Dero trifida Loden, 1979

Righi, Gilberto & Hamoui, Viviane, 2002, Oligochaeta, Naididae Of The West Indies And Adjacent Regions, Papéis Avulsos de Zoologia 42 (6), pp. 119-167 : 130

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.

Figures

Fig. 1. Nais barua: A, needle. B-C, ventral setae of III and XVII. Dero magna: D, needle. E-F, Ventral setae of V and XII. Dero trifida: G, branchial fossa. H, needle. I-J, ventral setae of II and VIII. Dero scalariformis: K, branchial fossa. L-M, ventral satae of II and XI. N, needle. O, hair and needle. Scales to Fig. G, K = 50 µm, to other figures 10 µm.