Cryptostylochus sesei, Soutullo & Cuadrado & Noreña, 2021

Soutullo, Patricia, Cuadrado, Daniel & Noreña, Carolina, 2021, First study of the Polycladida (Rhabditophora, Platyhelminthes) from the Pacific Coast of Costa Rica, Zootaxa 4964 (2), pp. 363-381 : 364-366

Cryptostylochus sesei n. sp.

( Fig. 1 )

Material examined: A single specimen designated as holotype

Holotype: sagittal serial sections stained in Azan. 119 slides: MNCN 4.01 /2267 a MNCN 4.01 /2385

Type locality: Playa Carbón, Las Baulas National Marine Park of Guanacaste, Costa Rica, 10 ° 20’53.4 “N 85 ° 51’44.5” W; May 17, 2018 ( Fig. 1B )

Habitat: Low intertidal, under stones and sand.

Etymology: The name of the species “ sesei ” is after Jose Manuel Soutullo, also known as “Sesé”, father of the first author.

Description: External characteristics ( Fig. 1A, C ): Body shape rounded. Length 35 mm. Background colour dark yellow densely speckled with orange. The pigmentation disappears towards the body edge and gets a transparent aspect. Ventral surface almost unpigmented, dirty white that turns almost coffee brown at the edges, also around the reproductive organs, in the medial region the silhouette of the pharynx is distinguished. Nuchal tentacles at the end of the first third of the body. Cerebral eyes between the tentacles on a depigmented patch. Tentacular eyes at the top of the tentacles; marginal eyes surrounding the body edge. Pharynx ruffled in the middle of the body (approx. 12 mm long, 7 mm wide in the holotype)

Reproductive System ( Fig. 1 D, E, F ): Reproductive organs are located in the last third of the body. Male copulatory organ encloses a seminal vesicle, a prostatic vesicle and a penis papilla lodged in a well-developed heart-shaped atrium. Seminal vesicle muscular, voluminous and elongated ( Fig. 1D ). The wide vasa deferentia open proximally through a single vas deferens in the seminal vesicle. The prostatic vesicle is surrounded by strong muscle fibres and covered by a monoglandular lining. With a caudo-frontal orientation lies dorsally of the whole female organ ( Fig. 1D ). The prostatic and seminal ducts join to give rise to the ejaculatory duct surrounded by the short penis papilla ( Fig. 1E ). The male copulatory organ is entirely bordered by a reticulated network of muscle fibres, but does not form a compact muscle bulb ( Fig. 1D,E ).

The female reproductive system is formed by the vagina interna and the vagina externa, without Lang’s vesicle. In the vagina externa pours the cement and shell glands. The female and male gonopore are separated, but close to each other ( Fig. 1F ).

Remarks: The species captured in Costa Rica belongs to the genus Cryptostylochus due to the presence of frontal, marginal, cerebral and tentacular eyes; absence of pseudosclerotized structures; monoglandular prostatic vesicle and absence of Lang’s vesicle.

Currently Cryptostylochus comprises 3 species; C. coseirensis ( Bock, 1925) , C. hullensis Faubel & Gollasch, 1996 and C. koreensis Bulnes, Faubel & Park, 2005 .

Cryptostylochus sesei n.sp. shares with C. coseirensis , C. koreensis and C. hullensis the presence of frontal, marginal, tentacular and cerebral eyes, as well as the presence of nuchal tentacles. However, it differs significantly from these species in the configuration of different types of eyes and in the size of the tentacles. C. sesei n.sp. present marginal eyes on the posterior and anterior regions of the body, while in C. coseirensis these occur only in the anterior region of the tentacles. In C. koreensis the marginal eyes surround the entire body edge and in C. hullensis they are found in their anterior body-end. Only C. koreensis presents frontal eyes.

The tentacles of C. sesei n.sp. are not very conspicuous and difficult to see; they are just two dorsal protuberances. In C. coseirensis , C. hullensis and C. koreensis , these are clearly developed.

Between the four species, significant differences can be found within the internal anatomy. C. hullensis and C. coseirensis present a spherical prostatic vesicle with inner large finger-like prolongations; C. koreensis and C. sesei n. sp. show an elongated monoglandular prostatic vesicle with short and numerous inner prolongations, marked in C. sesei n. sp., almost inconspicuous in C. koreensis .

On the other hand, C. sesei n. sp. differs from the other species in the entrance to the prostatic duct, which is practically in the distal region of the ejaculatory duct. On the contrary, in the other species of the genus, it is located in the middle region of the ejaculatory duct.

Finally, C. koreensis and C. hullensis have a short and small atrium and in C. sesei n. sp. and C. coseirensis the atrium is tall and elongated.

The differences and similarities found between the four species allow us to confirm that the species of Costa Rica is a new species of Cryptostylochus , closely related to the species of Korea, C. koreensis .

Figures

FIGURE 1: Cryptostylochus sesei n.sp. A. Whole live animal, dorsal view with nucal tentacles (white arrows); B. Distribution map and sample points; C. Ventral view of whole live animal with pharynx at the middle region (white arrows); D-E. Histological sections of the male copulatory organ stained with AZAN; F. Sagittal reconstruction of the reproduction system (D, E, F anterior end to the left).