Achaeta

Schmelz, Rüdiger M., Collado, Rut & Römbke, Jörg, 2008, Mata Atlântica enchytraeids (Paraná, Brazil): The genus Achaeta (Oligochaeta, Enchytraeidae), Zootaxa 1809, pp. 1-35 : 29-30

Achaeta sp. 1

Material: MZUSP #1372, two spms, one fully mature, one submature; urban parkland in Curitiba, close to entrance of Department of Soils and Agricultural Engineering, Federal University of Paraná ( UFPR), Section Agrosciences Agrarias. Spms as stained whole mounts.

Worms 3 mm long, 0.1 mm wide (viv), or 2 mm: 0.1 mm (fix). Both specimens with 21 segments. Pyriform glands absent. Six segmental epidermal gland cells, three on each side, in bilateral-symmetrical arrangement, cells larger than clitellar hyalocytes, up to twice as thick as body wall, outline circular or oval, diameter ca. 15 μm (fix); dorsally 4 cells in one transverse row, cells aequidistant from each other, slightly larger than ventral cells, ventrally one segmental pair in usual position, in row directly posterior of dorsal glands, directly anteriorly of septum. Body wall very thin (2–4 μm, fix), longitudinal muscle layer 1 μm thick or less, cuticle barely visible. Septa 4/5, 5/6 thickened, rest thin or as if absent. Head pore at tip of prostomium, epithelium beneath thickened, prostomial ganglia not seen. Brain rounded anteriorly and posteriorly, 70 µm: 30 μm (fix). Suboesophageal ganglion present, ventral nerve cord in segmental ganglia from V on. Oesophageal appendages as two sausage-like bodies in V, lining oesophagus laterally, diameter 14 μm (fix), circular in optical cross-section, connected by a mid-dorsal strand of about same diameter, no canal seen in IV. Pharyngeal glands in IV-VI, dorsally connected and with primary ventral lobes, largest in V and VI; lobes in VI perhaps also separate dorsally. Gut dilatation at 1/ 2 VII, no intestinal diverticula. Chloragocytes large, conspicuous, diameter 25–27 μm (viv), vesicles green-yellowish, size 2 μm (viv); in whole mounts, elongate and refractile greenish bodies embedded in dense, pale vesicles. Dorsal blood vessel from VII, large, pulsating. Pars tumida of midgut not seen. Two pairs of preclitellar nephridia, at 6/7, 7/8; anteseptale about as wide as long, truncate, postseptale gradually tapering towards ectal pore, no terminal vesicle; shape of postclitellar nephridia alike. Coelomocytes ca. 18 μm long (viv). All sexual organs except spermathecae shifted one segment anteriad: testis, sperm funnel in X, vas deferens, male copulatory organ and clitellum in XI. Clitellum ventrally open, dorsally (almost?) closed. Three longitudinal rows of hyaline gland cells on each side of dorsal half: First row truly dorsally, distance between rows of both sides not more than one cell diameter; row regular, consisting of 14-15 cells, all one behind the other; further down laterally 2 disordered rows of hyaline cells, cells not in straight line. Latero-ventrally only granulocytes, about half as wide as hyalocytes. Hyalocytes not projecting beneath muscle layer into body cavity, as high as long (ca. 8 μm), width up to 20 μm. Seminal vesicle absent. Spermatozoa short, measured head length 8 μm (fix). Sperm funnel small, collar narrower than funnel body, asymmetrical (28µm: 20 μm and 28 µm: 12 μm in the same animal, fix). Vas deferens narrow, with few coils, not straight. Male pore on body surface, surrounded by a compact gland, more or less spherical in side view, diameter 16 μm (fix). Accessory glands absent. Spermatheca very small, confined to V, ectal pores lateral, cuticularized ectal duct not seen, sperm in parallel at ca. 15–20 μm distance proximally of ectal pore, ental reservoir not thickened compared to rest of organ. One egg mature, extending over XI –XII.

The scope of the material is insufficient for a formal recognition of the species. The specimens are briefly described here to demonstrate that more Brazilian species of Achaeta await discovery, and to highlight the importance of detailed species descriptions, since the specimens resemble A. hanagarthi , A. paranensis and also A. singularis in some characters (comp. Table 4 ). The single fully mature specimen stands out by a dorsally almost closed clitellum. The most conspicuous trait in vivo of the two specimens were the large chloragocytes, causing as milky-white and opaque body colour. However, size and texture of these cells may be influenced by the availability and quality of food. Absence of pyriform glands and lateral spermathecal ectal pores agree with the character pattern common in other neotropical Achaeta species (see below).