Megalothorax poinsotae Panina, Bedos, Deharveng & Schneider, 2026, sp. nov.

Megalothorax poinsotae sp. nov. urn:lsid:zoobank.org:act: 491D0472-F156-4FCA-9C13-386A825FFF93 Figs 1F, 6–8, Tables 1–2 Diagnosis Megalothorax poinsotae sp. nov. can be attributed to the incertus -group with the common character states combination: cross connection of head channels with linea ventralis, serrated mucro, presence of s3 sensilla on abdomen, globular inner sensilla, 2+ 2 chaetae in the basolateral field of labium, 3 +3 chaetae on Abd. IV sternites and 4+ 4 teeth on the retinaculum. This species is similar to M. cellarincola sp. nov. by the presence of strong lanceolate chaetae on the back of the head and some parts of the thorax. These species are distinguished by the chaetotaxy of the abdomen. In M. poinsotae sp. nov. chaetae p4 and ε1 are absent (vs present in M. cellarincola). In chaetotaxy, the new species resembles M. perspicillum, apart from the absence (vs presence in M. perspicillum) of chaeta β3 and ε1 on abdomen. In M. poinsotae sp. nov. cuticular channels on abdomen are absent (vs present in M. perspicillum). Megalothorax poinsotae sp. nov. also resembles M. laevis Schneider et al., 2018, apart from the absence (vs presence in M. laevis) of the chaetae p4, β3 and ε1 on abdomen. In addition, M. poinsotae has chaeta β2 present (vs absent in M. laevis) and serrated mucro (vs smooth mucro in M. laevis). The widespread M. incertus differs from the new species by the absence of chaeta a3 on thorax II and chaeta ζ4 on abdomen (vs present in M. poinsotae sp. nov.). The closely related species M. boerneri has a chaetotaxy similar to M. poinsotae, but the chaetae β3, β4 and ε1 are absent in the new species (vs present in M. boerneri). Etymology The species is dedicated posthumously to Nicole Poinsot, for her work on the taxonomy and ecology of Collembola in Provence. Poinsot reported a so-called M. minimus (this species was ambiguously defined at the time) in the sansouire, an halophilous vegetal formation of Camargue (Poinsot 1975). Type material Holotype FRANCE • ♀; Var, Sainte-Maxime, plage de la Madrague, litter and algae among Salicornia L.; 6.65684° E, 43.31301° N; ca 1 m a.s.l.; 27 Jan. 2024; Deharveng and Bedos leg; SMNG, sample code no. 83-556, slide no. SMNG-APT-AA04667. Paratypes (6 ♀♀) FRANCE • 2 ♀♀; Var, Sainte-Maxime, plage de la Madrague; 6.65684° E, 43.31301° N; ca 1 m a.s.l.; 27 Jan. 2024; Deharveng and Bedos leg; litter and algae among Salicornia L.; Apterygota collection SMNG, slides nos SMNG-APT-AA04668 to 71 • 2 ♀♀; same data as for preceding; MPSU, slides nos 83-556–spec1, 83-556–spec2 • 2 ♀♀; same data as for preceding; MNHN, slides nos 83-556A, 83-556B. Other material FRANCE • several specs in ethanol; Var, Sainte-Maxime, plage de la Madrague, litter and algae among Salicornia L; 6.65684° E, 43.31301° N; ca 1 m a.s.l.; 27 Jan. 2024; Deharveng and Bedos leg; Apterygota collection SMNG, tubes no. SMNG-APT-EA-003-005 • several specs in ethanol; same data as for preceding; MNHN. Morphological description GENERAL ASPECT. Habitus and segmentation typical of the genus. Body length up to 400 µm. Specimens whitish in ethanol. Body chaetotaxy sparse including chaetae, s-chaetae, trichobothria, neosminthuroid chaetae, wax-rods and inner sensilla within sensory fields 2–6. Most of chaetae lanceolate on body, but some are of ordinary morphology. INTEGUMENT. Secondary granulation made of the usual dorsal rough granules. Integumentary channels not reaching the posterior part of the head, limited to short ventral channels forming a cross connection with the linea ventralis. SENSORY FIELDS AND WAX RODS (Fig. 6A). Sensory fields (sf 1–6) and their inner sensilla, as well as wax rods wrc1–7 with typical distribution of the genus. Inner sensilla of sf 2 broad flame-shaped, the other s are globular. MOUTHPARTS. Labrum as typical of the incertus -group with tips of a1-chaetae straightening up to point forward, a1 with two small external teeth, a2 external teeth imperceptible. LABIUM. With 4+4 proximal chaetae, basomedian fields with 3+3 chaetae, basolateral fields with 2 +2 chaetae (Fig. 6E). Labial palp (Fig. 6E) as common for the genus (A, B, C, D, E, b1, b2, d1, d 2, 2e, H, h1, h2). Oral fold and maxillary outer lobe as typical of the genus, with two sublobal hair (Fig. 6F). Maxillary head without strong modification (Fig. 6C). Mandibula ordinary (Fig. 6D). HEAD CHAETOTAXY. Forehead chaetotaxy as on Fig. 6B. Clypeal-labral formula: a0; 2, 4, 5, 4, 5, 4. Chaeta a0 present. Dorsal posterior area with 18 ordinary chaetae (Fig. 6B). Ventral side with three pairs of post-labial chaetae. Trend for posterior chaetae to be longer and stronger than anterior chaetae, including posterior lanceolate chaetae. ANTENNAL CHAETOTAXY (Fig. 7A, B). Ant. I and II with one and four chaetae, respectively. Ant. III with nine chaetae and two long S-chaetae (S1 and S4). Striations of Ant III sensory organ short sensilla (S2 and S3) distinguishable in light microscopy. Ant. IV with five chaetae (X-chaeta present) and ten S-chaetae. Sensory organ with Sx, Sy, Or, a, Sa. Organite (Or) of Ant IV short, seems apically flared. Summary on antennal chaetotaxy provided in Table 1. BODY CHAETOTAXY. Chaetotaxy of thorax and abdomen reduced. Th. II with 12 +12 chaetae, 1+1 tubular and curved s1-sensilla (Fig. 6A). All chaetae ordinary. Th. III with 9 + 9 chaetae (chaeta p4 absent) and 5+5 free wax-rods (wrc 2 absent). Chaeta a5 is longer and stronger than chaeta a6. Abd I–V terga with 17 +17 ordinary chaetae (chaetae β3, β4, ε1 absent) with 1+1 wrc (wrc 7 ordinary), 2+ 2 globular sensilla s2 and s3 (Fig. 6A). Sensilla s3 bigger than s2. LEGS CHAETOTAXY. Typical of the genus (Table 2), consisting of ordinary chaetae of variable size (Fig. 7C– E). CLAWS. Claw III bulkier than claw I and II. Claws subequal in unguis length (with a trend as unguis I> unguis II> unguis III). Unguis basal and posterior auxiliary lamellae well developed (Figs 7 C-E). Unguiculus 0.5–0.6 as long as unguis. ABD. IV STERNUM AND FURCa. Abd. IV sternum with 2 +2 neosminthuroid chaetae and 2 + 2 chaetae. Manubrium with 1+ 1 posterior chaetae (Fig. 7F). Proximal subsegment of dens with a posterior chaeta (Fig. 7F); distal subsegment posteriorly with two basal spines and one chaeta at the middle. Anterior side of dens with five apical spines, spines without elongated apex (Fig. 7F). Dens ordinary, as in Fig. 7F. Mucro serrated (Fig. 7F). ABD. VI. Typical of the genus: with nine dorsal chaetae; each anal valve with a chaeta. Mature females with 8+8 ventral chaetae. Genital plate: female with 2+ 2 chaetae. Male unknown. TENACULUM AND VENTRAL TUBE. Tenaculum with 4+4 hook-like teeth. Ventral tube bulky with two apical pairs of chaetae. Distribution and ecology So far known only from the type locality, it is the first species of Megalothorax to be found in a true littoral habitat (Salicornetium). Three species of Collembola were present in the same sample with Megalothorax poinsotae sp. nov.: an Hypogastrura sp., and two typically littoral species of Isotomidae: Archisotoma sp. and Halisotoma sp. Molecular data One topotype specimen sequenced (sample code 83-556), BOLD process id CSCOL001-25.