Lumbricillus verrucosus ( Claparede , 1861)

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 24-26

Lumbricillus verrucosus ( Claparede, 1861) Figs 3 C–D, 6

Pachydrilus verrucosus Claparède, 1861: pp. 82-85, pl. I, figs 1-6;

Lumbricillus verrucosus ; Michaelsen 1900: p. 80; Klinth et al. 2017.

Pachydrilus lineatus forma verrucosus ; Černosvitov 1937: p. 292.

Lumbricillus lineatus partim; Nielsen and Christensen 1959: pp. 100-102, figs 109-112.

Type material.

Typus amissus (Nomenclatura Oligochaetologica). Type locality: Sound of Sleat, Isle of Skye, Hebrides, United Kingdom ( Claparède, 1861). We did not designate a neotype as we do not have material from the type locality.

Material examined.

SMNH 152826 (CE968), one mature specimen from Sweden, ZMBN 107919 (CE21479), ZMBN 107920 (CE21486), ZMBN 107921 (CE21490), ZMBN 107922 (CE21494), ZMBN 107924 (CE21811), ZMBN 107925 (CE21816) & ZMBN 107926 (CE21821), seven 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 2.3-5.7 mm (amputated specimens), first 15 segments 2.3-3.4 mm long, width at clitellum 0.42-0.60 mm. More than 18-33 segments. Chaetae slightly sigmoid (Fig. 6A). Dorsal bundles with (2)3-5(6) chaetae anterior to clitellum, 2-4 chaetae in postclitellar segments. Ventral bundles with (2)3-6(7) chaetae anterior to clitellum, (2)3-4(5) chaetae posteriorly. Each worm’s longest measured chaetae 45-60 µm long, about 2.5 µm wide. Clitellum extending over XII–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. 6B). Dorsal vessel originating in XIII. Nephridia observed in XIV–XXV, 75-120 µm long. Anteseptale small, consisting of funnel only. Postseptale oval, tapering posteriorly into efferent duct. Brain twice as long as wide, with posterior incision.

Male genitalia paired (Fig. 6D). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 230-370 µm long, 125-175 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, 15-20 µm wide. Penial bulbs round, 105-140 µm in diameter. Ovaries in XII. One to five mature eggs present at a time.

Spermathecae (Figs 3 C–D, 6C) in V, spindle-shaped, without distinct ampulla. Ectal duct short, widening into ampulla. Ampulla with constriction midway to two thirds of the length, dividing it into two sections, the inner one of which connecting with oesophagus. Sperm filling lumen of ectal duct, heads of spermatozoa embedded in inner part of ampulla, sometimes also in outer part, forming aggregates. Spermathecae 180 -300 µm long, 65-110 µm wide at widest part of ampulla. Gland cells surrounding ectal pore, forming compact mass, whole glandular body 95-180 µm in diameter at its widest part. One or two midventral subneural glands in XIII–XIV, 90-125 µm and 95-125 µm long, respectively; gland in XIV not observed in all specimens.

Geographical distribution.

Originally described from the United Kingdom, now genetically identified from Norway and Sweden. The full extent of this species’ distribution is difficult to ascertain since it was previously synonymized with L. lineatus , a species distributed worldwide. BIN-number BOLD:ACV7714.

Remarks.

Lumbricillus verrucosus was originally described by Claparède (1861) and later synonymized with L. lineatus by Nielsen and Christensen (1959), probably following Černosvitov (1937) who had downgraded the former to a form of the latter. Specimens from the two species examined in this study are indeed very similar when considering the shape of the spermathecae (Fig. 3) and most body measurements, but they differ in body colour, chaetal number and the proportions of the sperm funnels: indeed Lumbricillus verrucosus was described as being pale yellow, having 3-5 chaetae and sperm funnels about three times longer than wide ( Claparède 1861), against L. lineatus being orange-red, having more chaetae and sperm funnels about five times longer than wide. Furthermore, the spermathecae of L. verrucosus seem to have an ampulla that is slightly longer and wider in the part ectal to the constriction, but the importance of this character remains to be proved. Even though the two species may be very difficult to separate morphologically, except perhaps by body colour, they are supported as separate species molecularly and avesiculate specimens have been found by us only in L. lineatus , not in L. verrucosus .

Interestingly, Lumbricillus verrucosus is genetically most closely related to L. rivalis (Levinsen, 1883) and not to L. lineatus (Fig. 1). However, these three species are well supported as closely related to each other.