Micronella najtae, Javier I. Arbea, 2017

Javier I. Arbea, 2017, Micronella najtae n. sp. (Collembola: Brachystomellidae), a new species from Tierra del Fuego with a key to the species Javier, Zoosystema 39 (1), pp. 15-20 : 16-20

Micronella najtae n.sp.

( Figs1 , 2 ; Tables1, 2)

type mAteriAl.— Holotype. ♀, Tierra de Fuego, near Rio Grande , Argentina, Chiliotrichum Cass. dense scrub, with Festuca gracillima Hook.F. and Chiliotrichum diffusum (G.Forst), S.M. Bonaventura and V.Mascitti leg., II.2001, deposited in MNCN .

Paratypes. All specimens from same locality as holotype, 2 ♀ and 1juvenile. ♀ paratype deposited in MNCN, ♀ and juvenil paratypes in MNHN.

type locAlity.— Argentina, Tierra del Fuego, near Rio Grande (53°36’S, 68°04’W).

DiAgnosis.—Habitus and buccal cone typical for the genus Micronella. Ant IV with six sensilla. PAO with 7-8 vesicles. Whitout eyes. On Abd tergites s-chaetae 2.3-2.6 times longer than ordinary chaetae, formula of s-chaetae per half tergum: 022/211110. Head with chaetae a0 and without chaeta d0/dx. Th I with 3 + 3 chaetae. Th II with a2 chaetae. Abd I-III with s-chaetae in position p4. Furca absent.Tibiotarsi I, II and III with 17, 17 and 16 chaetae, respectively. Claw without inner tooth. Each anal valve with 1 hr microchaetae.

etymology.—The new species is dedicated to the late Judith Najt, a prominent Argentinean-French researcher of Collembola .

Description Body

Habitus typical of the genus. Body length of holotype female: 0.63mm; body length of paratypes: 0.54-0.70mm. Colour in ethanol: white, no pigmentation.

Antennae

Ratio head diagonal: antenna = 1:0.66. Ant I with 7chaetae. Ant II with 12 chaetae. Ant III and IV fused dorsally, ventral separation marked. AIIIO with 2 small club shaped sensilla, 2longer and subcylindrical guard sensilla; ventral microsensillum present. Ant IV with simple apical bulb and 6 sensilla (S1-4, S7, S8), two weakly differentiated from ordinary chaetae (S3 and S8); dorsolateral microsensillum present; subapical organite round; with about 30 short ventral chaetae (Fig. 2D, E).

Head

Without eyes. PAO with 7-8 vesicles disposed in rosette (Fig. 1C). Maxilla rectangular with 5 teeth (Fig. 2F). Labral formula: 2/2334. Labium typical of Brachystomella (Fig. 2G), labial palp with one papillated chaeta (A) and 4 proximal chaetae (a1-2, p1-2); mentum with 5 chaetae (b, c, d, e, e’); submentum with 4 chaetae (E, F, G, f).

Dorsal chaetotaxy ( Fig. 1A )

Head with chaeta a0, 3+ 3 oc chaetae and without d0/dx chaeta. Dorsal chaetotaxy composed of ordinary smooth chaetae and s-chaetae becoming longer towards the distal segments of the body. Ratio of Abd I-III ordinary chaetae: s-chaetae = 1:2.3-2.6. Th I with 3 +3 chaetae. Sensillar formula by half tergum: 022/211110. Th II and III with s-chaetae in position p3 and m6; microsensillum adjacent to m6 s-chaetae on Th II. Abd I-III with s-chaetae in position p4; one s-chaeta also present on Abd I as p6. Abd IV-V with s-chaetae s in position p3 and p2 respectively. Full description of dorsal chaetotaxy is given in Table 1.

Ventral chaetotaxy ( Figs 1B ; 2A )

Head with 2+ 2 postlabial chaetae. Th I-III sterna without chaetae. Ventral tube with 3+3 distal chaetae. Abd I-III sterna with 0, 1+1, 3 +3 chaetae respectively.Furca completely absent, with well-defined furcal area with six microchaetae arranged in two rows: anterior row with four microchaetae and posterior row with two microchaetae (Fig. 2H). Abd IV sternum chaetotaxy, according to nomenclature of Massoud& Najt (1975): 6+ 6 peripheral chaetae, central polygon formed by 3+3 chaetae, 1 +1 anterior chaetae and 2+2 posterior chaetae (Fig. 2A). Abd V sternum with 4+ 4 chaetae between macrochaetae. Each anal valve with 11 chaetae and 1 hr microchaetae.

Legs

Chaetotaxy of legs I-III as follows: Scx I- 1, 2, 2; Scx II- 0, 2, 2; Cx- 3, 6, 7; Tr- 5, 5, 5; Fe- 12, 10, 10; Tita- 17(10 +7), 17(10+ 7), 16(10 +6). Tenent hair on tibiotarsi acuminate; unguis of legs I-III without median inner tooth (Fig. 2B, C).

Key to the species oF MICRONELLA Arlé, 1959 (pArtiAlly AFter Queiroz & menDonçA 2013)

1. PAO with up to 13 vesicles; unguis without or with minute inner tooth ..................................................... 2

— PAO with 15 vesicles, unguis with inner tooth ..................................... Micronella checayensis Massoud, 1967

2. Th II with a2 chaetae; Abd I-III with s-chaetae in position p4 .................................... Micronella najtae n.sp.

— Th II without a2 chaetae; Abd I-III with s-chaetae in position p3 ................................................................ 3

3. PAO with up to eight vesicles; ratio ordinary chaetae:s-chaetae on Abd I-III approximatly 1:1 .................... 4

— PAO with 12-13 vesicles; ratio ordinary chaetae: s-chaetae on Abd I-III = 1:2 ................................................ ...................................................................................... Micronella longisensilla Queiroz& Mendonça, 2013

4. Ant IV with six sensilla; smooth chaetae on body; unguis without inner tooth ...... Micronella porcus (Denis, 1933)

— Ant IV with five sensilla; serrated chaetae on body; unguis of Tita I and II with minute inner tooth .............. .......................................................................................... Micronella itacaman Queiroz& Mendonça, 2013

DISCUSSION

The new species, Micronella najtae n.sp., is well characterised in the genus. It can be distinguished from its congeners by dorsal chaetotaxy (a2 chaetae present on Th II and s-chaetae on Abd I-III in position p4). In relation to sense organs on antennae and number of vesicles on PAO, the new species is most similar to M. porcus , as they have six sensilla on Ant IV, sensory “clubs” on AIIIO and 6-8 vesicles on PAO. Main differences between all Micronella species are summarized in Table2.

Figures

FIG. 1. — Micronella najtae n. sp.: A, dorsal chaetotaxy; B, ventral chaetotaxy; C, PAO and its surrounding chaetae. Abbreviations: see Material and methods. Scale bars: A, B, 0.1 mm; C, 0.03 mm.

FIG. 2. — Micronella najtae n. sp.: A, anal valves and ventral view of Abd IV-VI; B, tita of leg I; C, tita of leg III; D, dorsal view of Ant III-IV; E, ventral view of Ant III- IV; F, maxillae; G, labium; H, furcal area and its surrounding chaetae. Abbreviations: see Material and methods. Scale bars: A, 0.1 mm; B-H, 0.03 mm.