NEWS107
10
Beautiful thoughmanysea-starsmaybe,nu-
merousspeciesareofonly limitedsuitability
for the reef aquariumas they canbe rather
predatory.
Archaster typicus
, theSand-Sifting
Sea-Star isaspeciesunlikelytobepurchased
onaccountof itscolorfulness,butthisspecies
doesn't actually need to be colorful as is
spends all the day buried in the substrate,
emerging from this domicile only at night
thenonlyoccasionally.But
Archaster
don'tjust
hide in thesubstrate,they feed thereaswell.
And thatmakes themextraordinarilyuseful,
asfirstly,theycontinuallydigthroughthebot-
tom todo soandpreventanyharmful com-
pacting;secondly,theycanbereliedontoeli-
minateuneaten food; and thirdly, theypre-
vent the ratherunattractivebrowndiatoma-
ceousalgae fromcolonizingthesubstrate,as
thesetoo formpartof thissea-star'sdiet.
With itsneon-colored facialmask,
Perconplanissimum
isratherattractive.
Perconplanissimum
,anoutstandingalgae-eater.
mum
.Thiscrab,whosebody isalmostsquare
inshape,growstoaround3-10cm insize,de-
pendingonwhat youmeasure. If you take
just the carapacewidth then you arrive at
about 3 cm, but if you take the entire leg-
spanthentheresult issometimesmorethan
10 cm. This crab leaves themajority of its
tankmates in the reef aquarium completely
inpeaceandprefers to feedonalgae.Apro-
rals, fishes,echinoderms,etc.) havebeen re-
ported todate.
Allcrabsareescapeartists,andthisshouldbe
borne inmindas otherwise sooner or later
you will either find a dehydrated crab, or
(more likely)bedeafenedbysomeone infear
oftheir lifescreamingatthetopoftheirvoice
whenadust-coated "giant spider" suddenly
inpairs,as individualsof the same sexwon't
tolerateoneanother.Thesexescanbeeasily
toldapartby the formof theposteriorbody
(thepleon).Thespecies isdistributed inwarm
seaspracticallyworldwide if
Percongibbesi
is
regardedasbeingthesamespecies,or inthe
easternpartoftheOldWorld if
P.gibbesi
isre-
gardedasawesternsiblingspecies.Sincethe
late1990sthe latterhasbeenregardedasan
invasivespecies intheMediterranean,where
it isspreadingrapidly.
Thestars inthesubstrate
Sea-starsnevercase to fascinate.This is, inter
alia,becauseof their unusual symmetry.Al-
mostall theanimalsonthisplanetarebilate-
rally symmetric, in other words if an axis is
drawnthe lengthoftheirbodiesthenweget
a left-handandaright-handhalfthatarevery
similar tooneanother.Not sowith sea-stars
andother echinoderms suchas seaurchins,
crinoids,andseacucumbers.Theyhavedeve-
loped a five-way symmetry, termedpenta-
mery,around fiveaxesof symmetry.Never-
thelesstheybelongtotheBilateria,that isani-
malswithbilateral symmetry,as their larvae
exhibitperfectlynormalbilateral symmetry.
pos of which, the same applies as stated
aboveregardinghermitcrabs.Youshouldbe
aware,however,that
Perconplanissimum
also
hasataste forgastropods.Butnoassaultsby
this crabonother aquariumoccupants (co-
scuttlesacross the room.Neither isdesirable,
soaids toescape suchas filterhoses,heater
cables,etcshouldallbemadecrab-proof.
Perconplanissimum
shouldbekept singlyor
