1. Dale Overmeyer 2355332 Dept. of Biodiversity and Conservation U.W.C
Echinoderms
Dale Overmeyer
Dept. of Biodiversity and Conservation
U.W.C

2. Contents 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

3. 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).
In order for an organism to be included in the phylum of echinodermata, they have to be able to be able to consist of the following four synapomorphies (Wray, 1999). Together, these synapomorphies define much of what makes the functional biology of echinoderms unique from that of other metazoans (Wray, 1999). Firstly, they must have a calcitic skeleton composed of many ossicles (Wray, 1999). Echinoderm skeletons are composed of calcium carbonate and several proteins (Wray, 1999). The distinguishing factor that makes ossicles unique to the phylum is not because they are solid but because they have a sponge like microstructure which is known as the stereom (Wray, 1999). Secondly, they must have a water vascular system (Wray, 1999). The water vascular system which operates hydraulically to perform many important functions such as locomotion, respiration, and feeding; in addition, most sensory neurons are located at the termini of podia (tubefeet) which are part of this organ system (Wray, 1999) The water vascular system is system of canals which branches around the anatomy, which branch further into many sections called tube feet ( .Thirdly, the body must contain alterable collagenous tissue which provides some interesting mechanical advantages, including the ability to maintain a variety of postures with no muscular effort (Wray, 1999). Lastly, there should be pentaradial body organization in adults (Wray, 1999).

4. Classification Kingdom: Animalia Subkingdom: Metazoa
Superphylum: Deuterostomia
Phylum: Echinodermata
Classes:
Asteroidea
Blastoidea (extinct)
Concentricycloidea
Crinoidea
Echinoidea
Holothuroidea
Ophiuroidea
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The scientific classification of the phylum echinodermata goes as follows.
Kingdom: Animalia
Subkingdom: Metazoa
Superphylum: Deuterostomia
Phylum: Echinodermata
Classes:
Asteroidea
Blastoidea (extinct)
Concentricycloidea
Crinoidea
Echinoidea
Holothuroidea
Ophiuroidea
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5. Reproduction
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
Reproduction
It should be acknowledged that Echinoderms belong to the branch of the animal kingdom that belongs to the deuterostomes and before larvae are formed there are certain developmental tendencies occurring as shown in (Fig 1.).
Forms of sexual reproduction among echinoderms include free spawning followed by external fertilization and indirect development to various forms of brooding and direct development (Brusca & Brusca, 1990). Echinoderms show rather complex life histories where the bilateral, planktonic larval stage (Fig 2.) alternates with a pentaradial adult benthic phase (Smith, 1997).
Fissiparity is a form of asexual reproduction occurring in some asteroids and ophiuroids, wherein the central disc divides into two and each half forms a complete animal by regeneration (Brusca & Brusca, 1990).
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6. Fig 2. Bilateral larval stage of Pisaster ochraceous
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7. Class Asteroidea Fig 3. Culcita novaeguineae (pincushion star)
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)
Includes species such as Culcita novaeguineae (pincushion star) (Fig 3.) and Acanthaster planci (Crown of thorns star) (Fig 4.). Sea stars, also known as starfishes are familiar along the shoreline where large numbers may 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 with tapering arms (Hickman et al 2004). The body is somewhat flattened, flexible and covered with a ciliated, pigmented epidermis (Hickman et al 2004). The mouth of a sea star is on the undersurface while the anus is situated dorsally ( Beneath the epidermis of sea stars is a mesodermal endoskeleton of small calcareous plates called ossicles, bound together with connective tissue (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). Structurally, the water vascular system opens to the outside through the small pores in the madreporite.
As far as reproduction is concerned, in some species liberated eggs are brooded, either under the oral side or in specialized aboral structures and development is direct, but 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).
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8. Fig 4. Acanthaster planci (Crown of thorns star)
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).
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9. Class 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)(
Have separate sexes, if their eggs develop through a larval stage, those larvae are called ophioplutei (
Some species brood their young, small adults brood while larger species tend to broadcast spawn (
Are scavengers and detritus feeders, while others prey on smaller live animals(
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)
They exist in all types of benthic marine habitats, also covering the abyssal sea bottom in many areas (Hickman et al 2004). Ophiuroidea contains two large clades, namely Ophiurida commonly known as brittle stars (Fig 5.) and Euryalida called basket stars (Fig 6.) (
As far as the physical structure is concerned, they have no pedicellariae or papulae, and their ambulacral grooves are closed and covered with arm ossicles (Hickman et al 2004).
Brittle stars generally have separate sexes, if their eggs develop through a larval stage, those larvae are called ophioplutei ( Some species brood their young, species with small adult size tend to brood while larger species tend to broadcast spawn ( This is because larger brittle star species can circulate water around the eggs inside the bursal brood chambers more efficiently and larger species have lower surface area to volume (of egg) ratios and therefore the ability to circulate water and oxygen to brooded eggs is less (
Most ophiuroids are scavengers and detritus feeders, they prey on small live animals and some such as the basket stars, filter-feed on plankton with their arms (
They have a similar water vascular system to asteroids, but as far as the location of the madreporite is concerned it is located on the oral surface of the central disc rather than off center as on the asteriodeans (Brusca & Brusca, 1990).
Locomotion is by arm movement because they lack suckers (Brusca & Brusca, 1990)

10. Fig 5. Ophiopholis aculeata (Daisy brittle star)
Fig 6. Gorgonocephalus eucnemis
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11. 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)
Class echinoidea:
A majority of living species of echinoids are termed “regular”, because they have a hemispherical shape, radial symmetry, and medium to long spines such as Strongylocentrotus purparatus (Purple sea urchin) (Fig 7.). Echinoids such as Encope micropora, Sand dollars (Fig 8.), are termed “irregular” because members of their orders have become secondarily bilateral; their spines are usually very short.
Regular urchins move by means of their tube feet, with some assistance of their spines, and irregular urchins move chiefly by their spines (Hickman et al 2004).
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12. Fig 8. Encope micropora
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13. Echinodea (cont.)
Sea urchins have separate sexes and spawn seasonally (
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
Sea urchins spawn seasonally every year, the sexes are separate, which allows eggs and sperm to be released into a water column allowing for fertilization (
A distinguishing feature of these echinoids is the possession of Aristotles lantern which is situated inside the test (dermical ossicles which become closely fitting plates) are a coiled digestive system and a complex chewing system to which teeth are attached (Fig 7.) (Hickman et al 2004)
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14. Class 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
Class Holothuroidea
Consists of species such as Cucumaria frondosa (Fig 10.) and Parastichopus californicus (Fig 11.). Ossicles are much greater reduced than in other echinoderms making them soft bodied (Hickman et al 2004). In sea cucumber the water vascular system is organized in a manner which is suitable for elongation of the body (Brusca & Brusca, 1990).
There have been a few reports of hermaphroditism in some species although male and female species are separate (Smiley et al. 1991). Sea cucumbers can reproduce sexually and there are 2 phases to sexual reproduction: gametogenesis and spawning (Smiley et al, 1991). Asexual reproduction is also undertaken in some species (Smiley et al, 1991).
Some species crawl on the floor, others are found beneath rocks, and some are burrowers (Hickman et al, 2004).
When irritated or subjected to unfavourable 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). Lost parts are soon regenerated (Hickman et al 2004). Certain species have organs of Cuvier (cuverian tubules), which are attached to the posterior part of the respiratory tree and can be expelled in the direction of the enemy (Hickman et al 2004). These tubules become long and sticky after expulsion, and some contain toxins (Hickman et al 2004).

15. Fig 10. Cucumaria frondosa
Fig 11. Parastichopus californicus
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16. Class Crinoidea Fig 12. Comantheria briareus
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).
Class Crinoidea
Commonly known as sea lillies and feather stars. Species which are present in this class are Comantheria briareus (Fig 9). They have several primitive characters as fossil records reveal, crinoids were far more numerous than they are now (Hickman et al 2004). They differ from other echinoderms by being attached during a substantial part of their lives (Hickman et al 2004). The anatomy of these crinoids consist of a poorly developed epidermis (Hickman et al 2004). The structure consists of a calyx, from which five flexible arms branch which contains pinnules, which all together makes up the crown (Hickman et al 2004). The sessile forms have a stalk attached to the calyx which consists of cirri (Fig 10).
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).
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17. Class Concentricycloidea
Fig 13. Xyloplax medusiformis
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)
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Class Concentricycloidea
They are small disc shaped animals, which are less than 1 cm in diameter and were discovered in water over 1000 m deep off New Zealand (Hickman et al 2004). Sometimes called sea daisies, they are the most recently described class of echinoderms (1986), and only 2 species are known so far (Hickman et al 2004). The water system of the sea daisies, Xyloplax, is unique (Brusca & Brusca, 1990). Instead of having a madreporite it consists of a hydropore which opens on the aboral surface, it should also be noted that these are the only echinoderms which has a water vascular system in which the podia are not arranged along the ambulacra (Brusca & Brusca, 1990).
As far as the feeding mechanisms are concerned the species, Xyloplax medusiformis (Fig 13.), lacks a digestive system, but absorb dissolved organic matter across the velum along its oral surface (Brusca & Brusca, 1990). On the other hand Xyloplax turnerae (Fig 14.) has a complete gut (Brusca & Brusca, 1990). The mouth opens into a shallow, saclike stomach but intestine and anus are lacking (Brusca & Brusca, 1990).

18. Fig 14. Xyloplax turnerae
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19. When did echinoderms first arrive on the scene?
Made their introduction in the Cambrian period (
Homalozoans (Fig 15.) and eocrinoids (dawn eocrinoids) and unusual helicoplacoids were some of the earliest echinoderms (
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 (
Ordovician period consisted of Asterozoans (starfish and brittle stars) and echinozoans (
Somasteroidea, which are the oldest asterozoans, show characteristics of both starfish and brittle stars (
Echinoderms are an ancient group of organisms that made their introduction in the Cambrian ( During the Cambrian, Homalozoans (Fig 15.) and eocrinoids (dawn eocrinoids) and unusual helicoplacoids were some of the earliest echinoderms ( Early eocrinoids, such as Gogia spiralis (Fig 16.) shown above, 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 ( .
Following the Cambrian was the Ordovician period, which consisted of Asterozoans (starfish and brittle stars) and echinozoans ( The Somasteroidea, which are the oldest asterozoans, show characteristics of both starfish and brittle stars; it is most likely that starfish and brittle stars diverged from a common somasteroid ancestor ( The later Paleozoic was dominated by crinoids and blastoids, such as the crinoid Agriocrinus (Fig 16), a crinoid from the Devonian period ( The most prominent echinoderms, the Asterozoans and echinozoans, have been the most prominent echinoderms ever since the end of the Permian while all blastoids and most crinoids became extinct ( The most common echinoderms today are the Holothurians (sea cucumbers) but they have a very sparse fossil record (

20. Fig 15. Homalozoa
Fig 16. Gogia spiralis
Fig 17. Agriocinus
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21. When did echinoderms first arrive on the scene?(cont.)
The later Paleozoic was dominated by crinoids and blastoids, such as the crinoid Agriocrinus (Fig 16.) (
Blastoids and most crinoids became extinct (
The most common echinoderms today are the Holothurians (sea cucumbers) but they have a very sparse fossil record (

22. Conditions which echinoderms faced in the Palaeozoic
Early Palaeozoic:
During the early Palaeozoic there was probably a moderate climate becoming warmer over the course of the Cambrian (
The second greatest sustained sea level rise was approaching (
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 (
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 (
Conditions which echinoderms faced during the Paleozoic
There was probably a moderate climate at first during the beginning of the Cambrian period, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic eon approached (
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 ( With the abrupt end of the early Paleozoic came the short and severe Late Ordovician Ice Age ( This cold spell caused the second-greatest mass extinction of Phanerozoic time (

23. Conditions which echinoderms faced in the Paleozoic (cont.)
Middle Palaeozoic:
There was considerable climate stability (
Sea levels had dropped coincident with the Ice Age (
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 (
There was considerable climate stability in the middle Paleozoic ( levels had dropped coincident with the Ice Age ( 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 (

24. Conditions which echinoderms faced in the 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 (
This led to one, and perhaps two, ice ages during the Carboniferous (
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 (
The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, resulting in the Permian – Triassic extinction (
During the late Paleozoic, 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 ( This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous (
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 ( Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, resulting in the Permian – Triassic extinction (

25. Theories for Permian Triassic extinction
The Permian Triassic extinction was an extinction event that occurred approximately million years ago (
Also known as the end P event (Fig 18.) (
90 % of marine and 70 % of terrestrial vertebrate species going extinct (
Theories involved are:
Plate tectonics
Impact event (comets and asteroids)
Supernova
Volcanism
Atmospheric hydrogen sulfide buildup
Methane hydrate gasification and a combination (
Fig 18. Permian Triassic Extinction extinction intensity
Theories for Permian Triassic extinction
The Permian Triassic extinction was an extinction event that occurred approximately million years ago ( Also known as the end P event (Fig 18.) ( It was the Earth's most severe extinction event, with about 90 % of all marine species and 70 % of terrestrial vertebrate species going extinct ( involved are Plate tectonics , Impact event (comets and asteroids) , Supernova ,Volcanism , Atmospheric hydrogen sulfide buildup, Methane hydrate gasification and a combination (
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26. So, who survived? Fig 19. Permian Triassic history of Crinoidea
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).
So, who survived?
According to Twitchett and Oji (2005) 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. However this is proven wrong because only Holothuroidea and Asteroidea lack early Triassic remnants (Twitchett and Oji, 2005).
Crinoidea (Fig 19.)
During the Paleozoic, crinoids were considered to be one of the major constituents of the benthic communities (Twitchett and Oji, 2005). When P-Tr extinction occurred they underwent the most striking decline of all the echinoderm groups (Twitchett and Oji, 2005). Fossil records of Latest Permian and Early Triassic crinoids are scarce and their diversity was very low (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).
The first crinoid to appear in the early Triassic is the Holocrinus belonging to the family Holocrinidae (Twitchett and Oji, 2005). After the Holocrinidae, the next families to appear in the fossil record are the Dadocrinidae then Encrinidae, followed by Traumatocrinidae, Ainigmacrinidae, Isocrinidae, Roveacrinidae then lastly Pentacrinitidae and the Paracomatulidae (Twitchett and Oji, 2005).
Ophiuroidea (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). Ophiuroid were however highly abundant in the lower Triassic strata worldwide (Twitchett and Oji, 2005). This high abundance could possibly show that ophiuroidea did not go through a bottleneck effect during the P-Tr event (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).
Source: Twitchett & Oji (2005)

27. So, who survived? (cont.)
Fig 20. Permian Triassic history of Ophiuroidea
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).
Source: Twitchett & Oji (2005)

28. So, who survived? (cont.)
Fig 21. Permian Triassic history of Asteroidea
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).
Asteroidea (Fig 21.)
According to Twitchett and Oji (2005), asteroidean fossils records are very poor. Only two genera of asteroidean have been found in the Upper Permian deposits (Permaster and Monaster) (Twitchett and Oji, 2005). There are no fossil records from the lower Triassic (Twitchett and Oji, 2005). Only three genera (Trichasteropsis, Berckhemeraster, and Noriaster) are known from the entire Triassic (Twitchett and Oji, 2005).
This probably indicates that they too went through a bottleneck effect near the P-Tr boundary (Twitchett and Oji, 2005).
The only other Triassic asteroid is Noriaster, which represents the earliest record of the extant family Poraniidae (Twitchett and Oji, 2005).
Echinoidea (Fig 22.)
Two echinoid families are recorded as fossils in the Late Permian: the Lepidocentridae and Miocidaridae, with the Miocidaridae crossing the P-Tr boundary (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).
Source: Twitchett & Oji (2005)

29. So, who survived? (cont.)
Fig 22. Permian Triassic history of Echinoidea
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)
Holothuroidea (Fig 23.)
The fossil records and preservation potential are extremely poor (Twitchett and Oji, 2005). According to Gilliland in Twitchett and Oji (2005), 450 described fossil species, compared to ca living species, and of those fossil examples less than 3% are described from complete body fossils. During the P–Tr interval the problems of fossil preservation manifested, 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). There was no family-level extinction during the P–Tr interval and that at least five lineages survived (Twitchett and Oji, 2005). This pattern is in stark contrast to the P–Tr evolutionary history of the other echinoderm classes.
The hypothesis is that an episode of primary productivity collapse would lead to the preferential extinction of suspension feeders and preferential survival of deposit feeders (Twitchett and Oji, 2005). Thus, primary productivity collapse during the P–Tr interval could explain the high levels of extinction amongst the suspension-feeding crinoids and the lack of extinction among the holothuroids, which are deposit feeders (Twitchett and Oji, 2005).
Source: Twitchett & Oji (2005)

30. Fig 23. Permian Triassic history of Holothuroidea
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).
Source: Twitchett & Oji (2005)

31. The 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 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

32. The debate over classification of echinoderms
Reasons for echinoderms being on the same lineage as chordata:
Chordates and echinoderms share an embryo growth pattern (
Genetic differences in the expression of Hox genes, which suggests that echinoderms and chordates share a key characteristic very distinct from other animal groups (
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 echinoderms
Firstly, echinoderms belong to the Deuterostome branch of the Animal kingdom (Hickman et al, 2004).
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 (Fig 18.).
The reason for placing echinoderms in the same lineage as chordata is given with the following evidence:
Chordates and echinoderms share an embryo growth pattern ( These embryological developmental patterns are guided by genetic differences in the expression of Hox genes, which suggests that echinoderms and chordates share a key characteristic very distinct from other animal groups (
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.

33. The 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).
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).

34. Echinoderms effect on their ecosystem
Fig 24. Strongylocentrotus franciscanus
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).
Echinoderms effect on their ecosystem
Upon researching the literature it was unquestionable that the importance of kelp was unquestionable. Kelp communities importance to near shore marine communities is well documented and results in large part from its very high productivity (Duggins, 1981). Kelps add spatial complexity to benthic communities, provides substratum for other organisms, and creates cover for pelagic predators (Duggins, 1981). Sea urchins such as Strongylocentrotus franciscanus (Fig 19.) are important in structuring these kelp communities (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).
Source :

35. References
Bromham, L.D. and Degnan B.M Hemichordates and deuterostome evolution: robust molecular phylogenetic support for a hemichordate + echinoderm clade. Evolution & Development 1:3,
California, USA
Brusca, R.C. and Brusca, G.J Invertebrates.Sinauer Associates, INC. Sunderland, Massachusetts.pp 812, 813, 818
Duggins, D.O 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 Food availability, Sea urchin grazing, and Kelp Forest Community Structure. Ecology, Vol. 66, No. 4., pp
Hickman. P, Roberts. L, Larson. A, I’Anson. H Integrated principles of zoology, twelfth edition, McGraw-Hill Companies. pp. 445, 450, 452, 455,456,457
References
Bromham, L.D. and Degnan B.M Hemichordates and deuterostome evolution: robust molecular phylogenetic support for a hemichordate + echinoderm clade. Evolution & Development 1:3,
California, USA
Brusca, R.C. and Brusca, G.J Invertebrates.Sinauer Associates, INC. Sunderland, Massachusetts.pp 812, 813, 818
Duggins, D.O 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 Food availability, Sea urchin grazing, and Kelp Forest Community Structure. Ecology, Vol. 66, No. 4., pp
Hickman. P, Roberts. L, Larson. A, I’Anson. H Integrated principles of zoology, twelfth edition, McGraw-Hill Companies. pp. 445, 450, 452, 455,456,457

36. References
Martinez, P., Rast, J.P., Arenas-Menas, C., Davidson, E.H Organization of an echinoderm Hox gene cluster.Proc. Natl. Acad. Sci. USA. Vol. 96, pp
Smiley, S., F. S. McEuen, C. Chaffee and S. Krishan Echinodermata: Holothuroidea. Pages in A.C. Giese, J. S. Pearse, and V. B. Pearse, editors. Reproduction of marine invertebrates, echinodermata and lophophorates. Volume VI.
Smith, Andrew B.­ ECHINODERM LARVAE AND PHYLOGENY. Annual Review of Ecology and Systematics Vol. 28:
Twitchett, R.J and Oji T Early Triassic recovery of echinoderms. Comptes Rendus Palevol Volume 4, Issues 6-7
Wray, Gregory A Echinodermata. Spiny-skinned animals: sea urchins, starfish, and their allies. Version 14 December 1999 (under construction). in The Tree of Life Web Project,
References
Martinez, P., Rast, J.P., Arenas-Menas, C., Davidson, E.H Organization of an echinoderm Hox gene cluster.Proc. Natl. Acad. Sci. USA. Vol. 96, pp
Smiley, S., F. S. McEuen, C. Chaffee and S. Krishan Echinodermata: Holothuroidea. Pages in A.C. Giese, J. S. Pearse, and V. B. Pearse, editors. Reproduction of marine invertebrates, echinodermata and lophophorates. Volume VI.
Smith, Andrew B.­ ECHINODERM LARVAE AND PHYLOGENY. Annual Review of Ecology and Systematics Vol. 28:
Twitchett, R.J and Oji T Early Triassic recovery of echinoderms. Comptes Rendus Palevol Volume 4, Issues 6-7
Wray, Gregory A Echinodermata. Spiny-skinned animals: sea urchins, starfish, and their allies. Version 14 December 1999 (under construction). in The Tree of Life Web Project,