Lumbricillus fennicus Nurminen, 1964

Klinth, Marten J., Rota, Emilia & Erseus, Christer, 2017, Taxonomy of North European Lumbricillus (Clitellata, Enchytraeidae), ZooKeys 703, pp. 15-96 : 33

Lumbricillus fennicus Nurminen, 1964 Fig. 13

Lumbricillus fennicus Nurminen, 1964: pp. 48-51, fig. 2; Graefe and Schmelz 1999: p. 61; Rota and Healy 1999: p. 54; Erséus et al. 1999; Klinth et al. 2017.

Type material.

HUZM (Nomenclatura Oligochaetologica). Type locality: Tvärminne, Finland ( Nurminen 1964). Not seen.

Material examined.

SMNH 152729 (CE2767), SMNH 152730 (CE2768), SMNH 152731 (CE2988) & SMNH 152732 (CE6092), four mature specimens from Sweden. For information on specimen collection localities and GenBank accession numbers see Appendix 1.

Description.

Colour of worms unknown. Length (fixed worms) more than 1.8-3.5 mm (amputated specimens), first 15 segments 2.0-2.3 mm long, width at clitellum 0.4-0.48 mm. More than 12-23 segments. Chaetae slightly sigmoid (Fig. 13A). Dorsal bundles with 3-5, rarely 2 or 7, chaetae anterior to clitellum, 2-5 chaetae in postclitellar segments. Ventral bundles with 3-7, usually 4-5, chaetae anterior to clitellum, 4-5 chaetae posteriorly. Each worm’s longest measured chaetae 35-50 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, 15-25 µm long, round, oval or spindle-shaped. Paired pharyngeal glands present in IV, V and VI; each pair converging dorsally (Fig. 13B). Dorsal vessel originating in XIII. Nephridia observed in XIII–XVI about 45 µm long, anteseptale consisting of funnel only, efferent duct originating at mid length of postseptale. Brain widening posteriorly, with posterior incision creating two hornlike structures.

Male genitalia paired (Fig. 13D). Testes originating in XI, extending forwards into X, sometimes IX, with testis sacs forming regular club-shaped lobes. Sperm funnels in XI, 100-125 µm long, 95-110 µm wide making them about 1-1.5 times longer than wide. Funnels lobed rather than cylindrical, and abruptly tapering towards vasa deferentia. Vasa with few irregular coils around ovaries in XII, and about 10 µm wide. Penial bulbs round/pear-shaped 45-50 µm in diameter. Three to four mature eggs present at a time.

Spermathecae (Fig. 13C) in V, spindle-shaped, without distinct ampulla. Ectal duct short, encircled by musculature, and rapidly widening into ampulla. Ampulla after maximum width making sharp bend inwards, entally connecting with oesophagus. Sperm evenly embedded in wall of ampulla, filling but not embedded in ental duct. Spermathecae 170-195 µm long, 45-65 µm wide at widest part of ampulla. Gland cells surrounding ectal pore, forming compact mass, somewhat lobed, whole glandular body 60-75 µm in diameter at its widest part. Midventral subneural glands in XIII, XIV and in one specimen in XV, measuring 45-70 µm, 75-90 µm and 70 µm respectively.

Geographical distribution.

Originally described from Finland, but also reported from Denmark, France ( Lafont and Vivier 2006), Germany ( Giere 1976), Ireland ( Healy 2007), Norway and Sweden, now genetically identified from Sweden.

Remarks.

The original description of L. fennicus matches the specimens of this study in most characters, but there are a few differences. Our specimens measured 2-3.5 mm in length after fixation, but considering that some had been cut directly posterior to the clitellum the length of the complete worms probably was 3-5 mm. This is smaller than the 8 mm reported by Nurminen (1964), but he based his description on living worms. Nurminen described the clitellum as covering 1/2 XI–XII while in our specimens, the clitellum extends over XII– 1/2XIII. The extension of the clitellum may vary as it develops, but the whole structures does not generally shift in position, and this suggests the possibility of a printing or observation error in the original description.

The lobed, as opposed to cylindrical, sperm funnels are so far (in European species) only reported for L. fennicus , and this, together with the matching shape of the spermathecae, allowed confident allocation of the specimens to this species despite some incongruence among the characters mentioned above. The interpretation of the lobes of the sperm funnels probably also differs between living and fixed specimens. Our Swedish specimens were collected in freshwater habitats, but the sites are possibly subjected to brackish water at times, making the range of salinity similar to the original records from the Gulf of Finland. Most other records in Europe are from coastal oligohaline or inland freshwater habitats.

Lumbricillus fennicus is both genetically (Fig. 1) and morphologically placed within the L. lineatus group.