Discodoris hummelincki

Alvim, Juliana & Pimenta, Alexandre Dias, 2013, Taxonomic review of the family Discodorididae (Mollusca: Gastropoda: Nudibranchia) from Brazil, with descriptions of two new species, Zootaxa 3745 (2), pp. 152-198 : 170-173

Discodoris hummelincki (Ev. Marcus & Er. Marcus, 1963) new combination

( Figures 1 E; 11–12)

Peltodoris crucis Bergh, 1880: 41 , plt. A, figs. 1–2 (in part).

Peltodoris hummelincki Ev. Marcus & Er. Marcus, 1963:27, figs. 32–35. Tayuva ketos gila Er. Marcus & Ev. Marcus, 1970: 65, figs. 118–120. Diaulula hummelincki: Valdés et al. (2006: 190) .

Diaulula phoca auct . non (Ev. Marcus & Er. Marcus, 1967a): García et al. (2008: 140).

Type material. Holotype ZMA Moll. 3.63.0 20, 0 3 March 1955, 48.0 mm preserved legth, P.W. Hummelinck leg; Paratype: ZMA Moll. 3.63.0 21, 0 3 March 1955, P.W. Hummelinck leg. [2].

Type locality. Santa Martha Bay, Curaçao.

Material examined. Curaçao: MZSP 76293 [1]; Brazil: Alagoas state: Recife da Ponta Verde: MNRJ 12939, 25 /ix/1996 [1]; Rio de Janeiro state: Cabo Frio: Canal de Itajurú: MNRJ 13997, 05 /vii/2009, coll. J. Alvim [1]; Praia das Conchas: MNRJ 13187, 28 /x/2007, coll. J. Bahia [1].

Geographical distribution. Aruba (Valdés et al., 2006); Curaçao: Santa Martha Bay (Ev. Marcus & Er. Marcus, 1963), Piscadera Bay (Ev. Marcus & Er. Marcus, 1963; Er. Marcus & Ev. Marcus, 1970), Cayman Islands (Dayrat, 2010), St. Thomas and Virgin Islands (Bergh, 1880); Brazil: Alagoas state; Rio de Janeiro state: Cabo Frio (present study); São Paulo state: Ilhabela (García et al., 2008).

Description. External morphology ( Figures 1 E; 11E): body oval, slightly depressed, up to 32.0 mm long alive, with 1.5 to 2.0 times greater length than width. Mantle covered by conical tubercles irregularly disposed, with different sizes throughout mantle (48 µm to 200 µm in diameter); tubercles lower in mantle edge and in center of mantle than those in sides of mantle. Some tubercles in center of mantle and on rhinophoral and branchial sheaths are white and bigger than other tubercles. Rhinophoral sheaths more prominent than branchial sheath, both covered by tubercles of same size as those of mantle edge. Rhinophores long, with cylindrical apex, 17 to 18 diagonal perfoliations. Gill with six retractile, tripinnate branchial leaves, positioned symmetrically about longitudinal axis of body; anal cone high, located between two most posterior branchial leaves. Foot narrower than mantle; anterior foot border notched on upper “lip”. Oral tentacles conical and small. Living specimens presents body predominantly whitish, with numerous brown spots/blotches of various sizes, usually circular, more concentrated in center of mantle; these blotches can be very concentrated, transforming dominant color of body to brownish, with white part restricted to mantle margin; two lateral rows with five darker brown circulars blotches of each side, from rhinophores to gill; rhinophores with basal portion of same color of rest of body; perfoliations brownish-yellow with numerous white spots on perfoliations; cylindrical apex white; branchial leaves of same color of rhinophores, with numerous tiny brown spots; ventrally, cream to white; brown blotches smaller and more concentrated in foot than in ventral part of mantle.

Labial cuticle and radula ( Figures 11 A–D): Yellow lateral plates with numerous elongated elements; approximately rectangular, long and filiform on outer margin and, low and short on inner margin. Radula formulae 21 x 24.0. 24 in preserved specimen measuring 19.0 mm in length; lateral plates smooth and hook-shaped, approximately in a right angle, larger and more developed in center of rows, which have a triangular protuberance at base of tooth; marginal teeth thinner with soft curves.

Reproductive system ( Figures 11 F–12): hermaphrodite duct connecting to long and slightly convoluted ampulla. Postampullary gonoduct short, connecting to oviduct and prostate. Prostate granular, divided into two parts, approximately of same size, less dense part proximal, denser distal part. Distal portion of vas deferent short and enlarged, opening in common atrium with vagina. Penis cylindrical near deferent duct and tapered at distal part. Muscular wall on base of genital atrium, very thick near opening of vas deferens and vagina. Vagina elongated, narrow and opening into rounded bursa copulatrix, partially covered by prostate. Bursa serially arranged, vaginal duct folding once and connecting to stalked seminal receptacle; uterine duct short. Bursa and receptacle of similar size.

Remarks. Bergh (1880) distinguished the genus Peltodoris from Discodoris on the basis of the former’s lack of jaws and harder body consistency. Based on a recent phylogenetic analysis, Valdés (2002) indicated that Discodoris and Peltodoris belong in two different clades.

Discodoris hummelincki was originally described in the genus Peltodoris (Ev. Marcus and Er. Marcus, 1963) due to the lack of labial armature in the two specimens that were dissected. However, Dayrat (2010) re-examined the holotype of Discodoris hummelincki and found the labial armature to be composed of different elements, therefore suggesting that perhaps Ev. Marcus and Er. Marcus (1963) simply missed the jaws, or that their dissected specimens did not have jaws. The presence of elements in the labial armature places this species in the genus Discodoris . Furthermore, Dayrat (2010), after analyzing the types of Discodoris hummelincki and Tayuva ketos gila Ev. Marcus and Er. Marcus, 1967a (also from the Caribbean Sea), established their synonymy. Dayrat (2010) examined Peltodoris crucis Bergh, 1880 and realized that one of its paratypes actually belongs to D. hummelincki .

However, Dayrat (2010) transferred this species to Tayuva Ev. Marcus & Er. Marcus (1967a), a genus previously considered junior synonym of Discodoris by Valdés (2002). Ev. Marcus and Er. Marcus (1967a) described the genus Tayuva as possessing many features in common with the genus Discodoris but distinguished by a large vestibule (atrium) stiffened by spicules and lodging the penial papilla and the vaginal aperture. This genital opening structure was considered ‘aberrant’ by Marcus and Marcus (1967a) and they could not find another genus that could ‘receive’ the species. Dayrat (2010) recognized the supposed ‘aberration’, that is actually a muscle wall at the distal part of the reproductive system, as a synapomorphy of Tayuva .

On the other hand, Dayrat (2010) did not recognize morphological differences to separate the various species in this genus. Instead, he treated all of them as a single species in the so-called "complex Tayuva lilacina Gould, 1852 ", which was divided into four geographic regions: Mediterranean and the eastern European Atlantic, Panamic eastern Pacific, tropical Indo-western Pacific and Caribbean, with various synonyms in each region. The specimens studied here belong to the Caribbean region. Among the names included in the "complex Tayuva lilacina " from the Caribbean, Discodoris hummelincki (Ev. Marcus & Er. Marcus, 1963) is the oldest name. Although the species treated in this paper corresponds to the "complex Tayuva lilacina " from the Caribbean proposed by Dayrat (2010), here, we denote this species using the name Discodoris hummelincki . We have chosen not to use the name Tayuva lilacina because we believe that Dayrat (2010) was dealing with more than one species; furthermore, the species Tayuva lilacina was originally described from Hawaii, thus it probably does not represent the morphotype treated herein, once there is no example of species having a confirmed range including Hawaii and Brazil in Nudibranchia . Moreover, Dayrat (2010) separated Tayuva from Discodoris based on a poorly resolved phylogenetic tree, and he did not provide support values to show if it is indeed monophyletic. We follow the position proposed by Valdés (2002), that Tayuva is a junior synonym of Discodoris . This is the first record of Discodoris hummelincki in Brazil.

The types of Discodoris hummelincki include a holotype and four paratypes (from different localities of the Piscadera Bay), of which the holotype and two paratypes are deposited in the Zöologisch Museum, Amsterdam. Ev. Marcus and Er. Marcus (1963) reported that only one paratype would be sent to the University of São Paulo. Therefore, according to Dayrat (2010), two paratypes were sent to University of São Paulo, one from St. Martha Bay and one from Piscadera Bay. We only found one specimen in the University of São Paulo labeled from Curaçao; this specimen is likely to be the paratype mentioned by Ev. Marcus and Er. Marcus (1963).

García et al. (2008: p. 140) listed Diaulula phoca Ev. Marcus & Er. Marcus, 1967a from the Brazilian coast, in São Paulo state. However, herein we are dealing with the same morphotype as described by García et al. (2008); we identified the species as Discodoris hummelincki due to certain characteristics: we did not find caryophyllidia ( Fig. 11 E), which are present in the genus Diaulula ; and the deferent duct is long, thin and convoluted in D. phoca , whereas in D. hummelincki the deferent duct is short with an enlarged and curved proximal part ( Fig.12 A). Moreover, we found some distinguishing features only present in D. hummelincki , such as the muscle wall at the distal part of the reproductive system ( Figs. 12 A–B), the deferent duct with an enlarged, curved proximal portion ( Fig. 12 A), lateral teeth with protuberance on the base of the teeth ( Fig. 11 C), and white tubercles on the rhinophoral and branchial sheaths. Therefore, given that the only record of Diaulula phoca was based on a specimen of Discodoris hummelincki , we consider that D. phoca does not occur in the Brazilian coast.

Figures

FIGURE 1. Living specimens; A, Thordisa diuda (MNRJ 13195, 9 mm), photo: V. Padula; B, Hoplodoris hansrosaorum (MNRJ 12924, 22 mm); C, Geitodoris pusae (MNRJ 11712, 12 mm); D, Discodoris branneri (MNRJ 14922, 87 mm); E, Discodoris hummelincki (MNRJ 13997, 32 mm); F, Diaulula greeleyi (MNRJ 14974, 10 mm); G, Rostanga byga (MNRJ 12371, 5 mm); H, Jorunna spazzola (MNRJ 13196, 5 mm), photo: V. Padula.

FIGURE 11. Discodoris hummelincki, SEM photographs; A, detail of the elements of the labial cuticle; B, innermost lateral tooth; C, midlateral teeth, triangular enlargement at the base indicated by white arrow; D, marginal teeth; E, detail of the tubercles; F, penis. A – B; D – E (MNRJ 13997); C, F (MNRJ 12939).

FIGURE 12. Discodoris hummelincki, reproductive system (MNRJ 13997); A, general view of reproductive system; B, detail near of the gonopore; C, penis. Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; f, female glands; go, gonopore; mw, muscular wall; ov, oviduct; p, penis; pr, prostate; s, seminal receptacle; va, vagina.