Castrella schareri Diez, 2026, sp. nov.

Castrella schareri sp. nov. urn:lsid:zoobank.org:act: 805206A8-C33D-4D74-9FF3-FD645A71E9CB Figs 1, 2A–E, 3 Diagnosis Species of Castrella with a ~66-µm long stylet. It shows a proximal rod-shaped part and distally, the stylet exhibits a single spiny plate, bearing numerous 5–9-µm-long, fine spines, and a lateral, triangular, 21–22 µm long hook. Etymology Species dedicated to my dear colleague Prof. Dr Lukas Schärer (Basel University, Switzerland) thanks to his enormous contribution to the study of microturbellarians, particularly Macrostomorpha. Lukas also collected and provided me with the material of the new species here described. Material examined Holotype SWITZERLAND • whole mount; Basel, Röserental; 47°29ʹ35.0ʺ N, 07°41ʹ37.8ʺ E; type locality; 12 Apr. 2024; in mosses in a spring; ZMH V13888. Other material Switzerland • (Observations on live animals); 2 whole mounts; same data as for holotype; HU XXVI.3.23–XXVI.3.24. • 1 specimen used for molecular analyses; same data as for holotype. • 3 specimens used for molecular analyses; Ticino, Centovalli; 46°9ʹ47.19ʺ N, 08°38ʹ17.94ʺ E; 8 Sep. 2024; in mosses over rocks in a small river. Description Live animals (Fig. 2A–B) measuring 0.46 – 0.69 mm long (x = 0.58 mm; n = 5), the anterior end is broad and the posterior pointy. They are brownish pigmented due to the presence of fine pigment granules in the epidermis. A pair of eyes (Fig. 2A–B: e) is located posterior to the anterior body’s margin. The eyes are bilobed and give the appearance of four eyes; however, both pigmented spots are connected, and they probably seem more separate because of the squeezing. Posterior to the eyes, the doliiform pharynx is located (Fig. 2A–B: ph). The gut contains diatoms. The atrial organs, testes, and ovaries are located in the posterior body’s third. The vitellaria are brownish and run along the body’s sides (Fig. 2A: vi), between the pharynx and the posterior end. Posteriorly, they fuse before entering the oviduct. The stylet (Fig. 2C: st, 2E, 3) has the typical structure of that in known species of Castrella; it shows a proximal rod-shaped part (Figs 2E, 3: rod) and a distal spiny plate (Figs 2E, 3: sp). It is 56–80 µm (x = 66 µm; n = 3). The proximal part is 20–30 µm (x = 24 µm; n = 3), representing about 36% of the total stylet length. The distal part carries more than 90 fine spines measuring 5–6 µm in the holotype to 7–9 µm in the other specimens. On one lateral side of the spiny plate, there is a strong triangular hook measuring 21–22 µm (n = 2) (Figs 2E, 3B–D: h). The copulatory bulb receives proximally the vas deferens and the necks of extracapsular prostatic glands. The ejaculatory duct forms an internal seminal vesicle (Fig. 2C: sv) in the proximal part of the bulb, which is followed by the prostate vesicle (Fig. 2C: pv). The ejaculatory duct opens into the male atrium at the level of the spiny plate of the stylet. The structure of the female system does not differ from that in other species of Castrella. The ovary (Fig. 2C–D: ov) has the oocytes organised in a row, and increasing in size from proximal to distal; the most anterior part of the ovary exhibits a proliferation area without differentiated oocytes. Distally, the ovary connects to the oviduct (Fig. 2D: od), and close to it opens the common vitelloduct. A seminal receptacle (Fig. 2D: sr) also empties in the anterior part of the oviduct. Both the oviduct and the bursa (Fig. 2D: b) open into the common atrium.