Proschizorhynchus reniformis Brunet, 1970

Gobert, Stefan, Monnens, Marlies, Eerdekens, Lise, Schockaert, Ernest, Reygel, Patrick & Artois, Tom, 2020, Schizorhynchia Meixner, 1928 (Platyhelminthes, Rhabdocoela) of the Iberian Peninsula, with a description of four new species from Portugal, European Journal of Taxonomy 595, pp. 1-17 : 9-10

Proschizorhynchus reniformis Brunet, 1970

Fig. 2H

Material examined

PORTUGAL • 1 whole-mount (photographs of live specimen available); Algarve region , Sagres, East of Mareta Beach; 37°00′10″ N, 08°56′06″ W; 20 May 2013; B. Tessens leg.; coarse sand and shell gravel at 12 m depth; HU X.1.45 .

Previously known distribution

Baie de Cassis, Provence-Alpes-Côte d’Azur, France ( Brunet 1970).

Remarks

The slender, curved stylet measures 65 μm in length and lies in a 30-μm-long, grooved cirrus sheath ( Fig. 2H ). A sclerotised, plate-like structure, approximately 25 μm in length, extends from the stylet’s proximal base, perpendicular to the rim of the cirrus sheath, towards the distal end of the stylet. The stylet is slightly longer than the size range described by Brunet (1970), who mentions stylet lengths of 40–45 μm. Otherwise, our specimen conforms well to the description of P. reniformis .

Taxonomic discussion: Proschizorhynchus

Proschizorhynchus is one of the most species-rich genera within Schizorhynchidae ( Tyler et al. 2006 – 2019b). The genus is relatively uniform in its general morphology and is characterised by a copulatory organ consisting of a grooved cirrus sheath, a stylet and a hardened penial papilla (see Noldt 1985).

The various species are distinguished from each other based largely on the structure of the copulatory organ.

The highly characteristic copulatory apparatus, with a sheath showing longitudinal striation, places our three newly-described species in the genus Proschizorhynchus . Within Schizorhynchia, only Typhlorhynchus Laidlaw, 1902 shares this feature of the male copulatory system. However, this genus is characterised by the lack of a proboscis, placing our specimens unambiguously within Proschizorhynchus .

The lack of spines or rods on the distal rim of the cirrus sheath in P. arnautsae sp. nov. is a feature shared with P. gullmarensis Karling, 1950 , P. reniformis Brunet, 1970 and P. lunatus Brunet, 1970 . In P. gullmarensis and P. reniformis , however, the stylet is much longer, protruding far beyond the rim of the cirrus sheath and, in P. reniformis , curved back upon itself. Furthermore, in both species, a bundle of spines is attached to the distal cirrus ridges (see Noldt & Hoxhold 1984), a feature not seen in P. arnautsae sp. nov. Finally, both species have a larger plate-like extension at the base of the stylet that is not present either in P. arnautsae sp. nov.

Proschizorhynchus lunatus has a stylet comparable in length to that of P. arnautsae sp. nov. (30–35 µm and 26–36 µm long, respectively) and is generally similar in the proportions of the copulatory organ. However, in P. lunatus , the cirrus sheath forms the base of a curved, hardened distal penis, with a narrow distal opening ( Brunet 1970; Noldt 1985). Such a structure is unique within the genus and was not observed in any of the specimens of P. arnautsae sp. nov. either.

Proschizorhynchus troglodytus sp. nov. resembles P. pectinatus l’Hardy, 1965 and P. arenarius de Beauchamp, 1927 in its strongly curved and very long (with respect to the cirrus sheath) stylet. Moreover, these three species all possess a plate-like extension at the base of the stylet, but this is shared with some other species within the genus (e.g., P. gullmarensis , see above). According to l’Hardy (1965), P. pectinatus and P. arenarius are very difficult to distinguish. This is, at least in part, due to the inadequate description of P. arenarius (see Noldt 1985). For example, it is unclear whether the continuation of the longitudinal ridges on the sheath of P. arenarius drawn and described by de Beauchamp (1927) represent spines of the type present in P. pectinatus and most other representatives of the genus, or are the result of partial eversion of the cirrus ( Noldt 1985). Both P. troglodytus sp. nov. and P. pectinatus have a sclerotised piece at the distal end of the stylet that is somewhat separated from the rest by a slight constriction. However, in P. pectinatus this piece is leaf-shaped, while in P. troglodytus sp. nov. it is cylindrical and robust. In fact, the entire stylet of P. troglodytus sp. nov. has a thicker and more robust appearance than that of P. pectinatus . Furthermore, the stylet in P. troglodytus sp. nov. barely protrudes beyond the distal end of the spines on the cirrus sheath, while in P. pectinatus (and P. arenarius ), the stylet is much longer relative to the cirrus sheath and spines.

The copulatory apparatus of P. algarvensis sp. nov. also bears a great resemblance to that of P. pectinatus in the shape of the stylet and the presence of long spines on the distal rim of the penis papilla. However, the stylet of P. algarvensis sp. nov. is longer and much more strongly curved than that of P. pectinatus (207 μm in P. algarvensis sp. nov., approx. 100 μm in P. pectinatus ). Moreover, it appears to protrude less far beyond the spines of the cirrus sheath in P. pectinatus than it does in P. algarvensis sp. nov. In P. pectinatus the stylet also has a distal constriction, which is lacking in P. algarvensis sp. nov. Furthermore, P. algarvensis sp. nov. has a pair of pigmented eyes, while P. pectinatus and P. arenarius are eyeless.

Figures

Fig. 2. Copulatory organ of species of Proschizorhynchus Meixner, 1928. A. Proschizorhynchus algarvensis sp. nov., holotype (HU 615). B–C. P. arnautsae sp. nov. B. Holotype (HU 616). C. Aspecimen from the reference collection of Hasselt University (HU X.1.35). D–E. P. troglodytus sp. nov. D. Holotype (HU 617). E. A specimen from the reference collection of Hasselt University (HU X.1.40). F–G. P. pectinatus l’Hardy, 1965 (HU X.1.43). F. Copulatory organ. G. Sclerotised spermatic duct. H. P. reniformis Brunet, 1970 (HU X.1.45). Scale bars: A, F = 50 µm; B–E, G–H = 20 µm.