Antarctic Brittle Stars

A day at the Natural History Museum

Rafael Martín-Ledo — Thu, 29 Dec 2011 10:21:22 +0000

One typical August morning in London (that means drizzling) Elena and me, accompanied by Chester Sands (molecular ecologist at the British Antarctic Survey BAS) found ourselves at the gates of the British Natural History Museum (NHM).

In the NHM, an architectural ensemble of unique and spectacular beauty, which blends a “cathedral” museum with modern research facilities, we were welcomed by Mr Andrew Cabrinovic, echinoderms curator of the Department of Zoology of the NHM. His kindness and attention to every single detail of our work were really praiseworthy.

The collections, magnificently preserved and neat, were at our disposal, and our “temporary” place of work was equipped with a great stereomicroscopy and a camera to take pictures of the specimens.

The research project which I participate in as ophiuroids taxonomist is about phylogeny and biogeography of Southern Ocean benthos. I’ve already identified several thousand of specimens from several expeditions made by the BAS. During my second stay in Cambridge, I identified the ophiuroids collected by Chester Sands during the expedition ANT XXVII / 3 to South Georgia, Larsen and Bouvet Island on board the German ship Polarstern, organized by the Alfred Wegener Institute.

To make the identifications reliable, it was necessary to compare our specimens with the specimens preserved in museums, either because some species are represented only by the holotype, or because of the variability or the lack of information of the original descriptions. Thus the aim of the visit was to see the specimens of the ophiuroids collected during expeditions Discovery I (1925) and Discovery II (1936) that constituted the base for one of the major monographs on the Southern Ocean ophiuroids, the work of Theodor Mortensen 1936. I also had the opportunity to see specimens from other expeditions (Challenger 1873-1876 and Quest 1921-1922).

What did that experience mean to me? I mean, the fact of spending a day working in one of the most important zoological research centers worldwide and having in my hands those specimens from the Discovery expeditions after years of rereading the work of Mortensen. Well, I suppose that, besides of a mere fact of collecting information necessary for identification, it could be comparable to the feelings of a Treki in a Star Trek convention being able to take a picture with Leonard Nimoy. Yes, just a day, but a day to remember.

lllustrations of Southern Ocean ophiuroids: the origen

Rafael Martín-Ledo — Sun, 20 Nov 2011 13:13:24 +0000

The scientific illustrations are an essential tool in the taxonomy. Drawings and photographs can be complementary and not redundant. The more precise in representing the characters of diagnosis, the more useful for identification of specimens. They should be used with the original descriptions and redescriptions which provide information on variability.

In 1843 the Germans Johannes Müller and Franz Hermann Troschel described the first species of ophiuroids in the Southern Ocean, it was Ophiolepis chilensis (species with subantarctic distribution) and was collected by Rudolph Amandus Philippi in the coastal waters of southern Chile. It was first illustrated only in 1875 by Theodore Lyman in Results of the Hassler Expedition. Quite poor drawing, if you can call it that way, that only represents one piece of a jaw and the first ventral arm segment of two arms. In the same work by Th. Lyman we can find a much more precise illustration of gorgonocephalidae Astrotoma agassizii and Astrophyton pourtalesii (Antarctic and sub-Antarctic species). Both illustrations were the first ones of the ophiuroids in the Southern Ocean.

Th. Studer described several species in 1876 (Gazelle expedition 1874-1876), but the illustrations made by him appeared in his later works only in 1880.

Th. Lyman made what is considered the most important work within the ophiurology: Report on the Ophiuroidea dredged by H.M.S. Challenger during the years 1873-76 which was published in 1882. In this major work he described numerous species present in the Southern Ocean. The illustrations are really beautiful and precise, but the descriptions of new species were published in two previous studies in 1878 and 1879 in the Bulletin of the Museum of Comparative Zoology of Harvard, with accurate illustrations but lacking the beauty of the anterior work.

In 1876 Edgar A. Smith from British Museum described the species Ophioglypha hexactis in the Magazine of Natural History. But only in 1879, in Echinodermata of Kerguelen Island of the Philosophical Transactions of the Royal Society he illustrates with great accuracy the species, as well as Ophiacantha vivipara ( species described by Ljungman in 1870 which had not been illustrated up to the date).

As far as the photographs of Southern Ocean species are concerned, the first of them which was photographed, was the aforementioned Ophiolepis chilensis, by Hubert Lyman Clark in Echinoderms of Peru in 1910. The photo of the brittle star is oral position, though you can hardly see any characters needed for correct identification.

The first photos of great descriptive quality were published in the monograph of Ophiuroidea of the Australian Antarctic Expedition (1911 – 1914) by Rene Koehler in 1922, it’s not known whether the pictures were taken by himself or by James Francis Hurley, the official photographer to the Australian Antarctic Expedition. There’s no doubt these pictures are the great example of good taxonomy work.

Another story is the case when the esthetic component was as important as the scientist one. Then, the purpose was to surprise an audience which from the last decade of the nineteenth century were being marveled at the risky scientific voyages of exploration as well as at the organisms collected. The organisms which, in the case of the Southern Ocean could survive in such hostile conditions for a human beeing. Thus we can enjoy the illustration dated on 1882 (Challenger expedition) of Ophiacantha vivipara carrying over its offspring as a good caring mother with her youngsters in a glacial ocean.

In conclusion, some pictures which still amaze me. Koehler in his monograph Ophiures et Echinides dated on 1902 on Belgica expedition (1897-1899) illustrated the specimens with an idealized touch, but the most surprising thing about it is the degree of precision of the drawings, they could perfectly be confused with some 3D computer graphics illustrations.

Can not be reproduced without author’s permission

Roofs and eyeglasses in Antarctic ophiuroids

Rafael Martín-Ledo — Wed, 16 Nov 2011 16:22:21 +0000

In 1961 Fell, in his monograph on the Ross Sea Ophiuroidea, drew attention to the development of skeletal excrecence in Antarctic ophiuroids from Euvondrea and Ophiosteira genera. Fell found no explaination for these outgrowths.

These expansions, especially in the dorsal arm plates, can also be seen in other Antarctic species such as Ophiura (Ophiuroglypha) carinifera, Anophiura banzarei, Ophiomages cristatus, Ophiomastus bispinosus and some species of Ophioplinthus genus.

Ignoring the mere evolutionary whim, there could be various interpretations. For example, passive defense: the protrusive elements could dissuade the predators which would prefer something easier to chew and swallow. Or, acting as peaked roofs somewhere in Siberia or Pirinei Mountains – little flat surface on aboral part protects them from heavy “snowfalls” and, so, doesn’t let them be buried in funds with a high degree of sedimentation. Or, the explanation could be the possible presence of amplifier lenses for photoreception (see symmetrical structures as honeycomb cells of Ophiosteira).

At any rate, nature manifests its spectacularity through the tiniest details of organisms which did not evolve to amaze us, nonetheless, we can’t help being marvelled at them.

Can not be reproduced without author’s permission

Ophiocymbium antarcticus Martynov, 2010 sp. nov.

Rafael Martín-Ledo — Fri, 10 Dec 2010 17:29:46 +0000

The study of the biodiversity of Antarctic waters has increased since 1993 so far, from 4000 to 8200 known species, many of which are brand new for the science. But it seemed that everything “was over” for the ophiuroids, since the last species of Antarctic waters ophiuroids was Ophiomastus trispinosus described by Bernasconi & D’Agostino in 1977, i.e. for the last 33 years the study of the biodiversity Antarctic ophiuroid fauna has not increased at all.
But everything has changed thanks to the great monograph of the Russian scientist Alexander Martynov (Zoological Museum, Moscow State University), called “Reassessment of the classification of the Ophiuroidea (Echinodermata), based on morphological characters. I. General character delineation and evaluation of the Families and Ophiacanthidae Ophiomyxidae“, and published in Zootaxa. This is the first one of a series that, when finished, will undoubtedly be one of the most important works on systematic of the ophiuroids in a global scale.
Based on a specimen deposited at the Smithsonian, collected in 1975 by the ship Orkney Islands (Expedition USAP) at a depth of about 2750 m in the waters of the Scotia Sea (South Sandwich Island) and identified due to a number of common characters as Ophiodaces cf. inanis Koehler, 1922, Martinov described a new species of Ophiocymbium.

In the monograph the author also makes (with the help of electron microscopy) an exhaustive morphological study of the taxonomical valuable characters of numerous species and, in some cases, making important systematic changes.

Antarctic species that have been studied in the monograph are Ophionotus victoriae, Ophiosparte gigas, Ophiolimna antarctica and Ophiolycus nutrix (formerly Ophioscolex), as well as other species of wider distribution and also present in sub-Antarctic waters Ophiocymbium cavernosum, Ophiomyxa brevirima, Ophiernus vallincola and Amphipholis squamata.
Thirty-three years’ drought is over!

Gigantism and dwarfism

Rafael Martín-Ledo — Sun, 21 Nov 2010 12:37:21 +0000

Gigantism is well known among Antarctic benthic organisms, although the fact is that size abnormalities occur in both directions (gigantism and dwarfism). Is it possible that it would be a case of evolution with a disruptive selection in which the organisms with extreme phenotypes would be the dominant forms? That means, being small size organisms (ophiuroids with disc less than 5mm) and large size ones (ophiuroids with disk of about 30mm) more abundant in species compared to the middle size organisms (ophiuroids with disk of approximately 10 mm).

A giant (Ophiosparte gigas) and a dwarf (Ophiosteira bullivanti)

The origin of dwarfism seems to be found in the difficulty to precipitate calcium carbonate at low temperatures, which is supposed to be a limiting factor for organisms with calcareous skeletons, such as calcareous foraminifera, prosobranch gastropods, bivalves and brachiopods, among which we can find Antarctic species of very small size. Antarctic echinoderms with a skeleton composed of calcareous dermal ossicles are “doomed” to higher energy consumption in order to incorporate calcium carbonate, compared to echinoderms from other geographical areas, for this reason, it seems logical to consider this enviroment to be a hostile one for this zoological group development, although it does not look to be like that, as the echinoderms are among the benthic groups with most diversity and biomass in the Antarctic benthos.
Whatever the case and considering dwarf ophiuroid species those that do not reach 5 mm disk diameter , we have: Ophiacantha paramedea, Ophiomitrella ingrata, Amphiophiura antarctica, Ophiocten banzarei, Ophiocten bisquamatum, Ophiomastus conveniens, Ophiomastus ludwigi, Ophiomastus perforatus, Ophiomastus primula, Ophiomastus trispinosus, Ophiosteira bullivanti, Ophiopyrgus australis, Amphiura lymani, Amphiura algida, Amphiura microplax, Amphiura monorima and Ophiozonella antarctica.

Antarctic animals with siliceous skeletons or those with no mineralized skeleton, can multiply by up to ten the size of the individuals of the species compared to ones of the same groups in other geographical areas, as it happens to nemerteans, pycnogonids and giant isopods, like if meeting the Bergmann’s rule. The waters with low temperatures and seasonal food shortages (in winter) reduce basal metabolism which may cause a delay in sexual maturity and increased longevity, the two factors that, along with an environment with little amount of predators can favor the development of a giant size.
Among the ophiuroids, even despite its calcareous skeleton, appear giant Antarctic species, considering giant the species with disk diameter over 30 mm, we have: Gorgonocephalus chilensis (though the gorgonocephalids in general have large size) Astrotoma agassizii, Ophiosparte gigas, Ophionotus victoriae, Ophionotus hexactis, Ophiura flexibilis, Ophiura lenticularis, Ophiocamax gigas and Ophiocamax drygalskii.

Taking the data of 117 species of ophiuroids present in Antarctic waters (I’ve excluded those with high distribution outside Antarctic waters) and represented according to disk sizes in ranges, we obtain the following graphic:

It shows a classic Gaussian bell curve, which clearly indicates an evolutionary “stabilizing type” tendency, i.e. where corporal phenotypes of middle size have been selected predominantly
When compared with species from other latitudes as in the case of brittle stars found in British waters (excluding cosmopolitan species), we have the following graphic as a result:

where we can see presented proportionally even more anomalous cases respecting size.
Therefore it doesn’t seem to be that the dwarfism or gigantism have been selective factors at group level in the Antarctic ophiuroids, but it is more about cases that have to be treated in a particular way.

Ophiosteira bullivanti: collected by Chester Sands (Britihs Antarctic Survey)

Ophiosparte gigas : collected by Pablo J. González-López (University of Seville)

Identified by Rafael Martín-Ledo

References

ARNAUD, P.M. 1974. Contribution a la bionomie marine benthique des regions antarctiques et subantartiques. Téthys, 6, 467–653.

SOUTHWARD, E.C. & CAMPBELL, A.C. 2006. Echinoderms. Synopses of the British Fauna. Edited by Crothers, J.H. & Hayward, P.J. The Linnean Society of London and Estuarine and Coastal Sciences Association.

TORTONESE, E. 1965. Echinodermata. Fauna D’Italia. Edizioni Calderini, Bologna.

Marine Aquarium -British Antarctic Survey (BAS)-

Rafael Martín-Ledo — Sat, 18 Sep 2010 10:12:08 +0000

One of the most impressive experiences of this summer was that of having live Antarctic brittle stars in my hands – and I took that unique opportunity to identify them. Where? In the Marine Aquarium of British Antarctic Survey (Cambridge).

Different aquariums with various zoological groups carefully selected according to their way of life: cnidarians, teleosts, pycnogonids or echinoderms live in marine aquariums situated in a cold room, specially designed to shelter the animals at Antarctic waters temperature.

Sandy Cordiner-Lawrie, Marine Aquarium Manager of Biological Sciences Division (BAS), combining professionalism and affection takes daily care of the fragile marine creatures caught selectively by scuba-divers in Rothera Research Station (Adelaide Island, Antarctida).Among her numerous responsibilities there are those of control of the physico-chemical parameters of the water and maintaining it clean, feeding the animals etc.

Sandy with Chester Sands (molecular ecologist, BAS)

Different studies are being carried out, from metabolic routes to growth physiology, and the isolation of the specimens is often needed.

There was a really interesting phenomenon – an “echinoderm swarm”, some kind of caotic concentration of the animals on the wall of one of the tanks, while the rest of the tank was almost empty. It seemed that sea urchins, starfishes (the predator Labidiaster !) and sea cucumbers were desperately seeking a refuge among themselves.

Thank you, Sandy!

Gorgonocephalus chilensis in Brazilian waters

Rafael Martín-Ledo — Wed, 30 Jun 2010 14:05:41 +0000

Echinodermata, Ophiuroidea, Gorgonocephalus Leach, 1815: First report of the genus for the Brazilian continental margin

Carlos A. M. Barboza ( Universidade Federal do Paraná) and Fabricio M. Mendes, Andrea Dalben and Luiz R. Tommasi

in Check List, Journal of species list and distribution http://www.checklist.org.br/index

With this observation, the authors extend the geographical distribution of Antarctic gorgonocephalid brittlestars to the waters of Brazil.

To see it, go to: http://www.checklist.org.br/getpdf?NGD018-10

There’s no need to travel back in time to change the evolutionary events

Rafael Martín-Ledo — Sat, 08 May 2010 10:44:16 +0000

Natural climate change at late Cenozoic, caused by Milankovitch cycles, led to the change in ecological predator-prey conditions: the exclusion of sharks, crabs and many groups of teleosts from Antarctic waters, which meant a return to the conditions of Paleozoic living, generating singular benthic communities, dominated by annelids and echinoderms.

This ophiura has no chance to survive

Global climate change, anthropogenic, supposes a drastic change in the status with the invasion of durophagous (king crabs), that causes a predation on exoskeleton zoological groups, and, thus, there can occur a reversion of the ecological and evolutionary conditions, when the Antarctic waters would come back to Cenozoic conditions to recover time lost and to lose its uniqueness compared to other planetary ocean waters. Such an achievement for the human being.

©Rafael Martín-Ledo 2010

References

Aronson RB, Blake D (2001) Global Climate Change and the Origin of Modern Benthic Communities in Antarctica AMER. ZOOL., 41:27–39

Aronson RB, Thatje S, Clarke A, Peck LlS, Blake DB, Wilga ChD,Seibel BA (2007) Climate Change and Invasibility of the Antarctic Benthos Annu. Rev. Ecol. Evol. Syst. 38:129–54

Thatje S, Hillenbrand CD, Larter R (2005) On the origin of Antarctic marine benthic community structure TRENDS in Ecology and Evolution Vol.20 No.10

Astrotoma agassizii Lyman, 1875

Rafael Martín-Ledo — Sat, 01 May 2010 17:22:21 +0000

One of the most emblematic animals from Antarctic waters is the euryalid Astrotoma agassizii Lyman, 1875. Gigant, long-lived, with a disk diameter of up to 70 mm and an age which could overpass 100 years; Dahm (1996) calculated, by the growth rings of the arm vertebrae, the age of 90 years for a specimen of disc less than 50 mm.

1. ambulacral pore, 2. arm spine, 3. arm ring with hooklets, 4. jaws, 5. genital slit, 6. radial shields, 7 madreporite

Astrotoma is a predator, who climbs up the gorgonians from Primnoella and Thouarella genus, waits patiently for the arrival of copepods which will be caught by its ambulacral tentacles Dearborn et al (1986). His rough and tough skin defends it from the nematocysts that the polyps of the Gorgon throw without success. Astrotoma grabs the gorgonia with its modified arm spines and the hooklets that cover the skin of its arms arranged in rings.

Arm ring with hooklets

Astrotoma is a hermaphrodite incubator Bernasconi (1965), something common in Antarctic Brittle stars, but the thing that is not so common is that, without a planktonic development that would help to expand its geographical distribution, it however presents a wide circumpolar distribution in shelf waters, in addition to being presented in the waters of Magellan. The Antarctic Circumpolar Current is a divisor of polar and magellanic populations Hunter (2008), there is no gene flow but these are isolated populations, molecularly distinct, although it doesn’t seem to be any morphological differentiation. Smirnov (1986) suggested the possibility of phoresis by macrophytes, an interesting option that could explain their wide distribution.

References

Bernasconi I (1965) Astrotoma agassizii Lyman, especie vivipara del Atlántico Sur. Physis 25 (69): 1-5

Dahm C (1996) Ökologie und populationsdynamik antarktischer ophiuroiden (Echinodermata). Ber Polarforsch 194: 1-289

Dearborn, JH, Ferrari FD, Edwards KC (1986) Can pelagic aggregations cause benthic satiation? Feeding biology of the Antarctic brittle star Astrotoma agassizii (Echinodermata: Ophiuroidea). Ant. Res. Ser., 44 (Biology of the Antarctic Seas XVII): 1-28

Hunter RL & Halanych KM (2008) Evaluating Connectivity in the Brooding Brittle Star Astrotoma agassizii across the Drake Passage in the Southern Ocean. J Hered 99:137-148

Smirnov IS (1984) Fauna of antarctic and subantarctic brittle-stars. Ph.D . Leningrad. 1984 [in Russian]

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8 Polarstern

Identified by Rafael Martín-Ledo

©Rafael Martín-Ledo 2010

Can not be reproduced without author’s permission

Ophioplinthus, Ophionotus / Nematoda

Rafael Martín-Ledo — Sun, 04 Apr 2010 10:51:23 +0000

Ophioplinthus gelida (Koehler, 1901): host
Ophionotus victoriae Bell, 1902: host
Nematoda (unidentified): coelomic cavity and bursae endoparasites

Nematodes identified as parasites of Antarctic ofiuroids belong to Thalassonema genus; they have been found in Ophiocten amitinum, although mentioned in sub-Antarctic waters, and in Ophiacantha antarctica. Mortensen 1936, cites the presence of nematodes, unidentified, in Amphiura microplax disjunta.
Nematodes, in some cases, can be seen going out from the openings in the disc and, on opening some ofiuroids, several nematodes can be seen spread all over the body cavity.

The presence of nematodes in these species has not been cited.

References

Jangoux M (1987) Diseases of Echinodermata. II: Agents metazoans (Mesozoa to Bryozoa) Dis aquat org, vol. 2: 205-234

Mortensen T (1936) Echinoidea and Ophiuroidea. Discovery Reports, National Institute of Oceanography Cambridge 12:199–348

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8 Polarstern

Identified by Rafael Martín-Ledo

Can not be reproduced without author’s permission

Ophioplinthus gelida / Iophon

Rafael Martín-Ledo — Sun, 04 Apr 2010 10:25:34 +0000

(a) Specimen without Iophon with normal growth of plates.

(b) Specimen with anomalous growth of plates from which Iophon has been removed sp.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8 Polarstern

Identified by Rafael Martín-Ledo

Ophiosparte gigas: Rediscovering the monster

Rafael Martín-Ledo — Fri, 02 Apr 2010 18:30:14 +0000

Ophiacanthidae or Ophiomyxidae?

Sometimes we have it just in front of our eyes, but only with the help of an open mind and a new form of seeing things it makes apparent.

Alexander Martynov from Zoological Museum of Moscow State University, carrying out a revolutionary systematic work in accordance with the structures of the arm-spine articulation ridges, establishes a surprising and convincing change: Ophiosparte gigas is an archaic member of Ophiuridae family.

Thank you, Alexander

Reference
Martynov AV (2010) Structure of the arm spine articulation ridges as a basis for taxonomy of Ophiuroidea (a preliminary report). Echinoderms: Durham. Proceedings of the 12th International Echinoderm Conference. 233-239

Vertebrae

Rafael Martín-Ledo — Wed, 31 Mar 2010 07:27:18 +0000

In the current ophiuroids, ambulacral plates are fused in pairs…

You can see in:

Pycnogonid on Ophioplinthus

Rafael Martín-Ledo — Sun, 14 Mar 2010 11:52:03 +0000

This morning, after a delicious breakfast at Vicente’s, I was in my laboratory ready to observe specimens, when I suddenly found a beautiful composition: a pycnogonid (Austrodecus sp) grasping the spicules of the Iophon sponge which covers the disk of a Ophioplinthus gelida.

The pycnogonids, sea spiders, are marine arthropods that feed mainly on hydroids, bryozoans, anemones and other soft-bodied animals in which insert their proboscis to suck their fluids. In Antarctic waters there are about 175 species, which amounts to be 18% of the pycnogonids on a world scale.

Hardly any brittle star can be found among their prey because of having the body covered with calcareous plates which, like an armor-plate, may dissuade many predators who are not armed with appropriate dentition or stylet (pricker).

So, this picture might seem to be a portrait of a process of micropredation or even ectoparasitism, but I tend to consider it just an accident, although there can appear a supposition that what the pycnogonid might have been really looking for could have been the abundat offspring of gemmules of the Iophon sponge.

Specimens conserved in 70% ethanol, all photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8 Polarstern

Identified by Rafael Martín-Ledo

Ophiuroidea – Foraminifera

Rafael Martín-Ledo — Sat, 13 Mar 2010 11:28:31 +0000

on Ophioplinthus gelida, what Foraminifera is this ?

Different states of the same species?

Cruiser ANTARKTIS XXIII/8 Polarstern

Photo by Rafael Martín-Ledo

Identified by Rafael Martín-Ledo