Aberrantidrilus Martin, 2015

Martin, Patrick, Schmelz, Rüdiger M. & Dole-Olivier, Marie-José, 2015, Groundwater oligochaetes (Annelida, Clitellata) from the Mercantour National Park (France), with the descriptions of one new genus and two new stygobiont species, Zoosystema 37 (4), pp. 551-569 : 556-559

Aberrantidrilus Martin , n. gen.

( Fig. 2 )

TYPE SPECIES. — Aberrantidrilus stephaniae Martin , n. sp. ( Fig. 2 )

OTHER INCLUDED SPECIES. — Aberrantidrilus cuspis ( Erséus & Dumnicka, 1988) n. comb. and A. subterraneus ( Rodriguez & Giani, 1989) n. comb.

DIAGNOSIS. — Freshwater subterranean phallodrilines. Somatic setae all bifid, similar in all bundles, or with upper tooth much reduced or absent in posterior bundles. Penial setae present, bifid or singlepointed, one per bundle, orientated in anterior direction. Atria covered by a thick muscular layer, opening to exterior on conical male protuberances (porophores). Posterior prostate gland small, attached by a short stalk to proximal end of atrium, at base of pseudopenis. Spermathecal pores in segment XII, on the ventral portion of the body; spermathecae with short ducts and thin-walled ampullae.

ETYMOLOGY. — The name Aberrantidrilus (from drilos, “worm” in Greek and aberrans, -tis, present active participle of the Latin aberrare, “wander, stray, deviating from”) refers to the aberrant location of the spermathecal pores of the species, in segment XII. Spermathecae are in X (or at least anterior to the atrial segment) in all tubificids except one other phallodriline, Mexidrilus postspermathecus ( Erséus 1980) .

REMARKS

The decision to erect a new genus to accommodate all the freshwater subterranean species formerly attributed to Abyssidrilus Erséus, 1992 is supported by a unique combination of characters, rather than formally proposed apomorphies, namely the location of spermathecal pores in XII, the unisetal condition of penial setae and their teeth directed anteriad. The fact that the three species included in Aberrantidrilus Martin , n. gen. are found in subterranean freshwater, as opposed to the marine Abyssidrilus , is considered as additional evidence to support this decision.

The genus Abyssidrilus is commonly defined as a monophyletic group of species sharing slender, often sharply single-pointed, somatic setae, a synapomorphy unique for the subfamily ( Erséus 1992). Although more or less seen in the subterranean freshwater forms A. cuspis n. comb. and A. subterraneus n. comb., this character is not present in A. stephaniae Martin , n. gen., n. sp. in spite of its great similarity and assumed phylogenetic closeness to those species. Aberrantidrilus stephaniae Martin , n. gen., n. sp. has all somatic setae bifid, with teeth of similar length (see description below), which would render questionable the synapomorphy proposed for Abyssidrilus if the species were kept in the latter genus.

The location of spermathecal pores in XII is an exceptional condition in tubificids, so far only seen in Aberrantidrilus Martin , n. gen. species and Mexidrilus postspermathecus Erséus, 1980 . If only for the rarity of this condition, it is tantalizing to consider the latter species as the closest relative to this assemblage of thalassoid stygobionts. Mexidrilus postspermathecus is a subtidal oligochaete, known from the West coast of Norway ( Erséus 1980), with a depth distribution in accordance with the hypothesis usually put forward to explain the origin of thalassoid lineages, namely an evolution from marine ancestors by stranding following the regression of marine embayments ( Notenboom 1991; Holsinger 1993; Boutin & Coineau 2005). Assuming a derivation from the Abyssidrilus clade, the closest relative to the thalassoid species would be a deep-sea species, Abyssidrilus stilus , so far only found at about 4900 m depth in the Indian Ocean. This implies an invasion of the subterranean domain via an unknown common ancestor that lived at moderate depths ( Erséus 1992). Although sharing a unisetal penial “bundles” condition with Aberrantidrilus Martin , n. gen., Abyssidrilus stilus differs from the latter in having spermathecae in X, with spermathecal pores dorsal to the lateral line, and penial setae directed posteriorly.

Aberrantidrilus stephaniae

Martin, n. sp. ( Fig. 2 )

TYPE MATERIAL. — Holotype. MNHN HEL 524 , slide 11.019.01, sexually mature, mated specimen. Legit M.-J. Dole-Olivier. Type locality: Bévéra River , Sospel, Mercantour National Park, France (station H2BEV, replicate sample No 1, sample code SED66, Sospel 1), 43°52’41.01”N, 7°26’56.94”E, 372 m a.m.s.l., hyporheic zone in alluvial aquifer, 5.VIII.2009.

Paratypes. Type locality (station H2BEV, replicate sample No 1, sample code SED66, Sospel 1), 5.VIII.2009 ; IRScNB, I.G. 32392, slide 11.017.01: 1 immature specimen (a) and 2 sexually mature, mated specimens (b, c); MNHN HEL 524 , slide 11.007.04: 1 mature, mated specimen ; IRScNB, I.G. 32392, vial AB31536628: 10 specimens in absolute alcohol (8 immature, 2 mature and mated, 2 fragments). Type locality (station H2BEV, replicate sample No 2, sample code SED58, Sospel 3), 5.VIII.2009 ; IRScNB, I.G. 32392, slide 11.019.06: 1 mature, mated specimen, slide 11.033.01: 1 immature specimen (b on slide).

OTHER MATERIAL. — Many specimens in absolute alcohol, from unsorted material, mostly immature and/or fragments. Type locality (station H2BEV, replicate sample No 2, sample code SED58, Sospel 3), 5.VIII.2009; IRScNB, I.G. 32392, vial AB31515995. Type locality (station H2BEV, replicate sample No 3, sample code SED 62, Sospel 2), 5.VIII.2009; IRScNB, I.G. 32392, vial AB31515997.

ETYMOLOGY. — The species is named after Stéphanie Marchais, playwright, in memory of the “Binôme #2” experience (“Universcience, Les sens des mots”), a dramatized “Art et science” meeting between a scientist and a dramatist, which led to “Baïkal Amour Magistral”, a play that draws inspiration from the scientific activity of one of us (PM) on oligochaetes from Lake Baikal, and on evolutionary relationships between Oligochaeta and Hirudinea. The name is a genitive.

DISTRIBUTION. — Currently only known from the Mercantour National Park, France, hyporheic habitats ( Fig. 3 ).

DESCRIPTION

Length of (fixed) holotype 4.5 mm, 23 segments (complete specimen). Maximum width 99-179 µm (in the genital region). Prostomium rounded or slightly pointed, about as long as wide. Segments II-VI with a slight secondary annulation, mostly visible on contracted specimens. Clitellum hardly noticeable, extending over XI-½ XII. Somatic setae 38-43 µm long, 1.5 µm thick, 2-5 per bundle anteriorly, 1-3 per bundle in postclitellar segments. Somatic setae all bifid, with upper tooth of similar length to lower or slightly shorter ( Fig. 2D [ds, vs]), similar in all bundles. Ventral setae of XI modified into penial setae ( Fig. 2B, D [ps]), one at each male pore, sigmoid, distinctly bifid, with upper tooth longer than lower, with teeth directed towards anterior end of worm. Penial setae 50-64 µm long, 3.3-3.5 µm thick, with distinct nodulus slightly proximal to middle. Ventral (penial) setae absent on XI in mature paratype MNHN Hel 11.007.04 ( Fig. 2A ). Male pores ( Fig. 2A, B [mp]) on prominent, external, protruded porophores ( Fig. 2A, B [pp]), posterior to middle of XI; penial setae between porophores and mid-ventral line. Spermathecal pores on distinct papillae ( Fig. 2C [spp]) near, or anterior to, middle of XII, between lateral lines and lines of ventral setae.

Pharyngeal glands in (IV)V-VI. Anterior and posterior sperm sacs projecting to IX and XI, respectively; egg sac extending to XIII. Male genitalia ( Fig. 2A ) paired. Vas deferens poorly visible, shorter than atrium ( Fig. 2A [vd]), entering apical end of atrium. Atrium ( Fig. 2A [a]) slender, spindle-shaped and curved near ectal part, terminating in a retractable pseudopenis, 207-287 µm long, 39-47 µm wide, with 3-6 µm thick outer muscular layer, giving atrium an crumpled external appearance; atrium with granular epithelium and lumen containing scattered bundles of sperm ( Fig. 2A [sp]); ciliation of inner epithelium not seen. Two prostates attached to atrium. Anterior prostate gland very large, attached by a short stalk to apical end of atrium, near junction with vas deferens. Posterior prostate gland small, attached by a short stalk to ectal end of atrium, at base of pseudopenis ( Fig. 2A, B [ppr]; gland often barely visible). One pair of spermathecae ( Fig. 2C ) in XII, with large, elongated, thin-walled ampulla ( Fig. 2C [spa]), extending into XIII, and short, muscular ducts ( Fig. 2C [spd]). Sperm as a random mass in ampullae, with amorphous round bodies ( Fig. 2C [ab]), possibly of secretory origin.

REMARKS

Aberrantidrilus stephaniae Martin , n. gen., n. sp. is the third species of the thalassoid, subterranean freshwater genus Aberrantidrilus Martin , n. gen. It is similar to Aberrantidrilus cuspis n. comb. in nearly all respects, except that the penial setae are distinctly bifid instead of lance-shaped with “sharply pointed tips”, and the bifid somatic setae have teeth of similar length on all segments, instead of having the upper tooth much reduced or absent on the posterior segments.In addition, compared with A. cuspis n. comb., the penial setae are smaller in length and diameter by roughly a factor of two in A. stephaniae Martin , n. gen., n. sp. Despite their similar body length (4.8 vs 4.5 mm, respectively), their penial to somatic setal length ratios are quite different (2.32 vs 1.39) ( Table 2). Aberrantidrilus subterraneus n. comb. is distinguished from its congeners by the shape of the spermathecae and the location of spermathecal ampullae in XII only, somatic setae with upper tooth shorter and much thinner than lower on all segments, and the penial setae simplepointed, slender and much thinner ( Table 2).

5° W 0

50°N

45°

40°

5° E 10° 15°

In their review of groundwater oligochaetes from Southern Europe, Sambugar et al. (1999) reported additional material from France, Italy and Slovenia ( Fig. 3 ), ascribed to A. cuspis n. comb. in spite of significant differences in penial setae (distinctly bifid and shorter than those of the type material). In this respect, those specimens are most similar to A. stephaniae Martin , n. gen., n. sp., which suggests their attribution to A. stephaniae Martin , n. gen., n. sp. but a proper comparison is hardly possible due to insufficient descriptions (see Table 2). Giani et al. (2011) recently mentioned “ Abyssidrilus sp. 1 ” from ground waters of Slovenia, which might be conspecific with specimens from Italy (Romana Cave, Trieste) and Slovenia (Škocjanske Cave), previously attributed to Abyssidrilus cf. cuspis by Sambugar et al. (1999), suggesting a complex of near-cryptic species (see also discussion below). However, without re-examining this material, it seems wiser, on the basis of current knowledge, to follow the taxonomic decision of Sambugar et al. (1999) and consider these specimens as conspecific with the form described by Erséus & Dumnicka (1988).

Figures

FIG. 2. — Aberrantidrilus stephaniae Martin, n. gen., n. sp.: A, male genitalia (paratype MNHN HEL 524 slide 11.007.04); B, detailed sketch of the pseudopenis area, showing posterior prostate (ppr) and penial seta (ps) (paratype IRScNB I.G. 32392 slide 11.019.06); C, spermathecae in segment XII (paratype IRScNB I.G. 32392 slide 11.017.01c); D, D’, unmodified and penial setae (ps) (D. IRScNB paratype I.G. 32392 slide 11.017.01b; D’. IRScNB holotype I.G. 32392 slide 11.019.01). Abbreviations: see Material and methods. Scale bars: A, C, 100 µm; B, D, D’, 50 µm.

FIG. 3. — Geographical distribution of groundwater Aberrantidrilus Martin,2015 species in Southern Europe.The shaded patterns indicate the areas of carbonate rock outcrops (exposed karst terrains; Williams & Fong 2010).