Neelus fimbriatus

Distribution. Ecuador and Colombia (Bretfeld & Trinklein 2000; Marín & Palacios-Vargas 2018; Mari-Mutt et al. 1997 – 2023; Bellinger et al. 1996 – 2023).

Type locality. Ecuador: Cotopaxi, Otonga (Bretfeld & Trinklein 2000: 179). Records from Colombia. Locality 20 (Marín & Palacios-Vargas 2018: 416).

Labrum with 4,5,5,4 setae (Figs 1 A and 5 A). Anterior labral setae a 1 and a 2 thick, curved; a 2 longer than a 1 (16 and 12 µm, respectively). Seta a 1 apically with 3 small serrations and one big basal tooth, a 2 medially with 3 _ 4 strong serrations and some small externally. Medial setae (m-row) subequal (12 µm), smooth, slightly curved, the central one displaced in a small anterior lobe (Figs 1 A, 5 B). Posterior setae (p-row) smooth, subequal and slightly curved (12 µm). Maxillary palp simple, with 1 enlarged terminal seta (11 µm). Basomedian field of labium with 4 + 4 setae (Figs 1 E, 5 D), medial setae longer (16 µm) than others (10 – 11 µm); basolateral field with 1 setae and hyaline microsetae on a big alveolus, as illustrated for N. murinus by Schneider (2017). Ventral side of head with 3 + 3 postlabial setae (18 µm): 2 + 2 distal and 1 + 1 proximal thicker and barbulate (Figs 1 E, 5 C, 5 D). Mandible strong, with 5 apical teeth, and one external appendage, right mandible with an internal triangular tooth between incisive area and molar surface (Fig. 1 D). Maxilla with 6 fringed lamellae (Fig. 1 C). Thorax and abdomen (Fig. 2). Dorsal side of thorax and abdomen covered with ordinary setae, wax rods, swollen S-setae and tertiary rods. Dorso-lateral area of Th. II with: 13 + 13 ordinary setae. Precoxal area of Th. II with 2 + 2 ordinary setae, 1 + 1 τ-setae and 1 + 1 flame-shaped S-setae (s 1). Dorso-lateral area of Th. III-anterior abdomen, with 5 + 5 setae, 2 + 2 round-shaped S setae (s 3, s 3 ’), 7 + 7 wrc (wrc 1 – 7), 8 + 8 τ-setae and several tertiary rods arranged as in Fig. 2 A. Precoxal area of Th. III with 2 + 2 ordinary setae and 1 + 1 τ-setae. Abdomen with about 50 + 50 microsetae (3 – 5 µm), 1 + 1 T-shaped S-setae (s 2), 1 + 1 wrc arranged as in Fig. 2 A. Abd. V, with 4 + 4 setae (17 – 20 µm), VI with 5 + 5 setae (16 – 17 µm), 1 + 1 microsetae (µ. av) and 1 paired posterior mesoseta of anal valve (av, 4 µm) (Fig. 2 E). Male genital plate with 9 + 10 microsetae (6 – 8 µm) arranged in circle (Fig. 2 D). Female genital plate with 4 + 4 setae (9 – 10 µm) and microsetae absent (Fig. 2 E). Abd. IV sternum with 4 + 4 setae (9 – 10 µm), and 1 + 1 distal seta (9 – 10 µm). Ventrally on Abd. III and IV there are one pair of acetabular structures on each side (Fig. 6 C) similar to those of dens. Lateral part of Abd. IV sternum with 1 + 1 short, sharp and curved neosminthuroid setae (8 µm). Appendages. Ant. III and IV distinctly separated (Fig. 4 A). Length of antennae 117 µm, ratio of antenna / head = 0.6. Ratio of Ant. I: II; III; IV as 1: 2,7; 3,7; 4,3. Ant. I with 3 short dorsal setae (5 µm). Ant. II with 4 apical dorsal setae arranged in a whorl. Ant. III with 13 ordinary setae in five whorls (distribution from base to apex: 1, 1, 3, 2 and 6 setae). Antennal organ of Ant. III with 5 apical sensorial elements: Sgd, and Sgv sensilla, two microsensilla; and one ventral m’ spine-shaped (sgd: 15 µm, m: 6 µm, m’: 4 µm). Ant. IV with 10 ordinary setae; 7 sensilla (15 - 19 µm), Sx (10 µm) and Sy (15 µm); 3 long sensilla and 2 rod-like curved setae in apical (a) and subapical position (sa) and subapical organite “ Or ” with two filaments (7 µm). Setation of legs I – III (Figs. 3 A-C): scx I: 1, 1, 3; scx II: 1, 1, 1; coxae: 1, 1, 1; trochantera: 4, 3, 4; femora: 9, 10, 8 and tibiotarsi: 16, 18, 17. Some tibiotarsal setae (table 2) are on a tuberculate alveolus (Fig. 6 B). For details of shape of setae of legs see table 2. Unguis narrow and elongated, both unguis and unguiculus different long in leg I, II and III: unguis 36, 33 and 31 µm, respectively; unguiculus 16, 14 and 16 µm, respectively. Unguis bears one dorsal pseudonychia. Unguiculus untoothed without apical filament, with basal tubercule. Ventral tube with 2 + 2 distal setae and posterior lobe (Fig. 2 B). Retinaculum with 3 + 3 teeth, seta on corpus absent (Fig. 2 C). Furcula well developed (Fig. 4 B), length of manubrium, dens and mucro: 52, 105, and 66 µm, respectively. Manubrium posteriorly with 3 + 3 setae (Fig. 4 B), two distal (17 µm), one proximal (20 µm). Posterior surface of dens I with one long (20 µm) and thick seta, posterio-external part of dens II, with 3 conical spines, one central seta, and one triangular spur on each side, two internal triangular spines in the internal side, anterior surface of dens II with one apical very thin spine (setola). Mucro with both lamellae serrate, tip of mucro rounded. Sensory fields 6 + 6 s. f. placed in depressions each with secretory rod (13 – 15 µm), blunt, straight seta with basal part inserted in the cuticle and placed in upper margin of the field. The fields have following arrangement: (a) anterior and posterior field on head (s. f. I and II; 16 x 9 and 15 x 14 µm respectively) each with secretory rod and 1 internal seta (on anterior field 17 µm, on posterior one 15 µm, and 11 and 9 respectively); (b) large thoracic field (s. f. III; 35 x 20 µm) with secretory rod, 3 internal spines arranged in triangle, 2 marginal setae (13 - 15 µm); and 3 spine-like setae (26 µm); anteriorly with 3 lanceolate spines (axial shorter than lateral); (c) abdominal field VI (s. f. 6; 19 x 14 µm) with secretory rod, 1 curved internal spine, 2 marginal setae (1 internal, 1 external; 8 µm and 13 µm respectively) and T-shaped S-setae (s 2); (d) fields in the precoxal area of Th. II and III (s. f. IV, V; 18 x 14, and 20 x 19 µm, respectively) each with secretory rod, 2 curved spines. Both s. f. with 2 marginal external setae (9 - 16 µm). Both sexes known. Males are smaller than females, the only other difference between sexes is in shape and chaetotaxy of genital area, 18 microsetae in males (Fig. 6 D) vs. 10 in females.

Diagnosis. Anterior part of head with mesosetae, posterior with microsetae. Anterior part of abdomen with microsetae, posterior with some mesosetae and tertiary rods. Anterior labral setae a 1 and a 2 thick, a 1 with a big tooth and externally with 3 small serrations, a 2 medially with 3 – 4 strong external serrations. Sensory field on thorax furnished with 3 anterior lanceolate spines. Ant. I with 3 setae. Ant. II with 4 setae. Ant. III with 13 ordinary setae and five sensorial elements. Ventral side of head with one pair of proximal barbulate seta, smaller than two distal pairs. Sterna III and IV with a pair of acetabular formations each. Manubrium with 3 + 3 posterior setae. Dens proximal with only one posterior seta. Dens distal with 3 conical externo-posterior spines. Mucro with both lamellae strongly serrate and tip rounded.

Remarks. N. fimbriatus is very different to N. desantisi Najt, 1971, the only other species known in Southamerica. If differs by the absence of stouter and longer lanceolate spines around thoracic s. f. and macrosetae on posterior part of abdomen. Other differences are that N. desantisi has only 1 + 1 apical seta on ventral tube and only 2 conical spines on postero-external surface of distal dens. Being those characters unknown in other member of the genus, what makes a revision of type material needed. Photos of types were sent to us, by they are dried up and need to be remounted for proper study. N. fimbriatus clearly differs from other Neelus species by the absence lanceolate anterior spines around thoracal s. f. Moreover, it has small body size of all Neelus congeners. Original description of N. fimbriatus was based on 3 females and one juvenile (in alcohol), 2 females and one male under slides and 2 alcoholic specimens from other sample. They were from Otonga, Cotopaxi Province, Ecuador, at 1,900 m alt. July, 1998. Ours come from Guacarí, Valle del Cauca, Colombia. The only diagnostic characters mentioned by Bretfeld & Trinklein (2000) are: “ upper setae pair of ventral head-back ciliate (apomorphy), setae of labial row “ a ” thick and roughly serrate (apomorphy), posterior side of dentes with 1 + 1 basal setae (other 2 + 2) ”. In addition, they mention the “ Total length up to 0.5 mm, length of neosminthururoid setae 6 – 7 µm. Manubrium: dens: mucro = 1.7: 1.8: 1. In our specimens this ratio is 0.78: 1.6: 1. Original description the labrum is very accurate, but basoextenal field of labium was not illustrated. Fig. 9 of Bretfeld & Trinklein (2000) does not illustrate the dental spurs AJ 1 and AE 1. The ratio of antennal segments of our specimens is very similar to that found by Schneider (2017) but the number of setae Ant. II is 4 in ours (5 after Schneider) The total length of the antenna in Colombian specimens is 117 – 120 µm, shorter than those of type material (143 µm). Organite “ Or ” also with two apical filaments. Genital plate of male with only 9 + 9 setae and not 13 + 13 as in the type material. In the discussion, Schneider (2017) states that N. fimbriatus differs from Neelus murinus and Neelus koseli in antennal chaetotaxy, labral setae morphology and post-labial setae morphology. Neelus koseli and N. murinus have 6 setae on Ant. II, our specimens from Colombia have 4 setae and the redescription of Schneider illustrate 5 setae in Fig. 36 A. As the only real diagnostic character of N. fimbriatus is the barbulate seta of the post-labial area of the head, we must consider our specimens belonging to this species.

Description based on Colombian specimens (Figs 1 – 6). Body length 0.4 – 0.5 mm, habitus typical of the genus. Body color on alcohol mostly whitish, dorsally with few brown dots of pigmentation on head, thorax and abdomen. Integumentary channels observed ventrally on head (Fig. 6 A), thorax, and abdomen. Most of setae are microsetae, abdomen with about 50 pairs of tertiary rods. Measurement of most of characters are in micrometers and are presented on table 1. Those of males are average of two specimens and those of female of one specimen. Head (Fig. 1 A). Head length and width as 184 and 176 µm, respectively. Dorsal setae on head smooth and acuminate, frontal setae longer (12 – 16 µm) than those posterior (5 – 7 µm). Antero-dorsal area with 8 + 8 setae and with unpaired seta a 0. Antero-lateral area with 2 + 2 setae. Posterodorsal area with 12 setae. Postero-lateral area with 3 + 3 setae.

Material studied. Male and female mounted on slide, Colombia: Valle del Cauca, Guacarí, Santa Rosa de Tapias (coordinates N 3.81583 ° W 76.24166 °, alt. 1300 m.), 10. vi. 2017, E. P. Marín col., ex. soil. Material deposited at Facultad of Ciencias, UNAM under the numbers 22314 and 22315 (two females); 22316 and 22317 (two males), 22318 and 22319 (unknown sex).

Description. Addendum to Bretfeld & Trinklein (2000). Antenna, adult. Total length of antenna ~ 143.3 µm; max width (Ant. III) ~ 19.4 µm; ratio width: length ~ 0.14; ratio length of Ant. I: Ant. II: Ant. III: Ant. IV ~ 0.22: 0.59: 0.82: 1. Ant. I with three chaetae on dorsal side (Fig. 36 A). Ant. II with five chaetae in two whorls, one chaeta in basal whorl, four chaetae in apical whorl (Fig. 36 A). Ant. III with 13 mesochaetae in five rough whorls (distribution from base to apex: 1, 1, 3, 2 and 6 chaetae), 10 of those chaetae particularly thick; five apical S-chaetae (S 1 – S 5), S 1 and S 4 long and tubular, S 2 and S 3 short and tubular, S 5 short and flam-shaped (Fig. 36 B). S 4 full length could not be assessed. Ant. IV with 15 thin mesochaetae; 11 S-chaetae, nine long with round apex (S), one shorter than S with pointed apex (Sx, 6 µm) and one thicker than S with round apex (Sy); two apical special chaetae with long and thin apex in apical (a) and sub-apical position (sa); a sub-apical organite Or with two apical filaments, in basal position in regard to sa, and apical position in regard to Sx (Fig. 36 C, D). Antenna, sub-adult. Total length of antenna ~ 107.5 µm; max width (Ant. III) ~ 22.3 µm; ratio width: length ~ 0.20; ratio length of Ant. I: Ant. II: Ant. III: Ant. IV ~ 0.35: 0.59: 0.75: 1. Only two chaetae could be see on Ant. I. Ant. II and III as the adult, S 4 full length could not be assessed (Fig. 36 E, F). Only 13 ordinary chaetae could be see on Ant. IV, rest of the chaetotaxy as the adult (Fig. 36 E, F). The chaetotaxic pattern of the apex of the antenna matches with Bretfeld & Trinklein (2000) — see their Fig. 6. Male sexual apparatus. Abd. VI sternum with at least 1 + 1 swollen chaetae sm, maybe 2 + 2 (Fig. 36 G); genital plate with 13 + 13 chaetae (Fig. 36 G); testis slender and curved (Fig. 36 H).

Diagnosis. Whitish with dark brown or reddish brown. 500 µm. Labrum: chaetae a 1 and a 2 with 3 to 7 external teeth. Posterior pair of post-labial chaetae ciliate. Ant. IV with nine S-chaetae S, a and sa acuminate. Abdomen with numerous microspines (tertiary rods). Manubrium with 3 + 3 posterior chaetae. dp with 1 + 1 chaetae.

Comments. There were two pairs of females labeled with the same number (“ ♀ 1 ” and “ ♀ 2 ”). I added a label “ ♀ 4 ” on one of the females “ ♀ 1 ” and a label “ ♀ 5 ” on one of the females “ ♀ 2 ”, at the back of the slides. Early instars were not available but most of the specimens of Neelus fimbriatus I observed did not seem to have reach full development of the antenna morphology (while having mature genital plate). Adult morphology of the antenna was drawn after the specimen “ ♀ 4 ” and sub-adult morphology was drawn after the specimen “ ♀ 5 ”. The antennae of the juvenile were not studied due to a poor positioning on the slide.

Discussion. Closely related to Neelus murinus and Neelus koseli from which it differs in antennal chaetotaxy, labral chaetae morphology and post-labial chaetae morphology.

Material examined. Holotype. ♀ on a slide, Cotopaxi Province, Otonga Reserve, cloud forest, 1900 m, litter sample C, 26. viii. 1996, N. Trinklein leg., [SMC]. Paratypes. 4 ♀ on 13 slides, 1 ♂ on a slide and 1 juvenile on a slide, same data as the holotype, [SMC].