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Figs. 2-7. Proboscidactyla flavicirrata. Fig. .2. Mature planula; scale: 0.1 mm. Fig. 3. Planula meta- 
morphosis, 3 hours after contact with sabellid worm; oral pole is to the right; the hypostomal endoderm (h) 
has differentiated; n, nematocyst; scale: 0.1 mm. Fig. 4. Planula metamorphosis, 4.5 hours after contact 
with worm; t, tentacle rudiment; scale: 0.1 mm. Fig. 5. Metamorphosis nearly complete, 7 hours after con- 
tact with worm; f, rudiment of "foot”; scale: 0.1 mm. Fig. 6 . Beginning of migration; f, "foot”; tissue 
to the left of foot represents stolon (s), which in this case has stretched to about 3 times its original length; 
12 hours after contact with worm; scale: 0.1 mm. Fig. 7. Newly metamorphosed polyp possessing two ten- 
tacles; small protrusion at left is the "foot”; scale: 0.1 mm. 
of the Proboscidactyla colony for the sabellid 
worm tubes. 
The initial attraction of the planula to the 
worm site, however, appears to be quite non- 
specific, involving water currents set up by the 
branchial cilia. In this respect the commensal 
specificity resembles that of Hydractinia for 
shells inhabited by hermit crabs: Schijfsma 
(1935:290-302) and Cazaux (1958:2195), 
showed that there is no attraction of the 
Hydractinia planula by the hermit crab, but 
rather that settling is apparently stimulated by 
particular conditions of waterflow across a hard 
substratum, conditions which are frequently 
presented by a hermit crab shell in its habitat 
of swiftly moving water. 
