Cycliophoralobster symbionts

Di­ver­sity

The phy­lum Cy­clio­phora, only re­cently de­scribed in 1995, con­sists of at least three species of acoelo­mate, bi­lat­er­ally sym­met­ri­cal or­gan­isms that are ob­lig­ate com­men­sal­ists on the mouth­parts of lob­sters. There are two for­mally de­scribed species in the phy­lum, Sym­bion pan­dora and Sym­bion amer­i­canus, with at least one ad­di­tional, un­de­scribed species known. Sym­bion pan­dora was first dis­cov­ered on the mouth­parts of Nor­way lob­sters (Nephrops norvegi­cus) in Scan­di­na­vian wa­ters, and Sym­bion amer­i­canus was de­scribed from Amer­i­can lob­sters (Homarus amer­i­canus) in North Amer­i­can wa­ters. The third, un­de­scribed, species may be found on Eu­ro­pean lob­sters (Homarus gam­marus), in Eu­ro­pean wa­ters. These or­gan­isms are among the small­est known free-liv­ing meta­zoans, with fe­males mea­sur­ing around 350 µm in length, and males only reach­ing lengths of 30 to 40 µm, and con­tain­ing (often sig­nif­i­cantly) fewer than 200 cells in their en­tire body. These or­gan­isms fil­ter feed on bac­te­ria and food par­ti­cles that es­cape from their host's mouth­parts, and de­spite their small size, ex­hibit a com­plex and dis­tinc­tive life cycle with mul­ti­ple stages, in­clud­ing asex­ual feed­ing stages that may re­pro­duce by bud­ding, as well as free-swim­ming male (Prometheus), fe­male (Pan­dora), and in­ter­nally brooded chor­doid lar­vae, and ses­sile dwarf males that live at­tached to the body wall of fe­males. ("Cy­clio­phora", 2012; Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Nedvěd, 2004; Neves, et al., 2009; Obst, et al., 2006; Shapiro, 2012)

Ge­o­graphic Range

Cy­clio­phorans are only known from ma­rine wa­ters of the North­ern hemi­sphere, with the same dis­tri­b­u­tions as the lob­ster species they live on. (Br­usca and Br­usca, 2008; Kris­tensen, 2002)

Habi­tat

Cy­clio­phorans live on the mouth­parts of their lob­ster hosts. Feed­ing in­di­vid­u­als and chor­doid cysts may be found on all six feed­ing mouth­parts, most often on in­di­vid­u­als with a cara­pace length greater than 35 mm. The num­bers of in­di­vid­u­als liv­ing on a host in­creases with size; over a thou­sand feed­ing cy­clio­phorans and nearly 200 chor­doid cysts have been found on larger lob­sters. Ses­sile lar­vae may set­tle near their fe­male prog­en­i­tors, or dis­perse and col­o­nize a new host. They have been found from the in­ter­tidal zone to depths of 720 m. (Br­usca and Br­usca, 2008; Kris­tensen, 2002; Obst and Funch, 2012; Obst, et al., 2006)

Sys­tem­atic and Tax­o­nomic His­tory

The phy­lum Cy­clio­phora was de­scribed by Peter Funch and Rein­hardt Kris­tensen in 1995. Due to its re­cent de­scrip­tion, no al­ter­na­tive names for this phy­lum or its mem­ber species exist. Based upon mor­pho­log­i­cal char­ac­ter­is­tics, the au­thors hy­poth­e­sized a sis­ter re­la­tion­ship to the phy­lum En­to­procta, or per­haps Poly­zoa (then re­ferred to as the su­per­phy­lum Bry­ozoa), which con­tains both En­to­procta and Bry­ozoa. Many sub­se­quent mol­e­c­u­lar and mor­pho­log­i­cal phy­lo­ge­netic analy­ses have sup­ported a sis­ter group re­la­tion­ship be­tween En­to­procta and Cy­clio­phora, and thus, their in­clu­sion in Poly­zoa. How­ever, other mol­e­c­u­lar and com­bined analy­ses have sug­gested a re­la­tion­ship to the taxon Gnathifera, a group which con­tains ro­tifers, thorny-headed worms, gnathos­to­mulids, and Mi­crog­natho­zoa (which con­tains a sin­gle species, Limnog­nathia maer­ski). Though their exact place­ment re­mains the sub­ject of de­bate, ei­ther set of re­la­tion­ships would war­rant their in­clu­sion in the su­per­phy­lum Lophotro­chozoa. (Funch and Kris­tensen, 1995; Funch, 1999; Giri­bet, et al., 2000; Obst and Funch, 2003; Paps, et al., 2009a; Paps, et al., 2009b; Pas­sama­neck and Ha­lanych, 2006; Pe­tersen and Eernisse, 2001; Sørensen, et al., 2000; Win­nepen­ninckx, et al., 1998; Zrzavý, et al., 1998; Zrzavý, 2003; Zrzavý, et al., 2001)

  • Synapomorphies
    • dwarf males
    • metagenesis in the life cycle
    • chordoid larva
    • ciliated mouth ring

Phys­i­cal De­scrip­tion

Cy­clio­phorans have an an­te­rior buc­cal fun­nel; oval-shaped trunk; and pos­te­rior, acel­lu­lar stalk, with an ad­he­sive disc they use to at­tach them­selves to their hosts’ mouth­parts. Ses­sile stage fe­males are ap­prox­i­mately 350 µm long and 100 µm wide. The trunk and ad­he­sive disc are cov­ered in a lay­ered cu­ti­cle (the disc it­self may also be com­prised of cu­ti­cle). Cy­clio­phorans are acoelo­mate, with the area be­tween their guts and body walls filled with mes­enchyme. They have a feed­ing ring around the buc­cal fun­nel that is densely packed with cilia and con­trac­tile cells, which form a pair of sphinc­ters ca­pa­ble of clos­ing the oral area. Two mus­cle fibers ex­tend dor­sally from the base to the ven­tral side of the trunk, and are likely used to move the buc­cal tube dur­ing feed­ing. The gut, which is en­tirely cil­i­ated, is U-shaped. A curved esoph­a­gus con­nects the buc­cal fun­nel to a stom­ach with large gland cells and a nar­row lumen. The in­tes­tine leads to a dor­sal rec­tum and anus, lo­cated near the buc­cal fun­nel. (Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Obst, et al., 2006)

Cy­clio­phorans ex­hibit sex­ual di­mor­phism. Males only mea­sure 30 to 40 µm in length with heav­ily cil­i­ated bod­ies and a ven­tral-pos­te­rior penis and as­so­ci­ated pouch. They are typ­i­cally found free swim­ming or on the body of a fe­male. Their bod­ies may be round or more rec­tan­gu­lar in shape. Once thought to have greatly re­duced body struc­tures, re­cent re­search has shown that males do pos­sess com­plex mus­cu­la­ture, a large cere­bral gan­glion and nerve cords, fully de­vel­oped go­nads and mat­ing struc­tures, and sen­sory or­gans, as do fe­males. (Neves, et al., 2012; Obst and Funch, 2003)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently

De­vel­op­ment

The most de­fin­i­tive char­ac­ter­is­tic of cy­clio­phorans is their com­plex re­pro­duc­tive cycle, con­sist­ing of an asex­ual and sex­ual gen­er­a­tion. There are two forms of asex­ual, ses­sile, feed­ing an­i­mals. One form may house “Pan­dora lar­vae” and the other form may house a pri­mary male and fe­male to­gether in a brood­ing cham­ber. Ses­sile an­i­mals may also un­dergo in­ter­nal bud­ding, in which they lose their buc­cal fun­nels and en­tire di­ges­tive sys­tems, re­plac­ing them with a new bud. The bud arises from em­bry­onic cells in the pos­te­rior re­gion of the an­i­mal’s trunk. This process is re­peated many times dur­ing the ses­sile an­i­mal’s life. Pan­dora lar­vae also un­dergo in­ter­nal bud­ding in order to form a feed­ing stage. (Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Obst and Funch, 2003)

Asex­ual feed­ing in­di­vid­u­als may change to sex­ual re­pro­duc­tion and cre­ate a pri­mary male and sex­u­ally ma­ture fe­male in­stead of asex­ual off­spring; this may be trig­gered by an im­pend­ing molt of the host, as sex­ual in­di­vid­u­als are ses­sile for a time. In this case, a pri­mary male, also known as a "Prometheus larva," is re­leased from the brood­ing cham­ber with no sex­ual or­gans or go­nads, only de­vel­op­ing them if it set­tles on a cham­ber hous­ing a fe­male. In this event, the male pro­duces sec­ondary males via bud­ding. A sec­ondary male has a cu­tic­u­lar, tubu­lar penis and one sper­ma­to­zoa com­part­ment. A sex­ual fe­male will not bud in­ter­nally; in­stead, she has one large an­te­rior oocyte. Fer­til­iza­tion oc­curs just be­fore or after her re­lease from the brood­ing cham­ber; the exact method of sperm trans­fer is not known. She will then set­tle and brood her­self into a chor­doid larva, which will en­gulf all of her tis­sue, leav­ing only her cu­ti­cle. The chor­doid lar­vae hatches and dis­perses, set­tling on a new host and be­gin­ning the cycle again by bud­ding a new, asex­ual, feed­ing cy­clio­phoran. (Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Neves, et al., 2012; Obst and Funch, 2003)

Re­pro­duc­tion

Cy­clio­phorans re­pro­duce both asex­u­ally (pro­duc­ing ei­ther Pan­dora lar­vae, which set­tle and be­come fe­males, or brood­ing cham­bers hous­ing male and fe­male in­di­vid­u­als) and sex­u­ally. When they re­pro­duce sex­u­ally, asex­ual males bud and cre­ates mul­ti­ple, sex­ual males, which are free swim­ming until they set­tle on a fe­male and trans­fer sperm to her. (Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Neves, et al., 2012)

In­di­vid­u­als re­pro­duce both sex­u­ally and asex­u­ally. No spe­cific breed­ing sea­son has been iden­ti­fied for these an­i­mals but the ap­pear­ance of sex­u­ally ma­ture in­di­vid­u­als is linked to the molt­ing cycle of their hosts. (Br­usca and Br­usca, 2008; Funch and Kris­tensen, 1995; Kris­tensen, 2002; Neves, et al., 2012)

Cy­clio­phorans ex­hibit no parental in­vest­ment be­yond pro­duc­tion of asex­ual and sex­ual off­spring. (Br­usca and Br­usca, 2008; Kris­tensen, 2002)

  • Parental Investment
  • no parental involvement

Lifes­pan/Longevity

There is no data cur­rently avail­able re­gard­ing the av­er­age lifes­pan of cy­clio­phorans.

Be­hav­ior

Al­though thou­sands of in­di­vid­u­als may be found on the mouth­parts of a sin­gle host, cy­clio­phorans are soli­tary. They are ses­sile, using the ad­he­sive discs at the end of their stalks to at­tach to their hosts’ mouth­parts. Only lar­vae and males are free-swim­ming. (Kris­tensen, 2002; Neves, et al., 2012)

Com­mu­ni­ca­tion and Per­cep­tion

Cy­clio­phorans pos­sess a rel­a­tively well-de­vel­oped cere­bral gan­glion and a pair of lon­gi­tu­di­nal nerves that pro­ceed ven­tro­lat­er­ally from this struc­ture. Males, fe­males, Pan­dora, and Prometheus lar­vae all pos­sess frontal and lat­eral head sen­silla that may serve as mechanosen­sory struc­tures. Elec­tron mi­croscopy of male cy­clio­phorans has re­vealed struc­tures that may rep­re­sent ad­di­tional tac­tile sen­sory or­gans, such as frontal palps and dor­sal papil­lae, and a struc­ture in the cere­bral gan­glion of one in­di­vid­ual that was ten­ta­tively iden­ti­fied as a sta­to­cyst. The preva­lence and func­tion of these struc­tures re­quires fur­ther in­ves­ti­ga­tion and ver­i­fi­ca­tion. It would ap­pear likely that cy­clio­phorans must pos­sess some chemosen­sory abil­ity as well, as they are able to syn­chro­nize their re­pro­duc­tive and de­vel­op­men­tal be­hav­iors with their host's molt­ing and feed­ing cy­cles. The basis of their in­ter­ac­tions with one an­other re­mains un­known. (Funch and Kris­tensen, 1997; Funch, et al., 2008; Neves, et al., 2009; Obst and Funch, 2003)

Food Habits

Cy­clio­phorans are fil­ter feed­ers dur­ing their ses­sile stage; they do not feed dur­ing free swim­ming stages. Their cir­cu­lar mouths are sur­rounded by a ring of com­pound cilia that cre­ate a feed­ing cur­rent; they typ­i­cally con­sume small food par­ti­cles from their hosts, or bac­te­ria. It has been hy­poth­e­sized that they de­pend solely on par­ti­cles gen­er­ated by their hosts and that the ses­sile stage is trig­gered by in­creased feed­ing by the host. (Funch, et al., 2008; Kris­tensen, 2002; Neves, et al., 2012)

Pre­da­tion

No preda­tors spe­cific to cy­clio­phorans have been iden­ti­fied; how­ever, any preda­tor of hosts car­ry­ing them, such as large de­m­er­sal fishes, would nec­es­sar­ily con­sume these an­i­mals as well. (Han­son and Lanteigne, 2000; van der Meeren, 2000)

Ecosys­tem Roles

Cy­clio­phorans are only found liv­ing as com­men­sals on (or, in free swim­ming stages, near) their lob­ster hosts. (Br­usca and Br­usca, 2008; Kris­tensen, 2002; Shapiro, 2012)

Species Used as Host

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

There are no known pos­i­tive ef­fects of cy­clio­phorans on hu­mans, out­side of the po­ten­tial for sci­en­tific re­search. (Shapiro, 2012)

  • Positive Impacts
  • research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Al­though these an­i­mals live on lob­sters, they do not gen­er­ally ad­versely af­fect their hosts, al­though it is pos­si­ble for large num­bers of cy­clio­phorans to clog their host's mouth­parts. There are no known ad­verse ef­fects of cy­clio­phorans on hu­mans. (Funch, et al., 2008; Shapiro, 2012)

Con­ser­va­tion Sta­tus

Cy­clio­phorans are not con­sid­ered threat­ened or en­dan­gered. (Shapiro, 2012)

  • IUCN Red List [Link]
    Not Evaluated

Con­trib­u­tors

Je­remy Wright (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Leila Si­cil­iano Mar­tina (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sessile

non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

year-round breeding

breeding takes place throughout the year

Ref­er­ences

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Funch, P., P. Thor, M. Obst. 2008. Sym­bi­otic re­la­tions and feed­ing bi­ol­ogy of sym­bion Pan­dora (Cy­clio­phora) and Trit­i­cella flava (Bry­ozoa). Vie et Mil­lieu, 58/2: 185-188. Ac­cessed April 02, 2013 at https://​www.​researchgate.​net/​publication/​224875336_​SYMBIOTIC_​RELATIONS_​AND_​FEEDING_​BIOLOGY_​OF_​SYMBION_​PANDORA_​(CY­CLIO­PHORA)_AND_TRIT­I­CEL­LA_FLA­VA_(BRY­OZOA)?ev=srch_pub.

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