Macrostomum

Schockaert, Ernest R., 2014, Marine Macrostomorpha (Platyhelminthes, Rhabditophora) from the Algarve (Southern Portugal), Zootaxa 3872 (5), pp. 577-590 : 579

Macrostomum species 1

Fig. 1 A

Localities in the Algarve. Faro ( Portugal), Ria Formosa, small beach under the bridge to the Praia de Faro. Medium fine sand with silt, pebbles and some sea grass in the mid-littoral zone (37° 00.842 N, 7° 99.43 W; 12 September 2011).

Material. One whole mount (HU nr. VI.3.17).

Small animal with eyes. The stylet of this individual is 35 µm long, measured along line a; it is 20 µm wide at the proximal opening, tapering to 2 µm width after 19 µm, where it bends over 90° to a spine of 16 µm length. Its length, measured along lines b and c is 22 µm and 24 µm, respectively. The prostate glands have their necks in the proximal part of the stylet and in the prostate vesicle.

With the data available, it is impossible to identify this individual to the species level. A hook-shaped stylet is found in several species of Macrostomum and slight differences may occur in size and shape, also depending on the degree of compression under the cover slip. Moreover, I cannot provide data on the living animal.

The size of the stylet of the individual from the Ria Formosa is close to that of M. pusillum Ax, 1951 (24–26 µm). However, it lacks the characteristic dots in the stylet. Mack-Fira (1971) describes M. peteraxi from the Danube estuary with a stylet of similar length (27–30 µm) but, as stated by Rieger (1977), her figures do not allow a precise comparison. On the other hand, the stylet of this animal is slightly smaller than that of representatives of M. hystricinum Beklemischev, 1951 : Ax (2008) gives lengths of 30–41 µm for the European populations and 35–40 µm for the Canadian populations; Rieger (1977) gives lengths of 30–42 µm for the N. American Atlantic populations and 33–38 µm for the Ligurian population. When considering the ratio length/proximal diameter, it appears that the length is about 2.2 times the proximal diameter in M. pusillum and in M. peteraxi and 1.5 times in M. hystricinum . In the Faro animal the ratio is about 1/1. It has most similarity with the stylet of Macrostomum sp. nov. 1 (specimen accession code MTP LS 302) used by Schärer et al. (2011). The length of the stylet in this species is 28 µm and the proximal diameter is 24 µm. With the data now available it is, however, impossible to say if the same species is concerned. In all other species with a similar shape of the stylet, this stylet is considerably larger.