. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 5. Growth in <7ri;< Gruwlh occurs through the addition of terminal setigers, immediately anterior to the pygidium. New setigers develop the parapodial lobes and chaetae characteristic of the tail (tl. Transitional setigers show branchiae buds (h) and tufts of dorsal cilia (d) as they gradually differentiate into abdominal setters (a). Scale bar = 10(1 /urn Figure 6. Bright field micrograph of a two-headed individual of P\- 'V"" cU'xuns, formed after a spontaneous asexual event. ments.
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 5. Growth in <7ri;< Gruwlh occurs through the addition of terminal setigers, immediately anterior to the pygidium. New setigers develop the parapodial lobes and chaetae characteristic of the tail (tl. Transitional setigers show branchiae buds (h) and tufts of dorsal cilia (d) as they gradually differentiate into abdominal setters (a). Scale bar = 10(1 /urn Figure 6. Bright field micrograph of a two-headed individual of P\- 'V"" cU'xuns, formed after a spontaneous asexual event. ments. Fragments were classified according to the remain- ing original body region into anterior (containing the orig- inal head, thorax, and anterior abdomen), mid-worm (abdominal setigers only), and posterior fragments (original pygidium. tail, and a few abdominal setigers). Anterior and mid-worm fragments had a relatively low mortality, approx- imately 14% for all three populations combined (Table 2), although few mid-fragments were observed because most worms spontaneously divided into two fragments (anterior, posterior) only. Posterior fragments had the highest mor- tality overall, about 80% among all three populations (Table 2). Discussion Morphogenesis after asexual reproduction in P\gospio elegans involved two phases: regeneration of lost body regions (, head, thorax, tail) followed by appositional growth as terminal setigers were added. During regenera- tion of the anterior region, the blastema extended to form the head and thorax, segmented to divide the thorax into 10-12 setigers, and subsequently developed segment-spe- cific structures (, chaetae). Regeneration of the posterior blastema was similar and also involved formation of a finite, though variable, number of setigers (6 to 12). The origin of blastemal tissues was not examined in the present study, but probably involves the growth of existing tissues (, epi- dermis) in combination with the migration of me
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
