*Description of the new species*

Adult females (measurements and statistics in Table 3). Body light yellow in live specimens (transparent after mounting in Hoyer's medium) (Figure 1A–C), eyes absent or not visible after mounting on microscope slides. Small and conical primary and secondary clavae present. Cirri *internus* and *externus* with poorly developed cirrophores. Cirri *internus* always shorter than cirri *externus*. Cirri *A* of a typical length for *Bryodelphax*, i.e., up to 25% of the total body length. Only lateral appendages cirri *A* present apart from head appendages.

Dorsal sculpture, visible in PCM, composed of intra-cuticular pillars (visible as dark dots/granules) and pores (visible as white dots) (Figure 2A–C). The cuticular pillars (granules) on scapular plate 0.6–1.8 μm in diameter, on caudal plate 0.6–1.6 μm in diameter and on other plates 0.6–1.4 μm in diameter. Pores large and easily detectable (Figure 2A–D), distributed unevenly on scapular plate (0.3–0.6 μm in diameter; 0–14 pores/100 μm2, x = 7.5, *N* = 10); on caudal plate (0.6–1.0 μm in diameter; 0–19 pores/100 μm2, x = 4.44, *N* = 10) and on other plates (0.3–0.8 μm in diameter; 1–16 pores/100 μm2, x = 6.3, *N* = 10). Median plates 1 and 2 divided by smooth transverse stripe, median plate 3 undivided. Median plate 2 largest among all median plates. Paired plates 1 and 2 also divided transversely into two parts by smooth stripes.

Ventral side with three rows of greyish plates (formula: III:2-2-1). First row with two plates just below the head (Figure 3A,D, filled arrowheads). Three genital plates surrounding the gonopore (two lateral, in line with the gonopore) and the third one situated posteriorly to the gonopore (Figure 3B–D, empty arrowheads)).

Papilla-like structure on leg I hardly visible under PCM but visible in SEM (Figures 1C and 4A,B, arrow). Papillae on leg IV present (Figures 1C and 4D, arrowhead). Dentate collar absent on leg IV (Figure 1A–C). All claws slender, claws IV always slightly longer than claws I–III. External claws smooth, internal ones with a small spur pointing downward and placed very close to the claw bases (Figure 4A–D). The female gonopore with the typical six-petal rosette.

**Males and Juveniles.** Not found.

**DNA sequences**

**COI**: three sequences; 584–672 bp;

**18S rRNA**: two sequences; 528 bp long;

**28S rRNA**: two sequences; 671 bp long.

**Differential diagnosis.** Presence of ventral plates attributes *Bryodelphax mareki* sp. nov. to the *weglarskae* group. Within this group, only *Bry. amphoterus* (Durante Pasa and Maucci [58]), *Bry. maculatus* G ˛asiorek, Stec, Morek, Marnissi and Michalczyk [58] and *Bry. nigripunctatus* Degma, G ˛asiorek, Vonˇcina and Michalczyk [30] have a reduced number of ventral plate rows to two or three, as in the new species [30]. Adult females of *Bry. mareki* sp. nov. differ from:

*Bry. amphoterus*, known only from Croatia and Greece (McInnes [59]), by different formula of ventral plates (III:2-2-1 in the new species vs. II:2-2 in *Bry. amphoterus*), presence of papilla-like structure on leg I and papillae on leg IV and absence of dentate collar on leg IV.

*Bry. maculatus*, known only from Tunisia and Greece (G ˛asiorek et al. [60]), by higher *sc* of clava (*20.4–33.0* in the new species vs. *11.5–19.1* in *Bry. maculaus*), longer cirrus *A* (35.2–46.7 μm in the new species vs. 27.3–34.9 μm in *Bry. maculatus*), higher *sc* of cirrus *A* (*174.1–212.9* in the new species vs. *114.8–152.5* in *Bry. maculatus*) and absence of dentate collar on leg IV.

*Bry. nigripunctatus* known only from Spain (G ˛asiorek et al. [30]), by absence of epicuticular granules, longer clava (4.3–6.2 μm in the new species vs. 2.7–3.1 μm in *Bry. nigripunctatus*), higher *sc* of clava (*20.4–33*.0 in the new species vs. *12.3–16.9* in *Bry. nigripunctatus*) and presence of papilla-like structure on leg I.
