven, position of these taxa in sciaroid phylogeny should be at the base of lineages leading to Mesosoic Mesosciophilidae and Archizelmiridae and Recent Sciaridae on the one hand and higher sciaroids such as Mycetophilidae and Lygistorrhinidae on the oth­ er.
description: Published as part of BLAGODEROV, VLADIMIR & GRIMALDI, DAVID, 2004, Fossil Sciaroidea (Diptera) in Cretaceous Ambers, Exclusive of Cecidomyiidae, Sciaridae, and Keroplatidae, pp. 1-76 in American Museum Novitates 3433 (1) on page 9, DOI: 10.1206/0003-0082(2004)433<0001:FSDICA>2.0.CO;2, http://zenodo.org/record/4712338