Bellisotoma Soto-Adames, Giordano & Christiansen

Soto-Adames, Felipe N., Giordano, Rosanna & Christiansen, Kenneth, 2013, Bellisotoma, a new genus of Isotomidae from North America (Hexapoda, Collembola), ZooKeys 283, pp. 7-13 : 8-9

Bellisotoma Soto-Adames, Giordano & Christiansen gen. n.

Type species.

Subisotoma joycei Soto-Adames & Giordano, 2011.

Etymology.

The new genus is dedicated to Ross and Joyce Bell, in celebration of their contributions to the study of the entomological fauna of Vermont.

Description.

General body shape short and stout, with sudden bend between abdominal segments 4-5 as in Folsomides . Cuticle smooth, granular complex formed by single light granules surrounded by 4-7 darker granules (Fig. 1), granular complexes irregular. Basal microsensilla on antennal segments 3-4 not differentiated; second antennal segment with 3 basal microsensilla; first antennal segment with 17-18 setae, 2 basal microsensilla, 3 basal ventral sensilla and 2 other distal sensilla. Prelabral setae 2; outer maxillary lobe with apical seta simple, sublobal plate with four appendages; labial palp with three proximal setae, all papilla present, guard seta e7 absent. Tergal microsensilla formula 10//101; number of tergal sensilla variable, but adults always with more than eight sensilla on each segment; medial abdominal sensilla inserted either on or just anterior to posterior row (Figs 7-8). Ventral thoracic setae absent. Sterna of second abdominal segment without isolated field of setae. All legs with more than 21 setae; legs with 1-3 weakly capitate or acuminate tenent hairs; setae B4 and B5 present, B5 longer than B4; adult males with setae B5 and x modified. Manubrium without ventral setae. Dens smooth, cylindrical, and shorter than manubrium; dorsal setae long and abundant, distributed throughout dens length; ventral setae few and restricted to distal half of dens. Mucro bidentate (Fig. 2), about half as long as dens, fused to dens dorsally, articulated ventrally; with wide dorsal lamellae that join clearly before the end of mucronal axis without forming a tooth (Fig. 3), and a ventral rib with basal notch that articulates with dens (Fig. 4).

Remarks.

Bellisotoma gen. n. belongs to the Isotopenola - Subisotoma genera complex, but unlike these genera, the new genus shows a furcula adapted to a neustonic mode of life, as evidenced by the thick polychaetotic dens and lamellate mucro. Bellisotoma gen. n. differs from all other genera by the combination of having a mucro with lamellae that join subapically without forming a tooth, by the presence of a large number of dorsal setae on dens, presence of sensillar polychaetosis, smooth cuticle and second abdominal sternum segment without isolated setae field. The new genus is similar Isotopenola Potapov, Babenko, Fjellberg and Greenslade and Subisotoma , as circumscribed by Potapov et al. (2009), in having reduced number of prelabral setae, simple outer maxillary palp, reduced number of guard setae on labial papilla E, reduced microsensillar chaetotaxy, absence of tibiotarsal seta B4/5 and smooth dens (Table 1). The three main characters given above distinguish the new genus from Subisotoma , whereas the new genus additionally differs from Isotopenola in the number of guard setae on labial papilla E (6 in Bellisotoma , 4-5 in Isotopenola ). Bellisotoma joycei keys out to Ballistura in Potapov (2001), but the two genera are clearly distinguished by maxillary palp structure, sensillar and microsensillar formulae, absence of tibiotarsal seta B4/5 and dens sculpturing. Additional differences between the new genus and other genera in the Proisotoma complex ( Potapov 2001, Fjellberg 2007, Potapov et al. 2006, 2009) are listed in Table 1. One other North American species, Ballistura ewingi (see below), belongs in the new genus.

Members of the new genus may be either psammophilous and/or acidophilus. The individuals of Ballistura joycei from Vermont were collected on sandy shores of Lake Champlain and the individuals from Quebec on acidic sandy soils (pH 3.75; Therrien et al. 1996) in a sugar maple grove ≈28Km east of the St. Lawrence River. The exact topotypical locality of Ballistura ewingi is not clear, but the soils around Vicksburg, Mississippi are also acidic, sometimes sandy.