Phonorhynchopsis sublinguatus Diez, Sanjuan, Reygel & Artois, 2018

Diez, Yander L., Hernández, Claudia Sanjuan, Reygel, Patrick, Roosen, Paulien & Artois, Tom, 2018, First record of Polycystididae (Platyhelminthes, Kalyptorhynchia) from Cuba, with the description of a new genus and five new species, and remarks and the description of one new species from Panama, Zootaxa 4514 (1), pp. 107-125 : 112-114

Phonorhynchopsis sublinguatus Diez, Sanjuan, Reygel & Artois sp. n.

( Fig. 1 G–I, 2I–J)

Material and distribution in Cuba . Observations on live animals. One specimen whole mounted, designated holotype (FMNH http://id.luomus.fi/KV.603) from Macabí (type locality) (April 23, 2017), in fine sand, 0.3–0.5 m depth, salinity 34 ‰. Two whole mounts (HU VIII.3.03–VIII.3.04) from Siboney (May 15, 2016 & March 22, 2017), one specimen from the intertidal, upper layer of the sand surface, and the other from the sublittoral, 0.6 m depth, salinity 32–35 ‰.

Etymology. The epithet refers to the resemblance of this species' prostate stylet to that of P. linguatus Artois & Tessens, 2008 .

Diagnosis. Species of Phonorhynchopsis with a prostate stylet type IV 76 µm long, with the distal third widened, ending in a broad, rounded tip, being 35% of the length of the accessory stylet type IV. Accessory stylet type IV 219 µm long, slightly undulate and tapering to a distal sharp tip.

Description. Living animals about 1.2 mm long. General morphology of the organs resembles that of P. haegheni . Body translucent; proboscis small, about 10% of the body length; a pair of pigmented eyes behind the proboscis; pharynx at 50%.

Prostate stylet type IV 75 –77 µm long (x̄ = 76 µm; n = 3), with a proximal flange 7–9 µm wide (x̄ = 8 µm; n = 3); distal third widened up to 7–8 µm (x̄ = 7 µm; n = 3), ending in a broad, rounded tip ( Fig. 1G , 2J ). Accessory stylet type IV 21 1 –227 µm long (x̄ = 219 µm; n = 3) with a proximally thickened short funnel 9–10 µm wide (x̄ = 9 µm; n = 3), and distally a sharp tip, bent aside ( Fig. 1 H–I, 2I). The general outline of the accessory stylet is symmetrically undulate in live animals. Stylet to stylet ratio (accessory stylet/prostate stylet) is 10/3.5. Bursa bipartite.

Discussion. The two new species show the typical features of Phonorhynchopsis (see Willems et al. 2017): prostate stylet type IV rather broad and tubular, shorter than the accessory stylet type IV; bursa bipartite, consisting of a muscular and a sperm-resorbing part. Both new species described here differ from P. haegheni Artois & Schockaert, 2001 as to the relative length of the stylets and mainly in the shape of the prostate stylet (see Table 2). The length of the prostate stylet is only 20% of that of the accessory stylet in P. capillaris sp. n., whereas the same relative length is 35% in P. sublinguatus sp. n.. In P. haegheni the relative length of the prostate stylet is rather variable (21% in specimens from Galapagos Islands to 34% in the Atlantic populations). The prostate stylet of P. haegheni is the only one within the genus tapering from 12 µm to 5 µm, ending in a sharp distal tip (see Artois & Schockaert 2001). In P. capillaris sp. n. the prostate stylet tapers, but ends in a rounded tip, and in P. sublinguatus sp. n. the distal third is widened, very much resembling that of P. linguatus . However, the prostate stylet is smaller in P. sublinguatus sp. n. than in P. linguatus ( Fig. 2 C– D: reference material HU III.4.47 from Kenya), and the accessory stylet length is comparable with the specimen from Mahé, Seychelles (219 µm) (see Artois & Tessens 2008). Therefore, the relative length of the prostate stylet in P. sublinguatus sp. n. (35% of the accessory stylet length) is lower than it is in the populations of P. linguatus (50% in Zanzibar, 65% in Seychelles and 65–71% in Kenya). The general morphology of the prostate stylet in P. sublinguatus sp. n. resembles that of P. linguatus , but the former species lacks the twist in the middle, a feature diagnostic of P. linguatus .

One specimen of P. linguatus from Zanzibar (HU IV.1.17) ( Figs. 2 E–F) is somewhat aberrant from the other specimens of the same species. Although the length of the prostate stylet is 50% that of the accessory stylet, as is the case in the holotype, which was collected in the same locality, the prostate stylet is not twisted in its midpart and its distal half is not markedly widened, hence more resembling that of P. sublinguatus sp. n.. The length of the prostate stylet in this specimen from Zanzibar is only 62% of that of the specimen of P. linguatus from Seychelles and ± 70% of that of the specimens from Kenya. The accessory stylet does not differ markedly in length between the different populations. Based on the shape and the absolute length of the stylets, it could be argued that specimen HU IV.1.17 of P. linguatus actually belongs to P. sublinguatus sp. n.. However, the relative length of the prostate stylet in this specimen is the same as in the holotype of P. linguatus (50%; 35% in P. sublinguatus sp. n.). Unfortunately, there is only one specimen that shows these features, which makes it impossible to decide whether this specimen belongs to P. linguatus , P. sublinguatus sp. n. or even another, yet undescribed species.

In P. haegheni and P. linguatus , the length of the accessory stylet varies greatly between specimens, even of the same population (e.g. within the Galapagos population of P. haegheni ). Its length seems to vary less in the other two species, but this could be because of the fact that only very few (two or three) specimens of each species are available. The absolute length of this stylet, hence, should be used with care in distinguishing or diagnosing species. The length of the accessory stylet is comparable between P. haegheni and P capillaris sp. n., showing some overlap. With a mean length of 292 µm, the accessory stylet of P. capillaris sp. n. is somewhat larger than that of P. haegheni (258 µm). The shortest accessory stylet is found in P. linguatus (mean length 189 µm), but the length range overlaps with that of the accessory stylet of P. sublinguatus sp. n., which has a mean length of 219 µm.

The proximal and distal ends of the accessory stylet show subtle differences between the species. The walls of the proximal funnel-shaped part are markedly thickened in P. sublinguatus sp. n., which is not the case in the other three species. The extreme distal sharp tip is typically curved in P. capillaris sp. n. and P. sublinguatus sp. n., showing a small dilatation just proximal from the tip.

Figures

FIGURE 1. Phonorhynchoides minor sp. n. A, Habitus (from the live animal). B, prostate stylet type IV. C, accessory stylet type IV. Phonorhynchopsis capillaris sp. n. D, prostate stylet type IV. E, proximal end of the accessory stylet type IV. F, distal end of the accessory stylet type IV. Phonorhynchopsis sublinguatus sp. n. G, prostate stylet type IV. H, proximal end of the accessory stylet type IV. I, distal end of the accessory stylet type IV. Drawings of the stylets are from the holotypes of the respective species.

FIGURE 2. Phonorhynchopsis haegheni (Artois & Schockaert, 2001) (specimen from Cuba). A, accessory stylet type IV. B, prostate stylet type IV. Phonorhynchopsis linguatus (Artois & Tessens, 2008). C, accessory stylet type IV. D, prostate stylet type IV (reference specimen HU III.4.47 from Kenya). E, accessory stylet type IV. F, prostate stylet type IV (reference specimen HU IV.1.17 from Zanzibar). Phonorhynchopsis capillaris sp. n. (holotype). G, accessory stylet type IV. H, prostate stylet type IV. Phonorhynchopsis sublinguatus sp. n. (holotype). I, accessory stylet type IV. J, prostate stylet type IV.