Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions
2001
Kawamura, T. (Tohoku National Fisheries Research Inst., Shiogama, Miyagi (Japan)) | Takami, H. | D Roberts, R. | Yamashita, Y.
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 deg C. The number of rows increased to 25 - 30 during the first several days after settlement, but then remained approximately constant throughout the post-larval period, increasing again in abalone larger than 4mm in shell length (SL). In post-larvae < - 1mm 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 0.9mm to 1.9mm SL. Marginal teeth were added steadily from one pair in larvae to 30 - 40 pairs at 3 - 4mm SL, 70 - 80 pairs in 30 - 40mm juveniles, and 70 - 90 pairs in 90 - 100mm 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 - 2mm SL, and from the outer lateral teeth (L3-L5) by 20 mm SL. For abalone larger than 1.5mm SL, the L3 - L5 teeth became longer and more pointed, which increased the space between adjacent rows of teeth. Post-larvae < 1mm 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.
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