This article is registered in ZooBank under http://Zoobank.org/F7633F9A-54E1-4080-8165-0C631C111BBB
Introduction
The monophyletic genus Trapania Pruvot-Fol, 1931 is one of the 11 genera of the family Goniodorididae, and the largest in the subfamily Anculinae Pruvot-Fol, 1954 (Paz-Sedano et al., Reference Paz-Sedano, Moles, Smirnoff, Gosliner and Pola2024a). Members of this highly diverse genus are characterized by having an elongated body and a single pair of extra-rhinophoral and extra-branchial appendages, with a single lateral tooth on each side of the radula (Smirnoff et al., Reference Smirnoff, Donohoo and Gosliner2022; Paz-Sedano et al., Reference Paz-Sedano, Moles, Smirnoff, Gosliner and Pola2024a). In recent years, many new species of Trapania have been described from different regions around the world, including the Indo-Pacific (Gosliner and Fahey, Reference Gosliner and Fahey2008; Smirnoff et al., Reference Smirnoff, Donohoo and Gosliner2022), the Eastern Pacific (Gosliner and Fahey, Reference Gosliner and Fahey2008), the Caribbean Sea (Valdés, Reference Valdés2009), Western Africa (Edmunds, Reference Edmunds2009), Argentina (Cetra and Roche, Reference Cetra and Roche2019) and Australia (Paz-Sedano et al., Reference Paz-Sedano, Cobb, Gosliner and Pola2024b). Recent studies have also led to the reassignment of certain species within the genus Trapania, particularly those found along the temperate coasts of the Eastern Atlantic and the Mediterranean Sea (Paz-Sedano et al., Reference Paz-Sedano, Álvarez, Gosliner and Pola2022). These changes include the reclassification of Trapania hispalensis Cervera and García-Gómez, 1989, Trapania lineata Haefelfinger, 1960 and Trapania pallida Kress, 1968 as synonyms, and have resulted in the recognition of 55 valid Trapania species (MolluscaBase, 2024), highlighting the need for ongoing taxonomic revision within the genus.
Five species of Trapania have been previously described from the Eastern Pacific based on morphological data: Trapania velox (Cockerell, Reference Cockerell1901) from California, Trapania goslineri Millen and Bertsch, Reference Millen and Bertsch2000 from the Gulf of California, Trapania goddardi Hermosillo and Valdés, Reference Hermosillo and Valdés2004 from Mexico, Trapania inbiotica Camacho-García and Ortea, Reference Camacho-García and Ortea2000 from Costa Rica and Trapania darwini Gosliner and Fahey, Reference Gosliner and Fahey2008 from the Galapagos Islands. Externally, T. darwini most closely resembles T. goslineri and T. velox (Gosliner and Fahey, Reference Gosliner and Fahey2008), all three species sharing a white body with dark markings and yellow ornamentations, although they differ in the pattern and distribution of these pigments. The body of T. goddardi is covered by irregular small or large brown blotches with no yellow pigment (Hermosillo and Valdés, Reference Hermosillo and Valdés2004), while T. inbiotica presents irregular red patches arranged over the entire dorsum, varying in shape and size (Camacho-García and Ortea, Reference Camacho-García and Ortea2000). Despite significant differences in the external coloration between these species the diagnostic nature of the colour patterns should be considered with caution because of intraspecific colour and morphological variability which direct the need to include molecular data to confirm taxonomic decisions (Padula et al., Reference Padula, Bahia, Stöger, Camacho-García, Malaquias, Cervera and SchrödL2016; Paz-Sedano et al., Reference Paz-Sedano, Ortigosa and Pola2017, Reference Paz-Sedano, Álvarez, Gosliner and Pola2022).
The coastal transition zone off northern Peru is characterized by the upwelling of nutrient-rich cool water, which dramatically increases biological diversity in benthic communities (Riascos et al., Reference Riascos, Uribe, Donayre, Flores, Galindo, Quispe and González2016). This zone includes habitat-forming species such as kelp forests, which are crucial for providing habitat complexity, food resources and shelter. Consequently, these forests support higher levels of biodiversity compared to adjacent ecosystems (Uribe et al., Reference Uribe, Perea and Ortiz2022). However, only 31 species of nudibranchs have been reported from the coast of Peru, indicating a relatively low species richness in this region compared to other areas of the continent (Grández et al., Reference Grández, Ampuero and Barahona2023). Notably, there are no recorded species of Trapania from Peruvian waters, and within the family Goniodorididae, only Okenia luna Millen, Schrödl, Vargas and Indacochea, 1994, has been reported from the central coast of Peru (Uribe et al., Reference Uribe, Nakamura, Indacochea, Pacheco, Hooker and Schrödl2013). The available information on nudibranchs in the South-eastern Pacific suggests a lack of research effort in this area (Uribe and Pacheco, Reference Uribe and Pacheco2012), emphasizing the need for further taxonomic attention.
In the present study, we described a new species of Trapania from the north-central coast of Peru based on the combined use of molecular and morphological analyses, an integrative approach that has proven very useful for determining new species in little-explored areas such as the South-eastern Pacific (Ornelas-Gatdula et al., Reference Ornelas-Gatdula, Camacho-García, Schroedl, Padula, Hooker, Gosliner and Valdés2012; Hoover et al., Reference Hoover, Padula, Schrödl, Hooker and Valdés2017; Uribe et al., Reference Uribe, Sepúlveda, Goddard and Valdés2018; Valdés et al., Reference Valdés, Breslau, Padula, Schrödl, Camacho, Malaquias, Alexander, Bottomley, Vital, Hooker and Gosliner2018). We performed a detailed anatomical study in conjunction with phylogenetic and species delimitation analyses to verify the status of these specimens, including ecological information when available. Additionally, we used these results to perform a comparative analysis with other recorded Trapania from the Eastern Pacific.
Materials and methods
Sampling
Six specimens of an undescribed species of Trapania were collected in April 2023 from rocky subtidal sites in Rio Seco, Huarmey province, Ancash region, north-centre of Peru (−78.228080°, −9.807092°), at 8 m depth by SCUBA diving, during a monitoring of the biodiversity associated with the kelp forest Eisenia cokeri Howe, 1914. Samples were preserved in 95–99% ethanol and deposited at the Colección Científica del Instituto del Mar del Peru (IMARPE).
DNA extraction, amplification and sequencing
Three specimens were used for the molecular analysis. A small sample of foot tissue was cut for the DNA extraction. The DNA was isolated following a modified protocol based on Miller et al. (Reference Miller, Dykes and Polesky1988) involving treatment with sodium dodecyl sulphate, digestion with proteinase K, NaCl protein precipitation and subsequent ethanol precipitation. DNA was eluted in nuclease-free water and quantified in a spectrophotometer BioSpec-nano.
Partial sequences from two mitochondrial genes, 16S ribosomal RNA (16S) and cytochrome oxidase c subunit I (COI), and one nuclear gene, histone 3 (H3), were amplified by polymerase chain reaction (PCR). The primers used were 16Sar-L and 16Sbr-H for 16S (Palumbi, Reference Palumbi, Martin, Romano, Owen, Macmillan, Stice and Grabowski1991), LCO1490 and HCO2198 for COI (Folmer et al., Reference Folmer, Hoeh, Black and Vrijenhoek1994) and HexAF and HexAR for H3 (Colgan et al., Reference Colgan, Mclauchlan, Wilson, Livingston, Macaranas, Edgecombe and Gray1998) (Supplementary Table S1). Each PCR had a final volume of 35 μl including five standard units of GoTaq DNA polymerase (Promega, Madison, USA), 7 μl 5X PCR buffer, 5.6 μl MgCl2 (25 mM), 2.1 μl BSA (10 mg ml−1), 0.7 μl of deoxynucleotide triphosphate (dNTP) (10 mM), 10 pM of each primer and 3 μl template DNA. The optimized PCR conditions for 16S and H3 datasets started with an initial DNA denaturation at 94°C for 2 min; followed by 35–40 cycles of 30 s denaturation at 94°C, 30 s annealing at 50°C and 45 s–1 min extension at 72°C; with a final extension at 72°C for 10 min. For COI, we used an initial denaturation at 94°C for 5 min, followed by 35 cycles of denaturation 94°C at 1 min, annealing 44°C at 30 s, extension 72°C at 1 min and final extension 72°C at 7 min. PCR amplifications were confirmed in a 1% agarose gel using GelRed™ fluorescent dye. PCR products were sent to Macrogen (http://www.macrogen.com) for purification and sequencing of both DNA forward and reverse strands. Complementary sequences were assembled and edited using ProSeq v2.9 (Filatov, Reference Filatov2002).
Sequence alignment
The sequences obtained in this study were aligned with the sequences of Trapania spp. retrieved from GenBank, along with seven other members of the Goniodorididae family and one member of each of the families Onchidorididae, Corambidae and Calycidordidae as outgroups (Table 1). The scientific names of all sequences used in this study were checked using MolluscaBase (2024). Each alignment was conducted using MAFFT v.7 (Katoh and Standley, Reference Katoh and Standley2013), using the L-INS-i iterative algorithm for 16S, and G-INS-I for COI and H3 following Paz-Sedano et al. (Reference Paz-Sedano, Moles, Smirnoff, Gosliner and Pola2024a). Ambiguous aligned regions (with internal gaps) of 16S were removed using relaxed parameters to allow half the gaps with the GBlock 0.91.1 program (Castresana, Reference Castresana2000; Talavera and Castresana, Reference Talavera and Castresana2007; Lemoine et al., Reference Lemoine, Correia, Lefort, Doppelt-Azeroual, Mareuil, Cohen-Boulakia and Gascuel2019). Finally, 16S, COI and H3 alignments were trimmed to 346, 594 and 328 base pairs, respectively. We concatenated the three aligned loci using Mesquite v.2.75 (Maddison and Maddison, Reference Maddison and Maddison2011). Sampled specimens used, voucher numbers, GenBank accession numbers and specimen localities are listed in Table 1.
Table 1. Specimens used for molecular analysis, including locality data, GenBank accession numbers and museum voucher numbers
Phylogenetic analyses
Phylogenetic reconstruction was conducted for the concatenated dataset, using the Bayesian Inference (BI) performed in MrBayes v.3.1.2 (Huelsenbeck and Ronquist, Reference Huelsenbeck and Ronquist2001) and the Maximum Likelihood (ML) performed in the webserver W-IQ-TREE v.2 (Trifinopoulos et al., Reference Trifinopoulos, Nguyen, Von Haeseler and Minh2016; http://iqtree.cibiv.univie.ac.at/). The evolutionary models were selected using jModelTest v.0.1.1 (Posada, Reference Posada2008), based on the corrected Akaike information criterion (Akaike, Reference Akaike1974). The optimal models found by jModelTest were TPM2uf + I + G for 16S, GTR + I + G for COI and TrN + G for H3, but, because not all evolutionary models are available in MrBayes software, we replaced them with GTR + G + I (Ronquist and Huelsenbeck, Reference Ronquist and Huelsenbeck2003).
BI was conducted with the following parameters: nst = 6, rates = invgamma and run for 10,000,000 generations. Analyses included two runs of four chains, with sampling every 1000 generations. Support for nodes in the BI tree topology was obtained by posterior probability burn-in the initial 25% of samples. Results were visualized in TRACER v.1.7 (Drummond and Rambaut, Reference Drummond and Rambaut2007). For the ML analyses, we used the default options in the server W-IQ-TREE. The robustness of ML tree topology was assessed by bootstrap reiterations of the observed data 1000 times. The trees were visualized and edited in FigTree v.1.4.4 (http://tree.bio.ed.ac.uk/software/figtree/). Following Muff et al. (Reference Muff, Nilsen, O'Hara and Nater2022) we defined the following five categories for BI nodal support as: PP = 1: fully supported; PP = 0.99–0.90: strongly supported; PP = 0.89–0.80: moderated support; PP = 0.79–0.70: weakly supported; PP ≤ 0.69: not supported.
Species delimitation analyses
The COI dataset was further interrogated to test the genetic relatedness of the candidate species T. huarmeyana sp. nov. sequences to congeners. Species delimitation was examined using Automatic Barcode Gap Discovery (ABGD; Puillandre et al., Reference Puillandre, Lambert, Brouillet and Achaz2012) and Assemble Species by Automatic Partitioning (ASAP; Puillandre et al., Reference Puillandre, Brouillet and Achaz2021). Sixty-six sequences of Trapania spp. were retrieved from GenBank and three were of the candidate species T. huarmeyana sp. nov. For the ABGD analysis, COI alignments were uploaded at https://bioinfo.mnhn.fr/abi/public/abgd/abgdweb.html using the default settings: Pmin = 0.001, Pmax = 0.1, Steps = 10, X (relative gap width) = 1.0, Nb bins = 20 and with Kimura (K2P) distance. The ASAP was conducted using the web tool (https://bioinfo.mnhn.fr/abi/public/asap/asapweb.html), and under the Kimura (K80) model, with a default ts/tv rate of 2.0, and a 0.05 threshold distance. Additionally, to compare the genetic distance among specimens of Trapania, we calculated the pairwise p-distance (between individual sequences and in average by species) for 16S, COI and H3 using MEGA v.6 (Tamura et al., Reference Tamura, Stecher, Peterson, Filipski and Kumar2013).
Morphological examination
The external morphology of all collected specimens was examined using a stereomicroscope. Additionally, the internal morphology of two specimens was examined, with a focus on the digestive and reproductive systems as the main internal traits for species identification and characterization. The reproductive organs were examined by removing them from the animal through a ventral incision and drawn under a Leica S APO dissecting microscope. The buccal mass of each examined specimen was removed and dissected to isolate the jaws and radula. Penises, jaws and radulae were rinsed in water, dried, mounted and sputter coated for examination under a FEI Inspect S50 variable pressure SEM at the Universidad Nacional Mayor de San Marcos (Lima, Peru).
Results
Phylogenetic analysis
A total of two partial sequences of 16S (of 453 bp), three of COI (of 631–666 bp) and two of H3 (of 339 bp) were obtained for T. huarmeyana sp. nov. The concatenated dataset contained 1268 bp, with 455 parsimony informative sites. The BI and ML analyses of the concatenated dataset, which included 32 of the 55 species of Trapania, produced phylogenetic trees with partial concordance of statistical support (BI posterior probabilities [pp] and ML bootstrap values [mlb]) (Figure 1). Both trees clustered the Trapania species in a monophyletic group (pp = 0.99; mlb = 100%), recovering two internal subclades with moderate-to-strong statistical support. The phylogenetic trees consistently grouped the Peruvian T. huarmeyana sp. nov. with Galapagos sequences identified as T. goddardi by Smirnoff et al. (Reference Smirnoff, Donohoo and Gosliner2022) showing strong-to-full support (pp = 1; mlb = 96%) as per Muff et al. (Reference Muff, Nilsen, O'Hara and Nater2022). Trapania huarmeyana and T. goddardi clustered with T. velox from California within an eastern Pacific clade. In addition, the eastern Pacific clade grouped with the European species: T. cirrita Gosliner and Fahey, Reference Gosliner and Fahey2008; T. sanctipetrensis Cervera, García-Gómez and Megina, 2000; T. orteai García-Gómez and Cervera, 1989; T. lineata Haefelfinger, 1960; T. maculata Haefelfinger, 1960 and the Indo-Pacific species T. palmula with strong support (pp = 1; mlb = 98%).
Figure 1. Bayesian consensus phylogenetic tree on the concatenate molecular data (16S + COI + H3) for Trapania spp. Values above branches refer to posterior probabilities of BI and values below branches represent bootstrap support values for ML. Only values >0.70 (Bayesian) and >75 (ML) are included. Coloured dots to the right of each species represent the geographic origin. Bars on the right indicate results of species delimitation analyses using ABGD (blue) and ASAP (grey) for COI dataset. White circle: no COI sequence to compare.
Species delimitation analysis
The ABGD analysis showed a tri-modal pairwise genetic distance (K2P) distribution with a gap located between 3 and 6% of the genetic distance and a second clear and wide barcode gap situated between 9 and 10% of the genetic distance (Supplementary Figure S1A). ABGD analysis of the genetic pairwise distance in the aligned COI dataset recovered one partition of 28 candidate species with a prior maximal distance = 2.15% and barcode gap distance = 0.049 (Figure 1; Supplementary Figure S1B). Meanwhile, the best ASAP-score (= 4.5) partitioned the COI dataset into 24 putative species (Figure 1). ASAP grouped as the same species those sequences whose genetic distance was < 7.5%: T. naeva and T. circinata; T. kamagong, Trapania sp. A and T. stegodon; T. tamarraw and Trapania sp. B; T. darvelli and T. reticulata (Figure 1). Although ABGD and ASAP methods show slightly different results, both support the genetic divergence of the new candidate species from other congeners.
Intraspecific variability of T. huarmeyana sp. nov. using the COI dataset was 0.2–0.6% (between 1 and 4 polymorphic sites). The genetic divergence of T. huarmeyana sp. nov. between its congeners was greater than 11% with a minimum of 11.3% divergence from its closest congeners, T. goddardi with 11.3% (Supplementary Table S2). For the 16S dataset, the intraspecific variability for T. huarmeyana sp. nov. was 0.6% (two polymorphic sites), with 4.5% divergence from T. goddardi with the next closest species being T. lineata (average = 6.5% sequence divergence) (Supplementary Table S3). Finally, using the H3 dataset, the two sequences of T. huarmeyana sp. nov. were 100% identical; and exhibited 3.4% divergence from T. goddardi and 4.5% from T. lineata with 4.5% (Supplementary Table S4).
Systematics
Order Nudibranchia Cuvier, 1817
Suborder Doridina
Superfamily Onchidoridoidea Gray, 1827
Family Goniodorididae H. Adams and A. Adams, 1854
Genus Trapania Pruvot-Fol, 1931
Trapania huarmeyana sp. nov.
The nomenclatural acts it contains have been registered in ZooBank (http://zoobank.org/). The Life Science Identifier (LSID) for this publication is: urn: lsid:zoobank.org:act:A98A017A-0FE1-44C1-AB4E-78CB132873AB.
Type material
Holotype: 1 specimen, IMARPE 04-002333, Huarmey, Ancash region, Peru, 5.5 mm preserved length, April 2023.
Paratypes: 5 specimens, IMARPE 04-002373–IMARPE 04-002377, Huarmey province, Ancash region, Peru (same coordinates as holotype), 5–7 mm preserved length, April 2023.
Type locality: Huarmey province, Ancash region, Peru (−78.228080°, −9.807092°).
Etymology: The name Trapania huarmeyana sp. nov. is dedicated to Huarmey province, the type locality where the specimens were collected.
Diagnosis: Body translucent white, with anterior and posterior midline dark brown stripes and some brown spots on dorsum; with brown blotches on base of extra-rhinophoral processes, extra-branchial processes and gill branches. Radular formula: 28 × 1.0.1, lateral teeth without outer denticles and with 9–10 inner denticles. Jaws with several rows of pointed jaw elements. Penis with 10 rows of penial hooks, less developed basally.
External morphology: Living specimens up to ~8 mm length. Body narrow, elongated, becoming wider and higher at level of gill, narrowing gradually towards elongated and pointed tail. Colour translucent white, with a middorsal dark brown stripe running from rhinophores to anterior margin of gill, with two anterior extensions on base of oral tentacles and a middorsal posterior brown stripe running from posterior margin of gill to subdistal tail. Body ornamented with elongated to circular dark brown spots, most of them between rhinophores and gill. Additionally, large dark brown blotches on base of extra-rhinophoral processes, extra-branchial processes and gill branches (Figure 2). Anterior margin of foot with a pair of thick propodial tentacles oriented backward (Figure 3: pt). Oral tentacles tapering, oriented forward, smaller than extra-rhinophoral processes, opaque white on distal half (Figure 3: ot). Rhinophores without rhinophoral sheath, with a pointed tip, with 7–8 lamellae decreasing in size distally, opaque white on frontal edge of lamellae and tip (Figure 3A: ri). Pair of extra-rhinophoral processes digitiform, oriented backward, smaller than extra-branchial processes, opaque white distally (Figure 3A: er). Gill of three tripinnate translucent branches, arranged in a semicircular fashion, opaque white on tip and frontal edge of gill branches (Figure 3A: gi). Pair of extra-branchial processes thick, digitiform, oriented backward, opaque white distally (Figure 3A: eb). Anus surrounded by a gill semicircle (Figure 3A: an). Genital opening on right side of body. Foot elongated, narrow, opaque white on tail (Figure 3B: f).
Figure 2. Photographs of living animals. (A, B) Grouped animals and mass egg (red arrow) on the kelp Eisenia cokeri holdfast. (C) Dorsal view. (D) Lateral view (photo credits: R. Uribe).
Figure 3. External morphology of T. huarmeyana sp. nov. (A) Dorsal view. (B) Ventral view. Abbreviations: eb, extra-branchial processes; extra-rhinophoral processes; f, foot; gi, gill; mo, mouth; ot, oral tentacles; pt, propodial tentacles; ri, rhinophores.
Reproductive system. Gonad immersed into frontal region of visceral mass. Hermaphroditic duct slender and curved, inserting into ventral surface of ampulla slightly posterior to its midline (Figure 4). Ampulla elongated, proximally pyriform, bifurcating distally into narrow oviduct and vas deferens (Figure 4A: am). Prostate thick and rounded, with a single loop, narrowing into short and slightly curved deferent duct. Penial sac thick and elongated (Figure 4B). Bursa copulatrix ovoid (Figure 4B, C: bc), smaller than prostate, connecting with long and slender vagina (Figure 4B, C: va). Seminal receptacle small and spherical (Figure 4B, C: sr), entering into bursa copulatrix through narrow duct, connected by delicate uterine duct to nidamental gland. Nidamental gland larger than bursa, connecting to genital opening through narrow duct (Figure 4: ng). Penis elongated, with several closely packed rows of hooked spines, thick and elongated distally, becoming smaller, slender and more densely packed proximally (Figure 5).
Figure 4. Schematic view of reproductive organs. (A) Dorsal view. (B) Ventral view. (C) Lateral view. Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; hd, hermaphroditic duct; ng, nidamental gland; pr, prostate; ps, penial sac; sr, seminal receptacle; va, vagina.
Figure 5. Scanning electron micrographs of penis of the specimen 5 (IMARPE 04-00276) of T. huarmeyana sp. nov.
Central nervous system. Nerve ring dorsal on buccal mass, surrounding oesophagus (Figure 6A, B). Cerebral and pleural ganglia fused forming a cerebro-pleural complex (Figure 6C: clg). Eyes sessile. Cerebral nerves: c1, slender, running anteriorly, innervating oral tentacles; c2, slender, arising posterior to c1, inserting anteriorly into dorsal region of mouth; c3, thick, inserting into rhinophores, rhinophoral ganglion not developed; c4, thick, arising close to c3, inserting into ventral region of mouth. Pleural ganglia on posterior region of cerebral ganglia, with a thick nerve (pl) running posteriorly, inserting into dorsal body wall. Cerebro-pedal connectives short. Cerebro-buccal connectives very long and thin. Buccal ganglia (Figure 6A–C: bg) small, oval, attached on posterior region of buccal mass below oesophagus and salivary glands, with four very slender nerves. Pedal ganglia (Figure 6C: pg) oval, smaller than cerebro-pleural complex, connected by a short pedal commissure. Pedal nerves: p1, slender, running anteriorly, innervating anteriormost foot and propodial tentacles; p2, slender, branched, arising posterior to p1, innervating anterior foot; p3, thick, running posteriorly, bifurcating into two branches, innervating medium and posterior foot, respectively; p4, only arising on right pedal ganglion, dorsal to p2–p3 nerves, running posteriorly inserting into penial sac and genital system. Visceral loop slender (Figure 6C: vl), with a nerve that runs posteriorly inserting into visceral mass.
Figure 6. Anatomical details in T. huarmeyana sp. nov. (A) Right view of buccal mass. (B) Posterior view of buccal mass. (C) Ventral view of central nervous system. (D) Dorsal view of pericardium. Abbreviations: au, auricle; bg, buccal ganglia; bp, buccal pump; c1–c4, cerebral nerves; clg, cerebro-pleural complex; es, oesophagus; og, oral glands; p1–p4; pedal nerves; pc, pericardium; pd, pedal ganglia; pl, pleural nerve; sg, salivary glands; ve, ventricle; vl, visceral loop.
Circulatory and excretory system. Heart on dorsal body wall inside pericardial cavity. Auricle funnel-shaped, translucent white, with internal longitudinal and transversal fibers. Ventricle pyriform, creamy yellow, thicker and longer than auricle. Blood gland not observed (Figure 6D).
Digestive system. Oral tube short with several oral glands on ventral surface. Buccal mass thick, with a slightly prominent dorsal rounded buccal pump extending anteriorly (Figure 6A, B). Radula long, widening towards newly developed teeth, translucent white, formula: 28 × 1.0.1. Rachidian tooth absent. Lateral teeth with slightly curved, long falcate cusp displaced towards outer margin; with 9–10 inner pointed denticles decreasing in size towards radula centre; outer denticles not observed (Figure 7A–D). Pair of triangular jaws, with 3–4 rows of closely packed yellow rodlets on masticatory border, rodlets lanceolated with a pointed tip (Figure 7E, F). Pair of salivary glands very small and rounded, attached at the junction of oesophagus with buccal mass (Figure 8A, B: sg). Oesophagus long, anteriorly swollen, posteriorly narrowing, inserting into frontal side of visceral mass (Figure 8A: es). Digestive gland creamy white, occupying most of visceral mass (Figure 8A: dg). Stomach small, on left surface of visceral mass (Figure 8B: st). Intestine narrow, running one whorl around dorsal surface of digestive gland, curving to right side to open into anus (Figure 8B: in).
Figure 7. Scanning electron micrographs of radula. (A–D) View of complete rows and innermost teeth of the specimen 5 (IMARPE 04-00276), and specimen 6 (IMARPE 04-002377). (E–F) Detail of the jaws of the specimen 5.
Figure 8. Haemocel organs in T. huarmeyana sp. nov. (A) Right view. (B) Left view. Abbreviations: bc, bursa copulatrix; dg, digestive gland; es, oesophagus; in, intestine; ng, nidamental gland; pr, prostate; ps, penial sac; st, stomach.
Distributional range: Collected only from Huarmey, Ancash region, north-central Peru. Trapania huarmeyana sp. nov. probably with affinity to warm waters since it was found during the El Niño 2023/24 event.
Ecology: Specimens of T. huarmeyana sp. nov. were observed and photographed on holdfast of the kelp E. cokeri covered by Hydrozoa species and a yellow sponge (Demospongiae Sollas, 1885) that probably constitutes their diet (Figure 2A, B). Solitary individuals were observed on rocky platforms inside the E. cokeri kelp forest (Figure 2C, D).
Reproduction: Trapania huarmeyana sp. nov. deposits spiral and transparent egg masses (Figure 2A, B).
Remarks: Externally, T. huarmeyana sp. nov. resembles T. velox from California and T. goslineri from Baja California and the Gulf of California, based on the white body and dark brown stripes and blotches on dorsum. However, T. velox has five brown stripes on the dorsum (Cockerell, Reference Cockerell1901; MacFarland, Reference MacFarland1929, Reference MacFarland1966) and T. goslineri has numerous brown blotches (Millen and Bertsch, Reference Millen and Bertsch2000), while T. huarmeyana sp. nov. has a single median brown stripe along the dorsum. Additionally, the appendages and the tails on these two species have an orange tip which is absent in T. huarmeyana sp. nov. Although T. darwini from Galapagos Islands also have brown blotches, these are dense and punctuated with cream spots (Camacho-García et al., Reference Camacho-García, Gosliner and Valdés2005; Gosliner and Fahey, Reference Gosliner and Fahey2008), while they are solid and scattered in T. huarmeyana sp. nov. Two additional species of Trapania have been described from the Eastern Pacific, T. inbiotica from Central America with dense red patches over the dorsum and appendages with tip yellow (Camacho-García and Ortea, Reference Camacho-García and Ortea2000; Camacho-García et al., Reference Camacho-García, Gosliner and Valdés2005), and T. goddardi from Mexico with irregular brown blotches on dorsum (Hermosillo and Valdés, Reference Hermosillo and Valdés2004), but T. huarmeyana sp. nov. differs from them by the dorsal brown stripes and the absence of additional marking on appendage tips (Table 2).
Table 2. Comparative characteristics of the species of Trapania living in the Eastern Pacific
The radular morphology of T. huarmeyana sp. nov. differs from T. goslineri, T. inbiotica and T. darwini by absence of outer denticles; T. inbiotica and T. darwini also differing from T. huarmeyana sp. nov. in the number of inner denticles. Although T. goddardi, T. goslineri and T. velox show a similar number of inner denticles to T. huarmeyana sp. nov., they differ in the number of rows: 17 in T. goddardi (Hermosillo and Valdés, Reference Hermosillo and Valdés2004), 24 in T. velox (MacFarland, Reference MacFarland1929), 37–41 in T. goslineri (Millen and Bertsch, Reference Millen and Bertsch2000) and 28 in T. huarmeyana sp. nov. Additionally, the jaws of T. inbiotica differ from T. huarmeyana sp. nov. in the presence of irregular elements (Camacho-García and Ortea, Reference Camacho-García and Ortea2000) (Table 2).
A comparison of the reproductive system of T. huarmeyana sp. nov. shows that the hermaphroditic duct or preampullary duct in these animals enter the ampulla close to its midline, whereas in T. velox, T. goddardi and T. inbiotica it enters on its proximal end. Although in T. goslineri and T. darwini the preampullary duct enters the ampulla slightly more distally, it is even more distally positioned in T. huarmeyana sp. nov. The seminal receptacle in T. huarmeyana sp. nov., T. velox, T. goddardi and T. inbiotica enters into the base of the bursa copulatrix, but in T. goslineri and T. darwini it enters below the bursa (Gosliner and Fahey, Reference Gosliner and Fahey2008). The deferent duct is long and narrow, widening into the thick penial sac in T. huarmeyana sp. nov., but this duct (also called ejaculatory duct) is wide in T. goddardi, T. darwini and T. inbiotica. In T. goslineri, the prostate narrows into a short deferent duct before widening again into a short penial sac (Millen and Bertsch, Reference Millen and Bertsch2000), but in T. huarmeyana sp. nov. the deferent duct and penial sac are longer. The penial sac is also elongated in T. velox (MacFarland, Reference MacFarland1966), but the deferent duct is much shorter than in T. huarmeyana sp. nov. (Table 2).
Discussion
A combination of morphological and molecular tools represents a significant advance in accelerating the biodiversity knowledge of some groups such as heterobranch sea slugs or which taxonomic data are lacking (Padula et al., Reference Padula, Bahia, Stöger, Camacho-García, Malaquias, Cervera and SchrödL2016; Valdés et al., Reference Valdés, Breslau, Padula, Schrödl, Camacho, Malaquias, Alexander, Bottomley, Vital, Hooker and Gosliner2018; Smirnoff et al., Reference Smirnoff, Donohoo and Gosliner2022; Paz-Sedano et al., Reference Paz-Sedano, Cobb, Gosliner and Pola2024b). This approach has been fundamental to increasing the species number in many taxa around the world, including the nudibranch family Goniodorididae from the tropical Indo-Pacific and Atlantic Oceans, with notable discoveries among the genera Trapania, Bermudella, Ceratodoris, Murphydoris and Naisdoris (Paz-Sedano et al., Reference Paz-Sedano, Cobb, Gosliner and Pola2024b). Here, we studied the external and internal morphology, along with DNA sequences, to describe a new species of Trapania from the Humboldt province (South-eastern Pacific), a region that is unusually cool despite its close affinity to the equator (Gutiérrez et al., Reference Gutiérrez, Akester and Naranjo2016; Ibanez-Erquiaga et al., Reference Ibanez-Erquiaga, Pacheco, Rivadeneira and Tejada2018). During strong El Niño events, many species (e.g. molluscs) extend their distributional range towards high latitudes due to the intrusion of larvae and adults (Goddard et al., Reference Goddard, Goddard and Goddard2020). However, when normal conditions are re-established, many may become trapped within coastal ecosystems. Although the genus Trapania has been mostly recorded in warm waters around the world, previous studies reported that it thrives in cold water regions with similar climate variability (Cetra and Roche, Reference Cetra and Roche2019; Paz-Sedano et al., Reference Paz-Sedano, Álvarez, Gosliner and Pola2022).
Stressors such as marine heatwaves along of the Eastern Pacific Ocean, produced by warm events, are directly related to habitat loss (e.g. kelp forests) and subsequent alteration of species richness. Many species may survive at specific locations such as caves, bays and kelp forests, that provide refuge during strong warming events (Uribe and Pacheco, Reference Uribe and Pacheco2012; Araya and Valdés, Reference Araya and Valdés2016). Recently, high temperatures recorded during the El Niño 2023/24 event have increased the migration of species of tropical origin to the temperate Humboldt province (authors observation), affecting the diversity of some taxonomic groups that inhabit coastal ecosystem, such as the little-known molluscs nudibranchs. Trapania huarmeyana sp. nov. may represent a recent migrant or may have been in the region for a long time but simply not been detected due to a lack of research effort, as suggested by Uribe and Pacheco (Reference Uribe and Pacheco2012) for other Nudibranchia records in this geographical area.
Our phylogenetic analyses indicate T. huarmeyana sp. nov. and T. goddardi are sister species, i.e. they have a common ancestor. The sequences from Galapagos, identified as T. goddardi by Smirnoff et al. (Reference Smirnoff, Donohoo and Gosliner2022) likely correspond to T. darwini (Gosliner and Fahey, Reference Gosliner and Fahey2008), since T. goddardi was originally recorded in Mexico (Hermosillo and Valdés, Reference Hermosillo and Valdés2004). Regardless of the above, the East Pacific species for which genetic sequences were available in this study (= T. huarmeyana n. sp, T. goddardi and T. velox) were grouped with species recorded in Europe, suggesting greater genetic closeness than with the Indo-Pacific species. The biogeographical zone of the Tropical Eastern Pacific extends from the Sea of Cortez (south of ~29° N) to the northern Pacific coast of Peru (about 5° S) and was isolated from the Caribbean about 3.1 myr with the closure of the Isthmus of Panama (Coates and Obando, Reference Coates, Obando, Jackson, Budd and Coates1996). The latitudinal limits of the region are set by western extensions of the continental coastline, where cool currents that flow towards the equator turn offshore towards the central Pacific (Robertson et al., Reference Robertson, Grove and McCosker2004). It is also isolated from the central and western Pacific by the world's widest deepwater marine barrier to the dispersal of marine shore organisms, the 4000–7000 km Eastern Pacific Barrier (EPB) (Ekman, Reference Ekman1953) which may have existed for the past 65 myr (Grigg and Hey, Reference Grigg and Hey1992). Consequently, the rise of the Panama isthmus is a more recent barrier to gene flow between the eastern Pacific and Atlantic Oceans. A scenario similar has been documented for the genus Phyllidiopsis (Phyllidiidae) and Hypselodoris (Chromodorididae), where several cases of vicariance between the tropical Indo-Pacific region and the Atlantic-eastern Pacific area followed by vicariance between the eastern Pacific and the Atlantic have been proposed (Valdés, Reference Valdés2001; Alejandrino and Valdés, Reference Alejandrino and Valdés2006). To test such biogeographic hypotheses in Trapania spp will require more sequencing of species from the eastern Pacific.
This record of T. huarmeyana sp. nov. adds support to the predictions of Uribe et al. (Reference Uribe, Nakamura, Indacochea, Pacheco, Hooker and Schrödl2013) of undiscovered species heterobranch sea slug species on this region. Although recent investigation efforts have been made in the last decade in the Humboldt province (South-eastern Pacific) (Uribe et al., Reference Uribe, Nakamura, Indacochea, Pacheco, Hooker and Schrödl2013, Reference Uribe, Sepúlveda, Goddard and Valdés2018; Schrödl and Hooker, Reference Schrödl and Hooker2014; Araya and Valdés, Reference Araya and Valdés2016; Hoover et al., Reference Hoover, Padula, Schrödl, Hooker and Valdés2017; Mendivil and Cardoso, Reference Mendivil and Cardoso2022a, Reference Mendivil and Cardoso2022b), this finding indicates that further research is necessary to better understand the distribution and variation of this group in specific localities such as the poorly explored kelp forest ecosystems.
Supplementary Material
The supplementary material for this article can be found at https://doi.org/10.1017/S0025315424001188.
Data
All data are available on request.
Acknowledgements
This research is part of the project ‘Diversidad Biológica de la región Áncash’ run by the Laboratorio Costero de Chimbote IMARPE. The genetic work was funded by the Plan de Fortalecimiento Universidades Estatales – Chile RED21992. We thank Niall McKeown for English editing on the manuscript.
Author contributions
R. A. U., A. M. and F. S. work in the conceptualization. R. P., R. A. U., D. A.-S., S. A. and L. F. collected samples. A. M. conducted the anatomical analysis. F. S. performed the molecular analysis. R. A. U., A. M. and F. S. wrote and revised the original draft. All authors read, revised and approved the final manuscript.
Competing interest
None.
Ethical standards
Not applicable.
Consent for publication
Not applicable.
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