Trichodrilus cf. tenuis Hrabě, 1960

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 : 564

Trichodrilus cf. tenuis Hrabě, 1960

Trichodrilus tenuis Hrabě, 1960: 271 . MATERIAL EXAMINED. — Many mature, mated specimens, IRScNB, I.G. 32392, station 1 (slides 11.006.04, 11.007.01, vial AB31536635), station 2 (slides 11.032.01, 11.032.02, vials AB31536765, AB31536719, AB31515927, AB31536665), station 15 (slide 11.252.01, vial AB31525637).

REMARKS

All these fragments probably belong to the same species, which can be ascribed to Trichodrilus sp. group II sensu Rodriguez & Giani (1994). This group of species is characterized by pear-shaped or spherical atria, not laterally compressed, all setae more or less alike, unmodified penial setae, two pairs of spermathecae in XI and XII, and posterior vasa deferentia penetrating into XI. According to Rodriguez & Giani (1994), the species within this group can barely be separated due to the variability of diagnostic characters within populations, or even to incorrect diagnoses in the original descriptions.

Our specimens have no lateral blood vessels in posterior segments, a character shared among this group by T. claparedei Hrabě, 1938 , T. hrabei Cook, 1967 , T. medius Hrabě, 1960 , T. moravicus Hrabě, 1937 , T. seirei Timm, 1979 , and T. tenuis Hrabě, 1960 . Our specimens can be characterized by spherical to ovoid atrial ampullae, 55-80 µm long, 54-68 µm wide, with thin muscle layer (2.5-4.0 µm thick), and distinct proximal ducts, which make them the closest to T. tenuis . However, atrial ampullae are entirely covered by high prostate cells, and ducts are half the size of diameter of ampullae, ending in small conical, external penes. In T. tenuis , atrial ampullae bear high prostate cells only in their distal part, ducts are very short, and end with minute porophores. Juget & des Châtelliers (2001) have described a peculiar structure of the spermathecae in material from the Lyon area ( France) ascribed to T. tenuis , in which the proximal part of ampulla (wrongly indicated as the distal part) is differentiated into a so-called “pseudovestibule” at junction with spermathecal ducts. Such a structure is not seen on our material.

This is probably a new species but its description would ideally lie within a revision of Trichodrilus sp. group II sensu Rodriguez & Giani (1994), based on additional material and genetic characterization via DNA barcoding.