Ameritulla Bernard, 2016, new genus

Ameritulla new genus

Diagnosis. Medium to large species. Color white. Cuticle with distinct fields of granulation, posterior margins distinct from more anterior areas; granules of Abd. VI not closely packed, not greatly enlarged. Pseudocelli crescentic. PAO with two rows of 15‒35 vesicles each. Labial palpus with spine of papilla A thickened. Pseudocellar formula 11/010/01011 or 11/111/11111. Sense organ of Ant. III with two convergent sense clubs and two sense rods, ventrally with one sense club. Tibiotarsi I, II, III with 15, 15, 14 setae, respectively. Unguiculus sharply pointed. One cephalic v-seta (v2) present. Seta p3 on Abd. V slender. Posterior regions of some segments with many distinct transverse rows of tightly packed granules. Abd. VI without crescentiform ridges. Venter of Abd. VI with full complement of setae (a1‒5, m2‒5, p1‒5, va1‒3). Two anal spines.

Type species. Ameritulla clavata (Mills, 1934) n. comb.

Other species. Ameritulla obscura n. sp.

Etymology. The prefix Ameri - refers to the fact that the two species included in this new genus are known only from temperate North America. Tulla is a variant of the first part of the type genus of the family.

Remarks. In the key of Dunger & Schlitt (2011) the two species of Ameritulla n. gen. will run to couplet 29, from which arise four genera separated largely by pseudocellus formula. These formulas are not sufficient for the placement of Ameritulla spp. The new genus is distinct from Psammophorura Thibaud & Weiner, 1994 in having Type III (crescentic) pseudocelli rather than Type I (stellate) or a mix of Type I and Type IV (convergently striate); from Boudinotia Weiner & Najt, 1991 in having no more than 1+1 pseudocelli per segment, rather than 2+2 on some thoracic and abdominal segments; and from Pongeiella Rusek, 1991 in having typical antennal sensilla and all five labial papillae (A‒E) rather than hammer-shaped sensilla and labial papillae A and B (Fjellberg 1999). Ameritulla n. gen. would appear to be similar to Tullbergiella Izarra, 1965 but this is due to a lapsus in the key of Dunger & Schlitt (2011), which states that Tullbergiella has an elongated PAO with about 60 vesicles in two rows. According to the descriptions of the two known species, T. humilis Izarra, 1965 and T. allendei Izarra, 1975, the PAO of Tullbergiella is round or broadly oval with about 60 round vesicles (Izarra 1965, 1975).

Tullbergia clavata Mills, 1934 was placed in Mesaphorura by Bagnall (1947) and kept there by Dunger & Schlitt (2011). The modern concept of Mesaphorura Börner, 1901 s . str. includes tullbergiids with stellate pseudocelli (Type I), an oval PAO containing two rows of rod-like vesicles and crescentiform ridges on Abd. VI (Dunger & Schlitt 2011) (Fig. 3C). The Ameritulla spp. described here have crescentic pseudocelli (Type III), much different PAOs and lack crescentiform ridges. Therefore, they cannot be included in Mesaphorura. Mills (1934) did not mention crescentiform ridges on T. clavata, and his description and figures are not very helpful in placing the species. The illustration by Christiansen & Bellinger (1980, 1998) of the abdominal chaetotaxy of T. clavata indicated crescentic ridges. Christiansen & Bellinger’s Tullbergia key (1998), however, contradicts the illustration; T. clavata specimens key to a group of species that do not have crescentic ridges. This character state was confirmed by examination of cotypes.

Mesaphorura hades (Christiansen & Bellinger, 1980), described from Iowa, probably belongs in Ameritulla based on the original illustrations (Christiansen & Bellinger 1980), but the number of tibiotarsal setae is unknown. It can be distinguished from Ameritulla spp. by its pseudocellar arrangement (11/011/11111). As described, it cannot be placed in Mesaphorura since it lacks crescentiform ridges, the pseudocelli are not stellate (featureless after original description) and the Abd. IV p3-seta is long and slender. Mesaphorura spp. possess crescentiform ridges and stellate pseudocelli, and seta p3 is short and broad.

J. Simón Benito (in litt. 2006, cited in Bellinger et al. 1996‒2015) suggested that several widespread North American species currently in Mesaphorura (including T. clavata) could belong to other genera such as Paratullbergia Womersley, 1930 or Pongeiella. Ameritulla n. gen. resembles Paratullbergia in the anterior placement of p2 on Abd. V, but differs in lacking crescentiform ridges and in many chaetotaxic characters, such as lacking m-setae on Abd. I ‒III (m4 present in Paratullbergia). Differences from Pongeiella have already been stated above.

Ameritulla spp. appear to be similar to Metaphorura Bagnall, 1936 in most setal characteristics, but differ from that genus in having broadly oval PAO vesicles and crescentic pseudocelli (Type III), possessing all five labial papillae of which the spine of papilla A is blunt, and lacking a ventral terminal projection. The PAO of Metaphorura has elongated or bifurcate vesicles, the pseudocelli are doubly striate (Type II) or stellate (Type I), the labial palp has four pointed papillae and Abd. VI has a terminal spine-like or stout projection under the anal spines (see Castaño-Meneses et al. 2000)

The two species included in Ameritulla n. gen., with 15 setae on the middle tibiotarsus, do not fit well in other currently recognized tullbergiid genera. The potential value of this character was recognized by Fjellberg (1991), who found that T. clavata had the most complete tibiotarsal chaetotaxy (15 setae). However, its possible phylogenetic value and how it applies to various taxa are not clear. Five genera were listed by Greenslade & Rusek (1996) as having 15 setae on the middle tibiotarsus: Boudinotia Weiner & Najt, 1991, Stenaphorurella Luciañez & Simón, 1992 (= Stenaphorura Absolon, 1900), Tasphorura Greenslade & Rusek, 1996, Tillieria Weiner & Najt, 1991 and Tullbergia Lubbock, 1876. Species of Dinaphorura Bagnall, 1935 also have 15 setae on the middle tibiotarsus (Najt & Rubio 1978, Rodgers & Greenslade 1996). Tasphorura is pigmented, has a blunt labial papilla A but lacks papilla C, and has a unique development of sensilla on the antennae (Greenslade & Rusek 1996). Boudinotia has 2+2 pseudocelli on most segments, pseudocelli are stellate and on Abd. V are close together on a prominence, and Abd. IV has abundant m-setae (m3‒m6) (Weiner & Najt 1991). Tillieria spp. have three sensilla in the Ant. III sense organ and stellate pseudocelli (Weiner & Najt 1991). Dinaphorura spp. also have three sensilla in the Ant. III sense organ and possess additional dorsal spines on Abd. VI (Rodgers & Greenslade 1 996). With two exceptions the only Tullbergia spp. known to have 15 tibiotarsal setae also have three sensilla in the Ant. III sense organ. Many important characters of the 17 Tullbergia spp. with two sensilla in the Ant. III sense organ, such as the labial papillae and tibiotarsal seta number, are too poorly known for a complete comparison. Two of the 17, T. harti (Rusek, 1991) and T. pomorskii (Smolis, 2010), have 11 or 12 setae (Rusek 1991, Smolis 2010).

Two Tullbergia spp. have 15,15,14 tibiotarsal setae and two sensilla in the Ant. III sense organ (Deharveng 1981). Tullbergia bisetosa Börner, 1903 has only three labial palp papillae, none of which are thickened (Fjellberg 1999). A recently redescribed species from Tierra del Fuego, Tullbergia meridionalis Cassagnau & Rapoport, 1962 (Arbea 2016) resembles Ameritulla spp. but has stellate pseudocelli and possesses 2 v-setae on each side of the head. Pseudocelli of Ameritulla spp. are crescentic and the head has seta v2 only.