Bryodrilus hondurensis Schmelz

Schmelz, Rüdiger M., Jocque, Merlijn & Collado, Rut, 2015, Microdrile Oligochaeta in bromeliad pools of a Honduran cloud forest, Zootaxa 3947 (4), pp. 508-526 : 510-513

Bryodrilus hondurensis Schmelz , sp. nov.

( Figure 2 )

Material examined. Holotype. IG 327183-01, adult specimen, unstained whole mount. Honduras, Cusuco National Park, Napacu [15.50834 -88.23274], 2057 m asl, bromeliad tank on the ground. M. Jocque 18/08/2006. Paratypes. IG 327183-02 to IG 327183-04, three adult specimens, unstained whole mounts, same plant and collection data as holotype. Holotype and three paratype specimens strongly contracted, segments 4– 6 x as wide as long, one paratype specimen less contracted, slightly macerated.

Etymology. Named after the country where it was found.

Description. Body cylindrical, slightly tapering anteriorly, strongly tapering posteriorly in hindmost 4–5 segments. Holotype 9 mm long and 0.8 mm wide, contracted paratypes 6.5, 8.8 mm long and 0.65, 0.9 mm wide at XII, macerated paratype 15 mm long and 1.0 mm wide at XII. Segment number 53 (holotype), 53, 48 (paratypes), 40 segments in a paratype specimen with regenerated posterior body end. Chaetae distinctly sigmoid, without nodulus, distally pointed and bent, proximally rounded, bend weaker. Chaetae in a bundle arranged in asymmetric fan, chaetae of unequal size, those towards dorsal and ventral midlines of body gradually smaller; largest ventral chaetae c. 70 by 6 Μm in II, 90 by 6.5 Μm in XI, 100–110 by 6–6.5 Μm in caudal segments; maximum number per bundle 10 (3 spms) or 11 (1 spm); chaetal formula 5-8-8-2: 5-10,(11) -10-3,(2). Chaetae absent at XII; in lateral preclitellar bundles mostly 7 chaetae, in lateral postclitellar bundles mostly 6–7 chaetae, in ventral preclitellar bundles mostly 9–10, or 10–11 chaetae, in ventral postclitellar bundles mostly 9–10 chaetae; numbers decreasing in all rows towards posterior end, in lateral bundles from 7 or 8 down to 2, in ventral bundles from 10 or 11 down to 2 or 3. Epidermal gland cells inconspicuous in posterior body half; in preclitellar segments 4–5 rows per segment, density increasing towards anterior end; anterior 4–5 segments completely covered with gland cells except at intersegmental furrows. Dorsal pore at 0/I, a transverse slit.

Body wall varying in thickness, dorsally ca. 40 µm, ventrally ca. 80 µm; cuticle thin, 1 µm thick or less; longitudinal muscle layer well-developed. Brain strongly compressed, probably triangular in shape with rounded edges and truncate posterior end. Pharyngeal glands 3 pairs in IV–VI, all with primary ventral lobes, glands in VI largest. Dorsal connection of dorsal lobes not ascertained. Oesophageal appendages in VI, four rounded bodies attached to oesophagus, one pair dorsal, one pair ventral; canals or cavities not ascertained. Nephridia 7 preclitellar pairs, from 4/5 to 10/11; anteseptale elongate, consisting of funnel and parts of nephridial body, tapering towards septum, length c. 50–80 µm, postseptale distinctly larger than anteseptale, exact shape not ascertained; medial rise of efferent duct. First postclitellar nephridia at 13/14. Coelomocytes nucleate, small, broadly oval, about 26 µm long and 21 µm wide, finely granulated, numerous but not filling coelom completely. Gut in contracted specimens widening abruptly in VII or over VII and VIII, lumen filled with dark plant debris from XII, XIII, or XV on. Dorsal blood vessel from XI. Pars tumida of midgut (ventrally inflated gut epithelium) not distinguished. Chloragocytes from VI, as a flat layer, cell height usually below 20 µm, occasionally up to 40 µm; cells conspicuous in preclitellar segments by numerous and minute strong-brown vesicles; cells pale in postclitellar segments.

Clitellum from XII–1 /2 XIII, extending to level of chaetae of XIII, girdle-shaped, cells in reticulate pattern; hyalocytes absent mid-ventrally, here only granulocytes. Thickness up to 50 µm dorsally, c. 20 µm ventrally, probably less in non-contracted specimens. Hyalocyte diameter c. 10 µm, granulocyte diameter c. 5–6 µm. Seminal vesicle absent, developing sperm dorsally in XI. Mature spermatozoa aligned on top of sperm funnel, ca. 110 µm long, heads ca. 40 µm long. Sperm funnel small, ca. 140 µm long and 90 µm wide, collar about half as wide as funnel body. Vas deferens densely coiled ventrally in XII, between sperm funnel and male glandular bulb. Bursal slit longitudinal, male glandular bulb spherical, diameter ca. 80–85 µm, pierced centrally by vas deferens. Subneural glands absent.

Spermathecae. Ectal pore a transverse slit laterally at 4/5, slightly below longitudinal line of lateral chaetal bundles. Ectal glands as a crown of ca. 8 glands, diameter of crown 1.2–1.5x ectal duct diameter. Ectal duct short and thick, diameter 40 µm, c. 2.5x as long as wide, thick-walled, surrounded by musculature; duct canal narrow, gradually widening into ampullar lumen; ampulla not or only slightly wider than ectal duct, with thin epithelium, spherical or ellispoid, continued into narrow, elongate, thin-walled ental duct that extends towards body center dorsally of oesophagus. Communication of ental ducts and dorsal attachment to oesophagus not ascertained.

Remarks. All visible details comply with the genus diagnosis of Bryodrilus : head pore at 0/I, chaetae sigmoid without nodulus, pharyngeal glands without secondary glands, nephridial anteseptale short, and above all, two pairs of compact oesophageal appendages in VI. The sudden gut enlargement disagrees with the genus diagnosis but is most likely a fixation artefact.

Within the genus Bryodrilus , B. hondurensis sp. nov. is most easily distinguished by (1) the high number of chaetae per bundle. The majority of the other 15 Bryodrilus species described so far have a maximum of 4, 5 or 6, rarely 7 or 8, chaetae per bundle, not 10 or 11 as B. hondurensis . All other diagnostic characters occur in other species of the genus as well, but not in such a combination: (2) Seven pairs of preclitellar nephridia, from 4/5 to 10/ 11, (3) nephridial anteseptale elongate, (4) seminal vesicle absent, (5) spermatheca with large crown of ectal glands, (6) short ectal duct, and (7) ampulla without diverticula. The number of preclitellar nephridia (7 pairs, from 4/5 to 10/11) is unusually high but shared by B. fuscistriatus Chen & Xie, 2006 from northeastern China and the boreal-temperate holarctic B. ehlersi Ude, 1892 (see redescription in Cech et al. 2012). Some differences of these species from B. hondurensis , apart from the chaetae, are as follows. B. fuscistriatus : spermathecae with two diverticula, seminal vesicle large, extending over 3 segments. B. ehlersi : nephridial anteseptale short, consisting almost of funnel only, spermathecal ectal gland small, not circumferal, ectal duct elongate.

Xie et al. (2000) describe seven pairs of preclitellar nephridia in specimens from north-eastern China identified as Bryodrilus parvus Nurminen, 1970 . According to Dózsa-Farkas et al. (2012), B. parvus has 5 preclitellar pairs, from 6/7 to 10/11, therefore the species in Xie et al. (2000) is a different, probably new, species. Dózsa-Farkas et al. (2012) reinvestigated types of B. parvus , and they recognized the species as a junior synonym of B. librus ( Nielsen & Christensen, 1959) , based on morphological and DNA data. B. parvus sensu Xie et al. (2000) differs from B. hondurensis in smaller body size (3.5–4.7 mm), fewer segments (32–38) and chaetae (up to 6 per bundle), among other characters.

Several details remain unknown or incompletely known and require further investigation from living or properly fixed material: Colour and texture in vivo of coelomocytes and epidermal gland cells, shape of brain, details of pharyngeal glands and postclitellar nephridia, presence/absence of lumina in the oesophageal appendages. There is probably a mid-dorsal connection of the spermathecae as in all other species of the genus (except in Bryodrilus librus , where blind-ending spermathecae occur, see Dózsa-Farkas et al. 2012 for a recent review), but this remains to be confirmed.

Other peculiarities are likely fixation artefacts: The sudden gut enlargement at VII or VIII is probably caused by the strong contraction of the animals and not present in vivo. Piper et al. (1982) and Christensen & Dózsa- Farkas (1999) observed the same in preserved specimens of other Bryodrilus species. A gradual gut enlargement is part of the genus diagnosis of Bryodrilus and one of the characters that separate it from Henlea , a genus with abrupt gut enlargement. Furthermore, the spermathecal ectal pore, a transverse slit in our specimens, may be rounded and widened in living material. Spermathecae may be more slender than seen here; the ectal duct is coated with musculature and most probably maximally contracted. And of course, body dimensions of living specimens will be different: we expect an adult live body length of about 20 mm and a diameter of 0.5 mm.

The gut of all specimens is filled with dark-brown, amorphous, humic organic matter, interspersed by fragments of sclerotized plant remains such as tissue walls, spines, twiglets or rootlets. No algal remains (e.g. diatom shells) were found. The worms appear to feed on the humus accumulating on the bottom of the phytotelmata.

This is the southernmost record of a Bryodrilus species. The genus is most diverse in arctic to subarctic regions of Siberia, Alaska, Canada and Greenland. Only one species, B. ehlersi Ude is widely distributed in temperate regions. Three species are described from north-eastern China ( B. longifistulatus Xie, Liang & Wang, 2000 , B. macrotheca Xie, Liang & Wang, 2000 , B. fuscistriatus Chen & Xie, 2006 ). Up to now the most southern record of a Bryodrilus species was from western Florida by Healy (1996) ( B. novaescotiae Bell, 1962 , originally described from Nova Scotia, Canada).

Figures

FIGURE 2. Bryodrilus hondurensis sp. nov. A. Anterior body region. oa, oesophageal appendages; pp, pharyngeal pad, in upright position here due to strong contraction of animal; st, spermatheca; in, intestine in VIII, widened. B. Ventral chaeta from X. C. Spermatheca. Right: Crown of ectal glands. D. Nephridium at 9 / 10. All drawings from unstained whole mounts.