Baikalodrilus trituberculum, 2019

BAIKALODRILUS TRITUBERCULUM MARTIN View in CoL , SP. NOV.

( FIGS 1D, 2A, 6C, F)

lsid: urn:lsid:zoobank.org:act:7BF41A46-DAD9-4B81-BBEA-49CA00DFD606

Holotype: RBINS 00.346.01, fragment (first 17 anterior segments) of one individual starting maturity (testes and ovaries in early stage present), stained in paracarmine and mounted in Canada balsam. COI barcode sequence, GenBank acc. no. MK984610 View Materials ; 16S sequence, GenBank acc. no. MN000035 View Materials ; ITS sequence, GenBank acc. no. MK999995 View Materials ; H3 sequence, GenBank acc. no. MK984655 View Materials .

Type locality: RUSSIA. Cape Kurly , Lake Baikal, 50 m, station 95.17, 55.6667° N, 109.4247° E (datum WGS84), sample No 336 GoogleMaps .

Other material: RBINS 01.076 About RBINS .06, two fragments of one immature individual: one (first 13 anterior segments) stained in paracarmine and mounted in Canada balsam, the second one (last 18 posterior segments) preserved in absolute ethanol. Akademichesky ridge, Lake Baikal, 315 m deep, station 96.57, 53.5283° N, 107.9142° E, sample B96.57. COI barcode sequence, GenBank acc. no. MK 984611 View Materials GoogleMaps ; 16 S sequence, GenBank acc. no. MN000036 View Materials ; ITS sequence, GenBank acc. no. MK999996 View Materials ; H3 sequence, GenBank acc. no. MK984656 View Materials .

Etymology: Noun in apposition, From Latin tria, three, and tuberculum, a small lump or swelling, in reference to the three pairs of glandular tubercles per segment, characteristics of the species.

Diagnosis: This species is unique in having three pairs of buttonhole-like glandular tubercles on the same line, one ventral, besides and in front of setae; dorsal setae midway between dorso-lateral and dorsal tubercles. It can be also distinguished from other species in Baikalodrilus by genetic data ( Fig. 3).

Description: Length of (fixed) holotype 4.5 mm, 17 segments (anterior fragment). Maximum width 1.49 mm (dissected specimen flattened between slide and coverslip). Prostomium triangular, 120 µm long, roughly as long as wide, well retracted into the mouth cavity and located between transversal setal lines III and IV when retracted ( Fig. 6C). Dorsal bundles with 1–2 smooth hair setae with straight tip, 1–2 simple pointed needles; 1–2 simple pointed setae in ventral bundles. Setae hardly visible on their full length. Ventral setae 147 µm long and 4.6 µm wide in II, 273 µm long (minimal value) and 6.4 µm wide in XV. Dorsal setae not visible on their full length. ‘Hülsenpapillen’ present all over the body fragments studied, sustained by small, internal, epidermal prickles. Two rows of ‘Sinnespapillen’ per segment ( Fig. 1D). Three pairs of buttonhole-like glandular tubercles on the same line, one ventral, besides and in front of setae; dorsal setae midway between dorsolateral and dorsal tubercles ( Figs 2A, 5F). Glandular tubercles weakly developed on immature individual.

Remarks: The combination of smooth hair setae, simple pointed needles and only simple pointed ventral setae is only seen in B. discolor acinacifer and B. discolor discolor . In our material, such a combination is also found in specimens of group 3 (see above). However, our specimens are genetically separated from the latter group ( Fig. 3). In addition, the presence of three pairs of glandular tubercles per segment is a feature unknown in any Baikalodrilus species described to date.

Geographical distribution and habitat: Lake Baikal: Akademichesky ridge, cape Kurly, 50 to 315 m deep, soft sediment.