. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 328 S. Q. IRVINE ET Figure 8. Juvenile worms within 1 day of metamorphosis at about 60 days. Anterior is to the left, (a) Dorsal view. Letters and numbers indicate adult setiger locations. Asterisk denotes the ciliary groove of the aliform notopodium of setiger BI, derived from the posterior mesotroch. Arrowhead points to a parapodium of the first 'abdominal' setiger Cl. (b) Two newly metamorphosed specimens. Upper specimen is in ventrolateral view and lower is in dorsolateral view. Arrowheads as in (a) above, afo. acce
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 328 S. Q. IRVINE ET Figure 8. Juvenile worms within 1 day of metamorphosis at about 60 days. Anterior is to the left, (a) Dorsal view. Letters and numbers indicate adult setiger locations. Asterisk denotes the ciliary groove of the aliform notopodium of setiger BI, derived from the posterior mesotroch. Arrowhead points to a parapodium of the first 'abdominal' setiger Cl. (b) Two newly metamorphosed specimens. Upper specimen is in ventrolateral view and lower is in dorsolateral view. Arrowheads as in (a) above, afo. accessory feeding organ rudiment; an. aliform notopodium rudiment; ao. adult ocellus; eg. ciliated groove; lo, larval ocellus; m, mouth; nr, notopodial rudiment of setigers AI-A9; pa, palp rudiment; pal, palette rudiment of setigers B3-B5; pol, postoral lobe; pyg. pygidium. Scale bar is 100 juni. Larval segmentation and relationship to adult bod\ plan The most commonly described form of larval develop- ment in polychaetes is the production of a trochophore larva that adds segments sequentially from a posterior growth zone to produce a nectochaete larva (Okada, 1957; Ander- son, 1966). There is some controversy over whether the first three larval segments develop in the same sequential man- ner as subsequent segments, but in typical cases the demar- cation of each of the segmental boundaries is evident in the external form of the larva from a very early stage. Chaetopterus represents a distinct departure from this gen- eral pattern. The first external signs of segmentation are the rudiments of segments B3-B5 visible at stage L4, at an age of 30 days. At no point does the metatrochophore take on the overtly segmented form of the typical nectochaete larva. However, some incipient segmentation is present before it becomes visible externally. Bonch-Bruevich and Malakhov (1987) describe three trunk coeloms existing at stage L2, which is consistent with our stage L3 sections (Fig. 3a). If
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
