. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 218 G. O. MACKIE AND C. L. SINGLA or not two botryllid colonies fuse during growth is determined by processes of self- nonself discrimination at the ampullae, which are the only contact points between the two colonies (Scofield et al, 1982; Watanabe and Taneda, 1982). Another function can now be added to this list: the ampullae and vascular vessels provide a conduction pathway mediating defensive behavior in the zooids. Any sharp or damaging stimulus to the ampullae or connecting vessels causes siphonal retraction and closur
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 218 G. O. MACKIE AND C. L. SINGLA or not two botryllid colonies fuse during growth is determined by processes of self- nonself discrimination at the ampullae, which are the only contact points between the two colonies (Scofield et al, 1982; Watanabe and Taneda, 1982). Another function can now be added to this list: the ampullae and vascular vessels provide a conduction pathway mediating defensive behavior in the zooids. Any sharp or damaging stimulus to the ampullae or connecting vessels causes siphonal retraction and closure along with ciliary arrest in nearby zooids, equivalent to the well known protective squirting of solitary sea squirts. Similar systems exist in other colonial forms, both sessile and pelagic. Most animal colonies are coordinated by nervous or non-nervous conduction pathways, sometimes by both. The closest par- allels to the botryllid system are to be found in certain hydroid colonies where non- nervous impulses are conducted along the stolons interconnecting the polyps. The polyps retract protectively on receiving the excitation (reviewed by Spencer and Schwab, 1982). Colonies of some other hydroids and of bryozoans and corals are coordinated by nerves, but the responses are again protective in character (reviewed by Shelton, 1982; Thorpe, 1982). Conducting epithelia can provide an adequate pathway for simple impulse con- duction over considerable distances, but the responses they mediate are complex and labile, and at the effector end they are nearly always organized by nerves (, Anderson and Bone, 1980; Mackie and Carre, 1983). In the botryllid system, there is no reason to suspect the involvement of nerves in the coordination of ampullar rhythms, but the effector responses of muscle contraction and ciliary arrest in the zooids are almost certainly organized by nerves. In every zooid two-way epithelio- m ne. FIGURE 7. Wiring diagram of an idealized botryllid colony. Ner
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
