Animal Diversity Web

Di­ver­sity

Holothruroidea, or sea cu­cum­bers, have around 1100 de­scribed ex­tant species. (Beirne, et al., 2001; Br­usca and Br­usca, 2003)

Ge­o­graphic Range

Holothuri­ans are found in oceans all over the world. (Barnes, 1987; Br­usca and Br­usca, 2003)

• Biogeographic Regions
• indian ocean
• atlantic ocean
• pacific ocean
• mediterranean sea

Habi­tat

Sea cu­cum­bers are com­mon in shal­low water areas to deep ocean floors. While most are ben­thic, a few are pelagic. (Br­usca and Br­usca, 2003; Wag­goner and Spear, 1994)

• Habitat Regions
• saltwater or marine

• Aquatic Biomes
• coastal

• Other Habitat Features
• intertidal or littoral

Phys­i­cal De­scrip­tion

Al­though they vary in color, most holothuri­ans are black, brown, or olive green. Rang­ing from three cm to one m long, the largest sea cu­cum­bers may have a di­am­e­ter of 24 cm.

Holothuri­ans gen­er­ally look long and worm-like, but re­tain the pen­tara­dial sym­me­try char­ac­ter­is­tic of the Echin­o­der­mata. Some may be spher­i­cal in body shape. The mouth and anus are lo­cated on op­po­site poles, and five rows of tube feet run from the mouth to the anus along the cylin­dri­cal body. Ten to 30 branch­ing ten­ta­cles sur­round the mouth. The ten­ta­cles are ac­tu­ally part of the water vas­cu­lar sys­tem.

The water vas­cu­lar sys­tem, found in all echin­o­derms, ac­com­mo­dates the elon­gated body of the holothuri­ans. Coelomic fluid, rather than sea water, cir­cu­lates through the water vas­cu­lar sys­tem. The ring canal around the gut has 1-50 po­lian ves­si­cles, which may func­tion for hy­draulic reg­u­la­tion. Each ra­dial canal has rows of am­pul­lae. Podia, which are the ex­ter­nal por­tion of the tube feet, may, be suck­ered, re­duced, or lost. Podia are more ran­domly scat­tered along the body than in other echin­o­derms. The esoph­a­gus, foregut and ra­dial canal of the water vas­cu­lar sys­tem are sup­ported by cal­care­ous plates.

Let­ters are used to de­scribe parts of echin­o­derms. The am­bu­lacrum op­po­site the madreorite is sec­tion A. Mov­ing clock­wise, other parts are coded B through E. Sec­tions C and D are termed the bivium while all the oth­ers are col­lec­tively termed the triv­ium. Holothuri­ans mainly ori­ent them­selves to have the triv­ium on the sub­strate (ven­tral side) and the bivium fac­ing up (dor­sal side).

In the Holothuroidea, the madreporite is un­at­tached to the coelom and is in­ter­nal, lying be­neath the phar­ynx in the CD-in­ter­am­bu­lacral po­si­tion. A short stone canal fol­lows the madreporite.

While sup­port in most echin­o­derms is from the skele­tal struc­ture, in sea cu­cum­bers, thick sheets of body wall mus­cles pro­vide sup­port. Mi­cro­scopic os­si­cles (or scle­ri­etes) are on the der­mal layer and are used in tax­o­nomic iden­ti­fi­ca­tion.

Res­pi­ra­tory trees, which branch out near the rec­tum of the an­i­mal are used for gas ex­change as water is pumped through the anus. The res­pi­ra­tory trees are part of the or­gans that are ex­pelled oc­ca­sion­ally by the sea cu­cum­ber. (Barnes, 1987; Beirne, et al., 2001; Br­usca and Br­usca, 2003; Uni­ver­sity of Pais­ley, 1998; Wag­goner and Spear, 1994)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry
• radial symmetry

De­vel­op­ment

As an echin­o­derm, mem­bers of the Holothuroidea are deuteros­tomes. The lar­vae, which are plank­totrophic or lecithotrophic, have 3-part paired coeloms. Em­bry­onic coelomic struc­tures have spe­cific fates as the bi­lat­er­ally sym­met­ri­cal lar­vae meta­mor­phose into ra­di­ally sym­met­ric adults.

The lar­vae de­velop in sea water. After three days the lar­val stage is called an au­ric­u­laria and is sim­i­lar to the bip­in­naria lar­vae of as­ter­oids. The au­ric­u­laria has a cil­i­ated lo­co­mo­tor band, then fur­ther de­vel­ops into a lar­val stage called a do­lio­laria, where the cil­i­ated band is bro­ken up into three to five cil­i­ated "gir­dles". Many species of holothuri­ans have an­other non-feed­ing, bar­rel shaped lar­val stage called a vitel­laria. Likely a spe­cial­ized con­di­tion, it de­vel­ops grad­u­ally, re­tain­ing many of the lar­val fea­tures. As it is meta­mor­phos­ing it is some­times called a pen­tac­tula larva.

After lar­val meta­mor­pho­sis, the young sea cu­cum­bers ul­ti­mately set­tle on the sub­strate and be­come adults. (Barnes, 1987; Br­usca and Br­usca, 2003)

• Development - Life Cycle
• metamorphosis

Re­pro­duc­tion

Holothuri­ans have a sin­gle gonad, and most are dioe­cious. Al­though most spawn and are fer­til­ized ex­ter­nally, there are ap­prox­i­mately thirty brood­ing species. Some cap­ture eggs with ten­ta­cles, plac­ing the eggs at the sole or dor­sal body sur­face for in­cu­ba­tion. A few have in­ter­nal fer­til­iza­tion and de­vel­op­ment, where hatched young are re­leased. (Barnes, 1987)

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• simultaneous hermaphrodite
• sexual
• fertilization
  • external
  • internal
• ovoviviparous
• oviparous

While most species re­lease eggs and have no perental in­vest­ment after spawn­ing, some species brood eggs. A few species also brood the eggs in­ter­nally until they hatch. (Barnes, 1987)

• Parental Investment
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

Most species live from five to ten years. (Barnes, 1987)

Be­hav­ior

Gen­er­ally, holothurid­i­ans are seden­tary and/or slow mov­ing, usu­ally bur­row­ing into soft sed­i­ments or are lodged in cracks or crevices under rocks. Holothuri­ans crawl using podia or by using body wall mus­cles. Some deep sea species have elon­gate podia used for walk­ing. In other species the triv­ium is mod­i­fied for creep­ing. A few pelatic species can swim (al­though not well) with webbed papil­lae.

Chem­i­cal stim­u­la­tion changes the me­chan­i­cal prop­er­ties of the der­mal por­tion of the sea cu­cum­bers. This al­lows the an­i­mal to be­come so flex­i­ble it can squeeze through nar­row pas­sages. Con­versely, it can be­come so rigid that it can­not be dis­lodged. (Barnes, 1987; Br­usca and Br­usca, 2003)

• Key Behaviors
• motile
• sedentary

Com­mu­ni­ca­tion and Per­cep­tion

The non-cen­tral­ized ner­vous sys­tem of echin­o­derms al­lows them to sense their en­vi­ron­ment from all sides. Holothuri­ans have a nerve ring near the base of the ten­ta­cles. The podia are touch-sen­si­tive. Adult pheromones may at­tract lar­vae, which tend to set­tle near con­spe­cific adults. (Barnes, 1987; Br­usca and Br­usca, 2003)

• Communication Channels
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• tactile
• chemical

Food Habits

As sus­pen­sion or de­posit feed­ers holothuri­ans trap par­ti­cles and plank­ton on mu­cus-cov­ered ten­ta­cles. The ten­ta­cles are pushed into the mouth to in­gest food. Se­cre­tory cells from papil­lae of the ten­ta­cles and gland cells of the foregut se­crete mucus.

In seden­tary forms, holothuri­ans hold out ex­tended ten­ta­cles to trap par­ti­cles and plank­ton. Motile species crawl across the sub­strate and use ten­ta­cles to cap­ture sed­i­ment and or­ganic de­tri­tus. Sed­i­ment feed­ers are highly se­lec­tive de­posit feed­ers, gen­er­ally con­sum­ing highly or­ganic sed­i­ments. Mem­bers of the sub­class Apo­dacea in­gest sed­i­ments as they bur­row through the sub­strate.

Branched buc­cal ten­ta­cles sur­round the mouth. From the mouth, the esophogus leads to the foregut and then in­tes­tine, where di­ges­tion and ab­sorb­tion occur. (Br­usca and Br­usca, 2003)

• Primary Diet
• planktivore
• detritivore

Pre­da­tion

Holothuri­ans in gen­eral are most vul­ner­a­ble in their lar­val stage. Some holothuri­ans dis­charge sticky tubules, known as Cu­vier­ian tubules, at a po­ten­tial preda­tor. The tubules are sticky clus­ters found at the base of the res­pi­ra­tory tree. Preda­tors in­clude sea stars, fish, gas­tropods, and crus­taceans as well as hu­mans. Holothuri­ans also ex­pell their or­gans, which are later re­gen­er­ated. This is a sea­sonal event, but is also thought to be an anti-preda­tor de­fense. (Beirne, et al., 2001; Br­usca and Br­usca, 2003)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • sea stars, Asteroidea
  • gastropods, Gastropoda
  • crustaceans, Crustacea
  • fish
  • humans, Homo sapiens

Ecosys­tem Roles

Holothuri­ans have an im­por­tant role as large scale de­tri­tus feed­ers. They cycle up to 90% ben­thic bio­mass in ocean. (Beirne, et al., 2001)

• Ecosystem Impact
• biodegradation

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Dried sea cu­cum­bers are an im­por­tant food source and fla­vor­ing source in Asia. Be­fore dry­ing, the sea cu­cum­bers are boiled and the bod­ies con­tract and thicken and or­gans are ex­pelled. Some­times sea cu­cum­bers are con­sid­ered an aphro­disiac.

Mac­er­ated sea cu­cum­bers that re­lease the toxin holothurin with the Cu­vier­ian tubules have been used by South Pa­cific Is­landers to catch tide pool fish. (Barnes, 1987; Beirne, et al., 2001)

• Positive Impacts
• food
• source of medicine or drug

Con­ser­va­tion Sta­tus

Some pop­u­la­tions of sea cu­cum­bers have been over­fished, which has an ef­fect on the ecosys­tem. Over­fish­ing has in some places re­duced their role in break­ing down or­gan­ics on the ocean floor. Areas with­out the sea cu­cum­bers have be­come uni­hab­it­able for other or­gan­isms.

Com­mer­cially ex­ploitable species are mainly in the order As­pi­dochi­rotida. Large amounts of dried sea cu­cum­bers are traded in Gala­pa­gos Is­lands to Asian mar­kets, mainly Japan, Hong Kong, Tai­wan, and Sin­ga­pore. Stocks have be­come de­pleted in these coun­tries, so they have been look­ing for other sources.

Sea cu­cum­bers in Baja Cal­i­for­nia, east­ern Rus­sia, and the Gala­pa­gos Arch­i­pel­ago have been the focus of re­cent at­ten­tion. In Baja Cal­i­for­nia Isos­ti­cho­pus fus­cus has been over­har­vested. In 1994, the Na­tional In­sti­tute of Ecol­ogy in Mex­ico de­clared that I. fus­cus was in dan­ger of ex­tinc­tion. In east­ern Rus­sia, in­creas­ing de­mand on Cu­cumaria japon­ica has led to con­cern for this species, which is har­vested for both food and cos­metic prod­ucts. Be­cause of com­mer­cial ex­ploita­tion in the Gala­pa­gos, Ecuador passed the Gala­pa­gos Ma­rine Man­age­ment Plan in 1999 to reg­u­late con­ser­va­tion of sea cu­cum­bers.

The Aus­tralian gov­ern­ment is try­ing to seed ju­ve­niles of sand­fish, Holothuroidea scabra which were re­duced by over­fish­ing. (Beirne, et al., 2001)

• IUCN Red List [Link]

  Not Evaluated

Other Com­ments

When ex­pelling or­gans, sea cu­cum­bers usu­ally re­lease one or both res­pi­ra­tory trees, the gut and the go­nads. This be­hav­ior may occur sea­son­ally or in re­sponse to pre­da­tion.

Holothuri­ans have the most de­vel­oped hemal sys­tem of echin­o­derms, hav­ing well de­vel­oped ves­sels and sev­eral sin­gle cham­bered hearts along the in­testi­nal sys­tem. The hemal sys­tem func­tions for gas and food trans­port. (Barnes, 1987; Uni­ver­sity of Pais­ley, 1998)

Con­trib­u­tors

Renee Sher­man Mul­crone (au­thor).

Ref­er­ences

Barnes, R. 1987. In­ver­te­brate Zo­ol­ogy. Or­lando, Florida: Dry­den Press.

Beirne, L., K. Fitzmier, M. Miller. 2001. "Holothuroidea" (On-line). Bi­o­log­i­cal Di­ver­sity 2001. Ac­cessed Jan­u­ary 28, 2005 at http://​www.​earlham.​edu/​~beirnlu/seacucumber.​htm.

Br­usca, R., G. Br­usca. 2003. In­ver­te­brates. Sun­der­land, Mass­a­chu­setts: Sin­auer As­so­ci­ates, Inc..

Uni­ver­sity of Pais­ley, 1998. "Class Holothuroidea" (On-line). Ac­cessed Jan­u­ary 28, 2005 at http://​www-biol.​paisley.​ac.​uk/​courses/​Tatner/​biomedia/​units/​echi6.​htm.

Wag­goner, D., B. Spear. 1994. "The Holothuroidea" (On-line). Ac­cessed Jan­u­ary 28, 2005 at http://​www.​ucmp.​berkeley.​edu/​echinodermata/​holothuroidea.​html.