Subisotoma joycei Soto-Adames & Giordano

Soto-Adames, Felipe N. & Giordano, Rosanna, 2011, New species of springtails in the Proisotoma genus complex from Vermont and New York, USA with descriptive notes on Ballistura alpa Christiansen & Bellinger 1980 (Hexapoda, Collembola, Isotomidae)., ZooKeys 147, pp. 19-37 : 24-27

Subisotoma joycei Soto-Adames & Giordano sp. n.

Material Examined.

Holotype– Locality G, Male, slide mounted. Paratypes– Locality G, 3 on slides, 3 in alcohol; H, 2 on slides, 2 in alcohol. Other Material– Locality F (9 in alcohol),

Type Locality.

USA,Vermont, Grand Isle Co., South Hero, White’s Beach, N44.62189 W73.32273.

Etymology.

This species is dedicated to Joyce Bell for her contributions and support to the study of the arthropod fauna of Vermont.

Description.

Length to 1.2 mm. Living individuals black, alcohol preserved specimens dark purplish brown to black, with pigment more or less uniformly distributed through out head, body and antennae, legs and manubrium purplish (Fig. 14); some individuals with paired black longitudinal lines extending from Th. 2-Abd. 3. General body shape short and stout, with sudden bend between Abd. 4-5 (Fig. 14) as in Folsomides . Ant. 4 without basal microsensilla (bms of Potapov 2001), with at least 13 well-developed thin-walled sensilla, and 14 other sensilla distributed along the length of the segment; subapical sense organ with 1 differentiated microsensilla and 1 microrod in a pit (Fig. 16). Ant. 3 with 1 poorly differentiated basal microsensilla; sense organ with 2 clubbed sensilla and 2 differentiated guard sensilla; 1 lateral sensilla present; females with 9-10, and males with up to 16 additional sensilla distributed mostly on dorsal face of segment. Ant. 2 with 3 basal microsensilla; and 1-2 distal sensilla. Ant. 1 with 2 basal microsensilla, 17-18 smooth, acuminate setae, and 2-3 sensilla. Eye patch with 8+8 subequal eyes and 3 interocellar setae; PAO elliptical, about 2X diameter of eye B, and 4-5 associated setae (Fig. 17). Prelabral and labral chaetotaxy 2/554; distal labral margin smooth. Papilla of outer maxillary lobe simple, sublobal plate with 4 appendages. Maxilla with lamella 1 narrow, with cilia only along margins, surpassing tip of capitulum. Labial palps with a full complement of papillae and 3 proximal setae; papillae E with lateral process and 6 guard setae, seta e7 absent (Fig. 18a-b); labial triangle with 5 anterior and 4 posterior setae; distribution of postlabial setae in columns I, C, E and L variable 4(5-6), 3/5 (1,6), 2-3, 5(4) (Figs. 20-22). Body dorsally covered by smooth hairs; some hairs on the pre-posterior row reaching base of setae on posterior row; tergal macrochaetae undifferentiated; thorax without ventral setae. Axial setae on Th. 2-Abd. 3 as 7-9; 7-8(9)//5(4/6-7); 5(3-4/6); 5. Th. 3 with 28/33(20) setae on posterior row; microsensillar formula 10(1)//101; sensillar formula variable, often asymmetric 14(17-18); 9-13//9(8/10); 8(9); 9(5/8/10); 11-19; 12(4/8/14/16) (Fig. 15); antero-lateral sensilla on Th. 2 posterior to microsensilla, but spatial relation among lateral sensilla variable between individuals; lateral sensilla on Th. 2-3 anterior to medial sensilla; medial thoracic sensilla inserted on preposterior row of setae, insertion of abdominal sensilla variable, just anterior or on posterior row of setae, or clearly anterior to subposterior row (Fig. 15); all sensilla on Abd. 5 similar in size. Proximal and medial subcoxae on legs 1-3 with 1, 0; 5-8, 4-9; 6-12, 6-15 setae. Lateral valve of Abd. 6 with 3 hr setae (Fig. 19). Ventral thoracic setae absent. Sculpturing of thoracic sterna smooth. Tibiotarsi 1-3 with 24, 27, 30 setae; tibiotarsal whorl B complete, with B5 clearly thicker and longer than B4 (Fig. 26); adult males with setae B5 and x truncate (Fig. 23); legs 1-3 with 1 (A1), 2 (A1, A7), 2 (A1, B7) capitate or acuminate tenent hairs (Fig. 27). Unguis and unguiculus toothless, unguiculus triangular. Ventral tube with 6-11 disto-lateral and 6-9 posterior setae. Tenaculum with 3+3 teeth and 1 seta. Sterna of Abd. 3 without isolated field of setae. Anterior and posterior furcal subcoxae with 9-19 and 4-11 setae, respectively. Proportion manubrium/dens/mucro as 3/2/1. Dens smooth, and cylindrical (Fig. 25). Chaetotaxy of manubrium and dens as in Fig. 28: manubrium with 5-8 basal setae, 15-24 dorsal and 0 ventral setae; dens with 18-20 (15/26) dorsal and 5 (4/6) ventral setae. Mucro with wide lamella, without basal notches, clearly separated from dens; bidentate, teeth subequal (Fig. 24a-b).

Remarks.

Three individuals show variation in the number and size of eyes. In the small juvenile eyes G and H are small, barely rising above the cuticle; one male is blind; and in one female all eyes in one patch are subequal, but on the other patch eye E is less than half the size of F. The axial setae are often disorganized and the number of setae in a column is open to interpretation. The number of tergal sensilla is variable. Most individuals have an asymmetric number of sensilla, and two individuals lack the microsensilla of Abd. 1 on one side. Tenent hair B7 on metathoracic legs often appears acuminate instead of capitate. Two individuals have 3+4 tenacular teeth.

The generic placement of the new species is problematic. It better fits in the genus Subisotoma (Table 2), but it is unique among species currently assigned to that genus in having more than 8+8 tergal sensilla on each segment, by the significantly larger number of dental setae (most Subisotoma species have 4 or fewer dorsal and 1-2 ventral setae, whereas Subisotoma joycei has 18-20 dorsal and 4-6 ventral setae), and by having a well developed furcula with mucro exhibiting a wide lamella and clearly separated from the dens. Subisotoma joycei is similar to species in the genus Isotopenola Potapov, Babenko, Fjellberg & Greenslade, 2009 in the presence of sensillar polychaetosis on body terga, but differs from all forms in that genus by having smooth thoracic sterna, lacking an isolated field of setae on Abd. 3 sterna and in the number of guard setae on labial papilla E. The strong polychaetotic furcula in Subisotoma joycei resembles the condition in Ballistura , but the new species clearly differs from Ballistura in maxillary palp structure, sensillar and microsensillar formulae, presence of a full complement of setae in tibiotarsal whorl B, and dens sculpturing (Table 2).

The new species is most similar to Ballistura ewingi James, 1933, sensu Folsom (1937) from which it differs in aspects of color pattern (trunk ventrally white in ewingi, dark purple brown in joycei), the number of tenent hairs (2-3 on all legs in ewingi, 1, 2, 2 in joycei), number of distal seta on ventral tube (4 on ewingi, 11 in joycei), and number of te nacular teeth (2 in ewingi, 3-4 in joycei). The new species may be the same as the Pennsylvania specimens preliminarily assigned to Ballistura ewingi by Christiansen and Bellinger (1998), although this form also seems to have considerably fewer distal setae on the ventral tube than S. joycei sp. n.(Table 3). Ballistura ewingi has been described as having smooth dens, and probably does not belong in Ballistura , which Potapov (2001) restricts to species with tuberculate dens. Important characters needed to determine the appropriate generic placement of Ballistura ewingi remain undescribed and require the study of fresh material.

The new species is also similar to Ballistura excavata Folsom, 1937, but the two species are easily separated by body color, eye number, shape of tenent hairs and unguiculus, and structure of the dens (Table 3).