Pleurobranchus iouspi, Ev. Marcus, 1984

Grzelak, Katarzyna & Sørensen, Martin V., 2022, Echinoderes galadrielae Grzelak & amp; Sørensen 2022, sp. nov., Zoological Studies 55 (15), pp. 1-31 : 28

Synonymy between Pleurobranchus iouspi and

P. emys

The spicule layer in the mantle suggest that Pleurobranchus emys and P. iouspi are potentially synonyms. A dense layer of radiating spicules was observed in the specimens analyzed here. Such a layer was previously described only for P. emys in the western Atlantic ( Dall and Simpson 1901; Verrill 1901; Thompson 1977; Ev. Marcus 1984). The analysis of transverse cuts of the mantle of the holotype of P. iouspi and P. emys showed that there is a dense layer of stellate spicules ( Figs. 17D , 13 B-D). Beneath it is another less dense layer of linear spicules ( Fig. 13A ). Ev. Marcus (1984) believed that the jaw platelets of P. emys differ sharply from other pleurobranchines in their narrow anterior part and the much wider posterior part; however, the type material (MZSP 119934) shows this difference only in a few parts of the jaw. This could be an artifact of preservation, because most of the jaw follows the same pattern as the genus, with 2-5 denticles on each side of the main cuspid ( Fig. 17C ). The radula teeth are all hook-shaped, and as stated above, the mantle is composed by stellate spicules ( Fig. 17D ). Since living specimens of P. iouspi vary widely in coloration ( Figs. 1 E-F), and the descriptions of P. emys and P. iouspi do not differ significantly (Ev. Marcus 1970, 1976b, 1984), it is considered that P. emys and P. iouspi in the present study.

The placement of P. emys into synonymy under P. areolatus made by Goodheart et al. (2015) seems arbitrary since the types were not examined not even specimens from the type locality, Colombia, and the authors did not provide a discussion about this synonymy. If P. emys is synonym of other species is P. iouspi due the similarities discussed above. Pleurobranchus areolatus differs from P. emys in relation to the general color of the body ( Table 1); the size and shape of the tubercles of the dorsum, in P. emys it is large and pointed, while in P. areolatus is low; and, due the dense layer of stellate spicules found in P. emys .

Figures

Fig. 17. Microscopic slides of the syntype of Pleurobranchus emys Ev. Marcus, 1984, for discussion about slide’s label, see text. (A) radula and jaw platelets (MZSP 119934). (B) cuts of the mantle (MZSP 119935). (C) elements of the jaw (MZSP 119934). (D) detail of mantle cut, showing the dense layer of radiating spicules (MZSP 119935).

Fig. 13. Pleurobranchus iouspi Ev. Marcus, 1984, spicules. (A) linear, rod-like (MZSP 119936). (B-D) stellate spicules (SAE ML 95). (B) three similar rays. (C) five rays, which four of them in the same plane. (D) transversal cut in the mantle.

Fig. 1. Living species of Pleurobranchus from Brazil. (A-B) Pleurobranchus reticulatus Rang, 1832. (A) adult (MNRJ 11710, 28 mm long alive). (B) juvenile (MNRJ 11710, 5 mm long alive). (C-D) Pleurobranchus areolatus Mörch, 1863 (MNRJ 18760, 27 mm long alive), photographs by V. Padula. (C) dorsal view. (D) ventral view. (E-F) Pleurobranchus iouspi Ev. Marcus, 1984. (E) bright yellow morphotype (MNRJ 33070, 99 mm length of preserved specimen), photograph by C. A. Rangel. (F) reddish morphotype (SAE ML 95, 75 mm length of preserved specimen), photograph by F. Moraes.