Semonia bauliensis, 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 : 369-370

Semonia bauliensis n. sp.

( Fig. 4 )

Material examined: A specimen from the type locality and designated as holotype. Sagittal histological sections and stained with AZAN. Deposited in the National Museum of Natural Sciences, Madrid, Spain. 26 slides: MNCN 4.01 / 2386 to MNCN 4.01 /2411.

Type locality: Playa Carbón Beach , in Las Baulas National Marine Park of Guanacaste, Costa Rica, 10 ° 20’53.4 “N 85 ° 51’44.5” W ; 19 May 2018 ( Fig 4A )

Habitat: Low intertidal, below stones on sand.

Etymology: The name of the species, Semonia bauliensis n.sp., refers to the locality where this new Semonia specimen was found in Las Baulas de Guanacaste National Marine Park.

Description: External characteristics ( Fig. 4B, D ): Body shape elongated. Length 23mm. Background colour ivory, honey brown on the area of the pharynx and copulatory organs. Ventral area beige with pharynx marked in white. In the sagittal series, as well as in the living organisms, small protuberances like tentacles can be appreciated at the anterior end. Tentacle eyes at the base of the protuberances and two cerebral eye groups. Ruffled pharynx elongated located in the middle of the body.

Reproductive system: located in the posterior part of the body. Male and female system opens in a common genital atrium ( Fig.4C ). Dorsally, the common atrium widens in a funnel-like male atrium that covers a short rodlike penis papilla ( Fig.4C ). The male copulatory organ comprises a seminal vesicle and a short penis papilla, but without prostatic vesicle. The seminal vesicle is located parallel to the central body axis forming an angle of almost 90º with the penis papilla ( Fig.4E ). The vasa deferentia are thin and lead to the distal region of the seminal vesicle. Prostate glands that extend along the vas deferens exert the function of vesicles.

The female copulatory organ consists of an elongated, S-shaped vagina, gradually widening distally ( Fig.4F ). Without Lang’s vesicle. Cement and shell glands pour at the end of the vagina externa, but the exact opening is diffuse.

Remarks: The species collected in Costa Rica belongs to the genus Semonia due to the presence of a male copulatory apparatus with seminal vesicle and rod-like penis, common atrium and genital pore, and the lack of a Lang’s vesicle. The only species described of the genus Semonia is S. maculata Plehn, 1896 of Indonesia. The differences from S. bauliensis n.sp. are visible in the external anatomy as well as in the internal morphology of the reproductive system. Externally, the differences are located in the disposition of the cerebral eyes, around the cephalic ganglion in S. maculata and in two elongated groups on both sides of the brain in S. bauliensis n.sp.. With respect to the internal anatomical differences, the most notable feature is the size of the penis papilla and the genital atrium, clearly more developed in S. maculata . These differences are sufficiently prominent to designate Semonia bauliensis n.sp. as a new species.

Figures

FIGURE 4: Semonia bauliensis n.sp. A. Distribution map and sample points; B. Whole live animal, dorsal view; C. Sagittal reconstruction of the reproduction system; D. Ventral view of whole live animal with pharynx at the middle region (white arrows); E-F. Histological sections of the copulatory organs stained with Azan (C, E, F anterior end to the left).