Paraplanocera oligoglenoides, Ramos-Sánchez & Bahia & Bastida-Zavala, 2019

Ramos-Sánchez, Mariela, Bahia, Juliana & Bastida-Zavala, J. Rolando, 2019, New genus, new species and new records of marine acotylean flatworms (Platyhelminthes: Polycladida: Acotylea) from Oaxaca, southern Mexican Pacific, Zootaxa 4700 (1), pp. 30-58 : 30-58

publication ID 10.11646/zootaxa.4700.1.2

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Paraplanocera oligoglenoides

sp. nov.

Paraplanocera oligoglenoides sp. nov.

( Figures 10 View FIGURE 10 A–H, 11A–H)

Type locality. Agua Blanca Beach , Puerto Escondido, Oaxaca, México (15°43’58”N, 96°48’40.21”W) GoogleMaps .

Type material. Eleven specimens. Holotype: UMAR-PLAT 012, as whole mount (Agua Blanca Beach, Puerto Escondido, Oaxaca, southern Mexican Pacific, under rocks in tidal pools, 0.5 m, Mar 24, 2010, coll. MRS). Paratypes: Six specimens as whole mounts; UMAR-PLAT 038 (Agua Blanca Beach, same as holotype); UMAR-PLAT 013, 013A (Panteón Beach, under rocks, 1 m, Feb 26, 2014, coll. ECL); UMAR-PLAT 014 (Camarón Beach, under rocks, 1.5 m, Dec 6, 2014, coll. ECL); UMAR-PLAT 015 (Cacaluta Bay, under rocks, 12 m, May 7, 2013, coll. EEA);UMAR-PLAT 038B–F, specimen in histological sections (sagittal sections of reproductive structures in four slides, the remaining portion of the specimen preserved in glycerin; Agua Blanca Beach, same as holotype). UMAR- PLAT 016, three specimens preserved in 70% ethanol: incomplete specimens (the region of the reproductive system was sectioned to subject it to the histological process, but it was not successful; Agua Blanca Beach, same as holotype); UMAR-PLAT 017, one specimen preserved in 70% ethanol (Panteón Beach, same as UMAR-PLAT 013).

Description of external features.

Color. The body in vivo is translucent, dorsally presenting a faintly pigmentation of light brown color, margins yellow; brown intestinal ramifications; slightly grayish and brown irregular specks distributed throughout the body and black dots distributed in the pharyngeal and reproductive region of the specimen ( Figs 10A View FIGURE 10 , F–G). Ventral region translucent with pharyngeal and reproductive whitish region. One specimen preserved in alcohol has brown coloration ( Fig. 10B View FIGURE 10 ). Specimen stained with Mayer’s carmalum has a purple to pink color ( Fig. 10C View FIGURE 10 ).

Form. Oval to round body; 13–40 mm (n= 10, µ= 25 mm, SD= 12.2) long and 10–36 mm (n= 10, µ= 21, SD= 11.5) wide ( Figs 10 View FIGURE 10 A–C).

Tentacles. Robust and conspicuous nuchal tentacles; located at 1.7–11.05 mm (n= 10, µ= 7 mm, SD= 3.8) from the anterior margin of the body; bicolored, the apical region is cream and the basal region is dark brown or black ( Figs 10D, F View FIGURE 10 ), the right tentacle is 0.68–1.19 mm (n= 10, µ= 1 mm, SD= 0.2) and the left tentacle is 0.68–1.36 mm (n= 10, µ= 1 mm, SD= 0.3), distance between tentacles is 0.85–1.7 mm (n= 10, µ= 1 mm, SD= 0.4).

Eyes. Without marginal eyes; with 68–106 (n= 10, µ= 85, SD= 8.5) tentacular eyes, distributed around each nuchal tentacle; with 7–115 (n= 10, µ= 94, SD= 11) cerebral eyes arranged in two clusters, one densely concentrated and located anteriorly to the brain, the second group is scattered and located posteriorly to the brain ( Fig. 10D View FIGURE 10 ).

Brain. Bilobed, 600 μm long and 620 μm wide; globuli cell masses located in the anterior region of the brain ( Fig. 10E View FIGURE 10 ).

Digestive system. The pharynx located in the central region of the body, at 4.6–11.05 mm (n= 10, µ= 9 mm, SD= 4.4) from the anterior margin, measuring 3.7–7.65 (n=10, µ= 5 mm, SD=2.3) of length and 0.2–7.65 mm (n= 10, µ= 2 mm, SD= 0.8) in width; pharynx sparsely branched with 4–9 (n= 10, µ= 6, SD= 1.6) lateral pharyngeal lobes. Mouth located in the last third of the pharynx ( Fig. 10G View FIGURE 10 ).

Gonopores. Gonopores separated, located in the median line of the body, posterior to the pharynx. Male gonopore located at 10–14 mm (n= 10, µ= 12 mm, SD= 2.8) from the anterior margin and 1.5 mm from the pharynx. Female gonopore located at 12–14 mm (n= 10, µ= 14 mm, SD= 3) from the anterior margin, 2 mm from the pharynx and 0.5 mm from the male gonopore ( Fig. 10H View FIGURE 10 ).

Description of internal features

Male reproductive system: Without seminal vesicle; with an oval accessory prostatic vesicle, separated from the prostatic vesicle by a thin epithelium and delimited with some eosinophilous granules; conspicuous oval prostatic vesicle ( Figs 10H View FIGURE 10 , 11A,D View FIGURE 11 ), 60–75 μm (n= 4, µ= 68 μm, SD= 7.5) long and 62–90 μm (n= 10, µ= 73 μm, SD= 10) wide, covered with highly folded epithelium; prostatic vesicle located anterior to the male gonopore and posterior to the pharynx ( Fig. 10H View FIGURE 10 ), connecting to the cirrus sac ( Figs 10H View FIGURE 10 , 11A View FIGURE 11 , E–F) through a spermiducal duct, which is attached to the prostatic duct ( Fig. 11D View FIGURE 11 ).

Cirrus sac slightly oval ( Figs 10H View FIGURE 10 ), with 70–170 μm (n= 10, µ= 124 μm, SD= 10) long and 63–130 μm (n= 10, µ= 87 μm, SD= 16.6) wide; the walls of the cirrus sac has surrounding intramuscular spaces apparently empty ( Fig. 11D View FIGURE 11 ); the cirrus sac is armed with spines ( Figs 11 View FIGURE 11 E–G) positioned transversely along the cirrus; dorsal and ventral spines triangular and with similar size ( Figs 11G View FIGURE 11 ); and with a pair of conspicuous and asymmetrical teeth ( Fig. 11B View FIGURE 11 )(ventral view); in sagittal view 200 μm long and wide at the basal region 190 μm and 200 μm at the apical region ( Figs 11 View FIGURE 11 A–C); the posterior region of the cirrus sac narrow, connecting it to male atrium ( Fig. 11A View FIGURE 11 ),the male atrium has a glandular sac ( Fig. 11E View FIGURE 11 ). Spermiducal vesicles ( Fig. 10H View FIGURE 10 ) extend transversely to the prostatic vesicle; short and oval spermiducal bulbs present ( Fig. 11A View FIGURE 11 ), each of them attached to the spermiducal duct by means of a sperm duct located posteriorly to the prostatic vesicle ( Fig. 11D View FIGURE 11 ).

Female reproductive system: Located in the postero-lateral region of the male reproductive system; with a pyriform bursa copulatrix ( Figs 10H View FIGURE 10 , 11A View FIGURE 11 ), i.e., a hollow oval sac, 160–360 μm (n= 10, µ= 200 μm, SD= 58) long and 62–180 μm (n= 10, µ= 111 μm, SD= 43) wide, covered by a very thin wall of fibrous tissue, which gives it the appearance of being cuticularized ( Fig. 11A View FIGURE 11 ). The bursa copulatrix is positioned on the left side of the cirrus sac and anterior to the female gonopore ( Fig. 10H View FIGURE 10 ). Vagina ( Fig. 11 H View FIGURE 11 ) directed towards the anterior region of the body, with scalloped epithelium, irregular walls and a short cement pouch ( Fig. 11H View FIGURE 11 ). Lang’s vesicle elongated and located posteriorly to female gonopore ( Figs 10H View FIGURE 10 , 11A View FIGURE 11 ); female gonopore oriented towards the posterior region of the body, connecting dorsally with the duct of Lang’s vesicle ( Fig. 10H View FIGURE 10 ). Cement glands very densely ( Figs 11A, H View FIGURE 11 ) arranged around the vagina ( Fig. 11H View FIGURE 11 ).

Habitat: Littoral to sublittoral (12 m); under rocks, associated with encrusting bryozoans, green seaweed and chitons. Paraplanocera oligoglenoides sp. nov. can be found in pairs or alone.

Distribution. Southern Mexican Pacific. Paraplanocera oligoglenoides sp. nov. was found at Agua Blanca, Camarón, Panteón and Puerto Angel beaches and in Cacaluta Bay, Oaxaca. This is the first record of the genus from the southern Mexican Pacific ( Fig. 12 View FIGURE 12 ).

Etymology: The specific epithet refers to the similarity of the new species with Paraplanocera oligoglena ( Schmarda, 1859) .

Taxonomic remarks. The status of the species of the genus Paraplanocera has generated much controversy ( Hyman 1959) and has been discussed by Kato (1936), Prudhoe (1945) and Hyman (1953a).

Kato (1936 in Prudhoe 1945) separated the species of this genus into two groups, characterized by the presence or absence of a pair of “glandular pockets” opening into the male antrum; posteriorly, Prudhoe (1945: 197–198, Figs 1–2 View FIGURE 1 View FIGURE 2 ) reduced the number of species of the genus from eight to three valid species: Paraplanocera oligoglena , P. aurora Laidlaw, 1903 and P. marginata Meyer, 1922 , and proposed a division of the genus in two groups based on the internal morphology of the male reproductive system:

Group 1: Species with the cirrus-cavity lined with numerous spines, comparatively large near the male antrum, while the spermiducal ducts (or “the canals from the seminal vesicles”) open into the ventral wall of the prostatic vesicle (or “prostatic organ”).

Group 2: Species with the cirrus-cavity lined with numerous small spines and a pair of very large projections covered with a layer of brownish hyaline substance, while the spermiducal ducts open into the prostatic vesicle only just before it enters the cirrus.

However, Hyman (1955) and Faubel (1983) considered that the criteria established by Prudhoe (1945) lacked a detailed review of the characters, due to the lack in the availability of the descriptions for each species of Paraplanocera ; therefore, Faubel (1983) considered ten Paraplanocera species to be valid in his classification.

Two species were recorded from Tropical Eastern Pacific: Paraplanocera oligoglena , originally described by Schmarda (1859) from Sri Lanka, Indian Ocean, and later recorded from Gulf of California ( Hyman 1953a; Brusca 1980; Lamothe-Argumedo et al. 1997); and P. oceanica described by Hyman (1953b), from Isabela Island, Galapagos. Other similar species, P. fritillata , was described by Hyman (1959) from Caroline Islands, Micronesian Archipelago.

Paraplanocera oligoglena was recorded from the Indo-Western Pacific ( Schmarda 1859, Stummer-Traunfels 1933, Hyman 1954, 1955, Prudhoe 1978, Ken-Ichi et al. 1991). In the Mexican Pacific, P. oligoglena was recorded from Coronado Island, Baja California; Punta San Marcial reef, Baja California Sur and Miramar Beach, Sonora ( Hyman 1953a, Brusca 1980, Lamothe-Argumedo et al. 1997). Prudhoe (1985) considered P. oligoglena as a circumtropical species.

Paraplanocera oligoglenoides sp. nov. differs from P. oligoglena in the dorsal coloration pattern, number of cerebral eyes, the intramuscular content of the surrounding spaces of the cirrus sac cavity, the accessory prostatic vesicle epithelium, the orientation, position and morphology of the vagina and of the bursa copulatrix (Table III).

Paraplanocera oligoglenoides sp. nov. differs from P. oceanica ( Hyman 1953b: 191–193; figs 8–11) in the composition of the male reproductive system, and because the latter species has a cirrus sac with an elongated penis papilla that is armed with small spines in the terminal region ( Hyman 1953b), while in P. oligoglenoides sp. nov. the cirrus sac lacks penis papilla; the entire cirrus sac has spines and conspicuous paired teeth.

Paraplanocera oligoglenoides sp. nov. differs from P. fritillata ( Hyman 1959: 558–562; Figs 5 View FIGURE 5 b–d, 6a) in the distribution of the spines in the cirrus sac ( P. fritillata lacks spines in the anterior region of the conspicuous tooth); the Lang’s vesicle positioned lateral to the bursa copulatrix (sagittal view); pharynx folded-circular and the mouth is positioned in the central region of the pharynx; while in P. oligoglenoides sp. nov. the spines of the cirrus sac are distributed anterior and posterior to the conspicuous tooth; the Lang’s vesicle positioned dorsally to the bursa copulatrix (sagittal view), pharynx folded-elongate and the mouth is positioned in the last third of the pharynx.

Although Prudhoe (1945) did not consider dorsal coloration pattern, being variable depending on the habitat and ecological parameters, as a character that permits a specific determination; however, Hyman (1959) and our study suggest taking this character also into account, because well-recorded coloration patterns in vivo allow the separation between P. oligoglena , P. fritillata and P. oligoglenoides sp. nov. (Table III).

Likewise, future studies should evaluate the number of teeth in the cirrus sac, accessory prostatic vesicles, and morphology and position of the bursa copulatrix and Lang’s vesicle. Both, P. oligoglena (see Hyman 1953a: 357, Fig. 124; 1955: 77–78, Fig. 4c View FIGURE 4 ) and P. oligoglenoides sp. nov., have variation in these characters, which previously had been considered as a intraspecific variation characters ( Prudhoe 1945; Hyman 1953a). In the same way, the historical records of P. oligoglena in the Gulf of California ( Hyman 1953a; Brusca 1980), should be revised for confirm if the determination was correct.

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