Pristina terrena Collado & Schmelz, 2000

Schmelz, Rüdiger M., Jocque, Merlijn & Collado, Rut, 2015, Microdrile Oligochaeta in bromeliad pools of a Honduran cloud forest, Zootaxa 3947 (4), pp. 508-526 : 518-519

Pristina terrena Collado & Schmelz, 2000

Pristina terrena Collado & Schmelz, 2000: 513 –514, figs 8, 9.

Material examined. Five specimens, sexually immature, IG 327183-23 to IG 327183-27; one specimen with budding zone and primordial testes in VIII and primordial ovaries in IX. Cusuco National Park, Honduras, [15.505813 -88.21473, 15.506299 -88.23704, 15.522537 -88.27598, 15.513245 -88.28807, 15.526152 -88.27662], respectively 2061 m, 1457 m, 1558 m, 1468 m and 1587 m asl, M. Jocque 07/07/2013 to 06/08/2013. Further 6 specimens in the 3rd author's collection, [15.52425 -88.28853, 15.50731 -88.29428], respectively 1659 m, 1347 m asl, M. Jocque 07/08/2006.

Description. Body length 1–2 mm, diameter 0.1–0.14 mm. Segment number of complete specimens 17–24 (17, 17, 19, 20, 24). Budding zone present in two specimens, between chaetae of XVII and XVIII (specimen with 24 segments) or XIV and XV (specimen with 20 segments). Posterior zooids with 6 or 7 segments. Dorsal bundles with 1 or 2 elongate, serrate hairs and 1 or 2 simple-pointed needles; more often just one hair and one needle per bundle. Hairs up to or more than three times as long as body diameter, increasing from II to VII to maximum length. From VII on, hair length 240–340 Μm, varying among bundles, segments and specimens. Hair length slightly reduced in hindmost 2 segments, not as much as in foremost segments. Hairs c. 2 Μm thick at base, tapering continuously ectad, less than 1 Μm thick at tip; serration distinct at x250 magnification on convex side of bent chaeta, serration 'teeth'> 1 Μm apart, distance between teeth wider at base than towards the tip. Needles tightly attached to proximal hair shaft and not always well-distinguished, c. 40 Μm long, straight without nodulus, about 1.5 Μm thick in ental 4/5, strongly thinning out in ectal 1/5, bent backwards towards hair, ectal tip parallel to hair shaft. Tip simple-pointed at x1000 magnification but somewhat widened. Chaetal follicle conspicuous, diameter c. 15 Μm. Ventral chaetae all alike, 37–40 Μm long, bifid, nodulus as a faint swelling at c. 2/5 from distal tip, teeth short, about 1.5 Μm long, upper tooth minutely shorter and thinner than lower; chaetae straight distally, only teeth bent here; proximal third of chaetae bent in opposite direction of teeth; in II 6–9 chaetae per bundle, varying among specimens, 5–7 in II–XI, in posterior body half 3–5 per bundle, decreasing posteriad from 5 to 4 or from 4 to 3.

Prostomium without proboscis, rounded, longer than wide in one specimen, wider than long in all others (c. 50–70 Μm long and 70–80 Μm wide). Prostomial epithelium with several bilateral-symmetrical protuberances projecting entad into prostomial lumen, protuberances larger ventrally near mouth opening than dorsally, absent mid-ventrally. Epidermal gland cells seen in some specimens, laterally of and level to dorsal chaetal bundles. Pharyngeal pad with tenuous protractor and retractor muscles. Pharyngeal glands in separate packages at 3/4, 4/5, and 5/6, enclosing septa. Gut diameter abruptly widened behind septum 6/7, from c. 80 to 180 Μm, not constricted in following segment (i.e. no stomach distinguishable), no cells with intracellular 'stomachal' canals distinguished. Dorsal blood vessel large in VI (and V), not seen posteriorly. Three simple and unbranched commissural vessels observed near 2/3, 3/4, 4/5. Pars tumida of midgut present. First nephridium in VII, unpaired. Most of following nephridia unpaired as well, on alternating sides, 10 nephridia counted altogether in a specimen with 20 segments. Nephrostome present, on anterior face of 6/7 ventro-laterally; wide and densely packed loops in all of VII, dorsally and ventrally. Nephropores ventral, anterior to ventral chaetal bundles. Coelomocytes spherical, diameter 6–10 Μm, with glassy irregular texture, vesicles not distinguished.

Remarks. Our specimens agree in all diagnostic details with Pristina terrena Collado & Schmelz, 2000 . Noteworthy are the long serrate hairs that increase in length from II to VII and vary in length from VIII on, seemingly simple-pointed needles without nodulus and a tapering distal fifth bent towards the hair, and ventral chaetae that differ very little in size and shape between anterior and posterior bundles, with short and more or less equal-sized teeth. Further similiarities of P. terrena extend to body size, segment number, blood vessels, blood commissurals, and location of the first nephridium. The only difference of possible taxonomic importance is the widening of the intestine, described as gradual in P. t errena and abrupt in our specimens. However, the latter is a fixation artefact due to strong contraction of the animals when fixed in ethanol. We reinvestigated non-type ethanol-preserved reference specimens of the original series from Collado's personal collection (see Collado & Schmelz 2000), and there the intestine shows an abrupt widening as well. A stomach was not seen in the Honduras material and is absent in P. t e r ren a as originally described. The coelomocyte granulation, conspicuous in living specimens, is no longer seen in ethanol-preserved material, but the non-type reference material (see above) has the same irregular glassy texture without distinct vesicle; such a pattern can be indicative of coarse refractile granules as seen in live P. t errena. The same correspondence has been observed in enchytraeids (comp. Rota 2013).

This is the first record of P. t er re n a after the original description from rain forest soils near Manaus, Brazil. The distance of approx. 3500 km between the two localities may suggest an extremely good dispersal ability of the species, but P. t e r re n a may also be common and widespread in Central and South America. Records of Pristina in Central and South America are scarce and mostly restricted to limnic, river and groundwater habitats, where this soil-dwelling species may not occur. Pristina species were regularly found in a non-flooded ("terra firme") primary forest plot of Amazonia, with six species described or recorded so far ( Collado & Schmelz 2000, 2001, 2002; Augustsson 2001) and also in the Mata Atlântica of the Brazilian State Paraná (Römbke et al. 2005).