Lumbricillus rivalis (Levinsen, 1883)

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 26

Lumbricillus rivalis (Levinsen, 1883) Fig. 7

Pachydrilus rivalis Levinsen, 1883: p. 231; Ditlevsen 1904: pp. 430-431.

Lumbricillus rivalis ; Nielsen and Christensen 1959: pp. 97-98, figs 107-108; Erséus et al. 1999; Erséus et al. 2010; Klinth et al. 2017.

Pachydrilus subterraneus Vejdovsky, 1889: pp. 1-3.

Pachydrilus germanicus Michaelsen, 1886: pp. 43-44.

Lumbricillus evansi Southern, 1909: pp. 151-152, pl. X, figs 10 a–f.

Non Lumbricillus enteromorphae von Bülow, 1957: pp. 82-84, pl. XXVI, figs 6-10, pl. XXVII, fig. 1, pl. XXX, fig. 16.

Type material.

Typus amissus (Nomenclatura Oligochaetologica). Type locality: Langelinie, Denmark (Levinsen, 1883). We did not designate a neotype as we do not have material from the type locality.

Material examined.

SMNH 152782 (CE1873), SMNH 152783 (CE1874) & SMNH 152785 (CE2503), three mature specimens from Sweden, ZMBN 107897 (CE22596), ZMBN 107898 (CE22600) & ZMBN 107899 (CE22602), three mature specimens from Norway. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Description.

Orange-red worms. Length (fixed worms) more than 3.4-7.6 mm (amputated specimens), first 15 segments 2.6-3.8 mm long, width at clitellum 0.60-0.85 mm. More than 17-44 segments. Chaetae slightly sigmoid (Fig. 7A). Dorsal bundles with 4-8(9) chaetae anterior to clitellum, (3)4-7(8) chaetae in postclitellar segments. Ventral bundles with (4)5-10(11) chaetae anterior to clitellum, (4)5-8(9) chaetae posteriorly. Each worm’s longest measured chaetae 85-105 µm long, about 5 µm wide. Clitellum extending over XII–XIII. Head pore at 0/1. Epidermis with transverse rows of gland cells.

Coelomocytes numerous, 15-20 µm long, spindle-shaped, oval, granulated. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally (Fig. 7B). Dorsal vessel originating in XIV. Nephridia observed in VII–X and XV–XXIII, about 145-170 µm long. Anteseptale small, consisting of funnel only. Postseptale oval, tapering posteriorly into efferent duct. Brain with posterior incision, about as long as wide.

Male genitalia paired (Fig. 7D). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 325-685 µm long, 110-295 µm wide, making them about 1.5-4.5 times longer than wide, funnels tapering towards vasa deferentia. Most of vasa irregularly coiled in XII, 25 µm wide. Penial bulbs round, 105-190 µm in diameter. Ovaries in XII. Two mature eggs present in one specimen.

Spermathecae (Fig. 7C) in V, spindle-shaped, without distinct ampulla. Ectal duct short, gradually widening into ampulla. Ampulla with constriction two thirds of the length from pore, dividing it into sections, entally connecting with oesophagus. Sperm evenly embedded in ampulla. Spermathecae 250-360 µm long, 85-140 µm wide at widest part of ampulla. Gland cells surrounding ectal pore forming lobed collar, 140-240 µm in diameter at its widest part. Up to three midventral subneural glands in XIII–XV, 90-130 µm, 80-145 µm and 80-90 µm long, respectively; glands in XV not observed in all specimens.

Geographical distribution.

Genetically identified from Greenland, Norway and Sweden; also recognized from Canada (BOLD:AAF9076). This species was originally described from Denmark and is considered well distributed throughout Europe, and North America.

Remarks.

Pachydrilus rivalis was originally defined by Levinsen (1884) as a species with up to 9 chaetae per bundle, spermatheca formed by a large, red, pear-shaped container (Danish “beholder”), ending ectally with a glandular rosette, but bearing no glands on duct. The nephridial efferent duct originated at the posterior end of postseptale; the postseptals had red spots; the body color was red. Michaelsen (1889, 1900) placed the species in synonymy with L. lineatus along with his own Pachydrilus germanicus Michaelsen, 1886, but Ditlevsen (1904) reinvestigated Levinsen’s type locality (Langelinie, a pier in the port of Copenhagen) and found that only one species conformed to Levinsen’s short primary diagnosis, a species that was different from L. lineatus . He thus expanded the description of rivalis by adding the following traits: body length 15-20 mm, copulatory glands in XIII–XV, dorsal vessel from XIV, chaetal number 6-9 dorsally, 8-11 ventrally. Nevertheless, Welch (1917) and Černosvitov (1937) adhered to Michaelsen’s opinion and the species had to await Nielsen and Christensen (1959) to be revalidated.

Our new specimens fit well with the more detailed re-descriptions, particularly in the number of chaetae and the shape of the spermathecae. The only differences concern the body size, where our worms are much smaller than those reported before, and the length/width ratio of the sperm funnels, which Nielsen and Christensen described as up to 10 times longer than wide, compared to our observed 4.5 times. These differences could be explained by our examination of fixed instead of live material.

Lumbricillus rivalis is genetically most closely related to L. verrucosus (Fig. 1), but it is morphologically more alike L. rutilus (see remarks for that species) and L. enteromorphae , although it can be distinguished from the latter by lacking an atrium-like part where the vas deferens meets the penial bulb (see remarks for L. rubidus ).