Spinaethorax, Papac, Vladimir & Palacios-Vargas, Jose G., 2016

Papac, Vladimir & Palacios-Vargas, Jose G., 2016, A new genus of Neelidae (Collembola) from Mexican caves, ZooKeys 569, pp. 37-51 : 39-44

Taxon classification Animalia Collembola Neelidae

Spinaethorax gen. n.

Diagnosis.

A genus of the Neelidae Folsom, 1896 with the following diagnostic characters:

Habitus of Neelidae . Small size, about 0.6 mm. Color white. Tegumentary grain fine and uniform. Apex of head with sword-like spines, body with several such spines, mainly around sensorial fields. Ant. III and IV fused and Ant. III with small globular sensillum in proximal position. Anterior labral setae R1 and R2 thick, curved and smooth. Oral fold with 1+1 sword-like macrosetae. Basomedian field of labium furnished with 6+6 setae. Presence of 3 setae around abdominal sensory fields, no E3 spine/setae on dd. Mid abdomen with swollen sensilla s3 and s3'. Base of Abd. IV sternite with 1+1 neosminthuroid setae, smooth and with pointed tip.

Type species.

Spinaethorax spinotricosus (Palacios-Vargas & Sánchez, 1999), comb. n.

Redescription.

Figs 1-15.

Type material.

Holotype: female mounted on slide. Original label: 23/00/1991, Mexico, Campeche, Cueva Xtancumbilxunaan (cave), 29.xii.1996, A. Ruíz and S. Aguilar col., ext. soil. Paratypes: 1 female on slide, 23.viii. 1991, J. G. Palacios col., direct collection and 2 juveniles on slides, the same data as the holotype. Type material deposited at Facultad de Ciencias, UNAM.

Other material.

Mexico, Campeche, Cueva Actún Guachapil (cave), 1 male, 1 female and 2 juveniles on slides. Original label: 14/iv/2012, 22.iii.1997, A. Ruiz and S. Aguilar col., ext. guano; 1 female on slide, 29.v. 1997, J. G. Palacios col., ext. guano. Material deposited at Facultad de Ciencias, UNAM.

Diagnosis.

Unpaired seta a0 between antennal basis. Labral chaetae R1 and R2 thick, curved and smooth. Oral fold with 1+1 sword-like macrosetae. Basomedian field of labium with 6+6 setae. Ant. III with small globular sensillum. Manubrium with 4+4 posterior setae. Mucro with both lamellae serrated and with rounded tip.

Description.

For lengths of different character see Table 1. Body length 0.5-0.7 mm. Habitus globular, as other members of Neelidae . No pigmentation, cuticle finely granulated, linea ventralis without crossing with integumentary channels on ventral head back. Mid and hind Abd. with numerous spine-like microsetae, stouter spines around all sensory fields on body and apex of head.

Head. Head length and width 215 and 145 µm, respectively. No eyes. Head with smooth, pointed ordinary setae and spines of different width and length (Fig. 1). Frontal part with ordinary setae (lateral ones longer than axial, 26-30 µm, respectively 10-16 µm), seta a0 present; medial part between posterior s.f. ordinary or slightly spine-like setae (20 µm); posterior part with 3+3 stouter spines IL1-IL3 of different lengths (28-42 µm) and 1+1 smaller axial spines IL4 (17-21 µm), others similar to smaller setae (10-14 µm). Labrum with 5,5,4 setae, 4 prelabrals. Pattern of labral setae (Fig. 2) after Massoud and Vannier (1967): a-row: 2R1 + 2R2, m-row: m + 2r1 + 2r2 and p-row with 5 ordinary setae (11 µm). Anterior R1 and R2 slightly thick, smooth and curved, R2 (11 µm) longer than R1 (9 µm). Medial setae (m-row) equal (11 µm), smooth median setae in one line with others. Maxillary palp simple, with 1 enlarged terminal seta (18 µm), 1 basal seta (14 µm) and 1 sublobal hair (Fig. 2). Basomedian field of labium with 6+6 setae (Fig. 5), median ones slightly longer (12 µm) than others (10 µm); basolateral field with 1+1 setae (10 µm), oral fold with 1+1 basal setae (8 µm) and 1+1 terminal sword-like macrosetae (25-30 µm). Head with 3+3 smooth postmedian setae ventrally (Fig. 5); 2+2 anterior setae equal (16 µm); posterior 1+1 seta slightly curved at tip (18 µm). Mandible with 4 apical teeth, medial ones longer (Fig. 3). Maxilla as in Fig. 4.

Thorax and abdomen (Fig. 6). Dorsally with ordinary setae, swollen sensilla s1, s2, s3, s3', spines of different size (4-6 and 25-45 μm), 6+6 wax rods (wrc1, 2, 4, 6-8) with straight setae (3-4 µm) and 2+2 (wrc 3 and 5) with thicker and longer straight setae (6-7 µm). All wrc placed in small cuticular depressions. Trichobothria or their sockets not observed. Th. II with 3+3 ordinary setae (12-14 µm) and 6+6 stouter spines (25-36 µm) around thoracic sensory fields, axial spines smaller (25 µm); sensory fields at leg II base with 2+2 ordinary setae (20 µm), 3+3 stouter spines, anterior ones longer (45 µm) than posterior (26-28 µm), 1+1 lateral sensillum s1 (8 µm) broadened at tip and 1+1 swollen transparent rod with bifid tip and no base (8 µm) above s.f. of leg II. Th. III with 5+5 ordinary setae (6-8 µm), 4+4 wrc (wrc 1-4) and several small spine-like microsetae, whose overall number is not seen clearly; at leg III base with 1+1 ordinary seta (16 µm), 3+3 stouter spines, medial ones longer (42 µm) than lateral (22 µm) and 2+2 wrc (5, 6). Anterior Abd. medially with 1+1 wrc 7 and 2+2 swollen sensilla s3 and s3'; hind Abd. with abdominal sensory fields, which are surrounded by 2+2 ordinary setae (12 and 18 μm), 1+1 stouter spines (30 µm), 1+1 swollen sensilla s2 and 1+1 wrc 8 above Abd. s.f. Dorso and dorso-lateral anterior and hind abdomen covered with numerous spine-like microsetae (4-6 μm) arranged as in Figs 6 and 10. Their overall number is not seen clearly. Abd. tergum VI with 3+3 setae (17 µm) and 1 unpaired axial seta (14 µm). Anal complex with three anal valves, each with on seta (7 µm). Abd. VI sternum with 4+4 setae (18-20 µm) and 2+2 very small globular structures (1-2 µm) next to anal valve setae. Female genital plate (Abd. V sternum, Fig. 10) with 4+4 setae (8-11 µm) and 1+1 axial microsetae (4 µm). Male genital plate with 5+5 ordinary setae (12 µm) arranged in circle and with 2+2 spine-like setae (7 µm) difficult to observe (Fig. 9), laterally surrounded with 4+4 setae (18 µm). Abd. IV sternum with 3+3 setae in one row (18-20 µm), one seta more laterally and 1+1 distal setae (8 µm). Lateral part of Abd. IV sternum with 1+1 short and pointed neosminthuroid setae (6 µm) (Fig. 10).

Appendages. Ant. III and IV not separated (Fig. 11). Length of antennae 140 µm, ratio antenna/head = 0.65; length of antennal segments I, II, III–IV as 11, 26 and 103 µm. Ant. I furnished with 3 short setae (8-10 µm). Ant. II with 1 medial seta and 5 apical setae arranged in a whorl. Ant. III organ consists of 2 transparent rods (7 µm), 1 leaf-like transparent sensillum Sg (12 µm) and spine-like seta (7 µm). Proximal part of Ant. III bears 1 globular sensillum Sg (4 µm). Ant. IV with 13 curved macrosensilla S finely blunt at tip (24-32 µm); subapically with 1 long and thick subapical sensillum Sy (16-18 µm) and with 1 thick shorter apical sensillum Sx broadened at tip (12-14 µm); Ant. IV organ like a tiny, hardly visible spine (5 µm); apically with curved setae a and sa apical in position (10 µm). Complete chaetotaxy of antennae provided in Table 2. Setae numbers of legs I–III (Figs 13-15): scx I: 1, 1, 3 (one spine); scx II: 1, 1, 1; coxae: 1, 1, 2; trochantera: 4, 3, 3; femora: 8, 8, 8 and tibiotarsi: 13, 14, 13. Thin meso- or microsetae as in following numbers on leg I: femur with 2; on leg II: femur with 1; on leg III: trochanter with 1, femur with 1. For complete setation of legs see Table 3. Tibiotarsal tenent hairs ordinary, straight and pointed (16-18 µm). Unguis narrow, in distal part bended; both unguis and unguiculus unequally long in leg I, II and III: unguis 31, 27 and 26 µm, respectively, unguiculus 14, 15 and 16 µm, respectively. Length ratio unguis I, II, III / ti. I, II, III width (31, 27, 26/ 17, 16, 17 µm) = 1.8, 1.7, 1.5. Unguis I and III with three auxiliary lamellae la, lp, Bp, unguis II with only lp and Bp (Fig. 14); unguiculus I with small internal tooth on distal part, II and III untoothed and III with bended tip; unguiculi without apical filament and basal lamellae. Ventral tube with 2+2 distal setae and without posterior lobe (Fig. 7). Retinaculum with 3+3 teeth, no setae on corpus (Fig. 8). Furcula well developed (Fig. 12), length of manubrium, dens (dp and dd) and mucro: 56, 31, 71 and 74 µm, respectively. Manubrium with 4+4 setae posteriorly, lateral ones shorter (10-15 µm) than axial (16-20 µm). Dens in proximal part (dp) with 2+2 posterior setae, lateral ones (14 µm) shorter than those axial (22 µm); distal part (dd) apically with 2+2 broad, blunt lateral spines (9 µm) and 1 medial sharp spine (7 µm) on anterior side; with 2 external (E1-E2) posteriorly and 2 internal (J1-J2) spines (6-7 µm each, distal with short apical filament), and 1 medial, subapical seta (18 µm). Mucro with serrated lamellae and rounded tip. Base of mucro furnished with small scale without base. Middle mucro width 7 µm.

Sensory fields (Figs 1, 6, 14 and 15). 6+6 s.f. placed in depressions each with secretory rod (10-12 µm), i.e. blunt seta with basal part inserted on cuticle and placed in upper margin of the field. Following arrangement: (a) anterior and posterior field on head (s.f. 1, 15 × 10 and s.f. 2, 20 × 10 µm) each with secretory rod and 1 seta on margin (14-18 µm); (b) thoracic field (s.f. 3; 35 × 20 µm) with secretory rod, 3 internal spines (4 µm) arranged in triangle, 2 external marginal setae (12-14 µm) and 6 sword-like spines of different lengths (25-36 µm), 3 spines are in anterior position and 3 spines above s.f. in axial position; (c) fields at base of legs II and III (s.f. 4, 5; 20 × 15 µm) each with secretory rod, 2 internal spines (4 µm) in s.f. 4 and 1 internal spine (4 µm) in s.f. 5. S.f 4 with 2 marginal external setae (20 µm), 3 stouter sword-like spines, medial ones longer (45 µm) than lateral (26-28 µm), 1 lateral sensillum s1 broadened at tip (8 µm) and 1 swollen rod with split tip and without base (8 µm) above s.f. 4. S.f. 5 with 1 marginal external seta (16 µm), 3 stouter sword-like spines, medial ones longer (42 µm) than lateral (22 µm); (d) abdominal field (s.f. 6; 30 × 25 µm) with secretory rod, 1 internal spine (4 µm), 2 marginal ordinary setae (12 and 18 μm), 1 sword-like spine above s.f. (30 µm) and 1 swollen sensillum s2 on the margin of s.f. (6 μm). Wrc 8 is located above Abd. s.f.

Both sexes known.

Etymology.

The genus is named after the spine-like setae on thorax and abdomen.

Distribution and ecology.

Spinaethorax spinotricosus is currently known from two caves and is putatively spread in the cave systems of Yucatán Peninsula, mainly in places with accumulation of bat guano or other type of rich organic material.

Variation.

The young have only one proximal seta on dens.