Bryodelphax decoratus Gasiorek , Voncina , Degma & Michalczyk, 2020

Gasiorek, Piotr, Voncina, Katarzyna, Degma, Peter & Michalczyk, Lukasz, 2020, Small is beautiful: the first phylogenetic analysis of Bryodelphax Thulin, 1928 (Heterotardigrada, Echiniscidae), Zoosystematics and Evolution 96 (1), pp. 217-236 : 217

Bryodelphax decoratus Gasiorek, Voncina, Degma & Michalczyk sp. nov. Figures 5 , 6 , 12 , Table 4

Locus typicus and type material.

1°50'33"S, 120°16'34"E, 800 m a.s.l.; Bada Lembah, Lore Lindu, Celebes (Sulawesi), Indonesia. Holotype (adult female, slide ID.546.15) and three paratypes (females; slide ID.546.12) deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University; three paratypes (females; slide ID.546.13) deposited in the Department of Zoology, Comenius University in Bratislava; three paratypes (females; slide ID.548.11) deposited in the Natural History Museum of Denmark, University of Copenhagen; one paratype (female; slide ID.546.14) deposited in the Department of Animal Biology, University of Catania; one paratype (female; slide ID.546.16) deposited in the Raffles Museum of Biodiversity Research, National University of Singapore.

Etymology.

From Latin decoratus = beautified, embellished. The name highlights the intricate and beautiful pattern of the dark epicuticular granules. Adjective in the nominative singular.

Adults.

Body translucent; eyes absent or not visible after mounting in Hoyer’s medium. Primary and secondary clavae minute and conical. Cirri interni and externi with poorly developed cirrophores. Cirri A of typical length for Bryodelphax , i.e. reaching around 25% of the total body length. All dorsal plates with well-visible intra-cuticular pillars, the largest pillars present on the scapular, posterior portions of paired segmental and the caudal (terminal) plates (Fig. 5 ). Dark epicuticular granules present on the dorsum (Figs 5 , 6 ), forming visible transverse lines on the scapular plate, distributed along the margins of all plates, lateral scapular sutures and caudal sutures; additionally, two lines of granules parallel to the lateral margins of paired segmental plates are visible (Figs 5 , 6 ). Pores large and easily detectable (Fig. 5 ), but their number varies considerably between both specimens and different elements of the armour, with the largest numbers present on the antero-central portion of the scapular plate and median plate 2 (23-48 pores/100 μm 2, x̅ = 32 and 23-47 pores/100 μm 2, x̅ = 33, respectively; N = 12) and lower numbers on the central portions of the caudal plate and paired segmental plate II (1-38 pores/100 μm 2, x̅ = 19 and 10-27 pores/100 μm 2, x̅ = 17, respectively; N = 12). Scapular plate with lighter rectangles (pseudofacets) between three or four transverse rows of merged dark epicuticular granules (Figs 5C , 6 ). Paired plates divided into two equal anterior and posterior parts by a transverse stripe (Fig. 5D ). Caudal (terminal) plate with poorly developed sutures (Fig. 5A ). Median plate 1 subdivided into the narrow anterior portion with dark epicuticular granules accumulated at the posterior edge and the posterior, unsculptured pentagonal portion with transverse suture (Fig. 5A, D ). Median plate 2 is notably the largest amongst median plates, with well-developed anterior pentagonal portion and weakly-sclerotised posterior portion (Fig. 5A, D ). Median plate 3 with the anterior portion fully developed, triangular and a smaller rounded posterior portion (Fig. 5A, D ). Supplementary lateral platelets present and detectable at lateral-most margins of the segmental plates (Fig. 5B ).

Venter with extremely weakly delineated plates (VII:4-2-2-4-2-2-1), only slightly darker than the surrounding ventral cuticle and without clear, sclerotised margins. Dark epicuticular granules and intra-cuticular pillars absent. Leg papillae undetectable under LCM. Both pulvini and pedal plates absent (Fig. 5B ). Dentate collar IV absent. External claws spurless, but internal ones with minute spurs barely divergent from the claw branches (Fig. 5A , insert).

Juveniles.

Not found.

Larvae.

Not found.

Eggs.

Not found.

DNA sequences.

Two 18S rRNA haplotypes (MT333469-70) and two 28S rRNA haplotypes (MT333462-3) and single ITS-1 haplotype (MT333478).

Phenotypic differential diagnosis.

The new species belongs to the weglarskae group and it must be compared with the three species ( B. instabilis , B. olszanowskii and B. sinensis ) with seven ventral plate rows or with ventrolateral plates in the first row present. Additionally, B. decoratus sp. nov. is compared with B. arenosus , as the new species can have very dim and barely discernible ventral plates and, in such cases, it resembles B. arenosus . Nevertheless, adult females of B. decoratus sp. nov. differ specifically from:

B. arenosus, currently considered endemic to Borneo, by body length (99-120 μm in the new species vs. 76-95 μm in B. arenosus) and dorsal plate sculpturing (separate granules present on entire dorsum in the new species vs. continuous, thickened ridges present on the lateral portions of plates in B. arenosus);

B. sinensis, by the ventral plate formula (VII:4-2-2-4-2-2-1 in the new species vs. VII:2-2-2-2-2-2-1 in B. sinensis) and the caudal (terminal) plate faceting (invisible under LCM in the new species vs. four facets formed by the raised plate areas between two longitudinal and one transversal sutures in B. sinensis);

B. instabilis, by the ventral plate formula (VII:4-2-2-4-2-2-1 in the new species vs. VII/IX:(2)-(1)- 2/4-2-2/4-2-2-2-1 in B. instabilis), the absence of dentate collar IV (present in B. instabilis), the detectability of papilla IV under LCM (undetectable in the new species vs. detectable in B. instabilis) and by the reproductive mode (parthenogenesis in the new species vs. dioecy in B. instabilis);

B. olszanowskii, by the ventral plate formula (VII:4-2-2-4-2-2-1 in the new species vs. VIII:4-1-1-2-2-2-2-2 in B. olszanowskii), the presence of dark epicuticular granules on the dorsum (absent in B. olszanowskii) and by the detectability of papilla IV under LCM (undetectable in the new species vs. detectable in B. olszanowskii).

Genotypic differential diagnosis: p -distances between the new species and the remaining Bryodelphax spp., for which DNA sequences are available, were as follows:

18S rRNA: from 0.3% (B. australasiaticus sp. nov., MT333468) to 3.1% (B. cf. parvulus, HM193371);

28S rRNA from 0.3% (B. australasiaticus sp. nov. and Bryodelphax sp. nov. from Celebes, MT333460, MT333461, and MT333467, respectively) to 9.5% (B. cf. parvulus, MT333466);

ITS-1: from 3.1% (B. arenosus, MT346599) to 23.4% (B. maculatus, MT333479).

Figures

Figure 5. Habitus of adult females of Bryodelphax decoratus sp. nov. (PCM): A - holotype, dorsal view (insert with the claws I, arrowhead indicates spur on internal claw); B - paratype, lateral view; C - frontal part of the body; D - central part of the body, sculpture of median and paired plates. Scale bars in µm.

Figure 6. Semi-schematic drawing of the arrangement of epicuticular granules on dorsal armour of Bryodelphax decoratus sp. nov.

Figure 12. Schematic arrangement of the ventral plates in all members of the weglarskae group (species are arranged in order of the increasing reduction of the ventral armature). Known cases of ontogenetic variability and sexual dimorphism are depicted. Following species taken from Kaczmarek et al. (2012): B. aaseae, B. iohannis, B. parvuspolaris, B. sinensis and B. weglarskae; Gasiorek et al. (2017 a): B. maculatus; Gasiorek & Degma (2018): B. instabilis.