Lumbricillus sp. – Dartnall & Smith, 2012.

Material examined: SAMC-A094449 (CE5447), one semi-mature specimen from Marion Island, southwestern Indian Ocean, from eutrophic freshwater in a coastal pool, possibly a wallow (a shallow depression enriched by seal and penguin excrements), April– May 2008, leg. Herbert Dartnall. GenBank accession numbers are given in Table 1 and the Supporting Information (Table S1).

Description: Length of first 26 segments 4.1 mm (fixed, amputated specimen); first 15 segments 2.1 mm long; width at clitellum 0.45 mm. Chaetae sigmoid (Fig. 7A). Upper bundles dorsolateral (closer to lateral line than the ventral bundles), with three to five chaetae anterior to clitellum, and three to four chaetae in postclitellar segments, at least to XXVI. Ventral bundles with four to six chaetae anterior to clitellum, and four to five chaetae posteriorly. The longest measured chaetae of the worm are 70 µm long, ~5 µm wide. Epidermis loosely covered with rows of pale gland cells. Clitellum not fully developed.

Coelomocytes numerous, ~10–20 µm long; round, oval or spindle shaped; granulated, with distinct nucleus. Paired pharyngeal glands (Fig. 7B) present in IV, V and VI; each pair converging dorsally, but connections not discernible. Dorsal vessel originating in XIV, with peristomial bifurcation. Nephridia ~150–180 µm long, observed in 13/14–15/16, 17/18, 18/19, 21/22 and 22/23. Anteseptale small, consisting of funnel only. Postseptale oval, tapering into posteroventral efferent duct. Brain with posterior incision.

Male genitalia paired, not fully developed. Testes in anterior of XI, with testis sacs forming regular clubshaped lobes. Sperm funnels not fully formed, without sperm on collars. Vasa deferentia irregularly coiled in XII, only 3 µm wide. Penial bulbs round, 40 µm in diameter. Spermathecae in V, not fully developed. Midventral subneural glands observed in XIII, XIV and possibly in XV; first two glands 70 and 65 µm long, respectively.

Geographical distribution: Known from Marion Island only.

Remarks: Unfortunately, this specimen was not fully mature and could not be identified or described, but we could observe developing regularly lobed testis sacs, which matches with the phylogenetic placement in the L. lineatus group.