Lumbricillus rubidus Finogenova & Streltsov, 1978

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 30-33

Lumbricillus rubidus Finogenova & Streltsov, 1978 Fig. 12

Lumbricillus rubidus Finogenova & Streltsov, 1978: pp. 17-23, fig. 1; Kossmagk-Stephan 1983: p. 8; Klinth et al. 2017.

Lumbricillus enteromorphae ; sensu Kossmagk-Stephan 1985; nec von Bülow, 1957.

Type material.

ZIAS 1/42509 (Nomenclatura Oligochaetologica). Type locality: Dal’nii Plyazh in Dal’nie Zelentsy Bay, Murmansk, Russia ( Finogenova and Streltsov 1978). Not studied.

Material examined.

SMNH 152792 (CE2549), SMNH 152793 (CE2551), SMNH 152794 (CE2553), SMNH 152795 (CE6105), SMNH 152796 (CE6106), SMNH 152797 (CE6107) & SMNH 152798 (CE6108), seven mature specimens from Sweden. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Description.

Pale to pinkish worms. Length (fixed worms) more than 2.2-3.9 mm (amputated specimens), first 15 segments 2.0-3.1 mm long, width at clitellum 0.31-0.68 mm. More than 17-23 segments. Chaetae slightly sigmoid (Fig. 12A). Dorsal bundles with 3-7 chaetae anterior to clitellum, 3-6 chaetae in postclitellar segments. Ventral bundles with 3-8 chaetae anterior to clitellum, 3-8 chaetae posteriorly. Each worm’s longest measured chaetae 45-50 µm long and 3-5 µm wide. Clitellum extending over XII– 1/2XIII. Head pore not observed. Epidermis with transverse rows of gland cells.

Coelomocytes numerous, 10-20 µm long, round, oval or spindle-shaped. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally (Fig. 12B). Dorsal vessel originating in XIII. One nephridium observed in X, pear-shaped, about 80 µm long, narrowing posteriorly. Anteseptale small, consisting of funnel only. Efferent duct originating at mid length. Brain widening posteriorly, but exact shape uncertain.

Male genitalia paired (Fig. 12E). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 135-265 µm long, 85-170 µm wide making them about 1.5-2 times longer than wide, funnels tapering towards vasa deferentia. Most of vasa irregularly coiled in XII, and 10-20 µm wide. Penial bulbs round, 70-130 µm in diameter. Ovaries in XII. One to five mature eggs present at a time.

Spermathecae (Fig. 12C, D) in V, spindle-shaped, without distinct ampulla. Ectal duct short, about 1/5 of total length of spermatheca, rapidly widening into ampulla. Conspicuous muscle cells encircling duct and connecting it to epidermis. Ampulla making sharp bend inwards and entally connecting with oesophagus. Sperm tightly packed in ectal duct, possibly covered by thin layer of secretion, spermatozoan tails occupying outer part of ampulla, heads aggregating into distinct clusters in inner part, and partly embedded in wall, of ampulla. Spermathecae 120-275 µm long, 60-110 µm wide at widest part of ampulla. Gland cells surrounding ectal pore, forming com pact body with few marginal lobes, glandular body 60-135 µm in diameter at its widest part. One midventral subneural gland in XIV, 60-150 µm long.

Geographical distribution.

Described from Russia and Germany, now genetically identified from Sweden.

Remarks.

The specimens in this study match the original description of L. rubidus by Finogenova and Streltsov (1978) in most characters such as length, number of chaetae and sperm funnel ratio. It seems that our specimens in general possessed larger internal organs, such as sperm funnels, penial bulbs and spermathecae. Nevertheless, the strong musculature around the ectal pore of the spermathecae, originally described as a muscular bulb, was found with clear resemblance in our specimens. This muscular sleeve covering the ectal duct of the spermathecae is conspicuous in all specimens. Several separate muscle bundles radiate around the base of the duct connecting to the body wall and may have a function in widening the pore in conjunction with copulation or fertilization of eggs. In one specimen, where one spermatheca was seen from above, the layers of musculature created a circle seemingly dividing the ectal gland in two. A closer examination revealed that the musculature more probably is tightly encircling the gland cells of the ectal gland without dividing them. The muscular bulb, as originally termed by Finogenova and Streltsov, is probably the same ectal part of the ectal gland, separated by the encircling musculature, rather than a compact mass of muscles. Similar muscle structures encircling the ectal pore of the spermathecae have been seen in most species of Lumbricillus during this study but they never appeared so conspicuous as in L. rubidus .

In 1959, Nielsen and Christensen classified the species L. enteromorphae von Bülow, 1957 as a hunger form of L. rivalis . Kossmagk-Stephan (1985) rejected this idea and instead synonymized L. rubidus with von Bülow’s species based on the fact that they both have muscular bulbs. We agree that L. enteromorphae should be considered a separate species from L. rivalis , because of the asymmetrical ectal glands of the spermathecae and the atrium-like part where the vasa deferentia meets the penial bulbs, observed only in the former species. However, we do not agree that L. rubidus is a synonym of L. enteromorphae , as the former has sperm funnels that are much shorter in relation to their width (2-4 compared to 8 times longer than wide) and lacks any atrium-like part of the vasa deferentia. It is true that von Bülow described a funnel-like thickening of the spermathecal ectal duct which could be a structure similar to the muscular bulb seen in L. rubidus . However, we have observed varied extents of muscular coverings of the ectal ducts in most species belonging to the lineatus group, and a true comparison of this character can only be made once we have specimens of von Bülow’s species.

Lumbricillus rubidus is genetically closely related to L. pumilio (Fig. 1), and shares morphological similarities with both L. pumilio and L. kaloensis (see remarks for each species respectively).