Xetadrilus Schmelz, Collado & Römbke, 2011, gen. nov.
Creators: name: Schmelz, Rüdiger M.
name: Collado, Rut
name: Römbke, Jörg
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Clitellata
Enchytraeida
Enchytraeidae
Xetadrilus

description: Xetadrilus gen. nov.
Genus "X" – Römbke et al. 2007: 144f.
Type species: Xetadrilus maacki sp. nov.
Included species:
Xetadrilus maacki sp. nov.
Xetadrilus aphanus sp. nov.
Xetadrilus fabryi sp. nov.
Xetadrilus pitucus (Righi, 1974a) (ex Marionina) Xetadrilus righianus (Xie & Rota, 2001) (ex Marionina) Xetadrilus ugandensis (Bell, 1954) (ex Stercutus)
Genus diagnosis. Small worms, adults in vivo 2–5 mm long and 0.1– 0.2 mm wide. Two chaetae per bundle, absent laterally from VIII on (absent from VII in X. pitucus), chaetae with proximal bend, distally mostly straight. Lateral chaetae not shifted dorsally. Epidermal gland cells pale, elliptical, not transversely elongate. Head pore on prostomium dorsally. Prostomial epithelium with frontal recess; prostomial papillae present. Brain incised posteriorly, longer than wide, with ganglia on prostomial nerves. Ventral nerve cord with suboesophageal ganglion in II– IV and segmental ganglia from V on. Pharyngeal glands variable, secondary ventral lobes present or absent. Oesophageal appendages absent. Intestinal diverticula absent, present at VII in X. fabryi. Gut often widened abruptly at 6/7, with thickened epithelium in VII. Dorsal blood vessel origin in clitellar or postclitellar region, anterior bifurcation in segment I. Nephridial anteseptale with parts of nephridial body, no constriction at septum, efferent duct short. Coelomocytes one type, mucocytes. Male reproductive system simple, vas deferens not widened, male pores on body surface. Spermathecae not attached to oesophagus, with ectal duct and ampulla; ectal pore in lateral line and at half-length between lateral chaetae of IV and V; no diverticula, no ectal glands.
Etymology. Named in honour of the Xetá people, the last ethnia in the Brazilian state of Paraná to come into contact with 'modern' civilization in the last century. Within a few years the Xetá were almost eradicated by forest destruction for coffee plantations. Survivors and their descendants merged into the Brazilian population. Today five persons still speak Xetá, a language that belongs to the Tupi-Guaraní language family.
Common traits: (1) Not more than 2 chaetae per bundle
(2) Head pore on prostomium
(3) Ventral nerve cord ganglionic from V, ganglia II-IV fused into suboesophageal gan-
glion
(4) Nephridial anteseptale including parts of nephridial body
(5) Spermathecae (when present) free, not attached to oesophagus
(6) Spermathecae (when present) without diverticula
(7) Brain incised posteriorly (truncate in T. marcusae)
(8) Male copulatory organ without bursa, male pore on body surface **
* absent from XIII in T. lacteus Righi, 1974b. ** bursa in T. marcusae.
Remarks. Xetadrilus is closely related to Guaranidrilus and Tupidrilus Righi, 1974b. Similarities and differences are listed in Table 1, see also below, discussion, and Figure 8. Within this triad of genera, Xetadrilus stands out by
(1) lateral chaetae absent from VIII, (2) inner prostomial papillae,
(3) conspicuous prostomial ganglia, (4) a frontal recess in the prostomial wall.
Trait (1) is the presumed apomorphy of the genus sensu stricto. Traits (2,3,4) are probably plesiomorphies because they are also present in Achaeta (comp. Schmelz et al. 2008). Trait (4) occurs also in some species of the marine Grania (Rota et al. 2003). The peculiar similarity of one species of Enchytronia will be dealt with below, see discussion. All species of Xetadrilus lack oesophageal appendages, and intestinal diverticula are absent in all but one species. Tupidrilus differs from Xetadrilus in the presence of oesophageal appendages and in the presence of lateral chaetae from VIII on (they are absent from XIII in T. lacteus); traits (2),(3),(4) are unkown. Tupidrilus differs from Guaranidrilus only in the absence of intestinal diverticula, and its status was considered doubtful after a phylogenetic analysis (Coates 1989), but the taxonomy of Tupidrilus is beyond the scope of this paper. The genus includes four species, all from Brazil.
Due to its similarity with Guaranidrilus and Achaeta, Xetadrilus may be accomodated in the Achaetinae Černosvitov, 1937. Achaetinae is recognized by a combination of characters (Table 1), there are currently no diagnostic traits, see below, discussion. Tupidrilus and Hemienchytraeus are also members of the subfamily.
Two species of Marionina and one species of Stercutus are included in the new genus; criteria for their inclusions were: (1) compliance with all traits common to Guaranidrilus, Tupidrilus, and Xetadrilus (Table 1), (2) absence of oesophageal appendages, (3) absence of lateral chaetae from VIII on (M. pituca from VII), (4) prostomium with ganglia, inner papillae, and frontal epithelial recess. Traits related to the prostomium are unknown in X. righianus and X. ugandensis; types of the latter are lost, so fresh material will be necessary to confirm the new combination. Types of X. righianus were not investigated during the time of this study. In X. pitucus, large prostomial ganglia are originally described (Righi, 1974a), although not recognized as such; and inner prostomial papillae and a frontal epithelial recess are present in the types (Schmelz & Collado, unpublished). The three species included in Xetadrilus do not comply in all details with the generic diagnosis (see Table 2), but they disagree considerably with the type species of their original genus (Stercutus niveus Michaelsen, 1888 and Marionina georgiana Michaelsen, 1888, respectively). S. ugandensis has been a species incertae sedis since Nielsen & Christensen (1959), and Marionina is a heterogeneous assemblage of species in need of revision (Rota et al. 2008, Schmelz & Collado 2008). The transfer of M. pituca and M. righiana to Xetadrilus is in agreement with the suggestion in Rota et al. (2008) to accomodate some species of Marionina in Achaetinae. Table 2 gives an overview of key traits of the included nominal species. Redescriptions of type material will be presented elsewhere.
Three further South American species of Marionina, M. patua Righi, Ayres & Bittencourt, 1978, M. ecuadoriensis Righi, 1981a, and M. tica Righi, 1981b, are very close to Xetadrilus based on the following traits: free spermathecae, head pore on prostomium, two chaetae per bundle, no oesophageal appendages, no intestinal diverticula. They differ from Xetadrilus in the presence of lateral chaetae from VIII on. These species probably belong to Achaetinae, too, but their generic placement within the subfamily is not straightforward. Type-based redescriptions of these species, together with suggestions as to their generic position, will be presented elsewhere.
With the African X. ugandensis and the Chinese X. righianus, Xetadrilus is a cosmopolitan genus. Its circumscription may change in the future when more species have been discovered and more species of Guaranidrilus, Tupidrilus, and Marionina have been reinvestigated.
description: Published as part of Schmelz, Rüdiger M., Collado, Rut & Römbke, Jörg, 2011, Mata Atlântica enchytraeids (Paraná, Brazil): A new genus, Xetadrilus gen. nov., with three new species, and four new species of Guaranidrilus Černosvitov (Enchytraeidae, Oligochaeta), pp. 1-29 in Zootaxa 2838 on pages 13-15, DOI: 10.5281/zenodo.203260