Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions
T. Kawamura, H. Takami, R.D. Roberts, Y.
Yamashita-2001
Fisheries Science, 67(4): 596-605
(from Current Contents)
Abstract :
The radula morphology of Haliotis discus hannai was
examined by scanning electron microscope from the larval to the adult stage.
The radula of competent larvae contained 11-13 transverse rows of teeth
after 6-7 days at 20 °C. The number of rows increased to 25-30 during the
first several days after settlement, but then remained approximately
constant throughout the postlarval period, increasing again in abalone
larger than 4 mm in shell length (SL). In post-larvae < <similar
to>1 mm SL, only two pairs of lateral teeth (L1, L2) were present in the
larval radula. An additional three pairs of lateral teeth (L3-L5) were added
progressively as post-larvae grew from 0.9 mm to 1.9 mm SL. Marginal teeth
were added steadily from one pair in larvae to 30-40 pairs at 3-4 mm SL,
70-80 pairs in 30-40 mm juveniles, and 70-90 pairs in 90-100 mm adults. The
serrations on the working edges of the rachidian (R) and lateral teeth
became less pronounced as the abalone grew. Nearly all serrations
disappeared from the rachidian (R) and inner lateral teeth (L1, L2) by
similar to2 mm SL, and from the outer lateral teeth (L3-L5) by 20 mm SL. For
abalone larger than 1.5 mm SIL, the L3-L5 teeth became longer and more
pointed, which increased the space between adjacent rows of teeth.
Post-larvae < 1 mm SL had highly curved teeth with clearance angles of
approximately or less than zero, whereas larger abalone had positive
clearance angles. These radula developments appear to be related to
transitions in feeding habits from microbial to macroalgal diets.
(Univ Tokyo, Ocean Res Inst, 1-15-1 Minamidai, Tokyo
1648639, Japan, e-mail: kawamura@ori.u-tokyo.ac.jp)