Pachyotoma primamexicana Palacios-Vargas & Arbea, 2022

Palacios-Vargas, José G. & Arbea, Javier I., 2022, The subfamily Pachyotominae in Mexico (Collembola: Isotomidae) with description of a new Pachyotoma species, Zootaxa 5194 (2), pp. 245-259 : 247-248

Pachyotoma primamexicana Palacios-Vargas & Arbea sp. nov.

Figs. 1–35

Type locality. Popocatépetl Volcano , Puebla, Morelos ( Mexico), 19°01′20″N 98°37′40″W .

Material type. Holotype: female, collection number FC-UNAM:LESM-AC:22584, on moss, pine forest, 3,600 m asl. R. Iglesias col. Paratypes: 19 females and 3 males, 2 juveniles FC-UNAM:LESM-AC:22585-22608 and about 2100 specimens in alcohol, same data as holotype ( Fig. 1 ). All specimens were collected in Popocatepetl Volcano at forest. Type material and alcoholic specimens are deposited in seniors author institution, except for two paratypes which are deposited at Museo Nacional de Ciencias Naturales at Madrid, Spain (MNCN) .

Description. Body length of females (n= 15) 1.4 mm (range 1.0–1.85 mm); length of males (n = 2) 1.2 mm, length of juveniles from 0.7 to 0.9 mm.

Colour. Very dark purple including appendages ( Figs 1, 2 ), with a pattern of several circular or elliptical paler patches on head body and legs ( Fig. 3 ); eyes patch black.

Integument. With subcuticular reticulation ( Fig. 4 ) and large secondary granulation all over the tergites; secondary granulation also present on appendages ( Figs 5, 6 ) but without inner reticulation. Dorsal setae short ( Fig. 4 ).

Head. Ommatidia 8+8, subequal, G slightly smaller than others ( Fig. 7 ). PAO oval ( Fig. 8 ), without distinct constriction but elliptical, no inner denticles, shorter than nearest eyes, and smaller than basal width of Ant. 1; with 2 guard setae along its outer margin ( Figs 8 , 29 ). Maxillary palps bifid, maxillary outer lobe with 4 sublobal hairs ( Fig. 27 ). Labral formula 4/5, 5, 4 ( Figs 9 , 27 ). Clypeus with about 20 setae, those closer to labrum stronger ( Fig. 27 ). Labium with 3+3 proximal and 4+4 basomedian setae ( Fig. 11 ). Hypopharynx, mandible and maxilla normal ( Fig. 10, 12 ). Ventral side of head along linea ventralis with 3+3 or 4+4 setae. Ant. I with 2 bms, dorsal and ventral, and 2 ventral s ( Fig. 25 ); Ant. II with 2 bms and 1 latero-distal s; Ant. III with 5 distal s (2 inner, 2 outer and 1 lateral) and without bms; inner sensilla of Ant. Org III elongate, shorter than guard sensilla, which are slightly shorter than common setae on Ant. III ( Fig. 5 ). Several sensilla present on Ant. IV, curved and shorter than ordinary setae ( Figs 6 , 24 ), subapical organ small.

Body chaetotaxy. ( Figs 30 , 31, 32 , 36). End of Abd. VI with 1+1 macrosetae, 2 times longer than common setae and almost equal in length to mucro. Most of body sensilla slightly shorter than common setae except those on Abd. IV, which are more curved than those on other body segments and relatively longer than common setae on the same segment ( Figs 14, 15 ). Tergites of Th. II–Abd. V with numerous sensilla along p-row and on their medial and lateral parts. Sensilla and common setae along p-rows of the segments alternating with setae as in Fig. 16 . Sensillar and microsensillar formula respectively as 25–28, 29–33/ 17–20, 28–31, 24–29, 51–57, 26–29(s) and 1, 1/1, 1, 1(ms) ( Fig. 21 ). Axial setae (common setae along median line on each side) of Th. II–Abd. II–V: 6–9, 6–8/5–7, 5–7, 5–7, 8 ( Figs 14, 15 ). Th. III with 45–48 setae in p-row. Thorax without ventral setae. Ventral tube with latero-distal 6+6 setae and posterior setae 9.Ventral Abd. II with 5 setae m (14 specimens), 6 (2), 7 (1). Anal valves completely in ventral position, each lateral valve with about 23 setae.

Appendages. Upper and lower subcoxa of leg I, II, III with 0, 2, 2 and 1, 5, 6 setae, respectively. Unguis of normal size and shape, with inner tooth. Tibiotarsi of all legs with numerous setae ( Fig.13 ). Tenent hairs thin and slightly clavate ( Figs 13 , 33, 35 ) with the formula 2, 3, 3. Femora with one long acuminate tenent hair ( Fig. 34 ). VT with 5+5 or 6+6 latero-distal and 8–12 posterior setae ( Figs 10 , 37). Retinaculum with 4+4 teeth ( Figs 16 , 39) and usually 2 setae on its corpus ( Fig. 17 ). Anterior part of furcal subcoxa divided into three groups, al with 12–16 setae, am with 22–37 and p with about 8 setae. Anterior side of manubrium smooth and without setae, posterior side granulated and with about 37 pairs of setae ( Figs 23 , 40). Medial part of manubrium with two thick, spine-like projections ( Fig. 18 ). Dens with 5 anterior setae thicker than those of ventral side ( Fig. 19 ). Posterior side of dens with clear secondary granulation ( Figs 20 , 38) and 12–17 setae, with 5–7 setae in basal part and 7–10 in distal part. Mucro strong, with 1 subapical tooth, with 2 lamellae ( Figs 22 , 40), with a hook-shaped apex ( Fig. 22 ). Ratio of mucro: dens: manubrium as 1: 3.9: 3.1.

Several hundred specimens were found, including, males and females. There are not dimorphic males.

Variations. The corpus retinacular setae varies from 1 to 6 (in parenthesis the number of cases observed): 1 seta (3), 2 setae (9), 3 setae (4), 4 setae (3), 6 setae (1). The anterior setae of dens are 5+5 (16), 5+6 (1), 6+6 (1), 7+7 (1); posterior setae on dens: 7+8 (1), 8+8 (10), 8+9 (2), 9+9 (2), 10+9 (1). Ventral tube also has some variation (frequency in parenthesis): latero-distal 4+5 setae (2), 5+5 (5), 6+6 (7), 7+6 (1); posterior setae 9 (3), 10 (1), 12 (2), 14 (1), 16 (1), 17 (1). Axial setae on Th. II has 6 setae (2); 7 (14), 8 (2), 9 (1). Th. III has 6 (2), 7 (14), 8 (1); Abd. I has 5 (9), 6 (4), 7 (1); Abd. II 5 (14), 6 (2), 7 (1). PAO size (n=15): 10.4 (range 9–15), eye size (n=15):17.4 (range 12–20).

Ecological remarks. Vegetation of type locality consists mainly of Pinus montezumae and Quercus sp. The new species was found in litter and moss samples of P. montezumae forest, at an altitude of more than 3,000 m asl. During the extraction there were many specimens (more than 200), including adults and juveniles.

Etymology. The new species is named for being the first Mexican species of the genus described from the country (primus = first).

Remarks. P. muskegis has few manubrial setae and is about twice the size of P. primamexicana sp. nov. ( Table 1 ). The new species is characterized by the presence of a very small PAO (about half the size of one eye, while in P. mustegis is about the size of short diameter of the eye); of 5 strong setae on distal anterior surface of dens, and 8 thin setae on posterior surface; retinaculum has 4 teeth on each ramus and from 1 to 4 setae on its corpus ( P. muskegis has 2 setae); manubrium with many setae (37 pairs) on posterior surface and without setae on anterior surface; ventral tube with 6+6 laterodistal setae and 9 posterior setae, of which 3 are longer. Tibiotarsus P. muskegis has a clear apical subdivision, which is lackining in P. primamexicana sp. nov. It is also similar to P. alpa ( Christiansen & Bellinger, 1980) from the USA, but differs in having a smaller PAO, slightly capitate tenent hairs 2, 3, 3 (versus 1, 2, 2 on P. alpa ) on tibiotarsi and a higher number of manubrial setae.

Figures

FIGURE 16. Pachyotoma primamexicana sp. nov. 16, dorsal sensillataxy from Th. II to Abd. VI.

FIGURES 1‒3. Pachyotoma primamexicana sp. nov. 1, sample with many specimens in alcohol; 2, adults and juveniles in cavity slide; 3, adult in lactic acid, cavity slide.

FIGURES 4‒6. Pachyotoma primamexicana sp. nov. contrast phase microscope photos: 4, subcuticular granulation; 5, Ant. III organ: sgd=dorsal guard sensillum, sgv=ventral guard sensillum, m=microsensillum (inner and lateral); 6, subapex of Ant. IV with setae (S) and sensilla (ss).

FIGURES 7‒12. Pachyotoma primamexicana sp. nov. contrast phase microscope photos: 7, hypopharynx; 8, labial chaetotaxy; 9, mandible and maxilla; 10, Tibiotarsus III: th=tenent hairs; 11, setae (S) and sensilla (ss) on thorax notum; 12, setae (S) and sensilla (ss) on abdominal notum.

FIGURES 13‒15. Pachyotoma primamexicana sp. nov. contrast phase microscope photos: 13, posterior setae of ventral tube; 14, distal thorns of posterior manubrium; 15, dental posterior setae with secondary granulation of cuticle.

FIGURES 17‒18. Pachyotoma primamexicana sp. nov. 17, anterior dental chaetotaxy; 18, posterior dental and manubrial chaetotaxy, mucro and distal thorns of posterior manubrium.

FIGURES 19‒24. Pachyotoma primamexicana sp. nov. SEM photos: 19, apex of antennae, 20 Ant. I partial ventral view: vs=ventral sensillum; 21, eyes; 22, mouth; 23, head dorsal view; 24, PAO.

FIGURES 25‒30. Pachyotoma primamexicana sp. nov. SEM photos: 25 Th. III dorsal chaetotaxy; 26, lateral sensillum (s) and microsensillum (ms); 27, lateral setae of abdominal segment; 28, apex of Tibiotarsus II; 29, apex of Tibiotarsus III; 30, setae and sensilla on Abd. IV and V.

FIGURES 31‒35. Pachyotoma primamexicana sp. nov. SEM photos; 31, ventral tube; 32, posterior surface of dentes and mucro; 33, retinaculum rami and setae; 34, lateral view of furcula; 35, anal plates and female genital opening.