Corethrella (Fossicorethrella) cretacea Szadziewski, 1995

Published, First, 2008, The Frog-Biting Midges of the World (Corethrellidae: Diptera), Zootaxa 1804, pp. 1-456 : 199-200

Corethrella (Fossicorethrella) cretacea Szadziewski

Corethrella cretacea Szadziewski 1995:178 . Type-locality: Lebanon. Holotype ď (STNS).

DIAGNOSIS: Male adult: only extant or fossil species of Corethrella with base of fifth tarsomere of each leg swollen (Fig. 75A). Female adult: unknown.

DESCRIPTION: Male adult. Habitus as in Fig. 112B. Descriptive statistics: see Tables 2–5. Head: Outline in anterior view uncertain. Number of large setae on frons between ventromedial area of ommatida uncertain. Antenna: pedicel without more elongate, stout, dorsal or dorsolateral setae; flagellomeres as in Fig. 1 in Szadziewski (1995); sensilla coeloconica not visible; flagellomere 13 rounded apically. Clypeus, palpus not visible. Thorax: Posterior portion of dorsocentral row with 2 elongate setae situated somewhat lateral to one another. Prescutal suture uncertain. Anterior anepisternum large, likely divided diagonally but uncertain. Shape of posterior anepisternum uncertain. Posterior anepisternum, anepimeron each with one setal socket. Wing: Only bases present. Basal veins denuded of setae and/or scales. Legs: Mostly denuded of setae, with patch of whip-like setae on posterior portion of hind tibia. Midleg without thick, subapical setae on each of tarsomeres 1–3. Apices of fore-, midleg fifth tarsomeres undivided, with claws slightly subapical to apical (Fig. 75A). Midleg femur slightly thicker than that of hind leg, possibly equal to that of foreleg (some distortion present). Midleg tibia with well-developed apical spur. Claws of each leg equally elongate. Each claw with inner tooth. Anterior claw of each of foreleg, midleg with a basal prong. Foreleg third tarsomere longer than fourth tarsomere. Empodia slender. Genitalia ( Fig. 8 in Szadziewski 1995): Gonocoxite gently tapering; anteromedial area with spicules similar in length to those elsewhere on gonocoxite; without well-defined dorsal row of setae. With 3 stout dorsomedial setae grouped near apex of gonocoxite, all tapering from base. Gonostylus (in extended position) curved, thick, expanded to rounded apex; subbasal seta uncertain; with thick apical peg. Aedeagus uncertain.

Female adult and immatures. Unknown.

DISTRIBUTION AND BIONOMICS: Corethrella cretacea is known only from Lebanese amber (Fig. 139), dated at 121 million years old. The foreleg tarsomeres of a second male are lying anterolaterally of the holotype thorax and are indistinguishable from that of the holotype and likely that of another Corethrella cretacea . The presence of two males in close proximity of one another in a single piece of amber suggests that this species formed swarms. There is another separate portion of a leg posterior to the holotype which is likely tarsomeres 1–3 of a Corethrella , but its exact identity is uncertain.

TAXONOMIC DISCUSSION: This species was well described by Szadziewski (1995) but a better understanding of the variation among fossil and extant species of Corethrella in this study made its partial redescription necessary here. Corethrella cretacea represents the earliest lineage of Corethrella known and its phylogenetic placement is discussed below.

Szadziewski (1995) suggested that the elongate empodia of the male of C. cretacea was unique within the Culicomorpha but it is actually present in nearly all other Culicomorpha . Nearly all other species of Corethrella also have empodia which are proportionally about as long as that of C. cretacea . These other Corethrella , with shorter claws, have empodia that are also nearly as long as their claws. This feature is discussed further in the phylogenetic analysis of the genus below. Szadziewski (1995) also indicated that the wing veins had setae but I was unable to locate any (the wing appeared denuded).

Szadziewski (1995) identified a median structure lying between the bases of the gonocoxites as the aedeagus. I was unable to clearly interpret this feature. It may be the aedeagus but almost might be a portion of segment 10 (bearing the anus) which is a sclerotized somewhat cone-shaped structure in male adults of extant Corethrella species. Considering that C. cretacea is the sister group of all remaining Corethrella , this structure might also be an elongate paramere or a subbasal lobe of the gonocoxite, present in other Culicomorpha but not present in other Corethrella .

The single male holotype is partially cleared and generally in good condition. The body is nearly devoid of setae and the wings are represented only by their bases.

MATERIAL EXAMINED: Holotype, adult male, tarsomeres of foreleg of second male, tarsomeres of additional Corethrella , all in a single piece of amber embedded in epoxy, stored in plastic box with labels “Lebanese amber C61/12 Diptera : Corethrellidae Corethrella cretacea Szadziewski sp. n., holotype ♂ ”, “Staatl. Museum für Naturkunde Stuttgart” ( STNS).

DERIVATION OF SPECIFIC EPITHET: The name cretacea refers to the age of the fossil.