Lumbricillus pumilio Stephenson, 1932

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

Lumbricillus pumilio Stephenson, 1932 Fig. 11

Lumbricillus pumilio Stephenson, 1932a: pp. 902-904, figs 1-3; Nielsen and Christensen 1959: p. 96; Tynen and Nurminen 1969: pp. 151-153; Klinth et al. 2017.

Lumbricillus pumillio (sic); Erséus 1976: p. 9.

Type material.

Typus amissus (Nomenclatura Oligochaetologica). Type locality: Wembury Bay, Plymouth, United Kingdom ( Stephenson 1932a). We did not designate a neotype as we do not have material from the type locality.

Material examined.

SMNH 152775 (CE3346), SMNH 152776 (CE3347), SMNH 152777 (CE3427), SMNH 152778 (CE3428), SMNH 152779 (CE3430), SMNH 152780 (CE3436) & SMNH 152781 (CE3437), seven mature specimens from the United Kingdom. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Description.

Short and stout worms. Colour unknown. Length (fixed worms) more than 1.7-3.2 mm (amputated specimens), first 15 segments 1.3-2.3 mm long, width at clitellum 0.24-0.38 mm. More than 15-23 segments. Chaetae slightly sigmoid (Fig. 11A). Dorsal bundles with 3-6 chaetae anterior to clitellum, 3-5 chaetae in postclitellar segments. Ventral bundles with 3-6, rarely 2 or 7, chaetae anterior to clitellum, 3-6 chaetae, rarely 2, posteriorly. Each worm’s longest measured chaetae 36-48 µm long and about 2.5 µm wide. Clitellum extending over XII– 1/2XIII. Head pore not observed. Epidermis with transverse rows of gland cells.

Coelomocytes difficult to identify as such in this species, but small round, oval or spindle-shaped granulated cells about 5-7 µm long were noted in the coelomic cavity. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally (Fig. 11B). Dorsal vessel originating in XII or XIII. Nephridia observed in IX and XV–XVIII, about 45-50 µm long. Anteseptale small, consisting of funnel only. Postseptale oval, tapering posteriorly into efferent duct. Brain longer than wide, with a marked posterior incision creating two horn-like structures.

Male genitalia paired (Fig. 11D). Testes originating in XI, extending forwards into X, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 115-190 µm long, 65-140 µm wide making them about 1.5-2 times longer than wide, funnels tapering towards vasa deferentia. Most of vasa deferentia irregularly coiled in XII together with ovaries, vasa 5-10 µm wide. Penial bulbs round, 55-80 µm in diameter. One or two mature eggs present at a time.

Spermathecae (Fig. 11C) in V, spindle-shaped. Ectal duct short, ampulla indistinct, lumen of ampulla usually filled with sperm, ental duct connected to oesophagus. Ampulla usually making a sharp bend caudad towards oesophagus at about half its length. Spermathecae 100-150 µm long, 30-50 µm wide at widest part of ampulla. Ectal pore surrounded by compact, roundish mass of gland cells; whole glandular body 45-110 µm in diameter at its widest part. One midventral subneural gland in XIV, 60-90 µm long.

Geographical distribution.

Genetically identified from the United Kingdom. Also reported and briefly described from Iceland ( Erséus 1976).

Remarks.

Our measurements of the coelomic corpuscles (5-7 µm long) contradict the original description where they are described as being 20-28 µm. This could either be due to a high degree of variation in this trait or that we are comparing non-homologous cell types. The smaller subneural gland in XV described by Stephenson could not be distinguished, either because of its small size or because it was absent. Despite a few discrepancies from the original description the small body size of the worms together with the shape of the spermathecae and other reproductive organs supports that the sampled specimens belong to L. pumilio .

Lumbricillus pumilio is genetically closely related to L. rubidus Finogenova & Streltsov, 1978 (Fig. 1), with which it also shares morphological similarities. However, L. pumilio is generally smaller than L. rubidus , and it does not have an as distinct muscular covering of the spermathecal ectal duct as that of the latter (compare Figs 11 and 12).