Some aspects of the development of eggs and larvae of Sabellaria alveolata (L.)
Wilson, D.P. (1968) Some aspects of the development of eggs and larvae of Sabellaria alveolata (L.). Journal of the Marine Biological Association of the United Kingdom, 48 (2). pp. 367-386.
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The rate of growth of larvae of Sabellaria alveolata (L.) reared in the laboratory varied greatly between different rearings and between individuals of the same age in the same rearing vessel, the temperature throughout being maintained close to 15°C. The shortest recorded time from fertilization to metamorphosis was 6 weeks, the longest nearly 8 months. Within any one rearing some larvae metamorphosed weeks or months earlier than the last to do so. The larvae were fed on phytoflagellates, especially Isochrysis galbana, and the variations in growth were partially due to differing quantities of food available and to the differing character of the food. The largest larvae obtained, up to 700 u long, fed in their later stages on an Olisthodiscus sp., alone or with another flagellate. The smallest larvae, only about 400 u long, ate voraciously large quantities of the coccolith Coccolithus huxleyi. The normal length of larvae fed on Isochrysis alone was about 500 u. The eggs as shed, primary oocytes, are much crumpled, each with a conspicuous germinal vesicle, a condition here abbreviated to C.G.V. Often ova remain in this state until fertilized, but some batches quickly round up after shedding, becoming opaque with loss of the germinal vesicles, and a crumpled membrane elevates around each ovum; this condition is here referred to as R.O.M. Some batches of ova of both types when fertilized have produced good-quality larvae which have completed development; other batches of both types have produced only poor-quality larvae which have died early. C.G.V. ova stay fertilizable for much longer than do R.O.M. ova, which cytolyse sooner. The evidence suggests that as they mature they pass from a C.G.V. to an R.O.M. state and then become over-ripe. Maximum maturity is probably at about the time of change from the C.G.V. to the R.O.M. state, this normally taking place about the end of July during the period of natural spawning. This change would explain disagreements in the literature concerning experiences with unfertilized eggs. The opportunity is taken to correct and amplify some details, mostly minor, in earlier accounts of the development, particularly those of Wilson (1929) and Cazaux (1964). Cazaux's criticism of the function of the 'grasping-cilia' is met, and it is reaffirmed that they hook on to the ends of the provisional bristles during normal swimming. The metamorphosing larva drawn by Wilson was of a rare type in which the post-telotrochal tail has appeared before rotation of the opercular peduncles with loss of all provisional bristles. Normally the tail does not appear until after the head has completed metamorphosis. Unlike adults, recently metamorphosed young worms, which have crawled out of or have been ejected from their first-formed tubes, are sometimes capable of making new sandy tubes.
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