Cernosvitoviella atrata ( Bretscher, 1903 )

Schmelz, Rüdiger M., Jocque, Merlijn & Collado, Rut, 2015, Microdrile Oligochaeta in bromeliad pools of a Honduran cloud forest, Zootaxa 3947 (4), pp. 508-526 : 516-517

Cernosvitoviella atrata ( Bretscher, 1903)

Marionina atrata Bretscher, 1903: 17 .

Enchytraeoides atratus (Bretscher) . Černosvitov 1928: 14 –16, text fig. 3, pl. 1 figs 8, 9. Cernosvitoviella atrata (Bretscher) . Nielsen & Christensen 1959: 38 –39, figs 15–18. Chalupský 1992: 140 –141, fig. 7. Rota & Healy 1999: 31. Timm 2009: 148 –149. Schmelz & Collado 2010: 57, 62.

Material examined. IG 327183-22, one adult specimen, unstained whole mount. Honduras, Cusuco National Park [15.505813 -88.21473], 2061 m asl, M. Jocque 29/06/2013.

Description. Length 1.8 mm, diameter at V 0.12 mm, 0.17 at XII, 0.1 mm at XX, 23 segments. Chaetae sigmoid with nodulus, formula 4,5-4,3: 5,6-4,3. Length c. 25 Μm, diameter c. 1.5 Μm in caudal segments, chaetae appear smaller in anterior segments, length not measurable. Lateral chaetae slightly shifted dorsally, bundles completely in dorsal body half; distance of dorsal bundles to lateral line about half of that of ventral bundles (c. 17 vs. 33 Μm). Epidermal gland cells not seen, circumferal epidermis somewhat rugose at chaetal level.

Body wall 4 Μm thick dorsally, up to 6 Μm ventrally. Prostomium 60 Μm high at base, 45 Μm long, hollow, very few transverse muscles inside, no papillae or protrusions, inner epithelial surface slightly wavy. Prostomium separated from peristomium by a medial dorsal-ventral ligament (musculature?). Dorsal and ventral chaetal bundles of one side in a segment interconnected with two transverse intracoelomic ligaments, possibly retractor muscles. Brain deeply incised posteriorly, 95 Μm long, width not measured. No oesophageal appendages, no intestinal diverticula. Four pairs pharyngeal glands, two primary pairs in IV, V, broadly attached to dorso-anterior face of respective septa, two ventral secondary pairs in V, VI, larger than primary glands, immediately behind but not attached to septa. Chloragocytes from V, dense coverage from VIII, cell diameter c. 10 Μm. Dorsal blood vessel from XIII, anterior bifurcation prostomial. Midgut pars tumida not distinguished. Ventral nerve cord medullar, with promiment segmental lateral swellings in IV–VI, swellings continuing in VII f., but gradually fading out. Preclitellar nephridia unpaired at 6/7 and 8/9 to the left, at 8/9 to the right. Anteseptale an elongate funnel, postseptale covering entire segment length, lobed, loops of canals visible. Coelomocytes few in number, different anteriorly and posteriorly; in anterior segments small and inconspicuous, oval to rhomboid, with fine irregular vesicles, length c. 12 Μm; in hindmost 4 segments an aggregation of larger cells, length 16–19 Μm, with conspicuous large vesicles of equal size at periphery; both types nucleated.

Clitellum absent ventrally and dorsally, in XII–XIII, 2 complete segment lengths, beginning 1 epidermal cell row behind chaetae of XI, ending 1 cell row behind chaetae of XIII, consisting of c. 31 transverse rows. Seminal vesicle absent, few cysts free dorsally in XI. Sperm funnel funnel-shaped, 2x as long as wide, c. 30 Μm long, tapering from 15 Μm entally to 8 Μm near septum; vas deferens thin-walled, widened to 6–8 Μm diameter behind septum 11/12, narrowing ectally to 3.5 Μm diameter near ectal pore. Male pores on body surface, with irregular glandular mass (diameter c. 16 Μm) surrounding most distal part of vas deferens. One mature egg. Spermathecae not attached to oesophagus, a simple tube c. 4x as long as wide, with ectal duct 8–10 Μm wide and elongate ampulla 10–12 Μm wide; no glands or other modifications near ectal pore.

Remarks. Cernosvitoviella is a Holarctic aquatic genus, common in temperate and boreal sediments of limnic and river habitats, and in moist soil. Its presence in phytotelmata of a tropical cloud forest is surprising from a biogeographical point of view but not in contradiction with the known habitat requirements. There are few records of the genus outside the Holarctic. Botea (1983) identified a single specimen from groundwater habitats in Cuba as " Cernosvitoviella sp." but the illustrations ( Botea 1983, fig. 18A,B) show a specimen with only two chaetae per bundle, which suggests that the specimen was misidentified. Reference material is no longer available (V. Pop. pers. com.). Cernosvitoviella has further been recorded from rain forest soil in Papua New Guinea ( Standen 1988). Recently it was also found in peat soil on mountain peaks of the Mata Atlântica in Paraná, Brazil (R. Schmelz, C. Niva, unpublished). We consider our find as the first record of the genus from Central America.

The single specimen is well-preserved and allows investigation of all relevant characters except presence/ absence of dark coelomocyte granules, seen only in living specimens. Our identification of specimens as C. atrata is mainly based on the shape of the spermatheca and the male efferent apparatus, the latter matching closely the redescription in Nielsen & Christensen (1959, Fig. 18, reproduced in Schmelz & Collado 2010). Further characters also fit the species diagnosis: coelomocytes differing in shape anteriorly and posteriorly, clitellum open ventrally and dorsally (Schmelz pers. obs.), 2+2 pattern of pharyngeal glands. C. atrata is highly variable and probably a species complex ( Timm 2009, Schmelz & Collado 2010). Several forms which may be separate species have been distinguished, based on body size, coelomocyte variations and size of spermathecae ( Nielsen & Christensen 1959, Chalupský 1992), but none of the forms are well-described; furthermore the original description ( Bretscher 1903) is poor and there are no types. Therefore it remains undecided whether this Honduras specimen belongs to one of the microspecies within C. atrata as known from the northern hemisphere, which would suggest a cosmopolitan distribution, or whether it is a species of its own. Nevertheless, referring to current taxonomic knowledge, this specimen belongs to C. atrata .