Lumbricillus scandicus, Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 39-41

Lumbricillus scandicus sp. n. Fig. 17

Lumbricillus cf. helgolandicus Nielsen and Christensen 1959: pp. 102-103, fig. 115; Finogenova and Timm 1988: 97-99, figs 6-10; Klinth et al. 2017.

Lumbricillus helgolandicus sensu von Bülow 1957: p. 79, pl. XXV, figs 11-12, pl. XXIX, figs 5-6; Tynen and Nurminen 1969: p. 152, fig. 1i.

Non Pachydrilus helgolandicus Michaelsen, 1927: p. 12, fig. 11; Michaelsen 1934: pp. 135-141, fig. 1.

Holotype.

SMNH Type-8923 [former SMNH 152721] (CE1905), a whole-mounted voucher of a sexually mature and DNA-barcoded worm (COI barcode is KU893950 in NCBI/GenBank; Klinth et al. 2017).

Type locality.

Sweden, Öland, Borgholm, Neptuni Åkrar, beach with mixed shelly sand, pebbles and organic material, 57.3346 N, 17.0102 E, collected 11 June 2006 by L. Matamoros.

Paratype.

SMNH Type-8925 [former SMNH 152722] (CE1907), a whole-mounted sexually mature specimen from the type locality.

Other material examined.

SMNH 152720 (CE975), SMNH 152723 (CE1915), SMNH 152724 (CE2548) & SMNH 152725 (CE2552), four mature specimens from Sweden. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Etymology.

Named after Scandinavia where the species has been found.

Diagnosis.

This species is morphologically most similar to L. helgolandicus and L. tuba . It is distinguished from L. helgolandicus in having shorter sperm funnels, sperm arranged circularly in the spermathecae and generally possessing more chaetae per bundle. Lumbricillus scandicus can be distinguished from L. tuba in having spermathecal ectal glands that are larger than the ampulla and generally possessing more chaetae per bundle.

Description of all material.

Pale, white to pinkish or orange worms. Length (fixed worms) more than 2.6-3.9 mm (amputated specimens), first 15 segments 2.0-2.9 mm long, width at clitellum 0.3-0.7 mm. More than 18-24 segments. Prostomium hemispherical, sometimes triangular. Chaetae slightly sigmoid (Fig. 17A). Dorsal bundles with 3-6, usually 4-5, chaetae anterior to clitellum, 2-5 chaetae in postclitellar segments. Ventral bundles with 4-7 chaetae anterior to clitellum, 3-6 chaetae posteriorly. Each worm’s longest measured chaetae 50-60 µm long and about 2.5 µm wide. Clitellum extending over XII– 1/2XIII, with granulated and hyaline cells irregularly distributed. Head pore not observed. Epidermis with transverse rows of gland cells.

Coelomocytes numerous, 15-20 µm long, round or oval. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally, with large ventral lobes (Fig. 17B). Posteriormost pair sometimes extending into VII. Dorsal vessel originating in either XII or XIII, difficult to distinguish due to presence of mature eggs. One nephridium observed in XIV about 85 µm long, anteseptale consisting of funnel only, duct originating posteroventrally. Brain widening posteriorly, possibly with posterior incision.

Male genitalia paired (Fig. 17D). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 95-205 µm long, 90-160 µm wide making them about 1-1.5 times longer than wide. Funnels cylindrical, abruptly tapering towards vasa deferentia. Vasa with few irregular coils around ovaries in XII, and about 7-10 µm wide. Penial bulbs round/pear-shaped 75-145 µm in diameter. Two to six mature eggs present at a time.

Spermathecae (Fig. 17C) in V, club-shaped, with ampulla distinctly set apart from ectal duct. Ectal duct wall with long cylindrical cells. Ampulla sub-spherical, thin-walled, entally communicating with oesophagus. Sperm following duct to ampulla, in ampulla aggregated into central mass haloed by circle of spermatozoa. Spermathecae 90-160 µm long, 65-115 µm wide at widest part of ampulla. Gland cells surrounding ectal pore, forming compact, slightly folded mass, 100-155 µm in diameter at its widest part. Up to three midventral subneural glands in XIII– XV, 85-90 µm, 90-140 µm and 70-100 µm long, respectively; glands in XIII and XIV not observed in all specimens.

Details of holotype.

Length 3.5 mm (amputated specimen), first 15 segments 2.7 mm long, width at clitellum 0.5 mm. More than 20 segments. Dorsal bundles with 3-5, chaetae anterior to clitellum, 3-4 chaetae in postclitellar segments. Ventral bundles with 4-7 chaetae anterior to clitellum, 3-5 chaetae posteriorly. Longest chaetae about 60 µm long and about 2.5 µm wide.

Coelomocytes about 20 µm long.

Sperm funnels about 155 µm long and 160 µm. Vasa deferentia about 7 µm wide. Penial bulbs 145 µm in diameter. Four mature eggs present.

Spermathecae (Fig. 17C) 120 µm long, 80 µm wide at widest part of ampulla. Gland cells surrounding ectal pore 155 µm in diameter at its widest part. Three midventral subneural glands in XIII–XV, 85 µm, 105 µm and 85 µm long, respectively.

Geographical distribution.

Genetically identified from Norway and Sweden. Also reported from Denmark and Russia (White Sea).

Remarks.

The new species corresponds well to the description of Lumbricillus cf. helgolandicus (Michaelsen, 1927) by Nielsen and Christensen (1959), which is why this name was used in the molecular study by Klinth et al. (2017). However, Nielsen and Christensen noted several differences in the morphology of their specimens in comparison to the extended description of L. helgolandicus given later by Michaelsen (1934), the most important being the morphology of the spermathecae and the sperm funnels. The spermathecal ampulla was interpreted by Michaelsen as being filled with an irregular mass of spermatozoa. Von Bülow (1957) instead redrew the spermathecae as having a distinct circle of spermatozoa which also corresponds to the interpretation by Nielsen and Christensen and what we observed in this study. Furthermore, Michaelsen originally described the sperm funnels as 12 times longer than wide. Nielsen and Christensen, on the other hand, found the funnels to be only 2-3 times longer than wide, which corresponds better to the ratio measured in our material. von Bülow, 1957, unfortunately did not comment on the length/width ratio of the funnels.

These circumstances prompted re-examination of the last remaining syntype of Pachydrilus helgolandicus from Michaelsen’s collection in the Zoological Museum in Hamburg (see description of that material below). We found that the sperm funnels were more than 4 times longer than wide, compared to his reported 12 times. This difference could be explained by Michaelsen having examined live material, whereas the syntype that we studied had been fixed (contracted) in formalin or alcohol, shortening the sperm funnels. Furthermore, we might have underestimated the true length of the sperm funnels due to the difficulties with measuring folded organs in mounted material. Regardless, compared to our material of " L. cf. helgolandicus ", here described as L. scandicus sp. n., the sperm funnels of L. helgolandicus sensu stricto clearly have a higher length/width ratio.

The spermathecae of L. helgolandicus are similar to those of L. scandicus in having a distinct ampulla and a very large ectal gland. However, in L. helgolandicus , the spermatheca contains sperm that are arranged in an irregular mass, and it has a very distinct musculature covering the ectal duct (possibly made more apparent by the aging of the material), whereas the spermatheca of L. scandicus has sperm arranged in a more circular manner and only weakly defined musculature covering the ectal duct.

Lumbricillus helgolandicus is larger than L. scandicus and has generally larger internal organs. It also has fewer chaetae per bundle, no more than 5 in preclitellar, and 2-3 in postclitellar bundles, whereas L. scandicus has up to 7 chaetae in preclitellar, and up to 6 in postclitellar bundles.

Nielsen and Christensen (1959) examined specimens that seem to have been larger than ours and closer to L. helgolandicus in size. However, like our material, they had sperm funnels that were not much longer than wide, more chaetae per bundle and spermathecae with sperm arranged in a circular manner. Similarly, the material that von Bülow (1957) referred to as L. helgolandicus also had more chaetae per bundle than Michaelsen’s worm and had spermathecae with sperm arranged in a circular manner.

Based on our assessment of the syntype from Helgoland, we conclude that our Scandinavian material is not conspecific with L. helgolandicus (Michaelsen, 1927), and instead deserves to be treated as a new species ( L. scandicus ). Furthermore, we conclude that L. helgolandicus sensu von Bülow 1957 and L. cf. helgolandicus sensu Nielsen and Christensen 1959 are identical to L. scandicus .

Lumbricillus scandicus was genetically found as sister to the L. lineatus group (Fig. 1).