Lumbricillus arenarius (Michaelsen, 1889)

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 47

Lumbricillus arenarius (Michaelsen, 1889) Fig. 21

Enchytraeus arenarius Michaelsen, 1889: pp. 12-14, figs 5 a–d.

Marionina arenaria ; Michaelsen 1900: pp. 74-75.

Enchytraeoides arenarius ; Ude 1929: pp. 62-63; von Bülow 1957: p. 84; Knöllner 1935: pp. 437-438, figs 7-8.

Lumbricillus arenarius ; Nielsen and Christensen 1959: pp. 107-108, figs 127-128; Rota and Healy 1999: pp. 53-54; Erséus et al. 1999; Erséus et al. 2010; Klinth et al. 2017.

Lumbricillus magdalenae Nurminen, 1965: pp. 6-7, figs 2 e–g.

Type material.

Typus amissus (Nomenclatura Oligochaetologica). Type locality: Elbe River, Hamburg, Germany ( Michaelsen 1889). We did not designate a neotype as we do not have material from the type locality.

Material examined.

SMNH 152716 (CE1001), one mature specimen from Sweden, and ZMBN 107784 (CE8474), ZMBN 107787 (CE20748), ZMBN 107788 (CE20749) & ZMBN 107789 (CE20750), four mature specimens from Norway. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Description.

White to yellow worms. Length (fixed worms) more than 5.0-8.6 mm (amputated specimens), first 15 segments 3.5-4.0 mm long, width at clitellum 0.31-0.51 mm. More than 19-35 segments. Chaetae straight or slightly sigmoid (Fig. 21A). Lateral bundles with 2-3 chaetae anterior to clitellum, 2 chaetae in postclitellar segments. Ventral bundles with 2-3(4) chaetae anterior to clitellum, 2-3 chaetae posteriorly. Each worm’s longest measured chaetae 40-70 µm long, about 5 µm wide. Clitellum extending over XII– 1/2XIII, in some covering all of XIII. Head pore at 0/1. Epidermis with transverse rows of gland cells.

Coelomocytes numerous, 20-50 µm long, spindle-shaped, oval, round, granulated with distinct nucleus, some with distally hooked ends. Paired pharyngeal glands present in IV, V and VI (Fig. 21B). Dorsal vessel originating in XIII. Nephridia observed in XV–XVI and XX–XXV, 105-145 µm long, anteseptale funnel only, postseptale oval, tapering into efferent duct. Brain with posterior incision.

Male genitalia paired (Fig. 21D). Testes originating in XI, extending forwards into X, with testis sacs covering mass of rather large irregularly arranged lobes. Sperm funnels in XI, in some specimens extending back into XII, 375-975 µm long, 55-103 µm wide, making them 6-13 times longer than wide, funnels tapering towards vasa deferentia. Most of vasa irregularly coiled in XII, in one specimen extending back into XIV, 5-10 µm wide. Penial bulbs round, 110-140 µm in diameter. Ovaries in XII. One to six mature eggs present at a time.

Spermathecae (Fig. 21C) in V, pouch-shaped. Ectal duct longer than and gradually widening into ampulla. Ampulla oval or round, entally connecting with oesophagus. Irregular mass of sperm aggregated in ampulla. Spermathecae 100-255 µm long, 50-115 µm wide at widest part of ampulla. Gland cells surrounding ectal pore, divided into several flaps, whole glandular body 75-135 µm in diameter at its widest part. Up to four midventral subneural glands in XIII–XVI, 75-110 µm, 90-115 µm, 75-85 µm and 95 µm long, respectively; glands in XVI not observed in all specimens.

Geographical distribution including BOLD data.

Genetically identified from Norway (mainland and Svalbard) and Sweden. Also reported from Denmark, Canada, Germany, Greenland, Iceland, Ireland, Wales and North–Western Australia ( Rota and Healy 1999). BIN-number: BOLD:AAT8953.

Remarks.

The original description by Michaelsen (1889) was later amended by Knöllner (1935) who redrew the shape of the nephridia and spermathecae, also confirmed by Nielsen and Christensen (1959). The newly examined material in this study resembles the original description in most characters but the spermathecae and nephridia are in agreement with the amended descriptions. Coelomic corpuscles were found with hooked ends which seemed to bind to the internal tissue in a way that is described by Michaelsen. The testes seemed to be either an irregular compact mass or divided into separate lobes, encased in testis sacs, but these lobes were not arranged in the bunch-shape seen in the lineatus , pagenstecheri and " tuba " groups.

Lumbricillus arenarius is genetically closely related to L. sp. H and L. dubius (Fig. 1).