Arm Plates Research Articles

A new species of the genus Ophiomyxa (Echinodermata: Ophiuroidea: Ophiomyxidae) from the Mallorca Channel seamounts in the western Mediterranean.

A new species belonging to the ophiuroid genus Ophiomyxa is described from the Mallorca Channel seamount, in the western Mediterranean Sea. It can be distinguished from other Ophiomyxa species by the lack of interradial marginal plates, three arm spines, the presence of two thin, transparent and completely perforated dorsal arm plates on each arm segment, the separate heptagonal ventral arm plates, the disk integument full of transparent rounded scales with scattered perforated ossicles, and a characteristic coloration of the disk, which in the living specimen is brown with abundant scattered bright white spots. Molecular analyses based on cytochrome c Oxidase subunit I (DNA barcode) clearly support the assignment of the new species to Ophiomyxa. This discovery highlights the importance of the Mallorca Channel seamounts for the Mediterranean biodiversity conservation, as they seem to provide a suitable habitat for several invertebrate species, including recent descriptions of species and new Mediterranean records, which apparently have not established permanent populations along the closest continental margin.

Deepest known novel species of the genus Ophiuroglypha Hertz, 1927 (Echinodermata: Ophiuroidea) from the central rift zone, Philippine Sea

A new species of brittle star was collected in 2021 by the manned submersible “Fendouzhe” from the central rift zone deep waters, Philippine Sea, at a depth of 7729 m. It is described as Ophiuroglypha fendouzhe sp. nov., and is distinguished from its congeners based on the following features: slender arms, separated dorsal and ventral arm plates, overlapping large disc scales, and distally contiguous radial shields. We provide comprehensive descriptions of the external morphological features, including characteristics of the arm skeleton, and a phylogenetic analysis based on COI sequences. The interspecific genetic distance variation in the genus Ophiuroglypha found in this study was 3.89% to 24.25%. The new species constitutes the deepest known record for the genus Ophiuroglypha.

Integrative species delimitation in the common ophiuroid Ophiothrix angulata (Echinodermata: Ophiuroidea): insights from COI, ITS2, arm coloration, and geometric morphometrics.

Ophiothrix angulata (Say, 1825) is one of the most common and well-known ophiuroids in the Western Atlantic, with a wide geographic and bathymetric range. The taxonomy of this species has been controversial for a century because of its high morphological variability. Here we integrate information from DNA sequence data, color patterns, and geometric morphometrics to assess species delimitation and geographic differentiation in O. angulata. We found three deeply divergent mtDNA-COI clades (K2P 17.0-27.9%). ITS2 nuclear gene and geometric morphometrics of dorsal and ventral arm plates differentiate one of these lineages, as do integrative species delineation analyses, making this a confirmed candidate species.

Evo-Devo in Ophiuroids: The Switch from Planktotrophy to Lecithotrophy in Ophionereis.

AbstractUnderstanding the evolution of development (evo-devo) in the Ophiuroidea and the pathways in the switch from a feeding to a nonfeeding larva is complicated by the variability in the phenotype of the metamorphic larva, being a reduced yolky ophiopluteus in some species (type I development) and a vitellaria larva in others (type II development). We investigated evo-devo in the family Ophionereididae, a group dominated by lecithotrophic development through a vitellaria larva. We reared the planktotrophic larvae of Ophionereis fasciata to settlement to determine the metamorphic phenotype. Counter to expectations, O. fasciata did not exhibit type II metamorphosis through a vitellaria, although it did exhibit transient vitellaria-like features. Resorption of the larval arms in the same interradial positions where the ciliary bands form in vitellariae gave them a fleeting vitellaria-like appearance. Development of O. fasciata exhibits heterochronic features in early formation of the skeletal primordium of the third pair (postoral) of larval arms and in the presettlement juvenile early appearance of the juvenile terminal arm plates on external view in parallel with larval arm resorption. Development of the fourth pair (posterodorsal) of larval arms, the last pair to be formed, is plastic, with 44% of larvae exhibiting partial arm growth. Heterochronic traits in development, as seen in O. fasciata, may have facilitated evolution of a lecithotrophic mode of development in Ophionereis. Comparison of the ophiopluteus of O. fasciata and the vestigial pluteus of O. schayeri provided insights into the simplification of larval form from the ancestral (feeding larva) state in Ophionereis. The diverse metamorphic phenotypes in ophiuroids indicate that type I and type II development may not be completely divergent lines of evo-devo and point to selective pressure in the pelagic-benthic transition in the evolution of ophiuroid development.

A New Asteroid (Echinodermata, Astropectinidae) and Ophiuroid (Echinodermata, Hemieuryalidae) from the Mid-Cretaceous of Southern Japan

Fairly well-preserved external molds of articulated starfish and brittle stars from the upper Albian (mid-Cretaceous) Hokahira Member of the Enokuchi Formation (Goshoura Group) in Goshoura Island (Kumamoto, southern Japan), are described as new species; Coulonia hokahira sp. nov. and Ophiozonella tumidasquama sp. nov., respectively. Of Coulonia, three Early to mid-Cretaceous species are known to date from Texas (USA), Europe and North Africa. The new Japanese species differs from two of these (C. reidi and C. platyspina) in having a proportionally narrower marginal border, and from the third (C. neocomiensis) in having a broader disk. With regard to the brittle stars, it can be stated that the three extinct species previously assigned to Ophiozonella (O. stoehrae, O. eloy and O. thomasi), from Barremian and Aptian (Lower Cretaceous) strata in Europe and the USA, differ from O. tumidasquama sp. nov. in having four spine articulations on lateral arm plates.

The New Brittle-Star Species Stegophiura takaisoensis (Echinodermata, Ophiuroidea) from the Pliocene of Ibaraki Prefecture, Central Japan

We describe three well-preserved, articulated brittle stars from the Pliocene Hatsuzaki Formation, Hitachi Group of Ibaraki, central Japan, as a new species, Stegophiura takaisoensis. It differs from its congeners in having dorsal arm plates with a high ridge and large swollen disk scales. The only other previously described extinct species unambiguously assigned to Stegophiura is S. miyazakii from the Upper Cretaceous of Japan. The new species from the Pliocene significantly adds to the fossil record of the genus, representing the second extinct species known to date and filling part of the fossil record gap between the Upper Cretaceous and the Recent representatives. The specimens have the disk and arms in intact live position, without any signs of transportation before buried. We assume that they were buried alive in their original deep shelf to upper slope habitat by rapid channel fills.

Deep-sea Ophiuroidea (Echinodermata) collected during the TALUD cruises in western Mexico

Deep-sea ophiuroids from western Mexico have been documented since 1899, but mostly by non-Mexican expeditions. TALUD is a Mexican project designed to study the deep-sea fauna from Mexico. As part of it, the present contribution provides for the first time detailed information about the taxonomy and distribution, as well as images, of deep-sea ophiuroids from western Mexico, representing a useful taxonomic identification tool for Ophiuroidea from the eastern Pacific. A total of 38 species of ophiuroid (35 identified at species level, one at genus level, and two as confer) were collected from 83 stations located at 123‒2,309 m depth. At a regional scale, several new species records are presented: six for western Baja California, five for western Baja California Sur, two for the Gulf of California, four for Jalisco, 14 for Colima, and five for Guerrero. Geographic (six) and bathymetric (seven) distribution ranges of species are extended. An updated list of deep-sea ophiuroids (61 species) from western Mexico is provided together with an identification key to species collected during this survey. In addition, nine records of deep-sea ophiuroids for the Mexican Pacific are unproven, doubtful or invalid. We corroborated the presence of Ophiacantha eurypoma and Ophiacantha pacifica in the study area and added Amphiura gymnogastra as the first record for Mexico. We propose to transfer Ophiacantha phragma to Ophiolimna on account of it having both granules and spines on the dorsal disc and striated arm plates. TALUD cruises collected 57 % of the total deep-sea species known to occur off Mexico, making it the most important survey of deep-sea Ophiuroidea carried out in western Mexico to date.

Amphiura multispina (Ophiuroidea, Amphiuridae) from the Upper Pleistocene Kioroshi Formation in a Drill Core at Nagareyama, Chiba, Central Japan

Over 100 well-preserved dissociated ophiuroid arm ossicles, i.e., lateral arm plates, dorsal arm plates, ventral arm plates, vertebrae and arm spines, were recovered from the upper Pleistocene Kioroshi Formation in the core of borehole GS-NY-1 at Nagareyama, Chiba Prefecture, central Japan. Following comparison with the lateral arm plates of ten extant amphiurid species occurring in the seas around Japan and with previously published fossil taxa in this family, the ossicles from Nagareyama were identified as belonging to the extant species, Amphiura multispina. This is the first fossil record of this form and the stratigraphically youngest of the Amphiuridae. The taphonomy and paleoenvironment of the brittle star fossils described are also discussed.

Description of two species of the genus Astrodia Verrill, 1899 (Ophiuroidea, Euryalida, Asteronychidae), including a new species from seamounts in the West Pacific.

Five specimens of Ophiuroidea from deep-sea seamounts in the West Pacific were collected and identified as two species, Astrodiaduospina sp. nov. and Astrodiaabyssicola. The new species, Astrodiaduospina sp. nov., can be distinguished from its congeners by having indistinct or underdeveloped oral papillae, relatively short genital slits, crescent-shaped lateral arm plates, and plate-shaped external ossicles on the aboral surface of the disc. One specimen was identified as Astrodiaabyssicola, which has been reported in the north-western Pacific and the north-eastern coast of Japan. The most recent tabular key of Astrodia was revised with two more key characteristics added, the shape and presence of oral papillae and the number of arm spines. The phylogenetic relationship of Astrodia and Asteronyx was analyzed based on 16S and COI sequences. The discovery of the two species further expanded the geographical distribution of the genus Astrodia.

Fossil Lateral Arm Plates of Stegophiura sladeni (Echinodermata: Ophiuroidea: Ophiurida) from the Middle Pleistocene of Japan

Disarticulated fossil lateral arm plates of brittle stars from the Middle Pleistocene Miyata Formation, Miura, Kanagawa Prefecture, eastern Japan, are described. They are assigned to Stegophiura sladeni on the basis of their microstructural morphology. This is the first description based on disarticulated fossil lateral arm plates of brittle stars from Japan and should encourage further exploration of the Japanese ophiuroid microfossil record.

Overlooked for over a century: Ophioderma occultum sp. nov. (Echinodermata), a new species of brittle star from the Eastern Pacific

ABSTRACT We describe a new species of ophiodermatid brittle star from the Eastern Pacific: Ophioderma occultum sp. nov. This species has been mistakenly recorded since 1899 as a colour phase of one of its congeners, Ophioderma panamense. However, the integrative use of morphological and molecular data, and comparison with type material of other Eastern Pacific Ophioderma, led to its differentiation as a novel species. Ophioderma occultum sp. nov. is characterised by having radial shields and adoral shields covered with granules, dorsal arm plates divided typically into two pieces, and a particular colour pattern: a dark grey to brown body, and arms with subtle lighter transverse bands and parallel longitudinal white bands over some median and distal segments. Molecular information based on the mitochondrial genes cytochrome oxidase subunit I (COI) and 16S also supported the species’ validity, coinciding with the morphological observations. In particular, the molecular marker 16S had not been used before for species delimitation in this genus and was proven here to be resolutive. In contrast to most species of Ophioderma from the area, Ophioderma occultum sp. nov. shows a restricted distribution to the northern Mexican Pacific (Gulf of California and islas Revillagigedo). This new species is the 10th Ophioderma described from the Eastern Pacific and the 34th worldwide. http://www.zoobank.org/urn:lsid:zoobank.org:pub:A5FFAC55-E5BE-42F6-8371-7B745911F157

Overlooked biodiversity of brittle stars from the Upper Pleistocene of Japan: descriptions of fossil ossicle assemblage in Indo-West Pacific

ABSTRACT Disarticulated fossil ossicles of brittle stars from the Upper Pleistocene Yokosuka Formation, Yokosuka, Kanagawa Prefecture, central Japan, are described. The ossicles of lateral arm plates and vertebrae are assigned to Gorgonocephalidae, Ophiocomidae, Ophiosphalmidae, Ophiopholis, Ophiothrix, Ophiarachnella, Stegophiura sladeni, Ophiuroglypha kinbergi and Ophiozonella longispina, on the basis of external morphology. This is the first faunal record mainly based on disarticulated fossil lateral arm plates of brittle stars from the Indo-Pacific region.

A new phosphatized ophiuroid from the lower Triassic of Nevada and its position in the evolutionary history of the Ophiuroidea (Echinodermata).

The Lower Triassic fossil record of brittle stars is relatively rich, yet most records published to date are based on poorly preserved or insufficiently known fossils. This hampers exhaustive morphological analyses, comparison with recent relatives or inclusion of Early Triassic ophiuroid taxa in phylogenetic estimates. Here, we describe a new ophiuroid from the Lower Triassic of Nevada, preserved as phosphatized skeletal parts and assigned to the new taxon Ophiosuperstes praeparvus gen. et sp. nov Maxwell, V. Pruss. S.B. This unusual preservation of the fossils allowed for acid-extraction of an entire suite of dissociated skeletal parts, including lateral arm plates, ventral arm plates, vertebrae and various disk plates, thus unlocking sufficient morphological information to explore the phylogenetic position of the new taxon. Bayesian phylogenetic inference suggests a basalmost position of O. praeparvus within the Ophintegrida, sister to all other sampled members of that superorder. The existence of coeval but more derived ophiuroids suggests that O. praeparvus probably represents a member of a more ancient stem ophintegrid group persisting into the Early Triassic.

Description of a New Brooding Species of Ophiodelos (Echinodermata: Ophiuroidea) from Japan.

A new species of brittle star, Ophiodelos okayoshitakai, is described from two specimens collected in Sagami Bay, central-eastern Japan. Photographic examination of the holotype specimen of the sole other congener, Ophiodelos insignis Koehler, 1930, indicates that Ophiodelos okayoshitakai sp. nov. is distinguished from O. insignis by i) the disc stumps covering on the dorsal side of the disc, ii) the dorsal and ventral arm plates being separated from each other on the proximal arm regions, iii) the dorsal arm plate being smooth, iv) the arm spines at proximal portion of the arm being six in number and smooth in shape, and v) the number and shape of the tentacle scales at proximal portion of the arm being up to two and spine-shaped adradially and oval abradially. Detailed morphological observations of this new species suggest the inclusion of Ophiodelos, whose familial affiliation remains unclear, in the suborder Ophiacanthina. More than 10 juveniles of various sizes were found in the disc of Ophiodelos okayoshitakai sp. nov., indicating a brooding reproduction. This is the first report of the genus Ophiodelos from Japanese waters. We also provided a nucleotide sequence for part of the cytochrome c oxidase subunit I (COI) gene in O. okayoshitakai sp. nov. for future studies of DNA barcoding and phylogeny.

Morphology of endoskeleton and spination in the sea star Midgardia xandaros (Brisingida: Brisingidae) from the Gulf of Mexico

Introduction. The deep-sea asteroid species of Brisingida have a nearly global distribution but have remained poorly understood due to their deep bathymetric distributions and fragile skeletons. Objective. To describe the external and internal morphology of Midgardia xandaros including the skeletal arrangement, through multifocal and SEM techniques. Methods. We examined a total of 21 specimens, including 27 arm fragments, from the Gulf of Mexico and Honduras. Two specimens were dissected. Results. Detailed descriptions of pedicellariae, abactinal, intercostal, inferomarginal, adambulacral, ambulacral, odontophore, and oral ossicles, and their spines are provided, emphasizing the articulations and muscle attachments. C-shaped valves pedicellariae and small pedicellariae valves with shorter denticulation areas were recognized. Conclusions. The morphological description of M. xandaros is expanded, providing the most extensive description of abactinal, first adambulacral, first and subsequent inferomarginal ossicles, abactinal spines, and C-shaped, crossed pedicellariae, as well as the distal arm plates, for a brisingid species using SEM to date.

Annotated checklist for the Gorgonocephalidae family (Echinodermata: Ophiuroidea) from the National Echinoderm Collection “Dra. Ma. E. Caso M.” of the Instituto de Ciencias del Mar y Limnología, UNAM

Introduction: The order Euryalida is represented by fragile ophiuroids with long and slender arms that can be ramified. Species within the family Gorgonocephalidae are characterized by the presence of tiny hooklets on the dorsal aspect of their arms. There are very few published studies referring to species of the family Gorgonocephalidae inhabiting Mexican waters. Objective: To review the taxonomic status of the species belonging to this taxonomic family, identifying their diagnostic taxonomic characteristics to create an illustrated guide of species kept at the CNE, UNAM. Methods: Specialized bibliography of the Gorgonocephalidae family was gathered. Subsequently, all the specimens from the CNE were photographed using Scanning Electron and Multifocal Microscopy photography, to show the structures of taxonomic relevance. Results: A total of 193 specimens corresponding to eight genera and nine species were reviewed. The genus Astrocaneum presented the highest species richness. Conclusions: For the species identified in this study and for the sake of accurate identification, morphological characters such as the shape of hooklets and arm plates were highlighted.

Morphometry and Relative Growth of Ophiolepis crassa (Echinodermata: Ophiuroidea), a Brittle Star from the Eastern Pacific.

Tropical ophiuroid fauna belonging to the family Ophiolepididae are almost unknown. This study deals with the relative growth and morphometric traits of the ophiuroid Ophiolepis crassa from the Gulf of California, Mexico. Specimens examined in this study came from the Colección Nacional de Equinodermos, Universidad Nacional Autónoma de México, and were collected over soft bottoms off Punta Gorda. Thirteen anatomical features were measured in a total of 152 specimens, including disk diameter, arm length, as well as length and width of dorsal and ventral arm plates, and radial, oral, and adoral shields. Based on the range of values of the disk diameter, varying from 4 to 19 mm, we provided quantitative data on each anatomical measurement considering three size classes. Morphometric data were adjusted to a power equation to detect the degree of allometry in the growth of anatomical traits. Results indicated that all the ventral and dorsal plates, as well as the radial, oral, and adoral shields, suffer changes in shape during growth, but these changes are stronger in the plates. In addition, an analysis of symmetry applied to both right and left radial shields revealed that these structures remain nearly symmetrical during growth. The disk diameter vs arm/disk relationship indicated that the species is a surface dweller inhabitant of the seafloor. This study, based on a single sample collected in a restricted area of the eastern Pacific, provides useful quantitative information for further taxonomic, systematic, or biogeographic studies.

A New Species of the Genus Ophiomonas Djakonov (Echinodermata: Ophiuroidea: Amphilepididae) from the Deep-Sea of Japan.

A new species, Ophiomonas shinseimaruae, is described based on five specimens collected from deep water settings, southeast of Cape Erimo, Hokkaido, Japan. Ophiomonas shinseimaruae sp. n. is distinguished from other congeners based on the following characters: elongate semi-circular and separated radial shields; triangular oral shields; flat and broad tentacle scales on the second tentacle pore; octagonal dorsal arm plates, approximately three times wider than long on proximal portion of the arm; and three arm spines present proximally on the arm. This is the first record of the genus Ophiomonas from Japanese waters. The COI nucleotide sequence for Ophiomonas shinseimaruae sp. n. is provided.

A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean.

Identifiable remains of large deep-sea invertebrates are exceedingly rare in the fossil record. Thus, every new discovery adds to a better understanding of ancient deep-sea environments based on direct fossil evidence. Here we describe a collection of dissociated skeletal parts of ophiuroids (brittle stars) from the latest Pliocene to earliest Pleistocene of Sicily, Italy, preserved as microfossils in sediments deposited at shallow bathyal depths. The material belongs to a previously unknown species of ophiacanthid brittle star, Ophiacantha oceani sp. nov. On the basis of morphological comparison of skeletal microstructures, in particular spine articulations and vertebral articular structures of the lateral arm plates, we conclude that the new species shares closest ties with Ophiacantha stellata, a recent species living in the present-day Caribbean at bathyal depths. Since colonization of the deep Mediterranean following the Messinian crisis at the end of the Miocene was only possibly via the Gibraltar Sill, the presence of tropical western Atlantic clades in the Plio-Pleistocene of the Mediterranean suggests a major deep-sea faunal turnover yet to be explored.

Unravelling the taxonomic identity ofOphiothelaVerrill, 1867 (Ophiuroidea) along the Brazilian coast

AbstractSince 2012, whenOphiothelawas first described in the Atlantic, there has been no consensus regarding its identification. It has been described asO.mirabilis,O. cf.mirabilis,O.danae, or onlyOphiothelasp. In order to fill these gaps, our aim was to test if specimens from Brazil areOphiothela mirabilisand/orOphiothela danae. Syntypes from the Museum of Comparative Zoology and United States National Museum, Smithsonian Institution, were used. We examined species boundaries of the small six-rayed brittle starOphiothelausing independent character sets utilizing morphology (external morphology and morphometry) and molecular data (16S and COI). Concordance was found between the analyses indicating thatOphiothelasp. from Brazil (BR),Ophiothela mirabilisandOphiothela danaeare closely related. We suggest thatO.danaeshould be considered as a junior synonym ofO.mirabilis. A detailed description ofO.mirabilisBR is presented using external morphology and microstructural ossicles (arm plates, vertebra, dental and oral plates). This description includes new diagnostic features, particularly regarding its microstructures: (i) transspondylous articulation (first record in Ophiotrichidae); (ii) eight smooth knobs on the dorsal surface of the vertebrae (to date only inOphiothela); (iii) vertebrae with distal keel divided into two separate end processes matching the two large dorsal grooves proximally (first time in the literature); and (iv) an opening on both sides of the oral plate (as seen in other fissiparous speciesOphiactis savignyiandOphiocomella ophiactoides).