Paromalostomum dubium

Schockaert, Ernest R., 2014, Marine Macrostomorpha (Platyhelminthes, Rhabditophora) from the Algarve (Southern Portugal), Zootaxa 3872 (5), pp. 577-590 : 581-582

Paromalostomum dubium (de Beauchamp, 1927)

Fig. 3

Localities in the Algarve. Faro ( Portugal), Ria Formosa, lower mid littoral, fine sand with the reduced layer 5–10 cm deep. (37° 01.037 N, 7° 48.674 W; 18 October 2013).

Known distribution. P. dubium was described from the Bay of Arcachon, France (de Beauchamp 1927), and is known from the North Sea, mainly around the Island of Sylt, Germany (e.g. Pawlak 1969; Hellwig 1987), Mariakerke, Belgium (S. Pyataeva, pers. comm.), the Swedish West Coast ( Westblad 1953), the Bight of Kiel, Germany (e.g. Ax 1951a and b) and in N. Wales ( Boaden 1963). Ax (1959) mentioned this species also from the Black Sea ( Sile, Turkish N. coast).

Material. Micrographs of the living animal, one whole mount (HU nr. VI.3.22).

The animal is around 0.8 mm in the whole mount. The shape and measurements of the hard parts of the genital system leave no doubt that this individual is a representative of P. dubium . The penis stylet is 194 µm long and the accessory stylet 129 µm (or 110 µm along a straight line). According to Rieger (1971b), the mean length of the penis stylet is 190 µm and that of the accessory stylet 105 µm. Rieger’s (1977) measurements of a population from Arcachon give a mean of 183.62 µm with a SD of 9.72 µm for the penis stylet and a mean of 103.92 µm, SD 5.28 µm for the accessory stylet, meaning that the Algarve individual has stylets with lengths that fall into the range of the animals in the Arcachon population. The conspicuous thick ring at the proximal opening of the penis stylet and the funnel-like terminal opening of the accessory stylet are, according to Ax (2008), characteristics of this species. In the female hard parts, the middle piece has the form as depicted by Rieger (1971b) and by Ax (2008) with a very short mouthpiece (10 µm). Both authors depict the terminal end of the penis stylet as sharp. Close observation shows that the opening has a diameter slightly less than the end part of the stylet (see Fig. 3 , insert).

c a mp

Ds

mi

st ps ⊂f D

Figures

FIGURE 3. Paromalostomum dubium. A. Living animal at low magnification. — B. Caudal end in the living animal. — C. Hard parts in the female system. — D. Hard part of the copulatory organs. — E. Micrograph showing terminal end of accessory stylet and of the penis stylet, indicated by an asterisk. (Scales = 20 µm).