Elysia canguzua Er. Marcus, 1955

Krug, Patrick J., Vendetti, Jann E. & Valdés, Ángel, 2016, Molecular and morphological systematics of Elysia Risso, 1818 (Heterobranchia: Sacoglossa) from the Caribbean region, Zootaxa 4148 (1), pp. 1-137 : 58-62

Elysia canguzua Er. Marcus, 1955

( Figs. 6 K, 30–32)

Elysia canguzua Er. Marcus 1955: 111 –113, figs. 45–48, 60–65 (Type locality: São Sebastião Island, Brazil) — Er. Marcus 1957: 415, fig. 47; Ev. Marcus 1980: 67 –68, figs. 10, 49; Jensen & Clark 1983: 4; Valdés et al. 2006: 64 –65; Ortigosa et al. 2013: 65; Christa et al. 2014: fig. 3; Krug et al. 2015: 990, fig. 3B.

Elysia eugeniae Ortea & Espinosa 2002: 130 –133, figs. 1–2; pl. 1, fig. A (Type locality: Manzanillo, Limón, Costa Rica) n. syn.

Elysia purchoni Thompson 1977: 129 –130, figs. 25f–g, 26h (Type locality: Lazaretto Cairn, approaches to Kingston Harbour, Jamaica) n. syn.

Type material. Elysia canguzua— untraceable, not at MZSP ( Siqueira Dornellas & Simone 2011); Elysia eugeniae— Holotype (MZUCR INB0001497478); Elysia purchoni— Holotype (BMNH 19775.W)

Material examined. Dry Tortugas National Park, Florida, USA, 2010, 1 specimen ( LACM 178644 ) ; Martinique, 14 July 2013, 1 specimen ( LACM 178643 ) ; Puerto Vargas, Cahuita , Costa Rica, 7 January 2006, 1 specimen ( LACM 178645 ) ; Manzanillo , Limón, Costa Rica, 1 specimen ( MZUCR INB 0001497478 ) .

Additional material examined. Martinique, 14 July 2013, 2 specimens (isolate Ecang _ 13Mar02, isolate Ecang _ 13Mar03; Carriacou island, St. Vincent and the Grenadines, July 1987, 1 specimen ( LACM 178645 ) ; Bocas del Toro, Panama, 30 July 2015, 10 specimens .

Live animal. The Dry Tortugas specimen, a juvenile, emerged from a collection of Bryopsis plumosa in 2 m depth from a seawall. Specimen fed on alga in the lab for 4.5 months, reaching 12 mm in length. While feeding, a strand of white exudate was frequently released from the anus. Parapodia were typically held open when resting. Specimen did not swim when disturbed. Specimens from Panama (n=10) were also obtained from B. plumosa growing in a sheltered cove, and conformed in all other respects to the previous specimen. Copulation was observed frequently.

External anatomy. Overall color dark to olive green on head and outer surface of parapodia, due to ramifying digestive diverticula. Exterior body surface generally smooth with sparse, low papillae; covered with dense, uniformly scattered tiny orange or red spots, and smaller iridescent blue specks. White spots scattered in uneven rows across sides of parapodia and head. White patches visible through epidermis from underlying white glands. Body shape dominated by a large siphonal opening just posterior to pericardium, with two smaller openings at the middle and end of body ( Fig. 30 A–B).

Raised bump at center top of head, between large eye spots. Upper lip with moustache of tiny black spots; lower lip lined in white. Digestive diverticula extend into both top and bottom lips. Rhinophores short relative to body length (1.5 mm on relaxed 12 mm animal), as long as distance from bump on head to anal papilla. Blunt tipped, with terminal white patch. Surface of rhinophores with same texture and color as rest of head, penetrated by green digestive diverticula throughout. Foot distinct from parapodia, set off by longitudinal groove on either side of body, but coloration same as parapodial surface ( Fig. 30 C). Transverse groove separating underside of head from the rest of the body. End of foot tapering to an elongated, pointed tail.

Large, anterior siphonal opening formed by laterally extended side-flaps of parapodia, which fold away from body; parapodia are one half body-length in width at widest point ( Fig. 30 C). Parapodia narrow about halfway down body, then widening into second, smaller siphonal opening. From anterior end to widest part of first siphon, parapodial margin green, crossed by regular white bars. Thereafter, thick white band running along margin, bordered by diverticula and white spots, with intermittent yellow-green splotches along margin; band extending to posterior end of second siphonal opening, thereafter margin green with regularly spaced white spots. Interior of parapodia milky white, with scattered clumps of dark green diverticula, and patches of white or light blue dots.

Large, raised anal papilla on dorsal surface, anterior and right of renopericardium inside large siphonal opening ( Fig. 30 A, D). Anus opening from center of papilla, ringed in white. Rounded pericardium covered by dense cap of green diverticula; short, tapering renopericardium, yellow-white with orange dots ( Fig. 30 D). One pair of dorsal vessels emerging from posterior end of pericardial complex, clear except for a few scattered white spots ( Fig. 31 ). Vessels thick, ~100 µm diameter, bifurcating. Posterior to first large siphon opening, dorsal vessels and accompanying clear swellings fusing one or both interior edges of parapodia to dorsal body surface, making parapodia thickened. At posterior end of body, parapodia form a third, smaller siphonal opening. Interior of parapodia and dorsal surface dominated by irregularly sized and shaped swollen white pustules, around which vessels may branch or wind; may be clear or filled with milky white fluid.

Internal anatomy. Radula with 14–16 teeth (LACM 178643–44, LACM 178646), 8–9 teeth in ascending limb and 6–7 in descending limb ( Fig. 32 A,C). Leading tooth elongate and robust with a subtle and smooth lateral edge on each side and cusp bearing approximately 67 very small, rounded denticles ( Fig. 32 B, D–F). Housing depression for interlocking teeth “V”-shaped and extending ¾ total tooth length ( Fig. 32 B). Tooth cusps, in lateral view, with two sections divided longitudinally, a thin and sharp basal half and a wider, thicker upper half. Base of tooth about ¼ total tooth length. Ascus containing jumbled heap of discarded teeth (not figured).

Penis large and elongate with rigid musculature resistant to desiccation (LACM 178644, LACM 178646), and tapering into a rounded tip devoid of armature ( Fig. 6 K). Deferent duct narrow and simple.

Reproduction and development. Development was reported as planktotrophic by Jensen & Clark (1983). Ortea & Espinosa (2002) reported an egg cordon of irregular shape, containing white eggs 85–103 µm, irregularly arranged in the jelly matrix. No ECY was present.

Host ecology. The Dry Tortugas specimen was collected from Bryopsis plumosa , on which it fed readily. Er. Marcus (1955) described specimens from Brazil as feeding on Codium , while Jensen & Clark (1983) reported both B. plumosa and Codium sp. as preferred hosts.

Phylogenetic relationships. Elysia canguzua was recovered as a member of subclade 2, sister to a clade comprising E. chlorotica + E. serca ( Fig. 4 ). The host algae of E. canguzua are also consumed by some other members of subclade 2, E. viridis ( Codium and Bryopsis ) and E. crispata (Bryopsis) .

Range. Brazil ( Er. Marcus 1955; Ev. Marcus 1980), Costa Rica ( Ortea & Espinosa 2002; Valdés et al. 2006), Florida, USA ( Jensen & Clark 1983), Jamaica ( Thompson 1977), Martinique (present study), Mexico ( Ortigosa et al. 2013), Carriacou island, St. Vincent and the Grenadines (present study), Panama (present study).

Remarks. Thompson (1977) described E. purchoni from a single specimen, 5 mm long, based on purportedly distinguishing characteristics: a row of black spots on the oral lobes; “numerous orange specks on all exposed surfaces;” a lateral ridge on the radular tooth; and the large anterior siphonal opening. His description of external morphology and radular teeth entirely conform to the description of E. canguzua . No mention of E. canguzua was made in Thompson’s (1977) remarks on E. purchoni , suggesting he was unaware of Er. Marcus’ (1955) description of E. canguzua . Er. Marcus (1955) referred to the moustache of black spots on the upper “lip”, or front of the oral lobes, as a “transverse arc on each side of the head,” and depicted the row of black spots in his illustration of the feeding animal ( Er. Marcus 1955: figs. 61–63). Although a similar moustache of black spots is present on E. cornigera , the extended lateral wing-flaps of E. cornigera do not form a rounded siphonal opening as depicted for E. purchoni ( Thompson 1977: fig 25f) whereas those of E. canguzua do form such an opening. Thus, E. purchoni is a junior synonym of E. canguzua .

Ortea & Espinosa (2002) described E. eugeniae (12 mm in body length) from Costa Rica, found on Bryopsis muscosa . Their description conforms in all respects to that of E. canguzua , without the crucial penial anatomy that is distinctive to this species. They noted that E. canguzua was similar in its dorsal vessels, color pattern and radular teeth, but identified their material as distinct from E. canguzua based on (1) the very prominent anal papilla, (2) absence of black pigment inside the rhinophores, and (3) longer radular teeth. To the first point, although an anal papilla was not explicitly mentioned in Er. Marcus’s (1955) description, the position of the anus is well described (“anus lies dorso-laterally in the shoulder fold and beneath it the single female opening”), and a raised papilla is clearly present on the close-up figure of the head ( Er. Marcus 1955: fig. 64). In terms of pigmentation, the type material was described as having black pigment lining the inside of the rhinophores, and forming a transverse arc on each side of the head, a patch on the shoulder fold, and a line along the parapodial margin in some specimens ( Er. Marcus 1955). Our specimens lacked any notable black pigment, but were otherwise identical to the description of Er. Marcus (1955); we therefore consider the presence or absence of black pigment to reflect intraspecific polymorphism. Fittingly, Er. Marcus (1955) noted in his remarks on E. canguzua that “the separation of the species of Elysia cannot continue on the basis of colour, thickness and extension of the parapodia, form of the head, and radula,” placing emphasis on the reproductive anatomy including the vaginal and penial morphology.

In terms of radulae, Er. Marcus (1955) described the tooth of E. canguzua as 80 µm long from a 9 mm long slug, having “a more or less pointed cusp, slightly marked lateral crests and a very finely serrulate medial crest.” Thompson (1977) reported a similar shape for the tooth of E. purchoni , with maximum length of 99 µm and minimum length of 36 µm, on a 5 mm long slug. Ortea & Espinosa (2002) reported a 125-µm-long tooth for E. eugeniae specimens measuring 12 mm in body length, with a lateral ridge and serrated medial cutting edge consistent with the descriptions of Er. Marcus (1955) for E. canguzua , and Thompson (1977) for E. purchoni . Given that Ortea & Espinosa (2002) studied larger slugs than Er. Marcus (1955) or Thomson (1977), it is not surprising that they measured longer teeth, and tooth length alone is not considered a species-diagnostic character in Sacoglossa . In the absence of any diagnostic difference, E. eugeniae is therefore a junior synonym of E. canguzua .

More recently, Ortea et al. (2011) proposed that E. cornigera was a junior synonym of E. purchoni , which they then “redescribed” from Caribbean material. The basis for their synonymy was that both species had some jumbled teeth in the ascus, red spots, a moustache of black dots on the oral lobes, and radulae with a lateral crest as well as a serrated cutting edge. Confusing matters further, the authors make no mention of E. eugeniae , despite the fact that it shares this suite of characters. Aside from the radular character noted, none of the other traits are unique to one species; for instance, numerous elysiids have an arc of black dots on the oral lobes, or tiny red spots on the body. These characters are therefore inappropriate for the basis of a synonymy in the absence of other data. In terms of the radula, Thompson (1977) referred to a lateral ridge on the tooth of E. purchoni , similar in drawings and descriptions to what Er. Marcus (1955) called a “slightly marked lateral crest” on the tooth of E. canguzua . The lateral ridge on the tooth of E. canguzua (= purchoni ) is not described as serrated by Thompson or Marcus, nor is it drawn with serrations in their respective figures. The tooth of E. canguzua is therefore distinctly different from the double, serrated cutting edge of the radular tooth in E. cornigera . Moreover, the siphonal opening depicted by Thompson (1977) for E. purchoni is consistent with the opening formed by the curved parapodia of E. canguzua , but not the extended lateral parapodial wing-flaps of E. cornigera . Thus, E. cornigera is not a synonymn of E. purchoni .

Developmentally, E. canguzua lacks ECY, a derived character state shared by all members of subclade 2. Given the biogeographic distribution of members of subclade 2, this lineage may have evolved in the warmtemperate West Atlantic; secondary loss of ECY may be favored in more productive temperate waters, while ECY could be selectively maintained in oligotrophic tropical waters to buffer larval offspring against starvation ( Krug et al. 2015).

Figures

FIGURE 4. Phylogenetic hypothesis for family Plakobranchidae rooted on genus Bosellia (not shown) to illustrate relationships within the genera Elysia, Plakobranchus and Thuridilla. Topology and branch lengths are from Maximum Likelihood analysis of concatenated DNA sequences (2,807 bp total) representing portions of two mitochondrial (COI, 16 S) and two nuclear (H 3, 28 S) genes. Significant support values are given as ML bootstrap percentages (below branch), or BI posterior probabilities (above branch); asterisk = 1.0 or 100 % support. Species discussed in this study are bolded. Triangle denotes presence of a penial stylet.

FIGURE 6. Penial morphology of some species examined. A, Elysia ornata (LACM 178583). B – E, Elysia crispata (LACM 178640) (B); (LACM 178641) (C); (LACM 2004.5.1) (D); (isolate Ecri _ 10 LKS 03) (E). F, Elysia chlorotica (LACM 178597). G – H, Elysia patina (LACM 178650) (G); (LACM 178651) (H). I, Elysia flava (LACM 178626). J, Elysia subornata (LACM 178629). K, Elysia canguzua (LACM 178644). L, Elysia serca (CPIC 00027). M, Elysia evelinae (MZUCR INB 0003312779). N, Elysia velutinus (LACM 178642), O, Elysia papillosa (LACM 178607). P, Elysia cornigera (LACM 173227). Q, Elysia marcusi (LACM 178647), R, Elysia pratensis (CPIC 00068). S, Elysia zuleicae (LACM 178656). Abbreviations: bw, body wall; dd, deferent duct; pe, penis; s, stylet.

FIGURE 30. Elysia canguzua, external morphology of live specimen from Dry Tortugas, FL, USA (length of slug = 12 mm). A, Dorsal view of head, showing raised anal papilla and renopericardium. B, Side view of same specimen. Swollen white pustular glands visible inside parapodia. C, Ventral surface of foot, showing transverse groove separating the head. D, Interior of parapodia, showing renopericardial complex and dorsal vessels.

FIGURE 31. Elysia canguzua, drawings of renopericardium and dorsal vessel network from a preserved specimen (LACM 178643; 5.5 mm long × 5 mm wide).

FIGURE 32. Elysia canguzua, SEM of radulae. A, Radula, without ascus (LACM 178643). B, Leading tooth (LACM 178643). C, Radula, without ascus (LACM 178644). D, Leading tooth, showing smooth lateral edge (LACM 178644). E, Close-up of cusp showing denticles. F, Leading tooth (LACM 178645).