Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/

EchinodermsEchinoderms

Dale Overmeyer

2355332

Dept. of Biodiversity and Conservation

U.W.C

ContentsContents What makes an organism an echinoderm? Classification Reproduction Different classes When did echinoderms first arrive on the scene? Conditions which echinoderms faced in the Palaeozoic Theories for Permian Triassic extinction So, who survived? The debate over classification of echinoderms Echinoderms effect on their ecosystem References

What makes an organism an echinoderm?What makes an organism an echinoderm?

Echinoderms have to be able to consist of the four following synapomorphies (Wray, 1999):

They must have a calcitic skeleton composed of many ossicles (Wray, 1999)

They must have a water vascular system (Wray, 1999) The body must contain alterable collagenous tissue (Wray, 1999) Lastly, there should be pentaradial body organization in adults (Wray,

1999).

ClassificationClassification

Kingdom: Animalia Subkingdom: Metazoa Superphylum: Deuterostomia Phylum: Echinodermata Classes: Asteroidea Blastoidea (extinct) Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Source: http://en.wikipedia.org/wiki/Echinoderm

ReproductionReproduction

Echinoderms are deuterostomes and before larvae are formed there are certain developmental tendencies (Fig 1.)

Forms of reproduction are free spawning followed by external fertilization and indirect development to various forms of brooding and direct development (Brusca & Brusca, 1990).

There is a bilateral planktonic stage (Fig 2.) which alternates with a pentaradial adult phase (Smith, 1997)

Fissiparity is a form of asexual reproduction occurring in some asteroids and ophiuroids (Brusca & Brusca, 1990)

Fig 1. Deuterostome development

Source:http://www.palaeos.com/Invertebrates/Images/DPComparison2.gif

Fig 2. Bilateral larval stage of Pisaster ochraceous

Source: http://depts.washington.edu/fhl/zoo432/plankton/plechinodermata/plEchinoderms.html

Class AsteroideaClass Asteroidea Includes species such as Culcita

novaeguineae (pincushion star) (Fig 3.) and Acanthaster planci (Crown of thorns star) (Fig 4.)

Aggregate on rocks and are also found sandy or muddy bottoms of coral reefs (Hickman et al, 2004)

These sea stars are composed of a central disc (Hickman et al, 2004)

In sea stars the water vascular system is responsible for locomotion and food gathering, in addition to respiration and excretion (Hickman et al 2004)

Fig 3. Culcita novaeguineae (pincushion star)

Source: http://silver.org/barnacle/scubapicts/040-cushionstar.jpg

As far as reproduction is concerned in some species liberated eggs are brooded (Hickman et al. 2004)

In other species embryonating eggs are free in water and hatch to free swimming larvae (Hickman et al 2004).

Metamorphosis involves a dramatic reorganization of a bilateral larva into a radial juvenile (Hickman et al 2004).

Fig 4. Acanthaster planci (Crown of thorns star)

Source:http://www.oceanservice.noaa.gov/education/kits/corals/media/coral08b_240.jpg

Class OphiuroideaClass Ophiuroidea They exist in all types of benthic marine habitats, also covering the abyssal sea

bottom in many areas (Hickman et al 2004). Contains 2 large clades, Ophiurida (brittle stars) (Fig 5) and Euryalida (basket

stars) (Fig6)(http://en.wikipedia.org/wiki/Brittle_star) Have separate sexes, if their eggs develop through a larval stage, those larvae

are called ophioplutei (http://www.google.co.za/search?hl=en&q=how+do+ophiuroids+reproduce%3F&meta=)

Some species brood their young, small adults brood while larger species tend to broadcast spawn (http://www.google.co.za/search?hl=en&q=how+do+ophiuroids+reproduce%3F&meta=)

Are scavengers and detritus feeders, while others prey on smaller live animals(http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html)

Water vascular system is somewhat similar to asteroids except for its position on oral surface (Brusca and Brusca, 1990)

Locomotion is achieved by arm waving (Brusca and Brusca, 1990)

Source:http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Echinodermata/Asterozoa/Ophiuroidea

Source:http://saltaquarium.about.com/gi/dynamic/offsite.htm?site=http://fins.actwin.com/species/index.php%3Ft=9%26i=324

Fig 6. Gorgonocephalus eucnemisFig 5. Ophiopholis aculeata (Daisy brittle star)

Class echinoidea:Class echinoidea:

  According to Hickman et al (2004) there are

“regular" and “irregular” sea urchins “Regular” sea urchins such as

Strongylocentrotus purparatus (Purple sea urchin) (Fig 7.) are called this because of their:

Hemispherical shape Radial symmetry Medium to long spines Move with tube feet “Irregular” sea urchins such as Encope

micropora (Sand dollars) (Fig 8.) are called “irregular” because they

Have become secondarily bilateral Their spines are short Move chiefly by spines

Fig 7. Strongylocentrotus purparatus (Purple sea urchin)

Source: http://home.earthlink.net/~huskertomkat/urch1.jpg

Fig 8. Encope micropora

Source: http://www.visualsunlimited.com/browse/vu228/vu228040.html

Echinodea (cont.)Echinodea (cont.)

Sea urchins have separate sexes and spawn seasonally (http://www.reef.edu.au/asp_pages/secb.asp?FormNo=42)

A distinguishing attribute of echinoidea is their unique feeding apparatus called Aristotles lantern which is situated inside the test (Fig 9.) (Hickman et al, 2004)

Fig 9. Aristotles lantern

Source: http://www.animals.uwa.edu.au/__data/page/54461/aristotle.jpg

Class HolothuroideaClass Holothuroidea

Consists of species such as Cucumaria frondosa (Fig 10.) and Parastichopus californicus (Fig 11.).

In sea cucumber the water vascular system is organized in a manner which is suitable for elongation of the body (Brusca & Brusca, 1990).

Species can reproduce sexually, which involves 2 phases : gametogenesis and spawning (Smiley et al, 1991)

Can also reproduce asexually (Smiley et al, 1991) Movement is achieved by crawling or burrowing (Hickman et al, 2004) When irritated or subjected to unfavorable conditions, many species

can cast out part of their viscera by a strong muscular contraction that may either rupture the body wall or evert its contents through the anus (Hickman et al 2004).

Some also contain organs of cuvier

Fig 10. Cucumaria frondosa Fig 11. Parastichopus californicus

Source:http://www.seawater.no/fauna/Pigghuder/images/dsc03064.jpg

Source:http://www.slugophile.org/taxon/pictures/Small/Parastichopus_californicus.jpg

Class CrinoideaClass Crinoidea

Species which are present in this class are Comantheria briareus (Fig 12.)

As fossil records reveal, crinoids were far more numerous than they are now (Hickman et al 2004).

They differ from other echinoderms because they are attached to a substratum for a large part of their lives (Hickman et al. 2004)

The structure consists of a calyx, which consists of arms, consisting of pinnules (Hickman et al. 2004)

The water vascular system operates entirely on coelomic fluid and there is no madreporite, instead there are a number of stone canals (Brusca & Brusca, 1990).

Fig 12. Comantheria briareus

Source: http://www.poppe-images.com/images/image_info.php#fs

Class ConcentricycloideaClass Concentricycloidea Disc shaped animals, less than 1 cm

in diameter (Hickman et al. 2004) Most recently found echinoderm

(1986) Only 2 known species, Xyloplax

medusiformis (Fig 13) and Xyloplax turnerae (Fig 14.)

No madreporite, but a hydropore (Brusca & Brusca, 1990)

Has a water vascular system in which the podia are not arranged along the ambulacra (Brusca & Brusca, 1990).

Xyloplax medusiformis lacks a digestive system (Brusca & Brusca 1990)

While Xyloplax turnerae has a complete gut (Brusca & Brusca, 1990)

Fig 13. Xyloplax medusiformis

Source: http://www.visualsunlimited.com/browse/vu419/vu419192.html

Fig 14. Xyloplax turnerae

Source: http://www.sfu.ca/~fankbone/v/xyloplax.jpg

When did echinoderms first arrive on the scene?When did echinoderms first arrive on the scene?

Made their introduction in the Cambrian period (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html).

Homalozoans (Fig 15.) and eocrinoids (dawn eocrinoids) and unusual helicoplacoids were some of the earliest echinoderms (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html)

Early eocrinoids, such as Gogia spiralis (Fig 16.) were attached to the substratum by a plate-covered thick stem or holdfast, whereas later species eocrinoids evolved a long stalk with columnals, like crinoids and blastoids (http://www.palaeos.com/Invertebrates/Echinoderms/echinodermata.htm)

Ordovician period consisted of Asterozoans (starfish and brittle stars) and echinozoans (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html)

Somasteroidea, which are the oldest asterozoans, show characteristics of both starfish and brittle stars (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html).

Source: http://www.palaeos.com/Invertebrates/Deuterostomia/Homalozoa/Images/Dendrocystites.jpg

Fig 15. HomalozoaFig 16. Gogia spiralis

Source: http://www.fossilshk.com/sea_life_image/sea_life_large/c46cu.jpg

Fig 17. Agriocinus

Source : http://www.ucmp.berkeley.edu/echinodermata/echinofr.html

When did echinoderms first arrive on the scene?When did echinoderms first arrive on the scene?(cont.)(cont.) The later Paleozoic was dominated by crinoids and blastoids, such as

the crinoid Agriocrinus (Fig 16.) (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html).

Blastoids and most crinoids became extinct (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html).

The most common echinoderms today are the Holothurians (sea cucumbers) but they have a very sparse fossil record (http://www.ucmp.berkeley.edu/echinodermata/echinofr.html).

Conditions which echinoderms faced in the Conditions which echinoderms faced in the PalaeozoicPalaeozoic Early Palaeozoic: During the early Palaeozoic there was probably a moderate climate

becoming warmer over the course of the Cambrian (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

The second greatest sustained sea level rise was approaching (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

The climate was also strongly zonal, with the result that the "climate", in an abstract sense became warmer, but the living space of most organisms of the time, the continental shelf marine environment, became steadily colder (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

The ice age in the Late Ordovician caused the second greatest mass extinction of Phanerozoic time The climate was also strongly zonal, with the result that the "climate", in an abstract sense became warmer, but the living space of most organisms of the time, the continental shelf marine environment, became steadily colder (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

Conditions which echinoderms faced in the Conditions which echinoderms faced in the Paleozoic (cont.)Paleozoic (cont.)

Middle Palaeozoic: There was considerable climate stability

(http://www.palaeos.com/Paleozoic/Paleozoic.htm). Sea levels had dropped coincident with the Ice Age

(http://www.palaeos.com/Paleozoic/Paleozoic.htm). As plants took hold on the continental margins when there was a slow

merger between the Baltica and Laurentia, oxygen levels increased and carbon dioxide dropped (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

Conditions which echinoderms faced in the Conditions which echinoderms faced in the Paleozoic (cont.)Paleozoic (cont.) Late Palaeozoic: Around the Permian period, there was an increase in atmospheric

oxygen, with an extreme plummet in carbon dioxide levels characterized the advent of the Mississippian epoch (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

This led to one, and perhaps two, ice ages during the Carboniferous (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

By the Silurian, both oxygen and carbon dioxide had recovered to more normal levels, but the assembly of Pangea (super continent) created huge arid inland areas subject to temperature extremes (http://www.palaeos.com/Paleozoic/Paleozoic.htm). 

The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, resulting in the Permian – Triassic extinction (http://www.palaeos.com/Paleozoic/Paleozoic.htm).

Theories for Permian Triassic extinctionTheories for Permian Triassic extinction The Permian Triassic extinction was an

extinction event that occurred approximately 251.0 million years ago (http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event)

Also known as the end P event (Fig 18.) (http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event).

90 % of marine and 70 % of terrestrial vertebrate species going extinct (http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event).

Theories involved are: Plate tectonics Impact event (comets and asteroids) Supernova Volcanism Atmospheric hydrogen sulfide buildup Methane hydrate gasification and a

combination (http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event).

Source: http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event

Fig 18. Permian Triassic Extinction extinction intensity

So, who survived?So, who survived? Details of the extinction and, in

particular the immediate post-extinction recovery in the Early Triassic, are seldom addressed because of a perception that the Permian–Triassic echinoderm fossil record is too poor (Twitchett and Oji, 2005).

 However this is proven wrong because only Holothuroidea and Asteroidea lack early Triassic remnants (Twitchett and Oji, 2005).

Crinoidea (Fig 19.) One of the major constituents of the

benthic communities (Twitchett and Oji, 2005)

Underwent the most striking decline of all the echinoderm groups (Twitchett and Oji, 2005)

To date there are no extant species of crinoids that existed in the Permian and Triassic period (Twitchett and Oji, 2005).

Fig 19. Permian Triassic history of Crinoidea

Source: Twitchett & Oji (2005)

So, who survived? (cont.)So, who survived? (cont.)

Families found: Holocrinidae Dadocrinidae Encrinidae Traumatocrinidae Ainigmacrinidae Isocrinidae Roveacrinidae then lastly Pentacrinitidae and the

Paracomatulidae (Twitchett and Oji, 2005).

Opiuroidea (Fig 20.) Only three ophiuroid taxa have been

described from Upper Permian strata, all from China, none of the species crossed the P–Tr boundary (Twitchett and Oji, 2005).

Fig 20. Permian Triassic history of Ophiuroidea

Source: Twitchett & Oji (2005)

So, who survived? (cont.)So, who survived? (cont.) Ophiuroidea had a high abundance in

the lower Triassic strata and did not go through a bottleneck effect (Twitchett and Oji, 2005).

It is known that modern ophiuroids are very tolerant of low salinities and low oxygen levels, which may have helped them to weather the environmental changes of the P–Tr interval (Twitchett and Oji, 2005).

Asteroidea (Fig 21.) According to Twitchett and Oji (2005),

asteroidean fossils records are very poor

Permaster and Monaster were the only two fossils found in the upper permian deposits (Twitchett and Oji, 2005).

Trichasteropsis, Berckhemeraster, and Noriaster are known from the entire Triassic (Twitchett and Oji, 2005).

This indicates that they went through a bottleneck effect (Twitchett and Oji, 2005).

Fig 21. Permian Triassic history of Asteroidea

Source: Twitchett & Oji (2005)

So, who survived? (cont.)So, who survived? (cont.) Echinoidea (Fig 22.) Two echinoid families are recorded as

fossils in the Late Permian: the Lepidocentridae and Miocidaridae (Twitchett and Oji, 2005).

No new fossil records of echinoidea appear until the carnian (Twitchett and Oji, 2005).

Post-Permian echinoids are divided into two subclasses: the Cidaroidea (comprising the families Miocidaridae and Cidaridae) and the Euechinoidea (comprising all the remaining echinoid taxa) (Twitchett and Oji, 2005).

Holothuroidea (Fig 23.) The fossil records and preservation

potential are extremely poor (Twitchett and Oji, 2005).

While there are records of body fossils as well as isolated ossicles from the Upper Permian and from the Middle-Upper Triassic, to date there is no definite reports from the Lower Triassic (Twitchett and Oji, 2005)

Fig 22. Permian Triassic history of Echinoidea

Source: Twitchett & Oji (2005)

So, who survived? (cont.)So, who survived? (cont.) There was no family-level

extinction during the P–Tr interval and that at least five lineages survived (Twitchett and Oji, 2005).

The theory for their survival is that because they were deposit feeders this aided their survival (Twitchett and Oji, 2005).

Fig 23. Permian Triassic history of Holothuroidea

Source: Twitchett & Oji (2005)

The debate over classification of echinodermsThe debate over classification of echinoderms

Upon reading the literature many scientists have argued that the current classification of echinoderms is wrong, they claim that echinoderms

should be on the same evolutionary line as chordates. Another group says that Echinoderms should be placed on the same line as

hemichordates. The current classification puts hemichordates on the same line of evolution as chordata

The debate over classification of echinodermsThe debate over classification of echinoderms

Reasons for echinoderms being on the same lineage as chordata: Chordates and echinoderms share an embryo growth pattern (

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter31/answers_to_text_questions.html).

Genetic differences in the expression of Hox genes, which suggests that echinoderms and chordates share a key characteristic very distinct from other animal groups (http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter31/answers_to_text_questions.html).

This was proven in Martinez et al (1998) where they showed that the echinoderm Hox gene cluster is essentially similar to those of the bilaterally organized chordates, despite the radically altered pentameral body plans of these animals.

The debate over classification of echinodermsThe debate over classification of echinoderms

Reasons for echinoderms being placed on the same line as hemichodata

Proof of an echinoderm connection to hemichordates is proven by Bromham and Degnan (1999).

A maximum likehood framework, including the parametric bootstrap, to reanalyze DNA data from complete mitochondrial genomes and nuclear 18s rRNA was used (Bromham & Degnan, 1999).

This provided the first statistically significant support for the hemichordate and echinoderm clade (Bromham & Degnan, 1999).

Echinoderms effect on their ecosystemEchinoderms effect on their ecosystem  Sea urchins such as

Strongylocentrotus franciscanus (Fig 24.) are important in structuring these kelp communities (Duggins, 1981).

Kelps add spatial complexity to benthic communities, provides substratum for other organisms, and creates cover for pelagic predators (Duggins, 1981).

Therefore intensive grazing by sea urchins not only impacts the algal assemblage but has been shown to have cascading effects on the rest of the community as well (Harold & Reed, 1985).

Fig 24. Strongylocentrotus franciscanus

Source : http://jellieszone.com/Output/British%20Columbia/Popup234.jpg - 19

References

Bromham, L.D. and Degnan B.M. 1999. Hemichordates and deuterostome evolution: robust molecular phylogenetic support for a hemichordate + echinoderm clade. Evolution & Development 1:3, 166-171

California, USA Brusca, R.C. and Brusca, G.J. 1990. Invertebrates.Sinauer Associates, INC. Sunderland,

Massachusetts.pp 812, 813, 818 Duggins, D.O. 1981. Sea urchins and kelp: the Effects of short term changes in Urchin diet. Limnology

and Oceanography, Vol. 26, No. 2. (Mar., 1981), pp 391 – 394 Harrold, C. and Reed, D.C.1985. Food availability, Sea urchin grazing, and Kelp Forest Community

Structure. Ecology, Vol. 66, No. 4., pp. 1160 -1169 Hickman. P, Roberts. L, Larson. A, I’Anson. H. 2004. Integrated principles of zoology, twelfth edition,

McGraw-Hill Companies. pp. 445, 450, 452, 455,456,457 http://en.wikipedia.org/wiki/Brittle_star http://en.wikipedia.org/wiki/Echinoderm http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter31/

answers_to_text_questions.html http://www.google.co.za/search?hl=en&q=how+do+ophiuroids+reproduce%3F&meta= http://www.palaeos.com/Invertebrates/Echinoderms/echinodermata.htm http://www.palaeos.com/Paleozoic/Paleozoic.htm. http://www.reef.edu.au/asp_pages/secb.asp?FormNo=42 http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Echinodermata/

Asterozoa/Asteroidea/

References

http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Echinodermata/Asterozoa/Asteroidea/

http://www.ucmp.berkeley.edu/echinodermata/echinofr.html http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html Martinez, P., Rast, J.P., Arenas-Menas, C., Davidson, E.H. 1999. Organization of

an echinoderm Hox gene cluster.Proc. Natl. Acad. Sci. USA. Vol. 96, pp 1469 -1474

Smiley, S., F. S. McEuen, C. Chaffee and S. Krishan. 1991. Echinodermata: Holothuroidea. Pages 663-750 in A.C. Giese, J. S. Pearse, and V. B. Pearse, editors. Reproduction of marine invertebrates, echinodermata and lophophorates. Volume VI.

Smith, Andrew B. 1997. ECHINODERM LARVAE AND PHYLOGENY. Annual Review of Ecology and SystematicsVol. 28: 219-241

Twitchett, R.J and Oji T. 2005. Early Triassic recovery of echinoderms. Comptes Rendus Palevol Volume 4, Issues 6-7

Wray, Gregory A. 1999. Echinodermata. Spiny-skinned animals: sea urchins, starfish, and their allies. Version 14 December 1999 (under construction). http://tolweb.org/Echinodermata/2497/1999.12.14 in The Tree of Life Web Project, http://tolweb.org