﻿Peruvian nudibranchs (Mollusca, Gastropoda, Heterobranchia): an updated literature review-based list of species

﻿Abstract Nudibranchs, as a group, have received limited attention in terms of scientific study along the coastline of Peru. Here, an updated and comprehensive list of nudibranch species found in the Peruvian sea is presented, compiled through an extensive review of relevant literature. This compilation encompasses a total of 31 species, classified into two suborders, 10 superfamilies, 20 families, and 28 genera. With respect to the biogeographic provinces along the Peruvian coast, 23 species inhabit the Warm Temperate Southeastern Pacific province, 18 species occur in the Tropical Eastern Pacific province, and 10 species are found in both provinces, crossing the transitional zone between them. In terms of distribution patterns, two species exhibit a cosmopolitan distribution (Glaucusatlanticus and Fionapinnata), while two species display a circumtropical distribution (Cephalopygetrematoides and Phylliroebucephala). One species exhibits a bipolar distribution in the Eastern Pacific and possesses an amphi-South American distribution (Rostangapulchra). Additionally, six species exhibit an amphi-South American distribution (Rostangapulchra, Diaululapunctuolata, Dotouva, Tyrinnaevelinae, Tyrinnadelicata, and Dorisfontainii), and two species are endemic to Peru (Corambemancorensis and Felimaresechurana). This study provides comprehensive information on biogeographical aspects, geographical distributions, and taxonomic updates within the nudibranch species documented in Peru. Furthermore, we discuss the status of species listed in previous literature that have not been confirmed by collections, referring to them as potentially occurring species.


Introduction
Nudibranchia Cuvier, 1817 (Subclass Heterobranchia, Infraclass Euthyneura, Superorder Nudipleura) represents an order of exclusively marine gastropod mollusks, distinguished by the absence of shells in the adult stage (Behrens et al. 2005;Wägele and Klussmann-Kolb 2005).These remarkable organisms exhibit striking aposematic body colorations, making them frequent targets of underwater photography.Approximately 3000 species of nudibranchs have been described worldwide inhabiting both cold and tropical regions (Shields 2009;Almada et al. 2016), primarily in shallow waters ranging from 0 to 30 m in depth (Wägele and Klussmann-Kolb 2005).However, novel species discov-eries have expanded our knowledge of nudibranchs in deeper habitats (Valdés 2001a(Valdés , 2001b;;Gosliner et al. 2008).The ecological importance of nudibranchs stems from their role in controlling populations of cnidarians and poriferans, from which they acquire and incorporate toxins for their own defense (Greenwood 2009;Faulkner and Ghiselin 1983).Furthermore, recent research has elucidated symbiotic associations between nudibranchs and bacteria, wherein the bacteria provide essential nutrients to the hosts (Zhukova et al. 2022).Certain species have been found to synthesize secondary metabolites with high biotechnological potential (Pereira et al. 2012;Dean and Prinsep 2017).Additionally, nudibranch species possess the potential to serve as environmental indicators, as they are sensitive to ocean stressors such as coastal pollution (Caballer et al. 2008).
The most recent inventory of aquatic mollusks in Peru, as documented by Ramírez et al. (2003), recorded a total of 1018 marine species, primarily comprising gastropods and bivalves, with only a limited number of nudibranch species reported.In fact, the Peruvian sea is recognized as one of the impoverished regions worldwide in terms of nudibranch diversity (Schrödl 1997(Schrödl , 2002(Schrödl , 2003;;Schrödl and Hooker 2014).In comparison, other regions such as the Caribbean Sea, the Tropical Eastern Pacific, the Indian Ocean, the Mediterranean Sea (Sachidhanandam et al. 2000;Valdés et al. 2006;Chavanich et al. 2013;Ah Shee Tee et al. 2019;Furfaro et al. 2020;Londoño-Cruz 2021), as well as other South American countries including Brazil, Chile, and Venezuela (Fischer and Cervera 2005b;Ardila et al. 2007;Aldea et al. 2011;Padula et al. 2011;Alvim and Pimenta 2013;Gutiérrez et al. 2015;Araya and Valdés 2016; Londoño-Cruz 2021) exhibit considerably higher richness of nudibranch species.
The earliest records of nudibranchs in Peru can be attributed to d 'Orbigny (1835'Orbigny ( -1846) ) and later to Dall (1909).Following a significant period without the discovery of new species, Millen et al. (1994) reported the presence of Okenia luna in Peruvian and Chilean waters.Subsequently, the first list of Peruvian aquatic mollusks was published, which included some nudibranch species (Álamo and Valdivieso 1997), and two years later, another list was published (Paredes et al. 1999), in which Sandra Millen was acknowledged for the preliminary list of species belonging to the infraclass Opisthobranchia (a taxonomic category that has since been abandoned and deprecated; see Jörger et al. 2010;Schrödl et al. 2011;Wägele et al. 2014).In 2003, an updated inventory of Peruvian aquatic mollusks was published (Ramírez et al. 2003), which included the nudibranch species reported up to that time.Several years later, four new species were reported on the northern coast of Peru, Felimida baumanni, Doriopsilla janaina, Kynaria cynara, and Cuthona sp.(Nakamura 2006), with the species Corambe mancorensis identified as endemic (Martynov et al. 2011), and the species Spurilla neapolitana (later corrected as Spurilla braziliana) (Uribe and Pacheco 2012).Subsequently, four additional nudibranch species were documented for the Peruvian coast (Uribe et al. 2013), and another study focused on the species shared with Chile (Schrödl and Hooker 2014).Felimare sechurana was identified as an endemic species in the transition zone of the northern coast (Hoover et al. 2017) and, additionally, two new species of planktonic nudibranchs were described (Quesquen 2017).ZooKeys 1176: 117-163 (2023), DOI: 10.3897/zookeys.1176.103167 Alessandra Grández et al.: Nudibranchs of Peru We must emphasize that certain species have been listed in previous publications as occurring in Peru without sufficient evidence, such as assumptions of geographic continuity (e.g., Cadlina sparsa; Álamo and Valdivieso 1997), reliance on personal communications only (e.g., Polycera cf.alabe; Paredes et al. 1999;Uribe et al. 2013), and misinterpretations (e.g., Gargamella immaculata and Thecacera darwini; Nakamura 2006), which has created problems as these listings have persisted in the literature.To distinguish them from the confirmed species, the term "potentially occurring" is used hereafter.However, such statuses can be revised in the future, as exemplified by the species Rostanga pulchra, which was initially predicted for Peruvian waters for many years until its confirmation (Schrödl and Hooker 2014).
El Niño-Southern Oscillation (ENSO) warm events have been observed to induce southward displacement of tropical species (Velez and Zeballos 1985;Paredes et al. 1998) while cold events tend to enhance the intensity of the Humboldt Current, resulting in the northward transport of larvae.Specifically, the northward transport of larvae by the Humboldt Current or the southward transport facilitated by warm ENSO events may introduce Magellanic or tropical species, respectively, into Peruvian waters, thereby influencing distribution ranges.In addition, the susceptibility of nudibranchs to temperature fluctuations, particularly during their larval stages (Leatherman 2019) due to the aragonite-based internal structure found in several species (Ehrlich 2010), their small body size, limited populations (Nybakken 1978), and the sensitivity of the Humboldt Current Ecosystem to oceanic stressors (Echevin et al. 2012) such as warming and acidification (Barnosky et al. 2011;Ceballos et al. 2015;Pievani 2014), collectively suggest that the diversity and distribution of nudibranchs could be impacted (Nimbs and Smith 2018).
The available information on Peruvian nudibranchs remains limited primarily due to a lack of research effort (Uribe and Pacheco 2012).Explorations specifically targeting nudibranchs have been extremely scarce, and most sightings and reports are sporadic (Nakamura 2006;Schrödl and Hooker 2014;Uribe et al. 2013).Given that the species richness of nudibranchs is likely underestimated in Peru (Hooker pers.comm.), this taxonomic order warrants further attention.Our aim was to update and revise the list of nudibranchs in the Peruvian sea, based on a comprehensive review of the scientific literature.

Materials and methods
A comprehensive review was conducted to compile all available literature pertaining to the order Nudibranchia in Peru.The literature search encompassed diverse sources of information, including peer-reviewed journal articles, books, book chapters, "grey literature" (such as scientific reports and theses), and the Sea Slug Forum (http://www.seaslugforum.net/).Key terms such as 'Opisthobranchia,' 'Heterobranchia,' 'Nudibranch,' 'Nudibranchia,' 'sea slug,' 'phylogeny,' 'checklist,' 'Peru,' 'Humboldt,' and 'taxonomy' were employed.Pertinent data, such as type material, geographic distribution, sampling/reporting sites, bathymetric distribution, and biogeographical provinces, were meticulously included.The most up-to-date scientific names were validated through the World Register of Marine Species (WoRMS, https://www.marinespecies.org/),and reports (occurrences) were cross-referenced using the Global Biodiversity Information Facility (GBIF, https://www.gbif.org/)and the iNaturalist database (https://www.inaturalist.org/).Any modifications, revalidations, or refutations pertaining to taxonomy are concisely presented as "Remarks", accompanied by justifications as needed.Endemic species of Peru are also duly indicated.The distribution map was made using QGIS 3.22.8software (QGIS Development Team 2022), while VENNY 2.1 online software (Oliveros 2016) was employed to visualize the number of species shared with some neighboring countries.Potentially occurring species were clearly distinguished from the confirmed ones.
The acronyms corresponding to the collections where the type material for certain species is deposited have been included, as follows:

Overview
A total of 31 species, encompassing two suborders, ten superfamilies, 20 families, and 28 genera (Table 1), has been confirmed within Peruvian waters.The suborder Cladobranchia comprises 16 species, spanning five superfamilies and 13 families.The suborder Doridina consists of 15 species, distributed among five superfamilies and seven families (Table 1).Notably, the families Chromodorididae and Discodorididae, both belonging to the suborder Doridina, exhibit remarkable species richness with five and four species, respectively (Fig. 1).Additionally, potentially occurring species (n = 9) are distributed across five superfamilies, eight families, and nine genera (Table 2).A chronological overview of articles documenting nudibranch species in the Peruvian sea can be found in Table 3, revealing the progressive increase in reported species and the latest updates in scientific nomenclature.Regarding the distribution of species along the Peruvian coast, according to the coastal marine biogeographical classification proposed by Spalding et al. (2007), 23 species inhabit within the Warm Temperate Southeastern Pacific province, 18 species are found within the Tropical Eastern Pacific province, and ten species are common to both provinces (Table 4, Fig. 2).Peru's inventory of nudibranch species is comparatively modest in comparison to other South American countries, such as Chile, Colombia, and Brazil (Fig. 3A).Concerning species shared with these countries, of the 31 species that have been conclusively documented in Peruvian waters, 19 species are found  in Chilean waters, four species in Colombian waters, and four species in Brazilian waters (Fig. 3B).The recorded collection/reporting sites of nudibranch species found in Peruvian waters, limited to South America, within the framework of the coastal-marine biogeographical classification proposed by Spalding et al. (2007), are illustrated in Fig. 4.

Spurilla braziliana
Distribution.This species exhibits a distribution range spanning the western Atlantic, extending from Florida to Brazil (Behrens and Hermosillo 2005;Marcus 1959), as well as the Pacific Ocean.
Remarks.Carmona et al. (2013), based on mitochondrial and nuclear sequences, revealed that Spurilla neapolitana MacFarland, 1909 comprises a complex of five cryptic species.In the light of this discovery, the name Spurilla braziliana has been assigned to populations found in the western Atlantic and Pacific regions.Carmona et al. (2013) further speculated that the occurrence of this species in the Pacific Ocean might be attributed to human-mediated introductions.
Remarks.Included in Paredes et al. (1999), probably based on a personal communication with Sandra Millen.The records of Glaucus distichoicus d' Or-bigny, 1837(d'Orbigny 1854;Dall 1909;Paredes et al. 1999;Ramírez et al. 2003) do not have enough evidence to formalize the species within the genus Glaucus and could refer to G. atlanticus.(Dall 1909;Baez et al. 2011).
Remarks.Molecular studies are needed to clarify the genetic identities of the populations on both sides of South America (Schrödl 2003;Uribe et al. 2013).
Remarks.Originally described as Phylliroe trematoides Chun, 1889.The samples described in Quesquen (2017) were reported in grey literature (Quesquen 2008) and had been previously reported by Quesquen and Guzmán (1999).Sampling/reporting sites.In Peru, it was reported in Tumbes and Piura (Quesquen 2017).It was also reported in the Canary Islands (Hernández and Jiménez 1996), off the coasts of Florida and Bermuda (Abbott 1974), in northeastern Atlantic waters near the African coast (van der Spoel 1970), and in the western Atlantic Ocean (Spencer et al. 2009).In the Mediterranean Sea there are reports from France and Syria (Durgham et al. 2016;Durgham and Ikhtiyar 2020;Pruvot-Fol 1954).Recorded south of the Pacific Ocean in Australia and New Zealand (Powell 1979;Spencer and Willan 1995).In the Indo-Pacific it has been reported from Vietnam (Sachidhanandam et al. 2000).
Remarks.Description provides a length of 5 mm, body completely white, including rhinophores and oral tentacles with a translucent base.In addition, the specimen had dark, reddish-brown cerata without the white tip, which would differentiate it from other species of the genus (Nakamura 2006).
Remarks.This species was originally identified as Tyrinna nobilis Bergh, 1898, a name that is currently not accepted.
Remarks.It was initially listed by Paredes et al. (1999).According to Uribe et al. (2013) molecular studies are necessary to confirm the consistency of reports of T. evelinae in both the Atlantic and Pacific populations that are morphologically difficult to distinguish (Valdés et al. 2006).
Remarks.The species was originally reported as Chromodoris baumanni Bertsch, 1970 in the Eastern Pacific (Rudman 1983).Years later, Gosliner et al. (2004) discussed the anatomical characteristics of this species to be like those attributed to the genus Glossodoris, suggesting a reclassification.Finally, the phylogenetic study by Johnson and Gosliner (2012) defined its new classification as part of the genus Felimida.Distribution.From San Lorenzo Island (Callao, Peru, 12°S) (d 'Orbigny 1835'Orbigny -1846) ) to Los Molles (Valparaíso, 32°15'S) (Fischer and Cervera 2005).
Remarks.This species was listed as Anisodoris punctuolata (d' Orbigny, 1836) and Doris punctuolata d'Orbigny, 1837 in previous Peruvian articles listing nudibranch species.Both names are currently not accepted.Distribution.This species presents a bipolar distribution in the Eastern Pacific and an amphi-South American distribution (Schrödl 2003;Schrödl and Grau 2006).
Remarks.Its distribution in Peruvian Waters was not certain; however, it was listed by Álamo and Valdivieso (1997) and Paredes et al. (1999).Rostanga pulchra is the only species of the genus in Peruvian and Chilean waters.Schrödl and Hooker (2014) mentioned that populations in the northern and southern hemispheres are likely to be distinct species based on preliminary unpublished molecular data.
Remarks.This species was listed by Nakamura (2006) based on Schrödl (1999b), who listed this species as present in the Peruvian province, referring to Chilean waters.Fischer and Cervera (2005b) argued against its occurrence off the Chilean coast, although they acknowledge a high likelihood of its presence in Peruvian waters.Uribe et al. (2013) and Fischer (2006) referred to Zagal and Hermosilla's (2001) presumed finding of this species in Peru.
Type material.Not available.

Distribution. Ica (Peru).
Sampling/reporting sites.In Peru, Quesquen (2017) reported specimens twice off the coast of Ica in 1995 and 1998.Currently, the only valid species of the genus Glaucus is G. atlanticus, reported in Peru by Uribe et al. (2013) from Isla Santa, Ancash.
Remarks.Quesquen (2017) offered a description of the specimens collected in Ica.He described a slender body that was ventrally flattened, with a small head and two cephalic tentacles.The dorsum was navy blue and green, and the ventral area was white.Additionally, the specimens had three or four branches on both sides of the body, and their body length could reach up to 43 mm.According to Valdés and Campillo's (2004) description, G. atlanticus is characterized by its slim and elongated body, along with a small head and sleek oral tentacles and rhinophores.The coloration of its dorsum can vary from deep blue to brown hues.It possesses up to three groups of cerata, and its ventral region exhibits a silver shade.
A confirmation of the taxonomic status of these specimens is necessary, using morphological and molecular analyses.
Type material.ZSM 20020700 (Chile), designated as the neotype due to absence of the holotype (Kienberger et al. 2016).
Remarks.It was reported off the coast of Chile by Schrödl (2003) as Aeolidia papillosa (Linnaeus, 1761), later reassigned to the species A. campbellii according to molecular studies by Kienberger et al. (2016).
Remarks.According to Schrödl (2003), the Peruvian records of this species by Zagal and Hermosilla (2001) are doubtful.However, in that compilation and in the most up-to-date publication (Zagal and Hermosilla 2007), Gargamella immaculata is not mentioned from Peruvian waters, but as an inhabitant of the Peruvian zoogeographic province from Juan López (Atacama) to the south.The species was mistakenly included in Kentrodorididae by Schrödl (1996a), until Valdés (2002) transferred it back to the Discodorididae.(Odhner, 1922) Common name: Dark-spot Cadlina Habitat.Benthic.
Distribution.It presents disjunct populations with a bipolar distribution in the eastern Pacific and an amphi-South American pattern.
Sampling/reporting sites.In the Pacific, the northernmost location is Baja California (Behrens 1991;Jaeckle 1983) and the southernmost location is the Comau Fjord in southern Chile.In the Atlantic, it was recorded in Camarones Bay in the central region of Argentina (Schrödl 2000(Schrödl , 2003)).In Chile, it has also been sampled in the Juan Fernández Islands (Odhner 1922), Chiloé Islands (Marcus 1959), and Coliumo Bay (Schrödl 1996a(Schrödl , 2003)).
Remarks.Cadlina sparsa was initially proposed as probable species in Peruvian water by Álamo and Valdivieso (1997).Subsequently, its presence was consistently mentioned in the lists compiled by Paredes et al. (1999), Ramírez et al. (2003), and Nakamura (2006).However, no actual specimens have been collected from intermediate Pacific locations, including Peru.Despite the absence of direct observations, a hypothetical distribution for Peru has been predicted through extrapolation, assuming a continuous geographic range (Uribe et al. 2013).Distribution.From Brazil to Gulf of California (Mexico) (Gosliner and Kuzirian 1990;Fischer et al. 2007).
Remarks.Originally named Flabellina marcusorum Gosliner & Kuzirian, 1990.Its presence in Peru needs be confirmed by future surveys.

Overview
This article presents an updated compilation of nudibranchs found in Peru, derived from an extensive literature review.The revised and updated scientific names are presented, while species not verified or erroneously listed in previous articles, referred to here as 'potentially occurring', are separated from those confirmed.
It is worth noting that there are areas along the Peruvian coast that remain unexplored.In the Tropical Eastern Pacific, only a limited number of locations have been sampled, including Pocitas, Punta Sal, Mancora, and Cancas.Within the transition zone, Sechura Bay and Foca Island are the common reporting sites, while within the Warm Temperate Southeastern Pacific, Santa, Casma, Huarmey (Ancash), Ancon, Callao, San Lorenzo Island, Pucusana (Lima), Pisco, Independencia Bay, San Juan de Marcona (Ica), Matarani, and Isla Blanca (Arequipa) are frequently mentioned.Factors such as limited exploration efforts, challenging diving conditions, a scarcity of nudibranch taxonomists, and a general lack of interest in this group in Peru should be highlighted.In addition, it is highly likely that several species remain unreported and undescribed, particularly in deeper waters.Therefore, the confirmed number of nudibranch species in Peruvian waters (n = 31) is presumed to represent only a fraction of the actual diversity present.

Potential influence of the Humboldt Current and El Niño
Several confirmed species exhibit a biogeographical affinity for the Warm Temperate Southeastern Pacific (n = 23) (Fig. 2).The Humboldt Current plays a significant role as an oceanographic factor, facilitating the influx of various species from the Chilean sea into Peruvian waters, with 19 of them occurring in both.For instance, Phidiana lottini, found in Callao and Puerto Malabrigo, may extend into tropical waters due to the influence of the Humboldt Current (Uribe et al. 2013).The occurrence of Polycera priva in Peru came as a surprise to researchers, considering that this species is typically Magellanic and endemic to the Patagonian fjords (Schrödl 1996a(Schrödl , 1999b(Schrödl , 2003(Schrödl , 2009)).Therefore, its presence in Peru is attributed to the influence of the Humboldt Current (Schrödl 1996a(Schrödl , 1999b(Schrödl , 2003(Schrödl , 2009;;Schrödl and Hooker 2014).Species such as Corambe lucea, Coryphellina cerverai, Janolus rebeccae, and Tritonia sp., collected in the Warm Temperate Southeastern Pacific province, have also been reported in Sechura Bay and Foca Island, situated in the biogeographical transition zone.This suggests their adaptation to slightly warmer waters (Fig. 4).
El Niño events can induce shifts in the distribution ranges of sea slugs (Goddard et al. 2018) and even result in species turnover (Valqui et al. 2021).During strong El Niño events, it is noteworthy that mollusk species endemic to tropical areas have been observed in Peruvian waters due to the displacement of warm-water masses (Velez and Zeballos 1985;Paredes et al. 1998;Ramírez et al. 2003).Species such as Armina californica, Felimida baumanni, Felimare agassizii, Tyrinna evelinae, and Bajaeolis bertschi, which are abundant in the Tropical Eastern Pacific province, Warm Temperate Northeast Pacific, or Cold Temperate Northeast Pacific, have only been recorded in Tumbes or Piura (the northernmost coastal areas of Peru) (Table 4).This suggests that their presence may be temporary, resulting from the displacement of warm-water masses, or they may have permanently adapted to similar conditions following multiple El Niño events (Ashton et al. 2008).
The distribution patterns of cosmopolitan and circumglobal species can be attributed to various biological factors, including their remarkable dispersal capabilities.Take, for instance, Glaucus atlanticus, which possesses intriguing adaptations for dispersal such as larval gas bubbles and specialized anatomy enabling it to exploit water surface tension (Thompson and McFarlane 1967;Valdés and Campillo 2004;Churchill et al. 2014a).Additionally, abiotic factors like ocean currents (Miller 1993) and indirect human influences such as buoy rafting (Astudillo et al. 2009), ballast water, or shipping activities can facilitate the dispersal of these species, expanding their geographic ranges (Borg et al. 2009).

Potentially occurring species
This group of species poses a challenge as they have been consistently listed and referenced in several previous articles (indicated by asterisks in Table 3) despite lack of substantiated records.One notable example is Cadlina sparsa.Initially mentioned as a probable species by Alamo and Valdivieso (1997), it persisted in the subsequent publications of Paredes et al. (1999), Ramírez et al. (2003), andNakamura (2006) without acknowledging its speculative status.In the work of Uribe et al. (2013), the authors discussed the predicted occurrence of Cadlina sparsa in Peruvian waters based on extrapolation, assuming a continuous distribution, due to its presence in Baja California and Chile.Paredes et al. (1999), based on personal communication with Sandra Millen, included Aeolidia campbellii (referred to as Aeolidia serotina) and Itaxia falklandica (referred to as Flabellina falklandica), which persisted in the subsequent lists of Nakamura (2006) and Ramírez et al. (2003), respectively.However, no additional published reports have surfaced to substantiate their presence.Ramírez et al. (2003) also included the species Phylliroe lichtensteinii without providing any justification for its inclusion.On the other hand, Nakamura (2006) mistakenly listed Gargamella immaculata and Thecacera darwini as present in Peruvian waters, referencing Schrödl (1999b).Nevertheless, Schrödl (1999b) only listed these species in a table as occurring in the 'zoogeographic Peruvian province', indicating their presence in the Chilean waters corresponding to this biogeographical province, but not in Peruvian waters.
A solitary specimen of Coryphellina marcusorum was recently documented through photography on the northern coast of Peru (Los Organos, Piura) (Torrejón 2023).Given the species' tropical distribution and a previous record near countries such as Ecuador (GBIF 2022), its occurrence in Peru is plausible.However, these two records do not provide evidence of an established population in this region, suggesting the possibility that it may have arrived independently through shipping or been displaced by ocean currents.Further collections and taxonomic verifications are necessary to confirm its presence definitively.
Potentially occurring species should not be included in the official list of Peruvian nudibranch species.However, considering their disjointed or patchy geographic distributions or unique observations, they may be reported in Peruvian waters in forthcoming papers.Rostanga pulchra, for instance, was a long-standing predicted species for Peruvian waters until its initial sighting in San Juan de Marcona (Ica) by Schrödl and Hooker (2014).As a cosmopolitan species, the presence of Phylliroe lichtensteinii in Peru is plausible.Fischer and Cervera (2005b) have deemed the presence of Thecacera darwini in Peruvian waters highly probable.The term "potentially occurring" signifies a provisional status, indicating that these species have not yet been officially confirmed.

Identification uncertainties
The genus Polycera displays remarkable color variability, seemingly correlated with its geographic range (Behrens and Hermosillo 2005).A genetic investigation identified clades with overlapping distributions in the Northeastern Pacific, strongly suggesting the existence of a species complex (Santander and Valdés 2013).One year later, a morphology-based study by Pola et al. (2014) revealed that specimens previously collected by Camacho-García et al. (2005) in Costa Rica, Panama, and Mexico actually belong to a new species, Polycera anae.Considering that P. alabe was solely "observed" by Millen in Tumbes, it is possible that it represents another Polycera species, such as P. anae, given its inclusion in a species complex (Santander and Valdés 2013).
The report of Glaucus sp., documented by Quesquen (2017), is based on a single poorly preserved specimen sampled in 1995, warranting verification through molecular methods.Currently, within the genus Glaucus, only the species G. atlanticus has been confirmed, as many previous records turned out to be synonyms (e.g., G. distichoicus) or were later reassigned to the genus Glaucilla.Similar circumstances apply to the reports of Tritonia sp. and Cuthona sp., as their species-level recognition is still pending.

Concluding remarks
This research contributes to the dissemination and diffusion of this understudied group of organisms in Peru.It is imperative to intensify monitoring efforts to verify the presence of doubtful species, evaluate anthropogenic impacts, and El Niño-driven displacements.Furthermore, considering the intricate nature of external morphological identification, frequent variability in coloration, and the probable existence of cryptic species, it is possible that a considerable number of species remain undiscovered.Consequently, there is an urgent need for comprehensive research involving detailed internal anatomy and the application of molecular tools, such as DNA barcoding and phylogenetic analyses.These methodologies will play a vital role in shedding light on the taxonomy and evolutionary relationships within this group.

Figure 1 .Figure 2 .Figure 3 .
Figure 1.Number of species by family and suborder of Nudibranchia in Peruvian waters.

Figure 4 .
Figure 4. Reporting sites for nudibranch species found in Peruvian waters whose geographic ranges are limited to South America.The gray band highlights the locations where these species have been reported along the Peruvian coastline.The coastal marine biogeographic classification introduced by Spalding et al. (2007) is presented to provide context.

Table 1 .
Nudibranch species confirmed for Peruvian waters according to the bibliographic compilation of this study.

Table 2 .
Nudibranch species that could potentially occur in Peruvian waters based on the bibliographic compilation of this study.

Table 4 .
Presence of nudibranch species inhabiting Peruvian waters along several marine coastal biogeographic provinces according the reporting sites.Legend: the asterisk (*) indicates potentially occurring species in Peruvian waters.