Severed linkia arm

[Delphinus]

I have a burgundy linkia in my tank. Today I found one of its arms (sans the rest the starfish) happily wandering around the tank.

Bizarre. I haven't seen the starfish in about a week or so, so I don't know how long it's been like this.

I'm a bit concerned that if the arm doesn't make it, I'll have to remove it. I wonder if I should fish it out and put it in a refugium to see if it will regrow a new body.

[Buccaneer]

Are you fragging your starfish now ? :razz: :eek: :lol:

Dibs on the arm :biggrin:

Cheers

[kari]

Dibs on the second arm :biggrin: :biggrin:

[Delphinus]

There is now a second arm. :confused:

Frankly I'm a bit concerned. I have to do more research, but I'm worried that this is a stress response of some kind.

Any other Canreefers have this happen with their linkias?

[Quinn]

Just in case, dibs on the third arm. No ideas on why though. :neutral:

[Buccaneer]

PHYLUM ECHINODERMATA
Body Plan
Coelomates. Calcareous endoskeleton composed of intradermal ossicles (plates) derived from single calcite crystals. Secondarily radially symmetrical (larvae are bilaterally symmetrical), usually with pentaradial symmetry. Unique feature is coelomically-derived water vascular system.

Locomotion
Body form and structural support by interlocking series of ossicles. Makes most echinoderms hard, though in some (e.g., sea cucumbers), ossicles are separate and body is soft, relying on hydrostatic skeleton. Movement is often by unique system of hydraulic podia or "tube feet", part of water vascular system. Other forms may (e.g., crinoids) use flexible arms for walking or swimming. Sea urchins use both podia and flexible spines.

Feeding and digestion
Much variety. Crinoids filter-feed, lying upside-down, with oral side up and arms outstretched, using cilia-lined ambulacral grooves to bring food to mouth. Asteroidea are mostly predators or scavengers (a few filter-feed). Cardiac portion of stomach everts, secretes enzymes, partially digested prey is drawn in with retracting stomach. Aboral to cardiac stomach is pyloric stomach with cecae into each arm and short intestine to aboral anus. Brittle stars use podia on arms or arms themselves to push small or large food to mouth for ingestion. Urchins use a masticatory apparatus called "Aristotle's lantern" inside mouth; in many forms this can be everted to scrape detritus off substrate, stones, etc. Holothurians are mostly suspension or deposit feeders, and use tentacles to bring food to mouth.

Sense Organs
No complex sense organs. Chemoreception is widespread. Some holothurians have statocysts. Many starfish have clusters of ocelli at the tip of each arm. Mechanoreception is via nerves innervating specialized epidermal structures (e.g., spines).

Nervous System
Decentralized and diffuse (commensurate with secondary radial symmetry). Three main networks, developed to different degrees in different groups: oral (ectoneural), primarily sensory; deep oral (hyponeural), primarily motor; and aboral (entoneural), absent in holothurians. Ectoneural and entoneural networks give rise to a diffuse sub- and intraepidermal nerve net with thickenings into a circumoral nerve ring and radial nerves extending along each ambulacrum.

Respiration and gas exchange
Asteroids and crinoids use special thin areas of epidermis for gas exchange, called dermal gills or papulae. Urchins use multiple invaginations of the body wall (bursae) opening to outside via slits, and ventillated with cilia or muscular action. Sand dollars use highly modified podia on aboral surface (petaloids) which are thin-walled and flaplike. Holothurians use a highly branched hindgut called the "respiratory tree" for exchange, with water drawn into and expelled from the anus.

Circulation
Mostly in perivisceral coelom, augmented by the water vascular system and a hemal system. Hemal system is a series of canals and spaces mostly inside c oelomic channels. Fluid movement is by cilia or in some cases by peristaltic pumps. Role seems mostly to distribute nutrients. No respiratory pigment present.

Osmoregulation and excretion
Often by simple diffusion of gaseous wastes. Precipitated nitrogenous wastes and particulate wastes are phagocytosed by coelomocytes which carry them to discharge sites (e.g., in asteroids they go to papulae where they themselves are phagocytosed and discharged through papular wall). Most echinoderms are marine and osmoconformers, though a few are brackish-water dwellers whose osmoregulation is not well understood.

Reproduction
Most are capable of regeneration provided some of the central disk remains (except in the asteroid Linkia which can regenerate from an arm). Hence some asexual reproduction is done by fission in asteroids and brittle stars. Sexual reproduction, however, predominates. Most are gonochoristic. Most have true gonads. Fertilization is usually external, though occasionally eggs are brooded on or in the body.

Embryology
Cleavage is radial, holoblastic, and results in a coeloblastula which is often ciliated and free-swimming. Development is typically deuterostomate, with mesoderm formation enterocoelic and trimeric, with the three pairs of coelomic cavities corresponding to the protocoels, mesocoels, and metacoels of other deuterostomes. Blastopore becomes anus, mouth develops from stomodeal inpocketing.


So Tony I still have dibs on that arm :smile: ... seems your Linkia is just using asexual reproduction ... when/if my blue linkia drops an arm you can have first dibs :cool:

Cheers

[Delphinus]

Four severed arms, and a two-armed linckia that looks to be trying to rip itself in half. So soon to be no more linckia and five arms.

Actually, only 4. The original arm that I first wrote about, looks like it was eaten by the worms.

Guess I won't be trying another linckia .... sounds like they maybe don't belong in captivity.

:sad:

[Buccaneer]

Sorry to hear that Tony :sad: ... by the article I posted it should be trying to reproduce but who knows with these creatures ... I still stand by my offer if my blue linkia does reproduce by dropping a arm you are welcome to it

Cheers

[Quinn]

Perhaps it is reproducing due to stress... not that anything in Tony's tank is off, but as we know they don't have the best track record. I don't think healthy asexual reproduction is too common in captivity.