Dero scalariformis, Viviane, 2002

Righi, Gilberto & Hamoui, Viviane, 2002, Oligochaeta, Naididae Of The West Indies And Adjacent Regions, Papéis Avulsos de Zoologia 42 (6), pp. 119-167 : 132-133

Dero scalariformis n. sp.

( Fig. 1 K-O)

Material: Curaçao 75: 5 specimens; 75a: 12 specimens (Holotype ZU-1318); 76A, 1 specimen; 77a: 1 specimen; 86: 5 specimens; 399: 7 specimens; Bonaire 44b: 1 specimen ; 44 Ba: 5 specimens; 44e: 2 specimens; 52d: 2 specimens; 52e: 7 specimens; 54: 3 specimens; 54c: 1 specimen. Habitat: Limnetic to oligohaline; salinity 0.16-1.08%.

Description: Length 1.5-2.5 mm. Diameter 165-172 µm. Number of segments 22-30. Division-zone in XV-XX. Prostomium short, semicircular. Eyes absent. Short branchial fossa with two pairs of somewhat flattened fingerlike gills ( Fig. 1K ). Bulky septal glands in V and VI. Wide thick walled stomach in VIII. Intestine begining at IX or X. Chloragogenous cells from VI backwards. Dorsal setae starting from VI, 1 hair and 1 needle per bundle. The hair setae present a thin aliform membrane at one side and smooth surfaces on the other sides; the width of the ala narrows making up two high stairs in the free border towards the apex. The view of the scalariform portion of the hairs depends upon the position of the setae ( Fig. 1O ). The needles are straight with a curve distal fourth; their apex is tricuspid ( Fig. 1N ), the proximal and distal teeth are alike in length and thickness and the medial tooth is thinner and a little shorter. The ventral setae are 3-5 per bundle in segments II-V, 3-4 from VI backwards, and 1-2 in the last segments. The setae of II-V have proximal nodulus and teeth of similar thickness but the distal tooth is almost 1.5 times longer than the proximal one ( Fig. 1L ). The setae from VI onwards have distal nodulus and much shorter teeth than in anterior segments; the distal tooth is a little shorter and distinctively thinner than the proximal one ( Fig. 1M ). The length of the setae are in the Table 1.

Origin Hairs Needles Ventral II-V Ventral VI

Curaçao 399 98-102 37-38 78-86 46-52 Bonaire 52a 78-81 33-39 71-78 39-42 Bonaire 52d 91-104 39-46 87-91 42-50

Remarks: Dero scalariformis has affinities with D. pectinata Aiyer (1929) in number of gills, number of setae per bundle and shape of the needle and ventral setae. They are distinguished by the hairs, which have one finely pilose side in pectinata or a thin smooth scalariform membrane in scalariformis . This introduces the questions of whether the hairs of the setae in pectinata are just cross thickenings of a thin alar membrane which is flat in scalariformis and whether the two of them are only varieties of a same species.

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.