External ultrastructure of Manayunkia speciosa (Fabriciidae) from Uruguay River, Argentina

Resumen

The external ultrastructure of Manayunkia speciosa Leidy, 1858 from specimens collected at the lowerUruguay River, South America is described using scanning-electron-microscopy. The branchial crown has a pairof semicircular lateral lobes, a pair of mediodorsal radioles and a pair of medioventral ones. Radiolar surfaces areciliated. The faecal groove is observed on peristomium middorsally. The anterior margin of the anterior peristomialring formed a rectangular lobe, with a ciliated band. Chaetal shape exemplifies the basic type of tapering cylinder.Two types of thoracic notochaetae: one wider distally, with a smooth handle, and covered on the surface by denticles,and other are significantly finer at the base and covered by thin structures with a free distal end. These structures werenot previously recorded in Fabriciidae. Rows of 3 aligned uncini anteriorly projected are found in the thorax. Eachuncinus presents a long manubrium which connects with the crest, extending to a main fang. The teeth of the crestare equal in size. The abdomen present 4 types of neurochaetae: one of small size than the other 3. In the abdomen 10-14 uncini form dense dorsal-transverse-lines. Each uncinus presents a short manubrium. The crest is covered withteeth of similar size.