Schizochilus maximus, Diez & Reygel & Artois, 2019

Diez, Yander L., Reygel, Patrick & Artois, Tom, 2019, Schizorhynchia (Platyhelminthes, Rhabdocoela) from eastern Cuba, with the description of fifteen new species, Zootaxa 4646 (1), pp. 1-30 : 26-28

Schizochilus maximus sp. n.

( Fig. 12H , 15F )

http://zoobank.org/ urn:lsid:zoobank.org:act:471E20E5-1C96-4EC0-A164-DEE5E3FAE86C

Material. One specimen studied alive and whole mounted, designated holotype ( FMNH https://id.luomus.fi/ KV.622), collected in Siboney (type locality) (February 7, 2016), fine-grained sand with small stones and silt, 0.5 m depth, salinity 35 ‰.

Etymology. The epithet refers to the fact that the new species has the largest cirrus and stylet among all the known species of the genus.

Diagnosis. Species of Schizochilus with a cirrus 129 μm long, unarmed in the proximal fourth of its length, ornamented with fine spines in the rest of its length; spines 3 μm long. Needle-shaped stylet 120 μm long, running centrally through the cirrus. Copulatory bulb with a distal cap, 19 μm long.

Description. Live animal about 2 mm long, translucent, without eyes. Habitus and internal organisation as in S. espinosai sp. n.. Proboscis lips 70 μm long, representing 3,5% of the body length in the live animal, with a pair of glands caudally. Pharynx located at the 75%, impossible to measure in the whole mount.

Copulatory bulb ( Figs 12H , 15F ) located caudally from the pharynx; it comprises the prostate vesicle and a spiny cirrus. The cirrus is 129 μm long, 7 μm wide proximally and 6 μm wide distally, unarmed in the proximal fourth of its length, the rest of the length is ornamented with fine spines. These spines are 2–4 μm long (x = 3 μm; n = 9). A 120-μm-long stylet lies centrally in the cirrus. It is needle-shaped, 5 μm wide proximally, 2 μm wide at the base of the proximal funnel, gradually tapering towards its sharp distal tip. Distal wall of the copulatory bulb sclerotized, forming a 19-μm-long cap. As such, it surrounds the cirrus for 15% of the latter’s length. Testes and female system not observed.

Discussion on Schizochilus . All new species described show the diagnostic features of the genus Schizochilus (see Boaden 1963; Gobert et al. 2017): symmetrical proboscis without any hard structures; pharynx situated in the posterior body half; a single ovary; several testes before the pharynx in a single row, often merged into a single or a few larger lobed testes; a copulatory organ proper consisting of a spiny cirrus, sometimes supplemented with a central stylet. Up to now, eleven species of Schizochilus have been described (Tyler et al. 2006–2018 b). Of these eleven species, eight have a copulatory organ proper consisting of a spiny cirrus surrounding a central stylet, as is the case in all six new species described in this contribution: S. bruneti Noldt & Hoxhold, 1984 , S. caecus L’Hardy, 1963 , S. choriurus Boaden, 1963 , S. hoxholdi Karling, 1989 , S. lanzarotensis Gobert, Reygel & Artois, 2017 , S. parvulus Brunet, 1970 , S. santacruzensis Noldt & Hoxhold, 1984 , and S. tubulatus Brunet, 1970 . An overview of the distinguishing characters among these known species is provided by Gobert et al. (2017).

Schizochilus maximus sp. n. can easily be recognised by its largest stylet (120 μm long) of all species of Schizochilus . Moreover, a cirrus unarmed in its proximal fourth is also a unique feature within the genus. In other species with a partly-unarmed cirrus, either the distal end is unarmed ( S. santacruzensis ) (see Noldt & Hoxhold 1984) or the cirrus bears longitudinal ridges and the spines are restricted to the distal part ( S. caecus and S. choriurus ) (see Boaden 1963; L’Hardy 1963).

The five other species described in this contribution have a cirrus that is completely covered with spines, i.e. over the entire length of the stylet. This situation is also found in three described species: S. lanzarotensis , S. hoxholdi and S. parvulus . An important distinguishing feature between these species is the fact whether or not the copulatory bulb forms a distal, sclerotized cap, which surrounds the distal part of the cirrus/stylet. In the three species mentioned, such a cap is only lacking in S. lanzarotensis . This is also the case in two of the newly-described species from Cuba: S. favus sp. n. and S. bueycabonensis sp. n..

Schizochilus bueycabonensis sp. n. can easily be recognized from S. lanzarotensis by the detailed morphology of the stylet and the cirrus. In S. bueycabonensis sp. n. the stylet is tubular, with a proximal funnel, 31 μm long, and has an oblique distal end. The cirrus of this species is armed over its entire length with fine, 0.5-µm-long spines. By studying the holotype of S. lanzarotensis for sake of detailed comparison, we noticed that the measurements for this species in Gobert et al. (2017) were erroneous, most probably because of a scale conversion mistake, and hence we provide new measurements for this species. In S. lanzarotensis , the stylet ( Fig. 14D ) is 80 μm long. It lacks the proximal funnel, and tapers to a distal sharp tip, and is therefore clearly distinguishable from this of S. bueycabonensis sp. n. The cirrus of the latter species is ornamented with two groups of shark-tooth-shaped spines: the smaller spines (3–5 μm long) proximally, and the larger ones (8–10 μm long) distally.

Schizochilus favus sp. n. can be distinguished from S. lanzarotensis , as well as from all other representatives of Schizochilus because it is the only species in which the spines are arranged in a way that the bases form a honeycomb structure in the right focal plane. Also the stylet is typical of this is species, lacking a proximal funnel and with longitudinal ridges, the latter also being a unique character for this species.

The general morphology of the cirrus and the stylet of S. atlanticus sp. n. is similar to that of S. bueycabonensis sp. n.. However, both species can easily be distinguished by the presence of a sclerotized cap in S. atlanticus sp. n. and its stylet ends in a sharp point distally, while it ends obliquely in S. bueycabonensis sp. n..

The general morphology of the cirrus and the stylet of S. espinosai sp. n. also resembles that of S. lanzarotensis . However, both species can easily be distinguished by the presence of a sclerotized cap in S. espinosai sp. n., which is lacking in S. lanzarotensis . Moreover, the stylet of S. espinosai sp. n. is needle shaped, with a proximal funnel, and is 52 μm long, while in S. lanzarotensis it is tubular, lacks the proximal funnel, and is 80 μm long. Both species have a cirrus armed over its entire length with shark-tooth-shaped spines, but in S. lanzarotensis these are distributed into two size groups (see above), while all spines are more or less 3 µm long in S. espinosai sp. n..

The general morphology of the copulatory organ of S. banesensis sp. n. is somewhat comparable to that of S. espinosai sp. n.. However, in the former species the cirrus is covered by much more, and much finer spines, and the sclerotized distal cap is much larger compared to the length of the stylet than it is in S. espinosai sp. n.. These features make both easily distinguishable.

Figures

FIGURE 12. Schizochilus espinosai sp. n.. A, body from the live animal. B, cirrus and stylet. Schizochilus atlanticus sp. n.. C–D, cirrus and stylet. Schizochilus bueycabonensis sp. n.. E–F, stylet. Schizochilus banesensis, sp. n.. G, cirrus and stylet. Schizochilus maximus sp. n.. H, cirrus and stylet. B–H, from whole mounts. B–C, F–H, from the holotype. D, E, from a Reference specimen (HU X.1.22).

FIGURE 14. Copulatory bulb of the species of Schizochilus without distal sclerotized cap in the cirrus. A–B, Schizochilus favus sp. n.. C, Schizochilus bueycabonensis sp. n.. D, Schizochilus lanzarotensis (from the holotype: SMNH Type-8911). A–D, from whole mounts. A, from a reference specimen (HU X.1.27). B–C, from the holotype.

FIGURE 15. Copulatory bulb in species of Schizochilus (from whole mounts). A–B, Schizochilus atlanticus sp. n.. C, Schizochilus banesensis sp. n.. D, Schizochilus bueycabonensis sp. n.. E, Schizochilus espinosai sp. n.. F, Schizochilus maximus sp. n.. A, C–F, from the holotype. B, from a reference specimen (HU X.1.22).