Lumbricillus rutilus Welch, 1914

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 22-23

Lumbricillus rutilus Welch, 1914 Fig. 4

Lumbricillus rutilus Welch, 1914: 143-151, pl. VIII, fig. 13, pl. IX, figs 14-24; Klinth et al. 2017.

" Lumbricillus rivalis "; BOLD (published records; Vivien et al. 2015)

Type material.

USNM 25507, 26318, 30863-4 (Nomenclatura Oligochaetologica). Type locality: Chicago Sewage Testing Station, United States ( Welch 1914). Not studied.

Material examined.

SMNH 152801 (CE1887), SMNH 152802 (CE1903), SMNH 152804 (CE2510), SMNH 152809 (CE2937), SMNH 152811 (CE2939), SMNH 152813 (CE3060), SMNH 152814 (CE3061) & SMNH 152819 (CE9267), eight mature specimens from Sweden; SMNH 152815 (CE3502) & SMNH 152816 (CE3506), two mature specimens from the United Kingdom. For information on specimen collection locality and GenBank accession numbers see Appendix 1.

Description.

Orange-reddish worms. Length (fixed worms) more than 2.7-7.2 mm (amputated specimens), first 15 segments 2.4-4.8 mm long, width at clitellum 0.39-0.65 mm. More than 14-30 segments. Chaetae (Fig. 4C) slightly sigmoid. Dorsal bundles with 3-6, rarely 2 or 7, chaetae anterior to clitellum, 2-5 chaetae in postclitellar segments. Ventral bundles with 3-9, usually 4-6, chaetae anterior to clitellum, 2-6 chaetae posteriorly. Each worm’s longest measured chaetae 70-105 µm long, about 3-5 µm wide. Clitellum generally extending over XII– 1/2XIII, sometimes including all of XIII. Head pore at 0/1. Epidermis with transverse rows of gland cells.

Coelomocytes in some specimens numerous, 10-25 µm long, round, oval or spindle-shaped, granulated. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally (Fig. 4B). Third pair larger, occupying most of VI, sometimes extending into VII. Dorsal vessel originating in XIV. Nephridia (Fig. 4D) observed in XV–XXI, about 120-170 µm long. Anteseptale small, consisting of funnel only. Postseptale oval, tapering posteriorly into efferent duct. Brain (Fig. 1B) slightly widening posteriorly, with posterior incision.

Male genitalia paired (Fig. 4F). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 295-395 µm long, 145-225 µm wide, making them about 1.5-2.5 times longer than wide, funnels tapering towards vasa deferentia. Most of vasa irregularly coiled in XII, 20-30 µm wide. Penial bulbs round, 110-175 µm in diameter. Ovaries in XII. Two to six mature eggs present at a time.

Spermathecae (Fig. 4D) in V, spindle-shaped, without distinct ampulla. Ectal duct short, muscular, widening into ampulla. Ampulla, after widest part, making sharp bend before entally connecting with oesophagus. Sperm evenly embedded in tissue of ectal duct and ampulla. Spermathecae 215-335 µm long, 70-115 µm wide at widest part of ampulla. Crown of gland cells surrounding ectal pore, lobed, whole glandular body 110-225 µm in diameter at its widest part. Up to four midventral subneural glands in XIII–XVI, 80-325 µm, 55-200 µm, 60-100 µm and 50 µm long, respectively; glands in XIII, XV or XVI not observed in all specimens.

Geographical distribution including BOLD data.

Originally described from USA, now genetically identified from Norway, Sweden and United Kingdom; also recognized from Canada and Switzerland (BIN-number: BOLD:ACV8942).

Remarks.

Our newly sampled material matches Welch’s (1914) description of Lumbricillus rutilus well in all characters, except for the sperm funnel shape, where our specimens had funnels less elongate in relation to their width. The material in this study was collected in Sweden and the United Kingdom, whereas this species was originally described from a sewage treatment plant in Chicago, USA. Interestingly, some of our sampled specimens also come from two such plants, in Sweden and the UK, respectively. The species was additionally collected in littoral and freshwater environments in Sweden, and it is likely to be an opportunist that thrives in nutrient-rich habitats. Specimens found in the treatment plants showed increased body size and reduced number of chaetae per bundle, compared to the specimens sampled in the sea, possibly a side effect of living in such rich environments.

Lumbricillus rutilus is genetically most closely related to L. lineatus and L. latithecatus sp. n. (Fig. 1). However, morphologically it is more similar to L. rivalis , particularly in the shape of the spermathecae. Lumbricillus rutilus has on average fewer chaetae per bundle compared with L. rivalis and sperm funnels that are shorter in relation to their width.