Megalothorax incertus Borner 1903
Creators: name: Schneider, Clément
name: Panina, Ksenia
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Collembola
Neelipleona
Neelidae
Megalothorax
Megalothorax incertus

description: Megalothorax incertus Börner, 1903 sensu nov.
Figs 1–4, 8A, B; Tables 1–2
Material examined. Neotype: female on slide (SMNG-APT-AA00012), Italy, Sicily, Palermo, Botanical Garden, 14 Nov. 2014, 38.1126°N, 13.3742°E, upper soil under a Cycas revoluta Thunb., leg. C. Schneider, original collection code: CS.011.IT. Five females on slides (SMNG-APT-AA00013–17), same data as the neotype. All specimens deposited in the Apterygota collection of the Senckenberg Museum f̧r Naturkunde G ̂rlitz.
Other material. Two females on slides (SMNG-APT-AA00018–19), Italy, Sicily, Scopella, Riserva naturale orientata dello Zingaro, coastal path, 22 Nov. 2014, 38.0995°N, 12.7969°E, mosses and upper layer of soil, leg. C. Schneider, original collection code: CS.035.IT. Two females on slides (SMNG-APT-AA00021, 22), France, Île-de-France, Essonne, Brunoy, Laboratoire d’Écologie Tropicale (garden), 01 May 2015, 48.6954°N, 2.4945°E, upper layer of soil under a rock, leg. C. Schneider, original collection code: Brunoy 06. Two females and one male on slide, Russia, Moscow region, near the village of Polyany, 27 June 2022, 55.459787°N, 37.229358°E, upper layer of soil (up to 10 cm), leg. K. Panina. Four females on slide, Russia, Krasnodar, 28 April 2021, 45.0644°N, 38.8144°E, upper layer of soil (up to 10 cm), leg. K. Panina.
Molecular data. One individual from CS.011.IT (same data as neotype) and one individual from Brunoy06 (Genbank accession number in Table 1). Vouchers have not been recovered.
Diagnosis. Colour whitish (in 96 % ethanol), connection of head channels with linea ventralis crossed, basomedian fields of labium with 3 + 3 chaetae, basolateral fields of labium with 2 + 2 chaetae, adult with reduced trunk chaetotaxy (Th. II without a3, abdomen without β2, β4 and ζ4), abdominal s-chaetae s3 present and larger than s2, 2 + 2 chaetae on Abd. IV sternite, retinaculum with 3 + 3 teeth, posterior lamellae of the mucro thin and serrated.
Description. General aspect. Habitus and segmentation typical of the genus. Length from labrum to anus: up to 350 µm. Colour whitish (in 96 % ethanol).
Integument. Secondary granulation present dorsally on the head (Figs. 1A, B), the thoracic region, the abdominal region and Abd. VI sternite. Integumentary channels limited to the lateral and posterior part of the head, with three short lateral crenelations (Fig. 1B) and 5–6 terminal branches and no cycles (Fig. 1B, C); no anterior channel, connection with linea ventralis crossed (Fig. 1D). Channels absent on the trunk.
Sensory fields and wax rods. Ordinary distribution of sensory fields and wax rods secretory crypts: 2 + 2 wrc on head, 12 + 12 wrc on body; including the ones associated with the 6 + 6 sensory fields (Fig. 2). Sensory fields include the swollen inner chaetae, all globular but often barely visible due to low contrast and small size: sf1–6: 0, 1, 3, 2, 1. wrc5 and 6 separated from sf5 by at least 3 granules (Fig. 2).
Head chaetotaxy. Number of chaetae: 12 + 12 in the postero-dorsal region, 10 + 10 and 2 unpaired in the antero-dorsal region, 1 + 1 in the antero-lateral region (Figs. 1A, 8A). With 7 + 7 postero-dorsal chaetae thickened, lanceolate (Fig. 1A–C),anterior chaetae shorter and ordinary (Fig. 1A). Ventrally, 3 + 3 post-labial chaetae (Fig. 1D).
Labium. Basomedian fields of labium with 3 + 3 chaetae, basolateral fields of labium with 2 + 2 chaetae (Fig. 1D, E). Labial palps ordinary, as in Fig. 1E.
Labrum. Chaetae a1, a2 with coarse external teeth, a1 with apical outward curvation (Fig. 1F, G). Lamellae of the labral anterior process indistinct.
Other mouthparts. Oral fold with 2 + 2 chaetae (Fig. 1H). Maxilla outer lobe with two chaetae (apical and basal), sublobal plate with a strong hair (Fig. 1H). Mandibula with 5 apical teeth, as in Fig. 3A. Maxilla as in Fig. 3B, C.
Antenna. As in Fig. 3D. Ant. I with one chaeta. Ant. II with four chaetae, the anterior one stronger than the three others. Ant. III with 10 chaetae and four S-chaetae S1–S4 of the sensory organ; S2 and S3 clearly protruding from the cupule; all S1–S4 with distinct ornamentation in light microscopy. Ant. IV with five ordinary chaetae (including X) and with 10 + 2 S-chaetae (Sb1–5, Sa1–5, Sx and Sy), Sb3 implanted basally, on the same level as S2 and S3 of Ant. III. Organite (Or) well developed. Presence of a distinct cuticular process next to Or.
Thoracic tergites. As in Fig. 3. τ-chaeta and pseudopores indistinct, not studied. Th. II with 11 + 11 chaetae (a3 missing) and 1 + 1 s-chaetae s1. Th. III with 10 + 10 chaetae, a5 sensibly stronger than a6, p4 close to wrc2. Diagram of chaetotaxy provided in Fig. 8B.
Abd. I–V tergites. With 17 + 17 ordinary chaetae, 2 + 2 globular s-chaetae (s2, s3) with s3 sensibly bigger than s2; chaetae β2, β4 and ζ4 absent (Figs 2, 8B).
Abd. VI. Tergite with 4 + 4 and 1 unpaired chaetae. Each anal valve with one small chaeta. Sternite: female with 7 + 7 chaetae, male only partly observed, with at least 1 pair of enlarged (spine-like) postero-axial chaetae.
Genital plate. Ordinary: female with 2 + 2 chaetae (Fig. 3E, F).
Abd. IV sternite. With 2 + 2 usual neosminthuroid chaetae, 2 + 2 ordinary chaetae and 1 + 1 small lobes (Fig. 3F).
Abdominal appendages. Manubrium with 2 + 2 posterior chaetae (Fig. 3F). Dens ordinary, as in Fig. 3G, H. Mucro with thin lamellae, with ~10 teeth on each posterior lamellae (Fig. 3G), with possible variations (Fig. 3H). Ventral tube with 2 + 2 apical chaetae, retinaculum with 3 + 3 distinct teeth.
Legs. Chaetal composition on each legs subcoxa 1, 2, coxa, trochanter, femur and tibiotarsus: leg I—1, 0, 1, 3, 7, 12 chaeta(e) (Fig. 4A); leg II—1, 1, 1, 3, 7 and 12 chaeta(e) (Fig. 4B); leg III—2, 1, 1, 4, 8 and 11 chaeta(e) (Fig. 4C). Claws as in Fig. 4A–C, ordinary, subequal in length. Basal and posterior lamellae of unguis well developed, anterior crest of unguis indistinct. Basal lobe of unguiculus not or feebly protruding.
Affinities. The most similar species are M. perspicillum, M. boerneri sp. nov. and M. laevis Denis, 1948. The differential diagnosis is provided in Table 2. Also see the updated interactive key of the Megalothorax species of the world (Schneider 2022).
Ecology. The species seems widespread, and is mostly found in anthropized environments. In the garden of the Laboratory of Tropical Ecology (France), it was co-existing with both M. willemi and M. minimus (found in the same sample). In Sicily, it was found in close proximity with M. perspicillum. This species assemblage is possibly resulting from the input of soils of various origins throughout the history of the laboratory. In Russia, this species was found in a dry meadow, which was used for a long time as pasture for cows and on agricultural fields using mulch. There, M. incertus sensu nov. also co-existed with both M. willemi and M. perspicillum. These species have not been found in natural habitats in Russia. It is also confirmed from Shanghai, China (see discussion).
description: Published as part of Schneider, Clément & Panina, Ksenia, 2023, Revision of Megalothorax incertus Börner, 1903 reveals it to be another widespread Palearctic species of the genus (Collembola, Neelidae), pp. 474-488 in Zootaxa 5318 (4) on pages 475-480, DOI: 10.11646/zootaxa.5318.4.2, http://zenodo.org/record/8181850