Oligochaeta, Naididae Of The West Indies And Adjacent Regions Author Righi, Gilberto Author Hamoui, Viviane text Papéis Avulsos de Zoologia 2002 2002-02-20 42 6 119 167 http://dx.doi.org/10.11606/0031-1049.2002.42.p119-167 journal article 10.11606/0031-1049.2002.42.p119-167 1807-0205 13226308 Dero trifida Loden, 1979 ( Fig. 1 G-J) Dero (D.) trifida Loden, 1979: 584 , fig. 1A-F Material : Aruba 98, 1 specimen . Surinam 120: 4 specimens (ZU-1317) . Habitat Limnetic; salinity 0.03-0.1%. Distribution: North America ( Loden, 1979 ). Neotropical Region: Aruba ; Surinam (Righi & Hamoui). Description: Length: 3.7-3.8 mm . Diameter 225-282 µm. Number of segments 35-37. Division-zone in XXI-XXII. Short semicircular prostomium. Branchial fossa ( Fig. 1G ) with a pair of slits in the posteriorlateral third and an hindmost wide gutter; a cross fold with the sphincter muscles lies between the fossa and gutter floors. Four pairs of gills are in the fossa; the first pair is dorsal, wide and flat, the other 3 pairs are ventral and fingerlike. All of the gills are contracted, in the side view they did not extend beyond the border of the fossa. A wide stomach with differentiated walls lies in IX followed by the intestine of similar diameter. There are a few chloragogenous cells from VII-VIII backwards. Thick commissural vessel are in VII-IX. Dorsal setae start from VI , 1 hair and 1 needle per bundle. The hairs are thin, bowed, smooth and 160-183 µm long. The needles ( Fig. 1H ) are 47-66 µm long, with a nodulus at the beginning of their bowed distal third. The apex has short teeth, 1-2 µm long, the distal tooth is a little longer than the proximal one; the shortest intermediate denticle departs from between the two main teeth. There are 4-5 ventral setae per bundle, generally 5. In II-V they are 113-120 µm long, the nodulus is medial or slightly distal, the teeth are alike in thickness but the distal tooth is 1.5 longer than the proximal one ( Fig. 1I ). Remarks: The species was only known in small populations in USA : Louisiana and North Carolina ( Loden, 1979 ). Unlike our worms the North American specimens have the posterior ventral setae with distal tooth a little shorter than the proximal one. This difference is seen as an intra-specific variation without taxonomical value due to similarity of the other characteristics.