Echinoderms (Echinodermata) from the Central Mexican Pacific

Introduction: The echinoderms from the Central Mexican Pacific are of high scientific interest and, prior to this present work, there was a lack of basic information that included incomplete checklists with inconsistencies in systematics and spatial distribution. Objective: To provide a historical review, and an updated checklist with a more complete richness of echinoderms for each state and island of the region. Methods: A checklist was elaborated based on an exhaustive literature search of the Echinodermata, and was complemented with taxonomical revisions of Ophiuroidea scientific collections. All the geographical coordinates of the records were validated. Results: The region harbors 187 species of Echinodermata: three Crinoidea, 35 Asteroidea, 67 Ophiuroidea, 32 Echinoidea, and 50 Holothuroidea. We detected 52 records in the literature that must be considered as invalid and five as doubtful. We provide 16 new records of Ophiuroidea from different states and islands; of them, four are new records for the region. Jalisco presented the highest number of species (84), followed by the coast of Nayarit (74), Michoacán (63), and Colima (55); among the islands, Revillagigedo showed the major number of species (85) followed by Marías (81), Marietas (48), and Isabel (44). Conclusions: The numbers of species known in the region are mostly related to both sampling effort and environmental characteristics that promote high biodiversity. The Central Mexican Pacific is an oceanographic region with mixed conditions from the North and South of the Mexican Pacific, and therefore, with a biogeographical importance reflected in its species richness.

The Central Mexican Pacific (CMP) region comprises the states of Nayarit, Jalisco, Colima and Michoacán as well as their coastal (Isabel and Marietas) and oceanic islands (Marías and Revillagigedo). The region is characterized by numerous geographic features such as bays, archipelagos and islands, as well as a heterogenic bottom that combines hard and soft components. The CMP is located in the Tropical Eastern Pacific Province nearby to the Warm Temperate Northeast Pacific Province (Spalding et al., 2007) and for this reason, it shelters northern and southern fauna of the Mexican Pacific (Arriaga-Cabrera et al., 1998). Due to its relevant flora and fauna, most of the islands of the CMP are catalogued as Natural Protected Areas (CONANP, 2005;CONANP, 2007a;CONANP, 2007b;CONANP, 2019).
Despite the above, the records have shown many inconsistencies such as: 1) the names of some species have been mentioned (written or registered) incorrectly across time (e.g. misspelling), 2) many of the recorded species for the CMP are invalid, and 3) the generated checklists are not complete because they are based only in museum records or material collected mostly in shallow-waters. Thus, the aim of the present manuscript is to provide an accurate and updated checklist of the valid names and synonyms of the Echinodermata from the CMP according to literature, including new distribution records of Ophiuroidea. Moreover, we provide a historical review of the study of each class of Echinodermata, as well as an updated number of species for each state and island in the region.

MATERIALS AND METHODS
An exhaustive search of published literature for the CMP regarding the classes Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea was performed (records dating from 1840 to 2019). Moreover, we visited reference collections in order to taxonomically identify specimens of Ophiuroidea: ICML-UNAM: Colección de Equinodermos "Dra. Ma. Elena Caso", Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad de México, México; LACM: Natural History Museum, Los Angeles County Museum, Los Angeles, United States of America (USA); and, MCZ: Museum of Comparative Zoology, Harvard University, Cambridge, USA.
When available, the geographical coordinates of the provided localities in the literature were validated using ArcMap 10.4.1 software, to corroborate distribution within the CMP maritime zone. Records were assigned to any of the following areas: coastlines of the states of Colima (COL), Jalisco (JAL), Michoacán (MICH), and Nayarit (NAY), and the islands Isabel (ISA), Marías (MAR), Marietas (MAT), and Revillagigedo (REV).
With this information, a checklist of the valid names and synonyms of Echinodermata from the CMP was constructed. The list includes those synonyms used exclusively in this area, yet some species may have larger synonym lists for other geographic areas. Systematics arrangements and valid names agree with Kroh and Mooi (2020), Mah (2020), Messing (2020), Stöhr, O´Hara, and Thuy (2020), and WoRMS (2020).

Historical review
Crinoidea: Six references documented the Crinoidea from the CMP; one during the 19 th , one in the 20 th , and four in the 21 st century. Among the Echinodermata, Crinoidea represents the less studied class of the CMP. The study of the Crinoidea from the CMP began in 1895 when Hartlaub (1895) recorded the species Florometra tanneri (as Antedon rhomboidea) for MAR at 1 236 m depth. Several years later, using a submersible, Roux (2004) collected one specimen of Hyocrinus foelli in COL at 3 030 m depth. Finally, during deepwater dredging by the TALUD cruises aboard the R/V "El Puma" of the Universidad Nacional Autónoma de México, Florometra serratissima was collected in two stations located in COL between 1 040 and 1 106 m depth (Valdés de Anda et al., 2018). Asteroidea: 57 references addressed the Asteroidea distributed along the CMP. During the 19 th century only two works were published, meanwhile the 20 th and 21 st centuries presented similar numbers of works, 28 and 27, respectively. The 19 th century represents the era with the lowest addition of Asteroidea. The first reported Asteroidea for the CMP were Luidia columbia and Astropecten regalis, both collected in San Blas, NAY (Gray, 1840).
The addition of new records of ophiuroids (22) during the 21 st century has been important. Frontana-Uribe et al. (2000) collected specimens of Ophiocomella schmitti associated with coral rubble in localities from Socorro Island (REV). Fuentes-Farías et al. (2005) included the record of Ophiothrix (Ophiothrix) rudis for MICH; in the same year, Maluf and Brusca (2005) published a checklist of the echinoderms from the Gulf of California, including the general distribution of the species, and the new records of Amphipholis elevata, Astrocaneum spinosum, Microphiopholis puntarenae, Ophiocomella sexradia, Ophiocnida hispida, Ophiolepis crassa, Ophiopholis bakeri, and Ophiophthalmus diplasia (MAR and REV). The genus Ophiophthalmus is an invalid junior synonym and a new assignment is needed (Hendler, 1996), but in the present work we kept this temporary genus in order to avoid systematic confusions. Later, Honey-Escandón et al. (2008)  Echinoidea: 73 references documented the presence of the Echinoidea from the CMP, representing the major number of works among all the classes. The 19 th century is represented only by two publications, the 20 th century for 39, and the 21 st century for 32 works. In the 19 th century all the work regarding Echinoidea was published by Alexander Agassiz whom documented for the first time in the CMP the species Eucidaris thouarsii and Echinometra vanbrunti, both collected in Manzanillo, COL (Agassiz, 1872), and who described Brisaster townsendi and Plexechinus cinctus for stations located in deep-waters of MAR (Agassiz, 1898).
Despite the number of published works during the 21 st century is similar to the previous century, only three new records for the area have been documented during the present era. These records correspond to species observed during field work and documented in the management and conservation programs of the National Park ISA (Centrostephanus coronatus; CONANP, 2005)  Holothuroidea: 53 references mention holothuroids from the CMP. During the 19 th century only one work was published, 19 during the 20 th century, and 33 during the 21 st century. In the 19 th century only one work was published and therefore, the number of records was low. Despite, Laetmophasma fecundum (= Pannychia moseleyi), Psolus pauper, and Ypsilothuria bitentaculata were first mentioned in Ludwig (1893), it was until 1864 when Ludwig (1894) provided an extended description of the species, reporting them in deep waters from MAR; moreover, Molpadia musculus was recorded in this work too, for the same locality.
The 20 th century was the most productive in terms of the addition of new records (28). In 1926, the Templeton Crocker expedition aboard the Zaca performed dredges in order to obtain echinoderms along the Eastern Pacific, and collected Holothuria (Cystipus) inhabilis and Holothuria (Platyperona) difficilis in REV (Deichmann, 1937). From 1932 to 1938, the Allan Hancock Expedition aboard the Velero III collected several specimens of holothuroids and Deichmann (1941) found that Thyone bidentata and Thyone parafusus, both discovered in Tenacatita, JAL corresponded to new species, and that Leptopentacta panamica, Neothyone gibber, and Pentamera chierchiae were new records of species for the CMP (JAL and REV). Caso (1954) collected for the first time Holothuria (Selenkothuria) lubrica in Puerto Vallarta, JAL and found a similar species which was designated as a new species: Holothuria (Selenkothuria) portovallartensis. The biggest contribution of new records of holothuroids for the CMP (Holothuria (Halodeima) kefersteinii, Holothuria (Lessonothuria) pardalis, Holothuria (Mertensiothuria) hilla, Holothuria (Mertensiothuria) leucospilota, Holothuria (Semperothuria) imitans, Holothuria (Semperothuria) languens, Holothuria (Theelothuria) paraprinceps, Holothuria (Thymiosycia) arenicola, Holothuria (Thymiosycia) impatiens, and Isostichopus fuscus) was made by Deichmann (1958) which correspond to a continuation and expansion of the material collected by the Velero III and IV in JAL, as well as in ISA, MAR and REV.
Based on literature records, Lophaster furcilliger (asteroid), Astrocaneum spinosum (ophiuroid), and Centrostephanus coronatus (echinoid) have been recorded in the program of management and conservation of REV (CONANP, 2019). The only records of L. furcilliger in the CMP correspond to MAR (Ludwig, 1905;Maluf, 1988;Maluf, 1991), therefore their inclusion in REV is incorrect. Despite it is very probable that A. spinosum and C. coronatus distributes in REV, we did not find any record in publications to back it up. Other species reported in a program of management and conservation (ISA; CONANP, 2005) are the echinoids Clypeaster europacificus and Lovenia cordiformis, but again no primary references supporting these records were found, and therefore are considered as invalid records.
Finally, based on a revision of literature, the asteroids Paulia horrida and Luidia bellonae were reported in MAR by Maluf (1988) and Maluf and Brusca (2005), respectively; nevertheless, we did not find any record of these species for MAR but for REV. Similarly, the asteroid Cnemidaster nudus has only one mention for COL (Solís-Marín et al., 2016b), but it corresponds to an erroneous record (F.A. Solís-Marín, personal communication, 01 April 2020). For these reasons, we consider both records as invalid.
The following records were considered as doubtful. The ophiuroid Amphiodia periercta inhabits in the North Pacific Ocean (from Aleutian Islands, Alaska to central California; Lambert & Austin, 2007), yet it has a report in Clarion Island, REV (Maluf, 1988;Bautista-Romero et al., 1994). Due to the northern affinity of A. periercta, its distribution in REV is unlikely. The record of Hymenaster pentagonalis in REV was obtained by the Expedition Ocean Exploration Trust/Nautilus Live 2017 (CONANP, 2019), yet this species distributes only in Hawaii (Mah, 2020).
New records: Following review of museum material, we add 16 new records of Ophiuroidea to different states (four NAY, one COL, and one MICH) and islands (two MAR, four ISA, and four REV) from the CMP (appendix 1). All the species were previously recorded in areas from the CMP (Table 1), excepting Amphiodia psara, Amphiodia tabogae, Microphiopholis geminata, and Ophiophragmus paucispinus, which represent new records for the CMP.
Amphiodia psara has previous records in USA (California;Clark, 1935) and México (Gulf of California and Guerrero; Maluf, 1988;Maluf & Brusca, 2005;Granja-Fernández et al., 2015b). After the taxonomic revision of A. psara in different museum collections, we did not find material from Guerrero, but for the Pacific of Baja California and Baja California Sur, the Gulf of California (Ángel de la Guarda Island, Tiburón Island, Consag Rock, and Sonora), and NAY. The records from Baja California, Baja California Sur and NAY are new, being Punta Mita, Nayarit, the southernmost area of its geographical distribution.
Amphiodia tabogae, M. geminata, and O. paucispinus distribute along the Eastern Pacific (México to Galápagos Islands; Solís-Marín et al., 2013a). Specifically, in México, the three species inhabit the Gulf of California; A. tabogae has been reported also in Guerrero (Granja-Fernández et al., 2015b). The finding of these species in Punta Mita, NAY (A. tabogae and M. geminata), and in MAR (O. paucispinus), represents new records in the CMP, and fills the distribution gap along the Mexican Pacific.

Diversity and distribution:
The diversity of the Echinodermata from the CMP is represented by 187 species of echinoderms belonging to 27 orders, 63 families, 110 genera, and 16 subgenera (Table 2). Compared to the total number of echinoderm species worldwide (7 437 species; WoRMS, 2020), the CMP shelters 2.5 %. The orders with the highest number of species in the CMP were Amphilepidida (Ophiuroidea, 40 species), Holothuriida and Dendrochirotida (Holothuroidea, 21 species, respectively), Ophiacanthida (Ophiuroidea, 16 species), and Valvatida (Asteroidea, 15 species), meanwhile the best represented families were Amphiuridae (Ophiuroidea, 26 species), and Holothuriidae (Holothuroidea, 21 species) (Table 1). On the other hand, the orders Ophiurida (45 species), Aspidochirotida (22 species), and Dendrochirotida (22 species) were the best represented in the Southern Mexican Pacific (SMP; Granja-Fernández et al. 2015b). Differences in the numbers of recorded orders between the CMP and the SMP are due to recent changes in the systematics of the Ophiuroidea (O´Hara, Stöhr, Hugall, Thuy & Martynov, 2018) in which most of the members previously included in the order Ophiurida, now are in Amphilepidida, and in the Holothuroidea, where most of the members of Aspidochirotida were changed to Holothuriida (Miller et al., 2017). If we compare both faunas in the same classification system, similar trends are shown, suggesting that both areas possess similar faunas in terms of orders and families of echinoderms.
In the CMP, the class Ophiuroidea was the most numerous with 67 species, followed by Holothuroidea (50), Asteroidea (35), Echinoidea (32), and Crinoidea (three) ( Table 2). In general, the number of species of Holothuroidea, Asteroidea and Echinoidea were similar between the CMP and the SMP, but Ophiuroidea was represented by more species in the CMP (67) than to the SMP (46); meanwhile, the class Crinoidea had not records in the SMP (Granja-Fernández et al., 2015b). Differences on the Ophiuroidea are related to the recent sampling effort directed in the CMP , and the extensive revision of samples from museum collections (reflected in the new records of species in this work). Nine species of Crinoidea from México to Perú (Solís-Marín et al., 2013a) and at least seven in the northern part of the American continent (Lambert & Austin, 2007) are reported in the literature therefore, finding crinoids in the CMP and SMP is likely. Despite the above, a null to a scarce number of species of Crinoidea are reported in both areas. We consider that the explanation of this pattern (and in general of the Eastern Pacific) is not due to the natural biogeographic distribution of the Crinoidea in the Eastern Pacific, yet to the scarce prospection in deep waters (the natural environment of the class in the Eastern Pacific), as well as to the low interest and lack of taxonomical specialists in the class. As previously mentioned, the CMP is represented by 187 species of echinoderms; of those, 122 inhabit in ~ 640 km of the coastline of the studied states, and 142 in an extensive maritime area of the islands (~ 155 000 km 2 ). The SMP has not extensive islands such as the CMP, therefore if only their coastlines are compared, the latter possesses a lower number of echinoderms species than the SMP (162 species; Granja-Fernández et al., 2015b). In order to have a better comprehension of the number of species between both areas, a standardization per area is required, therefore considering the whole CMP (~ 640 km) has 5.2 species/ km, and the SMP (~ 1 200 km) possesses 7.4 species/km. The collecting effort in more areas, habitats, and depths could explain higher biodiversity of echinoderms in the coastline of CMP, but further collections of material and biogeographic analysis are required in order to better understand their distribution pattern.
In terms of spatial distribution, the coast of the state of JAL presented the highest number of species (84), followed by the coast of NAY (74), MICH (63), and COL (55); among the islands, REV showed the major number of species (85) followed by MAR (81), MAT (48), and ISA (44) ( Table 3). Compared to the most complete and recent works of echinoderms by states (Honey-Escandón et al., 2008;Rodríguez-Troncoso et al., 2013;Solís-Marín et al., 2016b;Granja-Fernández et al., 2017;Ríos-Jara et al., 2017;Nava-Bravo et al., 2019) and islands (CONANP, 2005;CONANP, 2007a;CONANP, 2007b;CONANP, 2019;Honey-Escandón et al., 2008;Solís-Marín et al., 2013a;Granja-Fernández et al., 2017), this work increases the number of recorded species in 27 % for NAY, 49 % for JAL, 1.5 % for MICH, 70 % for MAR, 64 % for ISA, 48 % for MAT, 38 % for REV, and finally 45 % for the entire CMP region. We found the same number of species for COL as its most recent account of echinoderms (Solís-Marín et al., 2016b). Differences in the numbers of species among previous studies and the present one is attributed to a more intense literature review, the validation of geographical coordinates, the correction of records, and the addition of new ones. JAL, MAR and REV were the areas with the highest number of species and have been prospected in several shallow and deep-water localities/stations since late 1800´s by foreign (Albatross, Velero, and Zaca;e.g. Agassiz, 1898;Clark, 1940;Deichmann, 1958) and national expeditions (e.g. Caso, 1943b;Caso, 1961;Caso, 1962b). In contrast, the state of COL, as well as ISA and MAT islands have the lowest number of species, and their poor prospections initiated in the late 1900´s (e.g. Caso, 1961;Caso, 1980), and have been mostly performed during the 2000´s, strictly in shallow-waters (e.g. Chávez-Dagostino et al., 2000;Ríos-Jara et al., 2008a, Ríos-Jara et al., 2013Sotelo-Casas et al., 2018). On the other hand, MAR and REV (the unique oceanic islands of the CMP) display unique characteristics such as particular oceanographic and topographic conditions, high productivity, mesophotic reefs, great depths, among others, which promote high levels of general marine biodiversity and endemism (CONANP, 2007a;CONANP, 2019), explaining their highest number of echinoderms in the region. In conclusion, the obtained data shows that the number of species of echinoderms in the CMP region is mostly associated with a sampling effort, yet specific conditions of particular areas (i.e. MAR and REV) can be influencing their high biodiversity, but more collections of material and further biogeographic analysis are required in order to sustain this statement.

Final considerations:
The CMP is located in an oceanographic transitional zone, therefore fauna from the North and South regions of the Mexican Pacific (Arriaga-Cabrera et al., 1998), the Eastern Pacific (e.g. Solís-Marín et al., 2013a), and even of higher latitudes (e.g. Lambert & Austin, 2007), can inhabit in the region. In this sense, MAR and REV are important as they are considered a stepping stone to import organisms from the Indo-Pacific species into the Tropical Eastern Pacific (Reyes-Bonilla & López-Pérez, 1998), as well as in the connection for dispersal species to and from northern (Gulf of California) and the mainland CMP (López-Pérez et al., 2015).
All the islands considered in the present work possess their own programs of management and conservation (CONANP, 2005;CONANP, 2007a;CONANP, 2007b;CONANP, 2019) in which detailed descriptions of geographical, physical, demographical, social and environmental characteristics (among others) are provided. Despite the above, we detected that all these programs underestimated the number of species of echinoderms since they reported 16 species for ISAB (CONANP, 2005), 24 for MAR (CONANP, 2007a), 25 for MAT (CONANP, 2007b), and 52 for REV (CONANP, 2019). The inclusion of all the species reported in the present work on the lists of these natural protected areas will further emphasize the importance of the islands.
Due to the importance of the islands of the CMP, most of the research of echinoderms in the region have been conducted on them (e.g. Ríos-Jara et al., 2008a;Sotelo-Casas et al., 2018) relegating the mainland of the states of NAY, JAL, COL, and MICH, which remain almost unstudied and which have a high potential of finding numerous species of echinoderms since they have complex environments (extensive bays, coastal lagoons, estuaries, mangroves and coral reefs; Arriaga-Cabrera et al., 1998). Regardless the differences on the diversity of echinoderms and exploration of the mainland and islands from the CMP, all of them are important due to 34 species collected in the region have been described as new species (five Asteroidea, 16 Ophiuroidea, five Echinoidea, and eight Holothuroidea; Table 4). This highlights the potential of the CMP in finding more new species. Although the present manuscript provides the most-completed checklist of the echinoderms in the CMP, we encourage to intensify research in shallow and deep-waters and across different habitats of all the islands and mainland of the states of the region in order to better understand its biodiversity and distributional patterns. Finally, the preservation of the marine fauna of the entire CMP is key in the maintenance of the entire Mexican and Tropical Pacific; therefore, we encourage ensuring its effective protection through inventories of marine and coastal species.
Ethical statement: authors declare that they all agree with this publication and made significant contributions; that there is no conflict of interest of any kind; and that we followed all pertinent ethical and legal procedures and requirements. All financial sources are fully and clearly stated in the acknowledgements section. A signed document has been filed in the journal archives.

ACKNOWLEDGMENTS
We are very grateful to Alicia Durán, Alejandra Martínez-Melo, and Pedro Medina for providing valuable literature. We wish to express our sincere gratitude to Alicia Durán (ICML), Penny Benson and Adam Baldinger (MCZ), Gordon Hendler and Cathy Groves (LACM) for providing their support during collection´s visits. This work was supported by a scholarship from CONACYT 336853, and an Ernst Mayr Grant (MCZ), and is part of the post-doc of RGF at UdG supported by PRODEP (511-6/2019.-12278). We thank four anonymous reviewers and editor for commenting and improving the manuscript.