Phylum Echinodermata

echinoderms 

Echinodermata 

tagghudingar

general things 

Echinodermata

Echinodermata Klein, 1734 ex Bruguière, 1789 

Ethymology: Greek echinos (hedgehog, spine) and derma (integument, skin) 

Main characteristics: 

all echinoderms have a mesodermal skeleton of porous calcite plates 

but: reduced to absent among some holothuroids 

skeleton covered by a thin skin Endoskeleton 

radial symmetry, typically five-rayed / pentameral, as adults 

but: not developed in stem-group echinoderms, or carpoids 

lost or obscured by secondary adaptations 

water-vascular system (complex internal apparatus of tubes and bladders containing fluid) 

with extensions emerging through the skeleton to the outside as tube feet or podia 

(podia serve for locomotion, respiration and feeding a.o.) 

but: has not been confirmed in all fossil groups 

Echinodermata – general features

Porous calcite plates (ossicles) 

intracellular 

reducing the ossicle-producing stroma cell to a thin layer that lines the skeletal meshwork (stereom). 

each ossicle is a monocrystal 

high-magnesium calcite, which is a spathic mineral (crystalline with strong cleavage) 

• spathic fracture has been changed to conchoidal by inserting organic macromolecules 

into the crystal lattice 

• each ossicle is composed of two interlocked networks, one composed of 

mineral matter (stereom) and the other, of organic matter of mesodermal origin (stroma). 

• the trabecular structure of the stereom does not allow cracks to propagate 

farther than the next cavity 

• in fossils, pores of the stereom have become closed by diagenetic calcite in optical continuity. 

Echinodermata – general features – ossicles 

epidermis 

stroma 

stereom

Ossicles ... 

... can be fused into a test (sea urchins, crinoids) 

... can spread apart (sea cucumbers) 

... can be intermediate and variable (sea stars) 

Echinodermata – general features – ossicles

Exceptions! Primary polycrystalline calcite in ... 

Echinodermata – general features – ossicles 

... the cortex of primary spines of Cidaridae 

... tooth sceleton of Clypeaster 

... the accessory calcareous structures 

… filling the crevice fold in the chewing 

… areas of Diadematoida teeth. 

Cortex (primary polycrystalline) 

disturbed crystal structure (secondary!)

Water vascular system (= ambulacral system) 

Hydraulic system of fluid-filled canals 

• internal transport 

• locomotion 

• gas exchange 

• food capture 

• excretion 

• fluid similar to seawater and is moved 

through system with cilia 

Podia – tube feet 

• suction cups at the end 

• each tube foot works independently 

• moved by muscles and hydraulics 

Madreporite 

• perforated platelike structure which acts as the inlet for the water vascular system 

• (important for orientation, arms/ambulacralia) 

Stone canal 

• lime-walled tube which connects ring canal and madreporite 

Echinodermata – general features – water vascular system 

[Latin ambulacrum, walk planted with trees, from ambulare, to walk.]

Echinodermata – general features – water vascular system

ambulacra 

Echinodermata – general features – water vascular system

Other fearures: 

non-segmented 

no head 

open blood system 

nervous system simple without nerval center 

light sensors/eyespots but no eyes 

reproduce sexually (produce sperm and eggs) 

and asexually (regenerating lost parts) 

Echinodermata – other features

Ecology 

exclusively marine and stenohaline 

typically benthic (infaunal, epifaunal) but a few pelagic (planktonic and 

pseudo-planktonic) forms exist 

live free (vagile, floating, or active swimming) or attached (sessile) 

live on all kinds of substrates, littoral to abyssal, in all latitudes 

(today typical in shallow coastal waters and ocean trenches) 

carnivorous / herbivorous / detritus eaters 

Echinodermata – ecology



Luidia ciliaris (Asteroidea) 

Echinocardium cordatum (Echinoidea) 

Echinodermata – ecology 

Heterometra sp. 

Amphiura brachiata (Ophiuroidea, brittle star)

systematics 


1) Stem-group Echinodermata

Echinoderm classification 

Arkarua adami from the Ediacaran Hills of Australia 

oldest putative echinoderm 

Reference: 

Gehling, J.G. 1987. Earliest known echinoderm - a new Ediacaran fossil from the 

Pound Subgroup of South Australia. – Alcheringa, 11:337-345. 

Echinodermata – classification

Helicoplacoidea (Lower Cambrian) 

spirals of overlapping ossicles 

"mouth" was a long groove that also spiralled around their body 

lived probably in burrows and extending their bodies outward to feed 

three ambulacra 

complete fossils only found in the White Mountains in California 

Reference: 

Dornbos, S. Q. & Bottjer, D. J. 2000. Taphonomy and environmental distribution of 

helicoplacoid echinoderms. – Palaios, 16: 197-204. 

Echinodermata – classification – Helicoplacoidea

Mixed ossicles (Lower Cambrian)

Homlozoa systematics 


2) Homalozoa

Homalozoa [= Calcichordata, Carpoidea] (Middle Cambrian – Middle Devonian) 

bilateral or asymmetical 

main body (theca) constructed of two types of ossicles: marginalia and centralia 

theca typically flattened and with appendages (stele, aulacophore) 

use of appendages unknown (locomotion, feeding, tail for swimming etc.) 

Four main groups can be distinguished 

Ctenocystoidea – Homostelea (=Cincta) – Homoiostelea (= Soluta) – Stylophora 

Echinodermata – classification - Homalozoa 

[incl. Mitrata, 

Cornuta, 

Ankyroida]

marginalia 

presumed mouth 

”arm” =? ambulacrum 

centralia 


presumed anus 

proxi- mesi- dististele 

stele, aulacophore (tripartite) 

anterior? posterior?

Stylophora, Ankyroida 

Stylophora, Cornuta 


Homoiostelea 

Homostelea 

Ctenocystoidea

Calcichordate theory (Jefferies 1986): 

Chordates (ourselves) evolved from homalozoan echinoderms 

Stele=tail 

Calcite skeleton was replaced by an apatite one 

Theory more or less abandoned by now

systematics 


3) Pelmatozoa

Pelmatozoa (since Middle Cambrian) 

”attached living”, stalked echinoderms (some secondarily freeliving) 

cup-shaped head (the calyx) 

attached to the calyx are arms (brachiols/brachia) 

the calyx is usually connected 

oral plates 

tegmen 

to the bottom via a stem 

pentamere or radial symmetry 

Three main groups: 

Cystoidea 

Blastoidea 

Crinoidea (sea lilies) 

Echinodermata – classification – Pelmatozoa 

theca 

calyx 

stem 

nodal 

internodal 

’arm’ 

brachium 

brachiol 

columnars

Cystoidea (Ordovician to Devonian) [kristalläpplen] 

respiratory ”pore structures” traversing the plates of the theca 

pore structures are basis for taxonomy 

theca often slightly irregular 

stem short or absent 

well defined ”anal pyramid” surrounded by trigonal anal plates 

laterally to perioral plates 

hydropore (slit near the perisome, probably entrance of water vascular system) 

arms are non-branching, biserial brachiols 

two pore types typify the two main groups of cystoids 

Diploporita Rhombifera 

Echinodermata – classification – Pelmatozoa – Cystoidea 

diplopores dichopores 

rhomb-shaped contour

[anal pyramid, brachiols, dichopores] 

Echinodermata – classification – Pelmatozoa – Cystoidea

Blastoidea (Early Cambrian/Ordovician to Permian) 

typically with pentamere symmetry 

short stem (rarely preserved) 

crown of brachioles (rarely preserved) 

typical plating pattern: 

3 basal plates (BB) – 5 radial plates (RR) – 5 deltoid plates (Δ) – 

5 lancet plates below ambulacra 

star shaped mouth surrounded by spiracles (”outlet system”) 

Echinodermata – classification – Pelmatozoa – Blastoidea 

anispiracle

Blastoidea sensu stricto 

Echinodermata – classification – Pelmatozoa – Blastoidea 

Eocrinoidea (Early Cambrian to Silurian) 

Gogia palmeri

Crinoidea (since Ordovician) 

Most common palaeozoic 

echinoderm fossils 

Long stems 

Crinoid “meadows” in shallow water 

Disarticulated stems rockforming

Crinoidea (since Ordovician) 

radials 

basals 

radials 

basals 

infrabasals 

organized in stem, theka and brachia with ambulacra 

monocyclic calyx 

dicyclic calyx 

Echinodermata – classification – Pelmatozoa – Crinoidea 

radianal plate 

brachia 

brachials

Crinoidea (major groups and relationships) 

= Aethocrinea 

1 development of true arms with extension of the ambulacra 

2 loss of the basal circlet 

3 loss of the lintel circlet 

4 fixed brachials and fixed interradials incorporated into the calyx 

5 with the mouth exposed on the tegmen and loose plate sutures 

6 loss of the anal plate and an entoneural system enclosed within the calyx plates 

Echinodermata – classification – Pelmatozoa – Crinoidea 

Early Ordovician to Permian 

Ordovician 

since Triassic 

Early Ordovician to Permian 

Middle Ordovician to Permian 

Early Ordovician to Permian

Camerata 

Echinodermata – classification – Pelmatozoa – Crinoidea – Camerata

Articulata (Comatulida) 

occur from intertidal to abyssal depths 

retain a stalk as postlarvae, but shed 

all but the topmost segment and take up 

a free existence as juveniles and adults 

with cirri (columns of ossicles) radiating from the 

margin of the centrodorsal plate 

distal ossicle is a small claw (holdfast) 

Leptometra celtica 

Echinodermata – classification – Pelmatozoa – Crinoidea – Articulata – Comatulida 

Antedon bifida

In deep water settings: 

Stalked crinoids survive to 

the present 

Crown of arms directed 

against current for effective 

filtering

systematics 


4) Eleutherozoa

Eleutherozoa (since Early Cambrian / Ordovician) 

the non-stalked, vagile echinoderms (with exceptions!) 

= sea cucumbers, sea stars and brittle stars, sea urchins and sand dollars 

and some small fossil groups of uncertain affinity, as well as sea daisies 

Edrioasteroidea (Early Cambrian to Early Carboniferous) 

Holothuroidea (Ordovician?, since Early Devonian) 

(sea cucumbers) 

Concentricycloidea (Recent) 

(sea daisies) 

Asterozoa (since Early Ordovocian) 

(sea stars and cushion stars, brittle stars and basket stars, Somasteroidea) 

Echinozoa (since Early Ordovician) 

(sea urchins and sand dollars, Cyclocystoidea?) 

Echinodermata – classification – Eleutherozoa

Edrioasteroidea 

typically with well developed pentamere symmetry 

endothecal ambulacral system 

no arms or brachioles 

with anal pyramid and peristomal field 

sessile 

combine characteristics of 

Eleutherozoa and Pelmatozoa 

Early Cambrian to Early Carboniferous 

Spiraclavus (Carboniferous) 

Echinodermata – classification – Eleutherozoa – Edrioasteroidea 

Stromatocystites (Cambrian) 

Edrioaster (Cambrian) 

Carneyella (Ordovician)

Holothuroidea (sea cucumbers) 

mouth and anus at opposite ends (secondary 

ossicles are imbedded within leathery skin 

ossicles often reduced to little sclerites (typify certain families) 

only in mouth region is a rigid series of plates (perioral ring) 

ambulacra arranged in two sets parallel with the long axis (3 ventral, 2 dorsal) 

few complete fossils: 2 Upper Jurassic (Solnhofen), 1 Lower Devonian Hunsrück 

Ordovician?, since Early Devonian 

Palaeocucumaria hunsrueckiana 

Echinodermata – classification – Eleutherozoa – Holothuroidea 

modified tube feet 

for feeding

Concentricycloidea (sea daisies) 

discovered in 1986 

disk-shaped flat bodies and are less than 1 cm in diameter. The two 

species were located on wood found in deep waters off the coasts of New Zealand and the Bahamas 

recently found in the North Pacific (Voight, 2005) 

water-vascular system, with tube feet on the body surface around the edge of the disk 

no obvious arms or mouth; appear to absorb nutrients through their body wall 

possibly an aberrant asteroid 

Reference: 

Voight, J. R. 2005. First report of the enigmatic echinoderm Xyloplax from the North Pacific. – 

Biological Bulletin, 208: 77-80. 

Echinodermata – classification – Eleutherozoa – Concentricycloidea

Asterozoa 

echinoderms with depressed star-shaped body 

with central disc bearing mouth on underside 

symmetrical radiating arms 

tube feet normaly confined to lower side of body 

since Early Ordovician 

3 main groups: 

Asteroidea 

(sea stars and cushion stars) 

Somasteroidea 

Ophiuroidea 

(brittle stars and basket stars) 

Echinodermata – classification – Eleutherozoa – Asterozoa

Asteroidea (sea stars and cushion stars) 

Asterozoans with relatively broad arms 

considerable hollow space between ossicular frame 

arms not seperated from central disc 

oral side with open ambulacral grooves with rows of tube feed 


gen. et sp. indet. (Ordovician, Morocco) Crateraster (Cretaceous, England) 

Echinodermata – classification – Eleutherozoa – Asterozoa – Asteroidea

Somasteroidea 

Asterozoans with oral surface bearing shallow radial channels 

axial skeleton with ambulacral ossicles in double series 

each ambulacral giving rise to a transverse series of ossicles (metapinnules) 

Early Ordovician to Late Devonian 

appear prior to Asteroidea and Ophiuroidea 

Villebrunaster thorali (Early Ordovician, France) 

oral, ventral side 

Echinodermata – classification – Eleutherozoa – Asterozoa – Somasteroidea 

Archegonaster pentagonus (Early Ordovician, Czechia) 

oral, ventral side

Ophiuroidea (brittle stars and basket stars) 

5 thin, flexible snake-like arms 

arms clearly demarcated from central disks and made up 

of a single row of large calcite plates termed vertebrae 

[early members had double rows of alternating vertebrae] 

typically suspension feeders, few carnivores 

live today mainly in bathyal and abyssal depths 

haven’t chanched much since their first appearance 

since Ordovician 

modern brittle star 

Encrinaster (Devonian) 

Echinodermata – classification – Eleutherozoa – Asterozoa – Ophiuroidea 

Ophioderma (Jurassic) 

Furcaster (Devonian) 

Loriolaster (Devonian)

Echinozoa (”sea urchins”) 

echinoderms with globose or discoidal test 

typically with spines 

typical with 5 ambulacral fields 

2 main groups: 

1) Echinoidea (sea urchins and sand dollars) 

2) Cyclocystoidea 


Phymosoma sp. (Cretaceous) 

Echinodermata – classification – Eleutherozoa – Echinozoa

Echinoidea (sea urchins and sand dollars) 

test (= corona) constructed of 20 radial plate rows (= 10 segments) 

narrow segments = ambulacra, broad segments = interambulacra 

interambulacral plates are large and tubercular, without perforations 

ambulacral plates have pored plates through which the tube feet emerge 

mouth with five hard teeth arranged in a circlet (known as Aristotle's lantern) 

[reduced in derived forms; absent in stem group echinoids] (used for grazing) 

move with tube feet or ”walk” on their spines 

traditionally devided in regular (Regularia) and irregular echinoids (Irregularia) 

Echinodermata – classification – Eleutherozoa – Echinozoa - Echinoidea

Aristotle's lantern 

perignathic girdle 


“Regularia and Irregularia” 

represent no phylogentic groups, still used as a convenient, informal classification 

Regularia: strict pentamere symmetry 

upper surface (aboral) with central apical disc bearing periproct with anus 

long spines for protection 

epibenthic grazers 

paraphyletic group 

Irregularia: pentamere symmetry with superimposed bilateral symmetry 

mouth located more anterior 

anus at posterior end 

test covered with a mat of short spines 

infaunal depost feeders 

most probably monophyletic 


Echinoidea classification 

==o Echinoidea 

|--o Perischoechinoidea = “Paleozoic Regularia”, stem group 

| `--o Cidariida 

| |-- Cidaridae = advanced stem group 

| `-- Psychocidaridae 

`--+-- Euechinoidea [paraphyletic?] = “Regularia” 

|-- Gnathostomata = a.o. “sand dollars” 

`-- Atelostomata = a.o. “heart urchins” 

Perischoechinoidea 

- stem group Echinoidea 

- more than 20 radial plate rows 

- perignathic girdle rudimentary or absent 


adambulacral - perradial - interradial sutures 

Echinodermata – classification – Eleutherozoa – Echinozoa – Echinoidea – regular echinoids 

Classification: 

- Arrangement of plates 

in apical disc 

- Morphology of lantern 

- Construction of 

perignathic girdle

Echinodermata – classification – Eleutherozoa – Echinozoa – Echinoidea – heart urchins 

20 plare columns 

5 interambulacral 

5 ambulacral 

Classification 

- Apical disc 

- Shape of petals 

- Plating of plastron

Echinodermata – classification – Eleutherozoa – Echinozoa – Echinoidea – sand dollars 

5 interambulacral columns 

5 ambulacral columns 

Adapical portion of ambulacra 

developed int petals 

Spines are short and stubby 

5 food grooves radiating 

from peristome 

Often with elongated 

perforations (lunules) 

Have a lantern and perignathic 

Girdle, which, however, can be 

resorbed in adult stages

Cyclocystoidea 

enigmatic Paleozoic group (Early Ordovocian to Early Carboniferous) 

mainly known by their ring of submarginal plates 

mode of life and systematic position controverse 

in situ finds confirm ”oral side down” 

oral disc with complicated 

ambulacral system 

Echinodermata – classification – Eleutherozoa – Echinozoa – Cyclocystoidea

systematics 


5) Problematica

Echmatocrinus from the Middle Cambrian Burgess Shale 

described as the oldest known crinoid 

Echmatocrinus brachiatus 

• interpretation refused by several authors 

• probably best considered as a cnidarian 

with octocoral affinity 

(Ausich & Babcock, 2000) 

Reference: 

Ausich W. I. & Babcock, L. E. 2000. Echmatocrinus, a Burgess Shale animal reconsidered. - Lethaia, 33 (2): 92-94. 

Echinodermata – classification – Problematica 

surface pattern with scales/plates

Eldonia, Portalia and Redoubtia, all known from the Burgess Shale have originally 

been described as holothourians 

Eldonia is now considered to be a jelly fish 

Portalia and Redoubtia is of uncertain affinity (polychaete or sponge?) 

Eldonia ludwigi Middle Cambrian 

Echinodermata – classification – Problematica

systematics 


summary

Classical paleontological 

classification 

(e.g., Clarkson) 

Phylum Echinodermata 

Subphylum Blastozoa 

* Class Eocrinoidea (Cambrian - Silurian, 30-32 genera) 

* Class Parablastoidea (Ordovician, 3 genera) 

* Class Rhombifera = Cystoidea in part (Ordovician - Devonian, 60 genera) 

* Class Diploporita = Cystoidea in part (Ordovician - Devonian, 42 genera) 

* Class Blastoidea (Silurian - Permian, 95 genera) 

Subphylum Crinozoa 

* Class Crinoidea - sea lilies (Cambrian - Recent, 1005 genera) 

* Class Paracrinoidea (Ordovician - Silurian, 13-15 genera) 

Subphylum Echinozoa 

* Class Echinoidea (Sea Urchins) (Ordovician - Recent, 765 genera) 

* Class Holithuriudea (Sea Cucumbers) (Ordovician - Recent, 200 genera) 

* Class Edrioasteroidea (early Cambrian - Carboniferous, 35 genera) 

* Class Edrioblastoidea (Ordovician, 1 genus) 

* Class Helicoplacoidea (Cambrian, 3 genera) 

* Class Cyclocystoidea (Ordovician - Devonian, 8 genera) 

Subphylum Asterozoa (Stelleroidea) 

* Class Asteroidea - starfish - (early Ordovician - Recent, 430 genera) 

* Class Ophiuroidea - Brittle Stars -(Ordovician - Recent, 325 genera) 

Subphylum Homalozoa 

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

Echinodermata – systematics 

* Class Stylophora (Cambrian - Devonian, 32 genera) 

* Class Homoiostelea (Cambrian - Devonian, 12-13 genera) 

* Class Homostelea (Cambrian, 3 genera) 

* Class Ctenocystoidea (Cambrian, 2 genera)

Echinodermata – systematics




Echinodermata – evolution

slut 

Echinodermata

Phylum Echinodermata

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