Americanura Cassagnau, 1983

Arango, Ángela, Villagomez, Fernando & Palacios-Vargas, José G., 2017, On the genus Americanura Cassagnau, 1983 (Collembola: Neanuridae: Sensillanurini) with description of a new Mexican species and complement to the description of A. mexicana Cassagnau, 1983, Zoosystema 39 (1), pp. 49-54 : 50-51

Genus Americanura Cassagnau, 1983

TYPE SPECIES. — Americanura mexicana Cassagnau, 1983 .

DIAGNOSIS. — 2 + 2 dark pigmented eyes. Lack of any hypodermic body pigment. Reduced mouthparts, maxillae styliform. Antennal sensillum S7 on Ant. IV hypertrophied, at least twice the thickness of all the other S sensilla. Posterior cephalic setae in two groups, one dorsointernal (Di1) isolated from one to three other (Di2 plus De1 and De2). Seta De2 located behind Di2. Dorsolateral (DL) tubercle usually separately and with two setae. Lateral and subocular cephalic tubercles (L + So) difficult to distinguish. Dorsointernal tubercle (Di) and Di setae of prothorax (Th. I) always absent; tubercle De of Th. I with one or two setae and always one seta on tubercle DL. Tubercle Di of Abd. IV and V with one or two setae. Tubercle DE, DL and L of Abd. V often fused with reduced chaetotaxy. Six or eight crenulated setae between sensory setae on Abd. IV, and four or two setae between sensory Abd. V. Dorsal setae crenulated or barbulated, rarely palmate.

REMARKS

The sensorial setae of the body are very stable in all the members of the tribe, Americanura and the related genera Palmanura Cassagnau, 1983; Sensillanura Deharveng, 1981 and Tabasconura Palacios-Vargas & Catalán, 2015 . For the characterization of the members of these taxa it has been used mainly the dorsal chaetotaxy and sometimes the fusion of the cuticular tubercles, which sometimes is difficult to do because the low development they can have.

Some chaetotaxy characters in Americanura are very stable when the presence vs absence is taken into account, as we have realized after a comparison of 21 named valid species plus the new one described here and two further under preparation (Vázquez pers. comm.). Besides the tribe diagnostic morphology, the genus has always the cephalic setae F, G, B, Ocm, and Di1. Nevertheless, the seta G very rarely can lack but can be overlooked because it is always a tiny seta. The seta A, is found only in half of the species, Oca is present only in 25% of the cases and Ocp is lacking in 20%. The De tubercle has one seta (14 cases), two setae (three cases) or three setae (seven cases). Sometimes the microsetae (Di2 and De2) can be asymmetrically present. The combination of cephalic setae can be diagnostic for most species. In the dorso-external tubercle on Th. I, there is one seta (nine cases) or two setae (15 cases). On dorso-internal tubercle of Th. II, nine species had one seta, 13 had three setae and only two presented two setae. The dorso-external tubercle of Th. II has two setae in most of the taxa (15) and one in nine species, and the DL tubercle of the same thoraxic segment has one seta (three cases), two setae (seven) or three setae (14). A similar condition happens on Th. III. The abdominal segments I to III have always the same chaetotaxy, Di and De tubercles have one seta (nine cases) or two (15 cases) and DL has one (seven cases) or two setae (17 cases). The dorso-internal tubercle of the abdominal segments IV and V had in 50% of the species one seta and two in the other 50%.

Americanura mexicana Cassagnau, 1983