Paraplanocera oligoglena (Schmarda, 1859)

(Fig. 2)

Material examined: A single specimen. Sagittal sections stained with AZAN. 110 slides: MNCN 4.01/2105 to MNCN 4.01/2204

Location: Playa Carbón Beach in Las Baulas National Marine Park of Guanacaste, Costa Rica, 10 ° 20’53.4 “N 85 ° 51’44.5” W; May 17, 2018. (Fig. 2A)

Habitat: Low intertidal, below stones on sand.

Description: External characteristics (Fig. 2B,C): Body shape oval or round. Length 40 mm. Dorsal pigmentation marbled coffee brown on white background, sometimes translucent yellowish by transmitted light. Ventral region of ivory colours with darker spots (Fig 2C). Body edges waved with irregular dark tones and ends in a clear, almost white border, visible from the ventral and dorsal part. Nuchal tentacles at the end of the first body third. Tentacular eyes at the base of each tentacle. Two groups of cerebral eyes between tentacles. A cloud of black dots surround the pharynx and reproductive system. The ruffled pharynx is wide and with lateral projections (approx. 12 mm long, 5 mm wide).

Reproductive system (Fig 2D): male copulatory apparatus is located on the back of the specimen. Comprises a cirrus, a prostatic vesicle with accessory prostatic vesicles, two spermiducal bulbs, and lacks a seminal vesicle. The cirrus is covered with thorns from the genital pore to almost the insertion of the prostatic vesicle. Two pseudosclerotized teeth (or adenoids) are located the middle region of the cirrus (Fig. 2D). The spermiducal bulbs enter into the prostatic vesicle distally. The cirrus narrows into a short male atrium.

The female is close to the male gonopore. The atrium leads to a wide vagina externa, also called vagina bulbosa, anteriorly orientated and surrounded by a very developed and “spongy” glandular tissue. The vagina interna bifurcates forming two organs: an elongated, large Lang’s vesicle whose duct is lined by a highly developed cubic epithelium and the bursa copulatrix, anterior oriented, elongated and highly developed running parallel to the male copulatory bulb (Fig. 2D).

Distribution: Paraplanocera oligoglena is considered a species with a distribution located practically throughout the Pacific Ocean. It has been found in the Gulf of California and Baja California (Hyman 1953), Sri Lanka (Schmarda 1859), Hawaii (Hyman 1954, 1960), India; Maldives Islands; Fiji Islands; Papua New Guinea; New Caledonia; Red Sea; Japan; Taiwan (Kato 1944), Australia (Prudhoe 1978) and now in Costa Rica. The last record is the first for Central America and the southernmost of the Pacific coast of America. It should be noted that with the exception of the record of the Red Sea (Kato 1944), P. oligoglena has not been found outside the Pacific.