Phonorhynchoides linguatus, Artois, Tom J. & Tessens, Bart S., 2008

Artois, Tom J. & Tessens, Bart S., 2008, Polycystididae (Rhabditophora: Rhabdocoela: Kalyptorhynchia) from the Indian Ocean, with the description of twelve new species, Zootaxa 1849, pp. 1-27 : 20-22

Phonorhynchoides linguatus n. sp.

( Fig. 5 C–F)

Localities in the Indian Ocean. Zanzibar Island ( Tanzania): beach behind the Mbweni Ruins Hotel, south of the creek, in a higher part of the sand flat, with relatively coarse sand (11/8/1995) (type locality). Different localities at McKenzie point, Mombasa ( Kenya): near to the mangrove area in fine sand dried out during low tide (23 and 25/9/1991); near to the Four Seasons Hotel, in fine sand with shell parts exposed to the sun under the two stairs, near to a large mangrove area in the high-eulittoral (19/10/1991); same locality, between both stairs, in sand between rocks in the high eulittoral (21/10/1991). Seychelles: Mahé, Grande Anse (Beolière), high-eulittoral just before the mangrove area, fine sand with waste of shells ± 30 cm under the surface (19/12/ 1992); Des Roches, south-west side of the island, relatively coarse sand with Halimedia -like algae at about 60 m off the beach, 4 m deep at low tide (07/01/1993).

Material. Several animals studied alive. Two whole mounts from Zanzibar, one designated holotype ( SMNH, no. 7451). Seven whole mounts and seven sectioned specimens from Kenya. One whole mount from Mahé and one from Des Roches ( Seychelles)

Etymology. The prostate stylet type IV is tongue-shaped (lingua: tongue).

Description. Live animals are long and slender, colourless, with two eyes. They are 0,8–1,5 mm long (measured on whole mounts).

The structure of epidermis, proboscis, pharynx and the construction of the atrial organs are comparable with those of the other species of Phonorhynchoides Beklemischew, 1928 (for a description see Schockaert 1971; Artois & Schockaert 2001).

The sperm-conducting system consists of a seminal vesicle, a seminal duct with a prostate vesicle type IV and a prostate stylet type IV. This stylet is a simple tube, twisted around its longitudinal axis in about its middle. Only in the second specimen from Zanzibar it is completely straight (owing to compression?). Proximally from the twist it is 6–8 µm broad; distally from the twist it becomes broader (8–13 µm). It has a tongueshaped distal point. The stylet is shortest in the specimens from Zanzibar (88 and 91 µm), longest in the specimen from Mahé (143 µm), and intermediate (120–131 µm long, x = 125, n = 6) in the specimens from Kenya. However, measured relatively (in percentages) to the accessory stylet type IV (see further), the prostate stylet type IV of the Mahé specimen and that of the specimens from Kenya are comparable (65% in the Mahé specimen, 65–71% in the Kenyan specimens). The stylet type IV of the specimens from Zanzibar is only 50% of the length of the accessory stylet type IV.

The accessory vesicle type IV is rather small, of the same size as that of Phonorhynchoides somaliensis Schockaert, 1971 . A thick spiral, almost circular muscle layer surrounds it. It contains a coarse-grained eosinophilic secretion and is connected to an accessory stylet type IV that ends in a sharp point. This accessory stylet is of comparable length in the specimens from Zanzibar (174 and 183 µm) and Kenya (176–193 µm; = 184, n = 6). It is longer in the specimen from Mahé (219 µm).

The bursa is clearly bipartite, with a muscular distal part and a resorptive proximal part, communicating with each other through a muscular pore. Near to this pore, the female duct type I (“bursal stalk”) enters the muscular part of the bursa. The basal membrane of the female duct type I and of the muscular part of the bursa is very thick and at some places not covered by an epithelium (pseudocuticula). Where the epithelium is present, it is high without nuclei. A thin inner longitudinal and a thick outer circular muscle layer surround the female duct type I and the distal part of the bursa. The presence of a common oviduct connecting the bursa with the seminal receptacle is uncertain. Only in one specimen did we see the muscular beginning of a narrow duct starting from the muscular part of the bursa opposite the entrance of the female duct type I. Therefore we presume the presence of a common oviduct connecting the bursa with the female duct, but better-sectioned material is needed for verification.

Diagnosis. Species of Phonorhynchoides with a prostate stylet type IV between ca 90 and 143 µm long, twisted approximately in its middle, with a rounded, tongue-shaped distal end. Accessory stylet type IV between ca 179 and 219 µm long. Stylet /accessory stylet ratio between ca 1/2 and ca 7/10. Bursa with a strong muscular distal part, connected to the proximal part by a muscular pore.

Discussion. P. linguatus clearly belongs to the taxon Phonorhynchoides as it was diagnosed by Schockaert (1971): very small proboscis, proboscis retractor system consisting of 3 pairs of proboscis retractors and 2 pairs of integument retractors, presence of a prostate vesicle type IV and an accessory vesicle type IV, connected to a prostate stylet type IV and an accessory stylet type IV respectively, with a female bursa, a female duct type I (the “bursal stalk” of Schockaert 1971) and a female duct type II. Whether a common oviduct is present is uncertain (see above).

Within this taxon, P. linguatus and P. haegheni share two features that clearly distinguish them from the other species of Phonorhynchoides : the accessory stylet type IV is (much) longer than the prostate stylet type IV, and the bursa is bipartite, consisting of a muscular part and a sperm-resorbing part. P. linguatus can easily be distinguished from P. haegheni by the morphology of prostate stylet type IV. It is twisted and is tongueshaped distally in P. linguatus , whereas in P. haegheni it is straight and ends bluntly on a straight edge.

Of the five species of Phonorhynchoides , P. haegheni is clearly the most widespread, being recorded from Galapagos and Florida ( Artois & Schockaert 2001) and now also from Indonesia and Curaçao. P. linguatus is restricted to the Kenyan and Tanzanian coast and the Seychelles. Both species show considerable intraspecific geographical variation in stylet lengths, both of the prostate and of the accessory stylet. However, the relative length of the prostate stylet (compared to the accessory stylet) is fairly constant in both species, although the Galapagos population of P. haegheni and the Zanzibar population of P. linguatus appear to have relative shorter prostate stylets than populations of the same species from other areas.

The other three species of Phonorhynchoides all have a very restricted distribution, most of them only recorded once: P. carinostylis Ax & Armonies, 1987 from one locality in Canada ( Ax & Armonies 1987), P. flagellatus Beklemischew, 1928 from Lake Aral ( Beklemischew 1928) and Lake Golovitza, Romania (Mack- Fira 1974) and P. s o m a l i e n s i s Schockaert, 1971 from one locality in Somalia ( Schockaert 1971).

Figures

FIGURE 5. Phonorhynchoides haegheni Artois & Schockaert, 2001 A, Prostate stylet type IV (from the specimen from Indonesia). B, Accessory stylet type IV (from the same specimen from Indonesia). Phonorhynchoides linguatus n. sp. C, Prostate stylet type IV (from the holotype). D, Accessory stylet type IV (from the holotype). E, Habitus (from a live animal). F, Caudal body end (from a live animal).