Idioplana atlantica ( Bock, 1913 )

Cuadrado, Daniel, Hernández-Gonzalez, Alejandro, Noreña, Carolina & Simões, Nuno, 2024, Polyclads (Platyhelminthes) in the southern Gulf of Mexico: unveiling biodiversity and descriptions of two new species, ZooKeys 1221, pp. 103-144 : 103-144

Idioplana atlantica ( Bock, 1913)

Fig. 23 B – E

Material examined.

Yucatan coast, Mexico • 3; Dzilam; 21.5 ° N, 88.9 ° W; 13 m; 10 May 2018; A. Hernández leg.; CRPPY - 0096 .

Distribution.

Idioplana atlantica was originally recorded off St Thomas Island ( USA Virgin Island, Caribbean Sea; Bock 1913). Similar morphotypes of this species have been reported in Bocas del Toro ( Panama, Caribbean Sea; Litvaitis 2014–2024; Quiroga et al. 2004 b); Aguadores Beach near Santiago de Cuba (Caribbean Sea; Catalá et al. 2016). New record for the coasts of Yucatán, Mexico.

Description.

Body shape oval, with a rounded posterior end and a more pointed anterior end, 2 cm in length and 1 cm in width. Firm and dense consistency. Background colour ranges from yellowish-white to amber. Dorsally, is covered by dark rings with cream-pigmented inner. The shape of these rings is variable, appearing more rounded anteriorly and elongated posteriorly. Also, the central rings are larger compared to those along the body’s margin (Fig. 23 B, C, D, E ). Near the anterior end, two cylindrical nuchal tentacles are present. Tentacular eyes immersed along the tentacles (Fig. 23 E ). Two elongated scattered clusters of cerebral eyes and the marginal eyes limited to the anterior of the body.

Remarks.

Yucatan specimens show a resemblance to those documented by Litvaitis (2014–2024), as well as by Kate Rawlinson in Bocas del Toro, Panama (https://www.invertebase.org/portal/taxa/index.php?taxauthid1&taxon=146957&clid=57). In these instances, organisms identified as Idioplana atlantica ( Bock, 1913) exhibit rounded dark rings. However, the type description of Idioplana atlantica , based on fixed material, does not mention rounded spots or rings. The specimen documented by Bock (1913) exhibits a homogeneous yellowish colouration with a slightly orange tone in the central region, while the ventral side is white-grey. Also, the marginal eyes encircle the entire body edge, and the cerebral eyes are dispersed but abundantly present in the brain region. The living specimen and preserved Yucatan specimen displays dark rings covering its dorsal surface. Furthermore, marginal eyes are either absent or barely noticeable on the anterior end. The absence of pigmentation noted by Bock could be attributed to the fixation process. This differs from the Mexican material, where pigmentation remains intact throughout fixation processing. Also, the Bocas del Toro specimens ( Litvaitis 2014–2024) show specimens with and without pigmentation.

Although some doubts have arisen about the identity of this species, the presence or absence of pigmentation spots in the preserved specimens of Idioplana described from the Gulf of Mexico does not provide sufficient evidence to confirm the existence of a new species. Therefore, we have decided to classify the Idioplana specimens found in Yucatan as I. atlantica . Further morphological and molecular studies will be necessary to determine whether it represents a distinct species.

Figures

Figure 23. A Gnesioceros sargassicola Photograph in situ of the specimen captured B – E Idioplana atlantica B dorsal view of a live individual photographed on a black background C specimen photographed after fixation D, E specimens photographed in situ with the characteristic pigmentation rings.