Hofstenia arabiensis Nov. Sp. (Hofsteniidae)‎ : anew species of acoelan turbellaria from the Red Sea North of Jeddah

الملخص EN

A new Acoelan worm, Hofstenia arabiensis was found alive on the brown algae Sargassum vulgare (J.G.

Agardh), and Cystoseira myrica, in the reef flat shoreward of the fringing reef in front of the Old King's Palace, North of Jeddah (Saudi Arabia).

It is elongated having an anterior tip and a blunt posterior end.

The color of the body is nearly yellowish red.

The living worm is about 5 mm long and its breadth reaches about 1.25 mm.

Nearly 35 specimens of this worm were collected during the months of May and June 1986.

Reconstructions of the'new species were drawn from the median sagittal position by the examination of transverse, longitudinal and frontal sectipns of the worm stained by Haematoxylin-eosin and Mal-lory stain.

This worm is related to the genus Hofstenia due to the fact that it has an integumentary nerve plexus.

The mouth aperture is subterminal.

The pharynx is strongly muscular.

Vesicula seminalis is present and the ovary is follicular.

It is a new species due to the fact that the worm is tubular, having a rounded anterior tip and a blunt and smooth posterior end'.

It has a yellowish red color.

The worm has a network subepidermal nerve plexus extending from the anterior tip of the body till the end of its first half, moreover, the central brain mass surrounding the statocyst is totally absent.

The penis bulb is provided with only 4 chitinised spines.

The sunk epithelial layer of the pharynx is unciliated and the oesophagus is missing.