Cantabrodrilus pilarae Martínez-Ansemil, 2025

Cantabrodrilus pilarae Martínez-Ansemil sp. nov.

( Figs 7 View FIGURE 7 , 8 View FIGURE 8 )

Holotype. MHNUSC_10151: mature worm, incomplete (broken after the setae of segment XII), unstained and whole-mounted in Canada balsam. Leg. Ana I. Camacho.

Type locality. CAN177 Latarmá stream near Toyu cave, Venta Fresnedo, Cantabria, Spain, –4.48694, 43.28030 ( 3 September 2002) GoogleMaps .

Etymology. Named after Professor Pilar Rodriguez (University of the Basque Country, Spain), who contributes greatly to the knowledge of the oligochaetes in inland waters.

Description. Small worm, about 80 µm in diameter at segments V and XI (specimen broken after the setae of segment XII). Clitellum unnoticeable. Prostomium short (28 µm long), rounded. Secondary annulation not observed. Somatic setae bifid, 20–30 μm long, with short teeth, upper slightly shorter than lower, 2–3 somatic setae per bundle ( Fig. 8A View FIGURE 8 ); 5 single pointed hook-shaped penial setae per bundle in segment XI, about 20 μm long ( Figs 7B View FIGURE 7 , 8E View FIGURE 8 [ps]). One pair of male pores located in the posterior third of segment XI, in line with somatic ventral setae. One pair of spermathecal pores in segment X, surrounded by a glandular area, in the lateral anterior part of the segment ( Fig. 8B, D View FIGURE 8 [ga]).

Pharyngeal glands in segments III–V. Chloragogen cells beginning in VI. One pair of testes in segment X. One pair of ovaries in segment XI. Sperm sacs entering the posterior part of segment IX. Vasa deferentia short and twisted, 4–5 μm wide, entering apical ends of atria ( Fig. 7A View FIGURE 7 [vd]). Atria elongated, divided in three clearly differentiated parts. The ental part consist in a long, sigmoid, spindle shaped and heavily muscular structure (75–85 μm long, 13 μm in maximum diameter, muscular wall up to 4 μm thick) ( Figs 7A View FIGURE 7 , 8F View FIGURE 8 [ma, m]), the middle part is a simple short curved U-tube (about 5 μm in diameter) connecting the ental and the ectal part ( Fig. 7A View FIGURE 7 [ta]), and the latter is a pyriform, thin-walled and granulated ampulla (60–75 μm long, 20–22 μm in maximum diameter, muscular wall about 2 μm thick), which ends in a slightly curved and gradually narrowing ejaculatory duct (about 15 μm long) provided with a thin layer of circular muscles ( Figs 7A View FIGURE 7 , 8C, E View FIGURE 8 [pa, ad]). Two large prostate glands per atrium, one attached to the anterior end of its muscular ental part, and the other to the posterior end of the ectal ampulla ( Figs 7A View FIGURE 7 , 8B–C, F View FIGURE 8 [pr1, pr2]). Spermathecae composed by a tubular duct (36–40 μm long), and a very long, thin-walled ampulla (115–130 μm long, 20 μm in maximum diameter) directed backwards all along the segment X ( Figs 7C View FIGURE 7 , 8B View FIGURE 8 [sd, sa]).

Distribution and habitat. Hyporheic flow of the Latarmá stream, a tributary of the Lamasón stream at the left side of the Nansa stream basin, Cantabria, Spain. Alt. 180 m.

Remarks. The new species described here is a typical member of the Phallodrilinae , a characteristic subfamily of Naididae that, according to Erséus (1992a) has two important autapomorphies: the absence of coelomocytes and the presence of two compact prostate glands attached to each atrium, one to anterior face, another to posterior face of latter.

Cantabrodrilus pilarae gen. nov., sp. nov. is the only phallodriline with tripartite atria. The highest degree of complexity observed until know in the atria of the Phallodrilinae was the bipartite condition of the atria of Nootkadrilus Baker, 1982 ( atria elongate, bipartite and folded at middle), with which C. pilarae sp. nov. also shares the shape of the penial setae.At first glance, the well set-off U-tube connecting the ental and the ectal part of the atria in Cantabrodrilus could be interpreted as an evolved character with respect to the bipartite atria of Nootkadrilus , but the latter is an atypical genus among the Phallodrilinae , living in the Northwest Pacific Ocean, and defined not only by the bipartite condition of the atria but also by the following apomorphies: absence of anterior prostate gland in the atria, presence of thickened and heavily granulated walls, resembling (and functioning as?) prostate glands, or diffuse prostate-like cells in the ental part of the vasa deferentia (see Erséus 1992a).