Megalothorax incertus Börner, 1903

Schneider, Clément & Panina, Ksenia, 2023, Revision of Megalothorax incertus Börner, 1903 reveals it to be another widespread Palearctic species of the genus (Collembola, Neelidae), Zootaxa 5318 (4), pp. 474-488 : 475-480

publication ID	https://doi.org/ 10.11646/zootaxa.5318.4.2
publication LSID	lsid:zoobank.org:pub:10C3728D-B718-4074-AC83-142A98A88895
DOI	https://doi.org/10.5281/zenodo.8184063
persistent identifier	https://treatment.plazi.org/id/03FC6644-DC42-2C76-FF79-F8746E17FAAB
treatment provided by	Plazi
scientific name	Megalothorax incertus Börner, 1903
status

Treatment

Megalothorax incertus Börner, 1903 View in CoL View at ENA sensu nov.

Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 , 8A, B View FIGURE 8 ; Tables 1–2 View TABLE 1 View TABLE 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. GoogleMaps Five females on slides (SMNG-APT-AA00013–17), same data as the neotype. GoogleMaps 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. GoogleMaps 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. GoogleMaps 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. GoogleMaps 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. GoogleMaps

Molecular data. One individual from CS.011.IT (same data as neotype) and one individual from Brunoy06 (Genbank accession number in Table 1 View 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 View FIGURE 1 ), 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 View FIGURE 1 ) and 5–6 terminal branches and no cycles ( Fig. 1B, C View FIGURE 1 ); no anterior channel, connection with linea ventralis crossed ( Fig. 1D View FIGURE 1 ). 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 View FIGURE 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 View FIGURE 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 View FIGURE 1 , 8A View FIGURE 8 ). With 7 + 7 postero-dorsal chaetae thickened, lanceolate ( Fig. 1A–C View FIGURE 1 ),anterior chaetae shorter and ordinary ( Fig. 1A View FIGURE 1 ). Ventrally, 3 + 3 post-labial chaetae ( Fig. 1D View FIGURE 1 ).

Labium. Basomedian fields of labium with 3 + 3 chaetae, basolateral fields of labium with 2 + 2 chaetae ( Fig. 1D, E View FIGURE 1 ). Labial palps ordinary, as in Fig. 1E View FIGURE 1 .

Labrum. Chaetae a1, a2 with coarse external teeth, a1 with apical outward curvation ( Fig. 1F, G View FIGURE 1 ). Lamellae of the labral anterior process indistinct.

Other mouthparts. Oral fold with 2 + 2 chaetae ( Fig. 1H View FIGURE 1 ). Maxilla outer lobe with two chaetae (apical and basal), sublobal plate with a strong hair ( Fig. 1H View FIGURE 1 ). Mandibula with 5 apical teeth, as in Fig. 3A View FIGURE 3 . Maxilla as in Fig. 3B, C View FIGURE 3 .

Antenna. As in Fig. 3D View FIGURE 3 . 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 View FIGURE 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 View FIGURE 8 .

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 View FIGURE 2 , 8B View FIGURE 8 ).

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 View FIGURE 3 ).

Abd. IV sternite. With 2 + 2 usual neosminthuroid chaetae, 2 + 2 ordinary chaetae and 1 + 1 small lobes ( Fig. 3F View FIGURE 3 ).

Abdominal appendages. Manubrium with 2 + 2 posterior chaetae ( Fig. 3F View FIGURE 3 ). Dens ordinary, as in Fig. 3G, H View FIGURE 3 . Mucro with thin lamellae, with ~10 teeth on each posterior lamellae ( Fig. 3G View FIGURE 3 ), with possible variations ( Fig. 3H View FIGURE 3 ). 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 View FIGURE 4 ); leg II—1, 1, 1, 3, 7 and 12 chaeta(e) ( Fig. 4B View FIGURE 4 ); leg III—2, 1, 1, 4, 8 and 11 chaeta(e) ( Fig. 4C View FIGURE 4 ). Claws as in Fig. 4A–C View FIGURE 4 , 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 View 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).