Fendia cantabrica, Rodriguez, 2023

Fendia cantabrica View in CoL n. gen., n. sp.

( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Dorydrilus sp.1 : Achurra 2012. Tables 1, p.54; Table 2, p.56; Appendix 2, p.223.

Lumbriculidae gen. sp.: Achurra et al. 2015.Table 1, p. 151.

Holotype. MNCN16.03/3155 , 25 February 2012 (Pilar Rodriguez coll.)

Paratypes. 6 sexually mature individuals, all from the type locality, sampled on 25 February 2012; 3 dissected ( MNCN16.03/3156 -16.03/3158), and two whole mounted ( MNCN16.03/3159 -16.03/3160), all Stained in hematoxylin, dehydrated and mounted in Canada balsam; two specimens sectioned ( MNCN16.03/3161 -16.03/3171), stained in eosin-hematoxylin and mounted in DPX. (Pilar Rodriguez coll.)

Other material. One dissected individual, stained in hematoxylin, from Cave El Pindal , Piniango, Rivadedeva, Asturias ( Spain), located at 24 m asl. Coordinates: 30 T 4806099 N 375873E (Ana Camacho coll.), 18 March 1989 .

Four individuals from the type locality, sampled 7 July 2008 (Ainara Achurra and Pilar Rodriguez coll.): one whole mounted and 3 dissected, sexually mature individuals, Stained in hematoxylin, dehydrated and mounted in Canada balsam. Seven sexually mature individuals sampled 25 February 2012 (Pilar Rodriguez coll.): 4 dissected, 2 whole-mounted, Stained in hematoxylin, dehydrated and mounted in Canada balsam; 3 individuals sectioned, stained in eosin-hematoxylin and mounted in DPX, all Stained in hematoxylin, dehydrated and mounted in Canada balsam. One half-mature individual, whole-mounted, 25 February 2012 .

Type locality. La Borbolla, springs of the Cabra River, Cantabrian Mountains , Llanes, Asturias ( Spain). Coordinates: 30T 4802519 N, 0367630 W, at about 100 m asl.

Etymology. The genus is dedicated to Steven V. Fend, in recognition of his important contribution to the knowledge of the family Lumbriculidae , and for the opportunity he gave to the author for establishing a fruitful collaboration in the study of the aquatic oligochaetes from the Nearctic region. The species name refers to the Cantabrian Mountains.

Description. Complete specimens up to 77 segments. Width of the body 240–500 µm at the clitellum. Prostomium short and rounded, 90–124 µm long, 200 µm wide at the base. Male pores paired, posterior to, and in line with ventral setae of segment X, in circular depressions 104–106 µm diameter ( Figs. 1A View FIGURE 1 ; 2E View FIGURE 2 ). Spermathecal pores paired, 30 µm diameter, posterior to, and in line with ventral setae of segments XI and XII. One pair of female pores open ventrally, in 11/12 ( Fig. 1B View FIGURE 1 ). Secondary annuli present from segment III to segment IX. Two chaetae per bundle, sigmoid, single-pointed ( Fig. 2B View FIGURE 2 ). Anterior ventral chaetae (II to X) 60–123 µm long, shortest in segment II, and progressively longer up to VI; ventral chaetae in segment X usually somewhat shorter than those of adjacent segments (91–112 µm long). Dorsal chaetae in anterior segments 59–92 µm long, 0.6–0.9 times as long as the ventral ones of the same segment; shorter in II, and progressively longer up to VII. Posterior chaetae gradually shorter, down to 82–93 µm long. Ratio tip-nodulus/total length of chaetae = 0.35–0.42.

Body wall with epidermis 10–24 µm high and muscle layers up to 22 µm thick, measured in the anterior body section. Pharynx well developed dorsally and ventrally, to segment III ( Fig. 2A View FIGURE 2 ). Clitellar epithelium weakly developed from X to XII (or to anterior part of XIII), but well distinguished from non-clitellar epithelium ( Fig. 2C View FIGURE 2 ) and formed by squared glandular cells, ordered in lines ( Fig. 2D View FIGURE 2 ). Pharyngeal glands present in segments (IV) V to VII (VIII). Chloragogen cells inconspicuous, beginning in segment VI. Blind posterior lateral blood vessels absent. Nephridia from 12/13, forming long tubes in the ventral side of the segments; the ectal efferent duct forms a small vesicle, observed only in a few segments, and the nephridiopores open just in front of the ventral bundle of chaetae ( Fig. 2J View FIGURE 2 ). Sperm sacs forward to segment (VIII) IX and backward to segment XI or XII. Egg sac backward to segment XIII.

Two pair testes, in IX and X, and one pair ovaries in XI. Two pairs of tiny sperm funnels are located on septa 9/10 and 10/11 ( Figs. 1B, C View FIGURE 1 ; 2F View FIGURE 2 ). Vasa deferentia narrow (8–14 µm in diameter), barely visible in some cases. The posterior vas deferens does not penetrate the postatrial segment. Atria very large and heavily muscular, with both the duct and the ampulla covered by very thick musculature (35–100 µm) forming several crossing layers, the outer longitudinal ( Figs. 1B, C View FIGURE 1 ; 3A, B View FIGURE 3 ). Both atria are always oriented in opposite directions, one forward and the other backwards, and the latter can cross into segment XI ( Fig. 1B View FIGURE 1 ). The junction of the vas deferens to the atrium is not clearly seen due to the extraordinary thickness of the atrial musculature, but it appears to join through the base of the ampulla ( Figs. 1B View FIGURE 1 ; 3E, F View FIGURE 3 ). Atrial ampullae 120–325 µm long, 106–198 µm wide, covered by a layer of one-cell thick peritoneal (?) cells, and two well-separated clusters of prostatic glands, each formed by several cells, joined to the atrial ampulla by a single stalk which crosses the atrial musculature through a well-defined, straight passage (5–7 µm diameter). Two prostatic passages are shown at opposite poles of the ampulla joining the two-branched atrial lumen ( Figs. 1B, C View FIGURE 1 ; 2F View FIGURE 2 ; 3A, C View FIGURE 3 ). The lumen of the atrial ampulla (30–50 µm wide) is lined by a poorly defined layer of epithelial cells ( Figs. 2F View FIGURE 2 ; 3C, D View FIGURE 3 ); in some individuals, there is sperm within the atrial lumen. Atrial duct very thick (127–162 µm long, 106–111 µm wide), forming a muscular penial bulb with outer longitudinal (to 22 µm thick) and inner circular (to 15 µm) layers of muscles ( Figs. 1B, C View FIGURE 1 ; 3A, E–I View FIGURE 3 ). Large vacuoles in the penial epithelium ( Fig. 3G, H View FIGURE 3 ), probably providing a hydrostatic skeleton. It is a “type-2 penis”, as defined by Cook (1967) and Rodriguez & Giani (1994); it may protrude through the wide male pore to about 25 µm ( Figs. 2E View FIGURE 2 ; 3F View FIGURE 3 ). A dense ring of gland cells, up to 27–80 µm high, surrounds the base of the atrial duct, around the male pore ( Figs. 1B, C View FIGURE 1 ; 3A, E, F View FIGURE 3 ).

Spermathecae paired in segments XI and XII. They have sac-like, simple ampullae (first pair: 54–114 µm long, 38–72 µm wide; second pair: 55–111 µm long, 50–88 µm wide), and a narrow-duct (82–100 µm long, 11–23 µm diameter) that gets thinner toward the junction with the ampulla, and forms an ectal vestibulum (47–62 µm long, 38–43 µm wide, internal lumen 22 µm wide covered by a thin cuticle) ( Figs. 1B View FIGURE 1 ; 2G–I View FIGURE 2 ). The spermathecal vestibulum and the duct are covered by circular muscles (to 12 µm thick), and an outer longitudinal muscle layer (ca. 5 µm thick) ( Fig. 2H, I View FIGURE 2 ). Female funnels small, attached to the septum 11/12 ( Fig. 2I View FIGURE 2 ).

Taxonomic remarks. The species was originally attributed to the genus Dorydrilus Piguet , since only the anterior vas deferens was visible in the first collection of 2008. New material found in the later collection made it possible to observe the tiny anterior and posterior sperm funnels, thus establishing the semiprosoporous male duct pattern of the species.

Fendia cantabrica n. gen. n. sp. shows a unique combination of the following characters: very thick atrial musculature organized in several cross-hatched layers, protrusible penis assisted by both muscular and vacuolar (hydrostatic) systems, and petiolate prostatic glands forming clusters joined to the atrium through two opposite passages. Only the two latter characters can be considered as apomorphies of the new genus relative to the family Lumbriculidae (see discussion, below).

Among the semiprosoporous lumbriculid species with spermathecae in the ovarian and postovarian segments, the presence of atrial musculature with muscle bundles organized in a crossing pattern, a long protrusible penis and prostatic cells in few clusters is also known in Trichodrilus longipenis Rodriguez & Giani, 1994 ( Giani & Rodriguez 1994). That species presents a spherical atrium covered by a continuous layer of small prostatic cells and a few large clusters of prostatic glands attached to the atrium in a diffuse manner (not by common stalks). This species has a penis which also extends from the inner epithelial layer of the atrial duct through the male pore; however, there is not a vacuolar system in the penis nor glandular cells at the male pore.

Ecological remarks. Fendia cantabrica n. gen. n. sp. inhabits the unpolluted karst springs of the Cabra River, at La Borbolla and a small stream in the cave El Pindal. Those sites are only 9 km apart. Water characteristics and sediment particle distribution in the spring of the Cabra River were measured in only one occasion (7th July, 2008), showing pH= 7.4, 12.4 °C,> 97% dissolved oxygen, 296 μS cm-1, 2.7% loss on ignition, and 1.6 % silt-clay in the <1mm sediment fraction ( Achurra 2012). The gut content included organic detritus and large sand grains.