Deep-sea Asteroid Research Articles

Mitogenomics provides new insights into the phylogenetic relationships and evolutionary history of deep-sea sea stars (Asteroidea)

The deep sea (> 200 m) is considered as the largest and most remote biome, which characterized by low temperatures, low oxygen level, scarce food, constant darkness, and high hydrostatic pressure. The sea stars (class Asteroidea) are ecologically important and diverse echinoderms in all of the world’s oceans, occurring from the intertidal to the abyssal zone (to about 6000 m). To date, the phylogeny of the sea stars and the relationships of deep-sea and shallow water groups have not yet been fully resolved. Here, we recovered five mitochondrial genomes of deep-sea asteroids. The A+T content of the mtDNA in deep-sea asteroids were significantly higher than that of the shallow-water groups. The gene orders of the five new mitogenomes were identical to that of other asteroids. The phylogenetic analysis showed that the orders Valvatida, Paxillosida, Forcipulatida are paraphyletic. Velatida was the sister order of all the others and then the cladeValvatida-Spinulosida-Paxillosida-Notomyotida versus Forcipulatida-Brisingida. Deep-sea asteroids were nested in different lineages, instead of a well-supported clade. The tropical Western Pacific was suggested as the original area of asteroids, and the temperate water was initially colonized with asteroids by the migration events from the tropical and cold water. The time-calibrated phylogeny showed that Asteroidea originated during Devonian-Carboniferous boundary and the major lineages of Asteroidea originated during Permian–Triassic boundary. The divergence between the deep-sea and shallow-water asteroids coincided approximately with the Triassic-Jurassic extinction. Total 29 positively selected sites were detected in fifteen mitochondrial genes of five deep-sea lineages, implying a link between deep-sea adaption and mitochondrial molecular biology in asteroids.

The fossil record of the family Benthopectinidae (Echinodermata, Asteroidea), a reappraisal

Fossils assigned to the predominantly deep-sea asteroid family Benthopectinidae Verrill, 1894 are described and their affinities reappraised. Detailed comparative morphology of ambulacrals, adambulacrals and marginal ossicles has revealed that only some extinct taxa fall within the morphological range of the modern representatives of the family. These include Jurapecten hessi Gale, 2011, J. infrajurensis sp. nov. (both Jurassic), J. dhondtae sp. nov. (Upper Cretaceous) and Nearchaster spinosus (Blake, 1973) comb. nov. (Lower Oligocene). A new Late Cretaceous genus, Punkaster gen. nov. (P. spinifera gen. et sp. nov. and P. ruegenensis gen. et sp. nov.), appears to be a highly derived benthopectinid. A possible benthopectinid is described from the Upper Triassic (Carnian) of China. Other described records are distantly related to, but convergent in gross morphology with, benthopectinids. Thus, Plesiastropecten hallovensis Peyer, 1944 is here referred to the Jurassic spinulosidan family Plumasteridae Gale, 2011 and Xandarosaster hessi Blake, 1984 is interpreted as Spinulosida Perrier, 1884 incertae sedis. The mid-Cretaceous Alkaidia sumralli Blake & Reid, 1998 is reassigned to the Forcipulatida (Zorocallina). The “fossil benthopectinid” of Spencer & Wright in Moore (1966) is shown to belong to the goniopectinid genus Chrispaulia Gale, 2005, of which two new Cretaceous species are described, C. wrightorum sp. nov. and C. spinosa sp. nov. Finally, we consider Henricia? venturana Durham & Roberts, 1948 to be an indeterminate asteroid.

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.

Trophic ecology of deep-sea Asteroidea (Echinodermata) from eastern Canada

Asteroids (sea stars) can be important predators in benthic communities and are often present in ecologically important and vulnerable deep-sea coral and sponge habitats. However, explicit studies on the trophic ecology of deep-sea asteroids are rare. We investigated the diets of seven species of deep-sea asteroid from the bathyal zone of Newfoundland and Labrador, eastern Canada. A multifaceted approach including live animal observations, stomach content analysis, and stable isotope analysis revealed the asteroids to be either top predators of megafauna or secondary consumers (mud ingesters, infaunal predators, and suspension feeders). The stable isotope signatures of Ceramaster granularis, Hippasteria phrygiana, and Mediaster bairdi are characteristic of high-level predators, having δ15N values 4.4‰ (more than one trophic level) above Ctenodiscus crispatus, Leptychaster arcticus, Novodinia americana, and Zoroaster fulgens. We present strong evidence that corals and sponges are common food items for two of the predatory species, C. granularis and H. phrygiana. During laboratory feeding trials, live H. phrygiana fed on several species of soft coral and C. granularis fed on sponges. Stomach content analysis of wild-caught individuals revealed sclerites from sea pens (e.g. Pennatula sp.) in the stomachs of both asteroid species; H. phrygiana also contained sclerites from at least two other species of octocoral and siliceous sponge spicules were present in the stomachs of C. granularis. The stomach contents of the secondary consumers contained a range of invertebrate material. Leptychaster arcticus and Ctenodiscus crispatus feed infaunally on bulk sediment and molluscs, Zoroaster fulgens is a generalist infaunal predator, and the brisingid Novodinia americana is a specialist suspension feeder on benthopelagic crustaceans. This study provides a foundation for understanding the ecological roles of bathyal asteroids, and suggests that some species may have the potential to be important modulators of deep-sea benthic communities.

Range Extensions and Taxonomic Notes on Atlantic Myxasteridae (Velatida; Asteroidea)

Newly collected specimens of the Atlantic Myxaster sol and a further record of Pythonaster atlantidis add to the knownoccurrence records and the morphological variation of these rarely encountered species. Distribution data suggests thatboth M. sol and P. atlantidis are pan-Atlantic species and are similar to other widely distributed deep-sea asteroid species.Re-examination of the type of Myxaster perrieri further supports its placement within Myxaster and not Pythonaster as has been recently reported.

Depth-related shift in life history strategies of a brooding and broadcasting deep-sea asteroid

Combining field and laboratory work, this study investigated the reproductive cycle, aggregative behavior, spawning periodicity, development and early growth of the sea star Henricia lisa living at bathyal depths off eastern Canada. Marked differences were found between individuals from ~1,300 and ~600 m deep. The former had a male biased sex ratio and an aperiodic reproductive cycle, whereas the latter displayed an equal sex ratio and a biannual breeding pattern. Furthermore, the maximum size was larger and female fecundity roughly five times higher in shallower compared to deeper populations. In the tanks, aggregative behavior was recorded twice a year during the summer and winter breeding periods. The onset of aggregations and spawning coincided with a temperature of 3–4°C. Males spawned first and females typically responded inside 30–60 min. Between 12 and 20 eggs were retained to be brooded under the arched arms of the female, whereas the remainder were broadcasted and developed without parental care. The fertilized eggs underwent a first cleavage after 12 h, reached the brachiolaria stage in 1 month, became juveniles within 3–4 months and reached ~ 4 mm in diameter after 14–17 months of growth. The embryos and juveniles developed at the same rate whether brooded or not, and development of winter cohorts was typically slower due to lower prevailing temperatures. This study of H. lisa provides the first evidence of lecithotrophy in a seasonally breeding deep-sea echinoderm and of brooding in a deep-sea asteroid.

Not so poor—more deep-sea records from the Levant Sea, eastern Mediterranean

Among the biota collected during two surveys of deep-water dumping sites off the Israeli coast, four species of interest were identified: the bobtail squid, Neorossia caroli caroli , the deep-sea asteroid, Brisingella coronata , and the tonguesole, Symphurus ligulatus , are new for the Levant Sea, while the four-horned octopus, Pteroctopus tetracirrhus , is a new record for the Israeli coast. The growing list of bathybenthic species, resulting from expanding research efforts, challenges the conventional view of the Levant deep-sea biodiversity.

A western Pacific record for the eastern Pacific deep sea asteroid species Dytaster gilberti

A western Pacific record for the eastern Pacific deep sea asteroid species Dytaster gilberti

Reproductive biology of the deep-sea asteroid Henricia abyssicola from the NE Atlantic Ocean

The reproductive biology of the North Atlantic asteroid Henricia abyssicola is determined in time series samples taken from 1250 to 1900 m depth in the Porcupine Seabight (NE Atlantic). The male-female ratio, gonadosomatic index (GI), pyloric caecum index (PCI), fecundity and oocyte size distribution were determined and the results were corroborated by histological examination of the gonads. This species is a gonochoric asteroid and the male-female ratio did not differ significantly from the equality. Oogenesis was asynchronous. The previtellogenic oocytes grow to a size of ~230 µm before undergoing vitellogenesis. Maximum oocyte size was ~970 µm. The ovary volume was mainly occupied by large vitellogenic oocytes (400–500 µm) at any time. There were no seasonal variations in GI, PCI and fecundity. There were, however, variations in the production of vitellogenic oocytes of H. abyssicola superimposed on the continuous reproduction. We suggest that H. abyssicola makes use of the energy source provided by the deposition of phytodetritus by storing it in the developing oocytes and that it might have the benefit of a facultative planktotrophic larva.

Comparative Morphology of Tube Feet Among the Asteroidea: Phylogenetic Implications

Tube-foot morphology has been included among a variety of taxonomic criteria for the Asteroidea over the past twenty-five years. Other than a few families belonging to the order Paxillosida, which are thought to have pointed, non-suckered tube feet that are used for digging and burial in soft sediments, the presumption has been that asteroids have flat-tipped, suckered tube feet. This has become an accepted model despite the fact that the comparative morphology of asteroid tube feet has not been considered. In the present study we examine tube-foot morphology of 45 species of Asteroidea representing 19 families. Our analysis confirms that members of the Luidiidae and Astropectinidae (order Paxillosida) lack suckers on the tips of their pointed tube feet. We demonstrate that there is considerable variation in tube-foot morphology among members of the Asteroidea including an entirely new type of flat-tipped, non-suckered tube foot in species belonging to the order Valvatida. The external morphology of tube feet in species belonging to the order Velatida could not be distinguished from “typical” flat-tipped, suckered tube feet; nonetheless, histological sections revealed a distinctive internal morphology. Finally, we report the first observations of the tube-foot morphology of representatives of deep-sea asteroids belonging to the orders Notomyotida and Brisingida, a group that also lacks the typical flat-tipped, suckered tube-foot morphology. The results of our study demonstrate that the current tube-foot morphology model needs to be reconsidered, as there is considerably greater variation than was previously believed to be the case. Moreover, we conclude that while tube-foot morphologies show consistent similarities within orders, tube-foot morphology is less appropriate as a taxonomic character below this level.

Comparative Morphology of Tube Feet Among the Asteroidea: Phylogenetic Implications1

Tube-foot morphology has been included among a variety of taxonomic criteria for the Asteroidea over the past twenty-five years. Other than a few families belonging to the order Paxillosida, which are thought to have pointed, non-suckered tube feet that are used for digging and burial in soft sediments, the presumption has been that asteroids have flat-tipped, suckered tube feet. This has become an accepted model despite the fact that the comparative morphology of asteroid tube feet has not been considered. In the present study we examine tube-foot morphology of 45 species of Asteroidea representing 19 families. Our analysis confirms that members of the Luidiidae and Astropectinidae (order Paxillosida) lack suckers on the tips of their pointed tube feet. We demonstrate that there is considerable variation in tube-foot morphology among members of the Asteroidea including an entirely new type of flat-tipped, non-suckered tube foot in species belonging to the order Valvatida. The external morphology of tube feet in species belonging to the order Velatida could not be distinguished from “typical” flat-tipped, suckered tube feet; nonetheless, histological sections revealed a distinctive internal morphology. Finally, we report the first observations of the tube-foot morphology of representatives of deep-sea asteroids belonging to the orders Notomyotida and Brisingida, a group that also lacks the typical flat-tipped, suckered tube-foot morphology. The results of our study demonstrate that the current tube-foot morphology model needs to be reconsidered, as there is considerably greater variation than was previously believed to be the case. Moreover, we conclude that while tube-foot morphologies show consistent similarities within orders, tube-foot morphology is less appropriate as a taxonomic character below this level.

The reproductive biology of the deep-sea asteroids Benthopecten simplex (Perrier), Pectinaster filholi Perrier, and Pontaster tenuispinus Düben & Koren (phanerozonia : benthopectinidae) from the rockall trough

Samples of three species of benthopectinid starfish were collected in a time-series from stations in the northern Rockall Trough. A detailed study was made of the reproductive biology of Benthopecten simplex (Perrier) from a fixed station at 2200 m. Studies of the gametogenic cycles of Pectinaster fllholi Perrier and Pontaster tenuispinus Düben & Koren from less regular and more scattered samplings are also presented. The oogenic cycles of the three species are similar. Growing oocytes line the ovary wall and come to lie in the lumen only when well developed. Accessory cells surrounding young oocytes become more numerous as the oocytes develop. Vitellogenesis begins when oocyte diameter reaches ≈ 250–300 μm and oocytes attain a maximum diameter of 950 μm in Benthopecten simplex, 850 μm in Pectinaster filholi, and 800 μm in Pontaster tenuispinus. Unspent oocytes are broken down by phagocytes and degenerate ovaries become filled with the breakdown products. Internal degeneration of large oocytes is not common. Size frequency data show a dominance of previtellogenic oocytes and a pattern of continuous growth of vitellogenic oocytes. There is no evidence of synchrony of growth between individuals and no suggestion of seasonal reproduction is evident from summated sample data. Spermatogenesis follows the pattern previously established for deep-sea asteroids. A mature male remains in a state of constant ripeness, ready to shed sperm at any chance encounter with a female releasing ripe eggs. There is no evidence of brooding in any of the species and from the large size and yolk content of the egg, we can infer direct lecithotrophic development demersally.

REPRODUCTION SEXUÉE D'UNE ASTÉRIE FISSIPARE,SCLERASTERIAS RICHARDI(PERRIER, 1882) / SEXUAL REPRODUCTION IN A FISSIPAROUS ASTEROID,SCLERASTERIAS RICHARDI(PERRIER, 1882)

Sclerasterias richardi, a relatively deep sea asteroid (140–200 m) from the border of the Mediterranean continental shelf, is characterized by an asexual reproduction by fissiparity concomitant with a functional sexuality. A monthly sampling of a population from Calvi (Corsica) has allowed a study of the complete sexual cycle from 354 histologically-treated specimens. The 218 sexually defined animals (62% males, 38% females) show strict gonochorism. In males, spermatogenesis is cyclic and sexual maturity seems to be reached before that of the females. In females, the different stages of oogenesis are well marked: oogonia and parietal oocytes disappear only at maturity. Oligolecithic oocytes (120–150 μn) show a synchronous growth. The annual reproductive cycle is well defined in both sexes with one spawning period from mid-September to mid-October. After spawning, a resting period (from mid-October to mid-January) occurs during which unspawned oocytes are phagocytized by more or less isolated accessory cel...

Sexualit� et fissiparit� concomitantes chez l'ast�rie Sclerasterias richardi: premi�res donn�es

A systematic survey of the western Corsican shelf and slope was made, during which we collected on the border of the Continental Shelf an important number of Sclerasterias richardi (Perrier, 1882), a relatively deep-sea asteroid, considered to be fairly rare. After summarizing and enlarging earlier data concerning the distribution of this species, the present paper, based upon the most recent collections (July, 1974), describes some morphological features of the species as seen under the scanning microscope and provides the first histological description. Study of the gonads revealed that S. richardi is gonochoric; ovocytes have synchronous growth, and spermatogenesis is cyclic. However, the observed reproduction, together with the first biometric data indicate that, for the specimens studied, there is no relation between size, sex, degree of maturity and number of arms. The specimens examined are not the juvenile fissiparous stages of an unknown 5-rayed adult as formerly hypothesized. Moreover, fissiparity, which occurs always in this seastar, is here concomitant with sexual reproduction. Study of the reproductive cycle will enable the periodicity of the emission of sexual products to be determined. Rearing of collected specimens in the laboratory will allow artificial fecundation, by which means the as yet unknown larvae may be obtained.

DEEP-SEA ASTEROIDS: HIGH GENETIC VARIABILITY IN A STABLE ENVIRONMENT.

The distribution of geinetic variability in deep-sea organisms is virtually unknown, although estimates of genetic variability in the deep-sea fauna are directly relevant to some hypotheses concerning adaptive strategies in stable and unstable environments. One hypothesis, advanced to account for the great species diversity observed in the deep-sea, argues that deep-sea populations are highly specialized and possess little genetic variability (Grassle, 1972). Another hypothesis, also predicting that deep-sea populations should have little genetic variability, has been advanced by Bretsky and Lorenz (1969, 1970) to account for the waves of extinctions registered in the paleontological record. This hypothesis proposes that organisms living in stable environments should be genetically depauperate. Since the deep-sea provides one of the most stable environments in the world, both hypotheses can be tested by examining the amount of genetic variation in deep-sea organisms. In the course of a broad survey of genetic variability in diverse marine environments we have studied the genetic variability of four species of deep-sea asteroids from the San Diego Trough at a depth of 1,244 meters. Allelic variation at 24 individual loci coding for enzymes and other soluble proteins has been studied using the techniques of starch gel electrophoresis.

Food sources of sublittoral, bathyal and abyssal asteroids in the northeast Pacific Ocean

Abstract Sea stars from the sublittoral to the abyssal zone at 4260 meters depth in the northeast Pacific Ocean were examined for food source. A total of 491 specimens of 29 species were dissected for stomach content analyses. Seven species are predators; six, deposit-detritus feeders; thirteen, omnivores; and the feeding habits of three remain unknown. There are changes in feeding type with increasing depth; the relative abundance of predators decreases from 67 to 0%, and the deposit-detritus feeders, from 33 to 14%. The omnivores increase from 0% on the inner continental shelf at a depth of 50 meters to 71% on the abyssal plains. It is concluded that in the near-shore abyssal environment the deep-sea asteroids are generally facultative feeders and obtain food from the sediments as well as prey or animal remains, while in the food-rich shallow waters of the inner continental shelf the asteroid fauna are generally specialized carnivores.