Kytorhynchidae, Rieger, 1974

Diez, Yander L., Monnens, Marlies, Wuyts, Arlien, Brendonck, Luc, Reygel, Patrick, Schmidt-Rhaesa, Andreas & Artois, Tom, 2023, Taxonomy and phylogeny of Dalytyphloplanida Willems et al., 2006 (Platyhelminthes: Rhabdocoela), with the description of a new family, a new genus, and sixteen new species from Cuba and Panama, Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 631-681 : 670

Kytorhynchidae

The family Kytorhynchidae is best known from the seminal article by Rieger (1974), containing the first descriptions of two genera, Kytorhynchus and Kytorhynchella Rieger, 1974 , each with three species from the Atlantic coast of North America. Since that publication, only one other (monotypic) kytorhynchid genus was described: Neokytorhynchus pacificus Ehlers & Ehlers, 1974 from Galapagos Islands. However, the distribution of the family is much wider, as specimens of several new species were collected in Lanzarote, Sardinia, and Andalusia by members of Hasselt University group, some species of which were already included in the phylogenetic analysis by Van Steenkiste et al. (2013). With the findings of this paper, the distribution of Kytorhynchidae is extended to the Caribbean Sea.

The length of the stylet of K. microstylus in the specimens from Cuba (23–43 µm long) broadens the range of 30–35 µm thus far mentioned in literature ( Rieger, 1974). This author reported some degree of intraspecific variation in the morphology of the stylet, mainly in the distal part: it is either straight and slender, forms a pronounced hook or even is bifurcate in one specimen from Bermuda. Also in the specimens from Cuba, the same type of variation can be observed: some stylets show a distal hook ( Fig. 3b, d ), while others are more straight ( Fig. 3c ). These differences, however, are likely due to a difference in degree of squeezing, as the stylet is thin-walled and flexible. Nevertheless, K. microstylus appears paraphyletic in our analysis indicating that it might represent a species complex. The sequenced specimen indicated as ‘ K. microstylus B’ in our phylogeny was collected in Siboney and the specimens from this locality show a stylet with a typical distal hook ( Fig. 3b, d ), matching the diagnostic characteristics of the species provided by Rieger (1974). On the other hand, specimens from Bueycabón, where the specimen ‘ K. microstylus A’ of our phylogeny was also collected, present an almost straight stylet ( Fig. 3c ). These morphological and molecular phylogenetic differences suggest that K. microstylus , may constitute an unresolved species complex.

Kytorhynchus (Eukytorhynchus) yusdieli sp. n. fits the features of both the genus (testes located ventrally from the vitellaria, male genital canal short) and subgenus (no eyes, anterior invagination triangular, with a sclerotised and funnel-shaped stylet with longitudinal folds) ( Boyko, 1996; Rieger, 1974). Other features typical of the subgenus such as the single connection between ovary and atrium and the fact that the proximal, glandular part of the female genital canal is enlarged are only observable on sectioned material, which is currently not available for the Cuban populations. Kytorhynchus yusdieli sp. n. appears as the sister taxon of K. microstylus in our phylogeny.

The new species can easily be distinguished from K. microstylus , the only other species within the subgenus, based on stylet morphology: The stylet is 53–62 µm long in K. yusdieli sp. n. and 23–43 µm long in K. microstylus ( Rieger, 1974; our data on this work). Moreover, the funnel-shaped stylet of K. microstylus tapers to a distal blunt, curved hook, whereas in K. yusdieli sp. n., the stylet is much wide distally (20 µm), lacking such as a hook.

Figures

Fig.3 Kytorhynchus (Eukyto- rhynchus) microstylus Rieger, 1974. a Body organisation (live animal). b, c Stylet (from a whole mount). Kytorhynchus (Eukytorhynchus) yusdieli sp. n. d Body organisation (live speci- men). e, f Stylet (from the holo- type). a, d Structures oriented with the anterior end toward the right side of the plate. b, c, e, f Structures are oriented with the anterior end toward the top of the plate