Download glossary for the echinodermata

February 2011
©RBCM
Christina Ball
Phil Lambert
GLOSSARY FOR THE ECHINODERMATA
OVERVIEW
The echinoderms are a globally distributed and morphologically diverse group of
invertebrates whose history dates back 500 million years (Lambert 1997; Lambert 2000;
Lambert and Austin 2007; Pearse et al. 2007). The group includes the sea stars
(Asteroidea), sea cucumbers (Holothuroidea), sea lilies and feather stars (Crinoidea), the
sea urchins, heart urchins and sand dollars (Echinoidea) and the brittle stars
(Ophiuroidea). In some areas the group comprises up to 95% of the megafaunal biomass
(Miller and Pawson 1990). Today some 13,000 species occur around the world (Pearse et
al. 2007). Of those 13,000 species 194 are known to occur in British Columbia (Lambert
and Boutillier, in press).
The echinoderms are a group of almost exclusively marine organisms with the
few exceptions living in brackish water (Brusca and Brusca 1990). Almost all of the
echinoderms are benthic, meaning that they live on or in the substrate. There are a few
exceptions to this rule. For example several holothuroids (sea cucumbers) are capable of
swimming, sometimes hundreds of meters above the sea floor (Miller and Pawson 1990).
One species of holothuroid, Rynkatorpa pawsoni, lives as a commensal with a deep-sea
angler fish (Gigantactis macronema) (Martin 1969).
While the echinoderms are a diverse group, they do share four unique features
that define the group. These are pentaradial symmetry, an endoskeleton made up of
ossicles, a water vascular system and mutable collagenous tissue. While larval
echinoderms are bilaterally symmetrical the
adults are pentaradially symmetrical
(Brusca and Brusca 1990).
All echinoderms have an
endoskeleton made of calcareous ossicles
(figure 1). The density of the ossicles within
the mesoderm varies amoung groups and
species. In the Echinoidea (urchins and sand
dollars) the ossicles are fused together to
form a rigid test (Lambert and Austin 2007).
Similarly in the Crinoidea and Ophiuroidea
Figure 1. Scanning electron micrograph
many of the ossicles have fused together to
(SEM) of ossicles from a holothuroid.
form hard skeletal elements (e.g. the
brachials of crinoid arms) (Lambert and Austin 2007). In comparison the ossicles of the
holothuroids (sea cucumbers) are widely spaced (Lambert 1997).
The water vascular system is a complex network of canals and reservoirs. It uses
hydraulic pressure and the action of muscles to operate the various podia (Brusca and
Brusca 1990). Podia include both tube feet (used in locomotion and attachment) and
tentacles (used in feeding). The podia also function in gas exchange and sensory
reception. The water vascular system is usually open at one end to the surrounding
environment. This opening, called the madreporite, is where sea water enters the system.
While most asteroids and echinoids have relatively obvious madreporites, the
holothuroids have an internal madreporite that can only be seen upon dissection (Lambert
1997). The madreporite is absent in the crinoids.
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Phil Lambert
Mutable collagenous tissue is also unique to the echinoderms and is, perhaps,
their most fascinating trait. This tissue can change rapidly, in less then a second to several
minutes, from a rigid to a flaccid state. The change in physical state, from hard to soft or
vice versa, is not the result of muscle activation, but rather the result of changes to the
passive mechanical properties of the tissue itself. The current consensus is that mutable
collagenous tissue is made up of discrete collagen fibrils that are organized into bundles
(Wilkie 2002). Substances released by juxtaligamental cells change the cohesion between
the collagen bundles causing the tissue to either harden or soften (Wilkie 2002). These
changes are under the control of the nervous system.
Sea urchins and some sea stars have pedicellariae
on the aboral side: these are jaw-like structures often
mounted on flexible stalks (figure 2). The shape of the
three-part jaw varies, and any given species might have
two or more types of pedicellariae (Brusca and Brusca
1990). The pedicellariae are used to keep debris off the
organism, to hold and capture small prey and in defense.
The echinoderms, like some other groups of
animals, have the ability to regenerate lost body parts
(Brusca and Brusca 1990). The crinoids are particularly
adept at regenerating body parts and can regenerate both
Figure 2. SEM of the jaw of
their arms and visceral mass, assuming that a sufficient
a sea urchin pedicellaria.
amount of the main body remains undamaged (Kondo
and Akasaka, 2010). The crinoids also use regeneration to grow additional arms (i.e. they
autotomize one arm and re-grow two arms) (Kondo and Akasaka, 2010). A few
ophiuroids, though none in BC, rely on regeneration to reproduce asexually. In such
species the brittle star splits across its central disc and each half regenerates into a new
individual (Crawford and Crawford 2007).
a
b
Figure 3. Morphology of a generalized brittle star (Ophiuroidea) (a), and a sea
star (Asteroidea) (b).
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a
b
c
d
Figure 4. Morphology of a generalized feather star (Crinoidea) (a), sand dollar
(Echinoidea) (b), sea urchin (Echinoidea) (c), and sea cucumber (Holothuroidea) (d).
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SPECIES OF BRITISH COLUMBIA AND THE NORTHEAST PACIFIC
The following checklist lists all of the species known to occur in British Columbia
and adjacent regions. Species that are not known to occur in BC but do occur either
immediately north or south of the province are indicated by an asterisk. The list is from
Lambert and Boutillier (in press).
Depth ranges are given for each species if known. The species authorities (authors
and dates) are also provided. The species authority is the person or persons who first
publish a description about a new species. Many echinoderms do not have common
names and due to space constraints none are included here. Further information on many
of these species can be found in Lambert (1997; 2000) and Lambert and Austin (2007).
Echinodermata
Crinoidea – sea lilies, feather stars (five species)
Echinoidea – urchins, sand dollars, sea biscuits (eight species)
Ophiuroidea – brittle stars (45 species)
Holothuroidea – sea cucumbers (47 species)
Asteroidea – sea stars (88 species)
CRINOIDEA (Sea Lilies and Feather Stars – five species in BC)
Hyocrinida
Hyocrinidae
Gephyrocrinus n. sp. Roux and Lambert, in prep.
Ptilocrinus n. sp. Roux and Lambert, in prep.
Ptilocrinus pinnatus A.H. Clark, 1907
Bourgueticrinida
Bathycrinidae
*Bathycrinus pacificus A.H. Clark, 1907
Comatulida
Pentametrocrinidae
*Pentametrocrinus paucispinulus Messing, 2008
*Pentametrocrinus varians (Carpenter, 1882)
Zenometridae
Florometra serratissima (A.H. Clark, 1907)
*Retiometra alascana A.H. Clark, 1936
Zenometridae
Psathyrometra fragilis (A.H. Clark, 1907)
ECHINOIDEA (Sea Urchins and Sand Dollars - eight species in BC)
Cidaroida
Cidaridae
*Aporocidaris fragilis Agassiz and Clark, 1907
*Aporocidaris milleri Agassiz, 1898
Echinothurioida
Echinothuriidae (Soft Sea Urchins)
Sperosoma biseriatum Doderlein, 1901
*Sperosoma giganteum Agassiz and Clark, 1907
1859 – 1903 m
1164 – 2105 m
2904 m
1655 m
1768 m
457 – 2727 m
11 – 1252 m
291 – 1270 m
439 – 2903 m
3000 – 4000 m
850 – 4300 m
1019 – 3500 m
1211 m
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Echinoida
Strongylocentrotidae
Strongylocentrotus droebachiensis (Müller, 1776)
Strongylocentrotus fragilis Jackson, 1912
Strongylocentrotus franciscanus (Agassiz, 1863)
Strongylocentrotus pallidus (Sars, 1871)
Strongylocentrotus purpuratus (Stimpson, 1857)
Clypeasteroida
Dendrasteridae
Dendraster excentricus (Eschscholtz, 1831)
Holasteroida
Urechinidae
*Cystechinus loveni Agassiz, 1898
Pourtalesiidae (Deep-sea Urchins)
*Ceratophysa ceratopyga valvaecristata Mironov, 1976
*Cystocrepis setigera (Agassiz, 1898)
*Echinocrepis rostrata Mironov, 1973
*Pourtalesia tanneri Agassiz, 1898
*Pourtalesia thomsoni Mironov, 1976
Spatangoida
Schizasteridae
Brisaster latifrons (Agassiz, 1898)
Aeropsidae
*Aeropsis fulva (Agassiz, 1898)
OPHIUROIDEA (Basket Stars and Brittle Stars - 45 species in BC)
Euryalida
Asteronychidae
Asteronyx loveni Müller and Troschel, 1842
Gorgonocephalidae (Basket Stars)
Gorgonocephalus eucnemis Müller and Troschel, 1842
Asteroschematidae
Asteroschema sublaeve Lütken and Mortensen, 1899
Ophiurida (Brittle Stars)
Ophiomyxidae
Ophioscolex corynetes (H.L. Clark, 1911)
Ophiacanthidae
Ophiacantha bathybia H.L. Clark, 1911
Ophiacantha cataleimmoida H.L. Clark, 1911
Ophiacantha diplasia H.L. Clark, 1911
Ophiacantha eurypoma H.L. Clark, 1911
Ophiacantha normani Lyman, 1879
Ophiacantha rhachophora H.L. Clark, 1911
Ophiacantha trachybactra H.L. Clark, 1911
Ophiolimna bairdi (Lyman, 1883)
Chilophiurina
Ophiuridae
Amphiophiura bullata pacifica Litvinova, 1971
Stegophiura ponderosa (Lyman, 1878)
Christina Ball
Phil Lambert
0 – 300 m
50 – 1200 m
0 – 125 m
5 – 1600 m
0 – 161 m
0 – 232 m
2600 – 4080 m
4200 – 6320 m
2876 – 4072 m
3315 – 5020 m
1450 – 3954 m
3315 – 4321 m
20 – 1900 m
1463 – 5390 m
115 – 2963 m
10 – 2000 m
605 – 1909 m
538 – 1253 m
1587 – 6450 m
130 – 1940 m
71 – 1330 m
1394 – 2869 m
37 – 2600 m
50 – 1700 m
406 – 2014 m
521 – 2600 m
2507 – 6380 m
137 – 1436 m
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Amphiophiura superba (Lütken and Mortensen, 1899)
Ophiocten hastatum Lyman, 1878
Ophiosphalma jolliense (McClendon, 1909)
Ophiura bathybia H.L. Clark, 1911
Ophiura cryptolepis H.L. Clark, 1911
Ophiura flagellata (Lyman, 1878)
Ophiura leptoctenia H.L. Clark, 1911
Ophiura luetkenii (Lyman, 1860)
Ophiura sarsii Lütken, 1855
Stegophiura carinata D‟yakonov, 1954
Gnathophiurina
Amphiuridae
Amphiodia occidentalis (Lyman, 1860)
Amphiodia periercta H.L. Clark, 1911
Amphiodia urtica (Lyman, 1860)
Amphioplus euryaspis (H.L Clark, 1911)
Amphioplus macraspis (H.L. Clark, 1911)
Amphioplus strongyloplax (H.L. Clark, 1911)
Amphipholis pugetana (Lyman, 1860)
Amphipholis squamata (Delle Chiaje, 1829)
Amphiura diomedeae Lütken and Mortensen, 1899
Amphilepis patens Lyman, 1879
Ophiotrichidae
Ophiothrix spiculata Le Conte, 1851
Ophiactidae
Ophiopholis aculeata Linnaeus, 1767
Ophiopholis bakeri McClendon, 1909
Ophiopholis japonica Lyman, 1879
Ophiopholis kennerlyi Lyman, 1860
Ophiopholis longispina H.L.Clark, 1911
Ophiocomidae
Ophiopteris papillosa Lyman, 1875
Ophiolepidina
Ophiolepididae
Ophiomusium glabrum Lütken and Mortensen, 1899
Ophiomusium lymani Wyville Thompson, 1873
Ophiomusium multispinum H.L. Clark, 1911
Ophioplocus esmarki Lyman, 1874
HOLOTHUROIDEA (Sea Cucumbers – 47 species in BC)
Aspidochirotida
Stichopodidae
Parastichopus californicus (Stimpson, 1857)
Parastichopus leukothele Lambert, 1986
Synallactidae
Capheira mollis Ohshima, 1915
Capheira sulcata Ludwig,
Mesothuria murrayi (Théel, 1886)
Paelopatides confundens Théel, 1886
Christina Ball
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825 – 1867 m
916 – 2877 m
155 – 2105 m
2869 – 4872 m
420 – 1280 m
128 – 2014 m
27 – 3239 m
0 – 1097 m
0 – 1898 m
950 – 2300 m
0 – 367 m
9 – 315 m
0 – 1624 m
124 – 582 m
7 – 1400 m
4 – 1408 m
4 – 1620 m
0 – 823 m
71 – 3030 m
1790 – 3608 m
0 – 2059 m
0 – 366 m
9 – 1006 m
15 – 1884 m
0 – 732 m
51 – 1746 m
0 – 170 m
878 – 4082 m
130 – 3435 m
878 – 3219 m
0 – 74 m
0 – 249 m
24 – 285 m
1353 – 2200 m
706 – 3400 m
483 – 2515 m
1986 – 4069 m
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Pseudostichopus mollis Théel, 1886
Pseudostichopus tuberosus O'Loughlin and Ahearn, 2005
Synallactes cf. challengeri (Théel, 1886)
Elasipoda (Deep-sea Cucumbers)
Laetmogonidae
Pannychia moseleyi Théel, 1881
Elpidiidae
Amperima naresi (Théel, 1882)
Scotoplanes globosa (Théel, 1879)
Scotoplanes theeli Ohshima, 1915
Peniagone japonica Ohshima, 1915
Dactylochirotida
Ypsilothuriidae
Ypsilothuria bitentaculata Ludwig, 1893
Dendrochirotida
Psolidae
Psolidium bidiscum Lambert, 1996
Psolus chitonoides Clark, 1901
Psolus squamatus (Koren, 1844)
Cucumariidae
Cucumaria frondosa japonica (Gunnerus, 1767)
Cucumaria miniata (Brandt, 1835)
Cucumaria pallida Kirkendale and Lambert, 1995
Cucumaria piperata (Stimpson, 1864)
Cucumaria pseudocurata Deichmann, 1938
Cucumaria vegae Théel, 1886
Pseudocnus curatus (Cowles, 1907)
Pseudocnus lubricus (H.L. Clark, 1901)
Ekmania diomedeae (Ohshima, 1915)
Thyonidium kurilensis (Levin, 1984)
Phyllophoridae
Pentamera lissoplaca (H.L. Clark, 1924)
Pentamera pediparva Lambert, 1998
Pentamera populifera (Stimpson, 1864)
Pentamera pseudocalcigera Deichmann, 1938
Pentamera rigida Lambert, 1998
Pentamera trachyplaca (H.L. Clark, 1924)
Thyone benti Deichmann, 1937
Sclerodactylidae
Eupentacta pseudoquinquesemita Deichmann, 1938
Eupentacta quinquesemita (Selenka, 1867)
Pseudothyone levini Lambert and Oliver, 2001
Molpadiida
Molpadiidae
Molpadia musculus Risso 1826
Molpadia intermedia (Ludwig, 1894)
Caudinidae
Hedingia californica (Ludwig, 1894)
Paracaudina chilensis (Müller, 1850)
Christina Ball
Phil Lambert
179 – 2200 m
1859 – 2105 m
20 – 366 m
212 – 2598 m
1889 – 7130 m
2100 – 5630 m
545 – 2500 m
1135 – 1669 m
1318 – 4000 m
0 – 220 m
0 – 247 m
37 – 1061 m
25 – 130 m
0 – 225 m
0 – 91 m
0 – 137 m
intertidal
intertidal
0 – 20 m
0 – 78 m
37 – 220 m
10 – 228 m
0 – 90 m
7 – 150 m
0 – 256 m
22 – 300 m
18 – 421 m
0 – 27 m
0 – 135 m
0 – 200 m
0 – 55 m
0 – 70 m
800 – 3000 m
7 – 2925 m
595 – 2850 m
0 – 100 m
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Apodida
Synaptidae
Leptosynapta clarki Heding, 1928
Leptosynapta transgressor Heding, 1928
Chiridotidae
Chiridota albatrossii Edwards, 1907
Chiridota discolor Eschscholtz, 1829
Chiridota nanaimensis Heding, 1928
ASTEROIDEA (Sea Stars - 89 species in BC)
Paxillosida
Luidiidae
Luidia foliolata Grube, 1866
Astropectinidae
Dipsacaster anoplus Fisher, 1910
Dipsacaster borealis Fisher, 1910
Dipsacaster laetmophilus Fisher, 1910
Leptychaster anomalus Fisher, 1906
Leptychaster arcticus (Sars, 1851)
*Leptychaster inermis (Ludwig, 1905)
Leptychaster pacificus Fisher, 1906
Psilaster pectinatus (Fisher, 1905)
Thrissacanthias penicillatus (Fisher, 1905)
Porcellanasteridae (Deep-sea Mud Stars)
Eremicaster pacificus (Ludwig, 1905)
Eremicaster crassus (Sladen, 1883)
Ctenodiscidae
Ctenodiscus crispatus (Retzius, 1805)
Notomyotida
Benthopectinidae
Benthopecten acanthonotus Fisher, 1905
Benthopecten claviger claviger Fisher, 1910
Benthopecten mutabilis Fisher, 1910
Cheiraster dawsoni (Verrill, 1880)
Nearchaster aciculosus (Fisher, 1910)
Nearchaster variabilis variabilis (Fisher, 1910)
Pectinaster agassizi evoplus (Fisher, 1910)
Valvatida
Asterinidae
Patiria miniata (Brandt, 1835)
Poraniidae
Poraniopsis inflatus inflatus
Goniasteridae
Ceramaster arcticus (Verrill, 1909)
*Ceramaster clarki Fisher, 1910
*Ceramaster japonicus (Sladen, 1889)
Ceramaster patagonicus (Sladen, 1889)
Cladaster validus Fisher, 1910
Cryptopeltaster lepidonotus Fisher, 1905
Christina Ball
Phil Lambert
0 – 73 m
6 – 40 m
46 – 732 m
intertidal SE Alaska
46 m
4 – 613 m
146 – 2200 m
201 – 1195 m
1271 – 1903 m
59 – 1258 m
40 – 1261 m
1180 – 2000 m
10 – 435 m
1500 – 3000 m
507 – 1503 m
1570 – 4090 m
1570 – 6330 m
10 – 1890 m
1800 – 2125 m
1100 – 2400 m
2870 m
73 – 384 m
84– 1492 m
198 – 1061 m
1100 – 2200 m
0 – 302 m
11 – 366 m
0 – 186 m
611 – 1098 m
195 – 1438 m
10 – 245 m
116 – 621 m
486 – 1244 m
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Gephyreaster swifti (Fisher, 1905)
Hippasteria californica Fisher, 1905
Hippasteria spinosa Verrill, 1909
Mediaster aequalis Stimpson, 1857
Mediaster tenellus Fisher, 1905
Pseudarchaster dissonus Fisher, 1910
Pseudarchaster parelii (Duben and Koren, 1846)
Pseudarchaster alascensis Fisher, 1905
Asteropseidae
Dermasterias imbricata (Grube, 1857)
Velatida
Solasteridae
Crossaster papposus (Linnaeus, 1767)
Heterozonias alternatus (Fisher, 1906)
Lophaster furcilliger Fisher, 1905
Lophaster furcilliger vexator Fisher, 1910
Solaster borealis (Fisher, 1906)
Solaster dawsoni Verrill, 1880
Solaster endeca (Linnaeus, 1771)
Solaster paxillatus Sladen, 1889
Solaster stimpsoni Verrill, 1880
Solaster sp. A
New Genus sp. B
Pterasteridae (Cushion Stars)
Diplopteraster multipes (Sars, 1865)
*Hymenaster koehleri Fisher, 1910
Hymenaster perissonotus Fisher, 1910
Hymenaster quadrispinosus Fisher, 1905
Pteraster coscinopeplus Fisher, 1910
Pteraster jordani Fisher, 1905
*Pteraster marsippus Fisher, 1910
Pteraster militaris (Müller, 1776)
Pteraster tesselatus Ives, 1888
Pteraster trigonodon Fisher, 1910
Myxasteridae
Asthenactis fisheri Alton, 1966
Korethrasteridae
*Peribolaster biserialis Fisher, 1905
Spinulosida
Echinasteridae
Henricia aspera aspera Fisher, 1906
Henricia asthenactis Fisher 1910
Henricia clarki Fisher, 1910
Henricia leviuscula leviuscula (Stimpson, 1857)
Henricia leviuscula annectens Fisher, 1910
Henricia leviuscula spiculifera Clark, 1901
Henricia longispina longispina Fisher, 1910
Henricia polyacantha Fisher, 1906
Christina Ball
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11 – 344 m
300 – 2200 m
10 – 512 m
0 – 293 m
532 – 2125 m
846 – 2300 m
15 – 2500 m
92 – 1947 m
0 – 91 m
0 – 1200 m
302 – 1594 m
229 – 2125 m
21 – 670 m
161 – 2300 m
0 – 420 m
0 – 475 m
11 – 640 m
0 – 60 m
1291 – 2083 m
571 – 621 m
57 – 1171 m
3239 m
412 – 3239 m
1097 – 3610 m
857 – 1942 m
457 – 1903 m
95 – 642 m
10 – 1100 m
6 – 436 m
706 – 1259
1152 – 1922 m
104 – 805 m
6 – 904 m
91 – 1250 m
227 – 1955 m
0 – 400 m
10 – 228 m
9 – 680 m
28 – 512 m
227 – 1171 m
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Henricia sanguinolenta (Müller, 1776)
Forcipulatida (Sea Stars with pedicellariae)
Zoroasteridae
Myxoderma sacculatum (Fisher, 1905)
Sagenaster evermanni (Fisher, 1905)
Zoroaster ophiurus Fisher, 1905
Asteriidae
Evasterias troschelii (Stimpson, 1862)
Leptasterias aequalis sp. complex
Leptasterias alaskensis sp. complex
Leptasterias hexactis sp. complex
*Leptasterias coei Verrill, 1914
Leptasterias polaris katherinae (Grey, 1840)
*Lethasterias nanimensis (Verrill, 1914)
Orthasterias koehleri (de Loriol, 1897)
Pisaster brevispinus (Stimpson, 1857)
Pisaster ochraceus (Brandt, 1835)
Pycnopodia helianthoides (Brandt, 1835)
Stylasterias forreri (de Loriol, 1887)
Pedicellasteridae
Ampheraster marianus (Ludwig, 1905)
Anteliaster coscinactis Fisher, 1923
Pedicellaster magister Fisher, 1923
Tarsaster alaskanus Fisher, 1928
Labidiasteridae
Rathbunaster californicus Fisher, 1906
Brisingida
Brisingidae (Deep-sea Suspension feeders)
Brisinga synaptoma (Fisher, 1917)
Freyellidae
Astrocles actinodetus Fisher, 1917
Freyella microplax (Fisher, 1917)
Freyellaster fecundus (Fisher, 1905)
Hymenodiscididae (after Mah, 1997)
Astrolirus panamensis (Ludwig, 1905)
Hymenodiscus pannychia (Fisher, 1928)
Hymenodiscus pusilla (Fisher, 1917)
Christina Ball
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15 – 518 m
329 – 2012 m
100 – 2710 m
696 – 2300 m
0 – 75
intertidal/shallow
intertidal/shallow
intertidal/shallow
18 – 187 m
intertidal to 10 m
0 – 224 m
0 – 230 m
0 – 128 m
0 – 97 m
0 – 120 m
6 – 532 m
507 – 1240 m
817 – 950 m
77 – 1776 m
198 – 2100 m
134 – 675 m
1353 – 3176 m
2870 – 4200 m
1722 – 3176 m
880 – 2124 m
1353 – 2418 m
1410 – 2300 m
602 – 2118 m
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GLOSSARY OF TERMS
Aboral surface – The side opposite to the mouth. In most echinoderms this refers to the
dorsal side of the body.
Ambulacral furrow – Furrow (groove) on the oral side of each arm that houses the tube
feet. This is formed by pairs of ambulacral plates.
Ambulacral plate – In the echinoids these plates are found in between the
interambulacral plates. The ambulacral plates are associated with the water vascular
system and have pores to allow the tube feet to penetrate the test.
Ampulla – The ampulla is a bulb-like reservoir at the base of a tube foot. The contraction
of the ampulla causes the tube foot to extend; much like squeezing one end of a balloon
causes the other end to swell.
Aristotle’s Lantern – The five-sided jaw apparatus found only in the Echinoidea. It is
made up of five plate-like teeth and numerous ligaments, muscles and levers.
Arm – An appendage radiating out laterally from the disc. Found in the asteroids,
crinoids and ophiuroids.
Asexual – A form of reproduction that does not involve the gametes of two separate
individuals. Asexual reproduction results in offspring that are clones of the parent.
Benthic – Pertaining to the benthos or bottom of a body of water. Benthic organisms live
on or in the substrate.
Brachial – In the crinoids this is a calcareous segment. The brachials, connected by
ligaments, muscles and fibers, form the arms. In the ophiuroids brachial refers to
structures attached to the arm
Cilia – Cilia are hair-like structures, found in many groups of invertebrates, which move
to create small water currents.
Circular muscles – The circular muscles encircle the body. They are found in the
Holothuroidea and they run perpendicular to the longitudinal muscles.
Cirri – Appendages at the base of a feather star (Crinoidea) that are used to grasp the
substrate.
Coelom – A fluid filled cavity inside the mesoderm.
Commensal – An organism that lives in close association with another species but does
not provide benefits to the other organism or cause it harm.
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Conspecific – The term conspecific refers to other members of the same species. For
example in a congregation of sea urchins the members of species “A” would all be
conspecific to one another. The members of species „A‟ would be heterospecific to
members of species „B‟.
Dendritic tentacles – A type of feeding tentacle found in suspension feeding
holothuroids (sea cucumbers). This type of tentacle is highly branched and is feathery or
fern-like in appearance.
Deposit feeding – Deposit feeders obtain nutrients by consuming detritus located in the
substrate.
Digitate tentacles – A type of feeding tentacle found in some holothuroids that ingest
sediment while they burrow into the substrate. This type of tentacle resembles a cross or
four-pointed star on a short stalk.
Disc – The central part of the sea star body to which the arms attach.
Distal – The portion of an organism located away from the central axis or disc of an
organism.
Dorsal – The back or top side of an animal. In the asteroids and ophiuroids this is the
same side as the aboral side.
Endoskeleton – An internal skeleton covered by skin and muscles. Vertebrates and some
invertebrates have endoskeletons.
Epidermis – This is the outermost layer of tissue (i.e. the skin) and forms a barrier
between the organism and the outside environment.
Evert – To turn a body part inside out. Some sea stars feed by everting their stomach.
That is they push their stomach through their mouth so that it is outside of their body.
Gonads – The sex organs.
Gonopore – In echinoderms, the opening in the body wall through which eggs and sperm
are released.
Hermaphrodite – An organism that has both male and female sex organs.
Hermaphrodites can have both male and female sex organs at the same time
(simultaneous hermaphrodite). Alternatively they can change from being a male to a
female, or vice versa, over the course of their life (sequential hermaphrodite).
Heterospecific – Members of different species. For example in a congregation of sea
urchins the members of species “A” would be heterospecific to members of species “B”.
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Interambulacral plate – In the echinoids these plates are found between the ambulacral
plates. There are no pores for tube feet in the interambulacral plates.
Juxtaligamental cells – These are special cells in echinoderms that are associated with,
and control, through their secretions, mutable collagenous tissue.
Longitudinal muscles – These are muscles the run the length of an organism. For
example in the sea cucumbers (Holothuroidea) bands of longitudinal muscles run along
the long axis from end to end.
Mamelon – A knob-like tubercle to which moveable spines attach. These are found only
in the Echinoidea (urchins, sand dollars).
Madreporite – A perforated ossicle through which water enters the water vascular
system.
Mesoderm – Mesoderm is the middle of the three basic tissue layers in an organism.
Some invertebrates (i.e. sponges and jelly fish) do not have mesoderm.
Morphology – The overall shape of an organism and the structure of its parts.
Mutable collagenous tissue – This type of tissue is found only in the echinoderms and
can rapidly change from a soft to a rigid state. The change in state is due to changes in the
physical nature of the tissue, mediated by the juxtaligamental cells. The nervous system
controls the mutable collagenous tissue.
Oral surface – The side of an organism that contains the mouth.
Ossicle – A single calcified element of an echinoderm endoskeleton.
Papulae – Functionally, these are the gills of a sea star and serve in respiration and waste
removal. They are thin walled, small and found on the aboral surface of asteroids.
Pedicellariae – These are small pincher-like structures that occur on the outside of many
echinoderms. They consist of a muscular stem with a jaw-like head (usually three jaws).
Pelagic – Relating to or living in the middle layers of the water column (i.e. not on the
bottom and not at the surface).
Peltate tentacles – A type of feeding tentacle found in surface deposit feeding
holothuroids. This type of tentacles somewhat resembles a head of broccoli.
Pentaradial symmetry - A type of radial symmetry, characteristic of echinoderms, in
which body parts are arranged along five rays of symmetry.
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Pinnate tentacles – A type of feeding tentacle found in some holothuroids that ingest
sediment while they burrow.
Pinnule – A side branch of a brachial in crinoids (sea lilies and feather stars).
Podia – Another name for tube feet.
Proximal – Close to center of the disc or central axis of an organism.
Radial canal – The radial canals are part of the water vascular system and branch off the
ring canal. The radial canal occurs internally and adjacent to the ambulacral furrow or
plate.
Ring canal – The ring canal is part of the water vascular system and surrounds the
mouth.
Sedentary – Organisms that lead a sedentary lifestyle have the ability to move, though
often only very slowly, but normally do not move. For example, suspension feeding sea
cucumbers are usually sedentary, only moving to reach areas with better water currents or
to evade predators.
Sessile – Sessile organisms are permanently attached or fixed to the substrate and are
unable to move. Some crinoids (e.g. sea lilies) are often considered sessile.
Suspension feeding – Suspension feeding is often called filter feeding. Animals that
suspension feed strain food particles out of the water using specialized structures and/or a
mucus coating.
Syzygy joints – In the crinoids, a non-muscular rigid joint between two brachials. The
joint resembles a perforated line.
Tube feet – In the echinoderms these are hollow cylindrically shaped extensions of the
water vascular system that function in respiration, locomotion and food collection.
Test – The hard spherical or semi-spherical skeleton of a sea urchin. The test is made up
of many small plates made of fused ossicles.
Ventral – Usually the lower part of an invertebrate animal closest to the substrate. In the
asteroids and ophiuroids this is the same side as the oral side.
Water vascular system – A system of water filled canals and chambers that uses
hydraulic pressure and muscle contractions to operate the tube feet.
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