In:
Canadian Journal of Zoology, Canadian Science Publishing, Vol. 74, No. 12 ( 1996-12-01), p. 2143-2153
Abstract:
Several members of the Annelida bear apically curved or hooked setae that are aligned in a transverse row inside the neuropodial rim. Based on the hypothesis that these specific setae characterize a monophyletic group within the Annelida, the structure and development of the hooked seta in Owenia fusiformis are analysed and compared with data from other annelids with such setae. The neuropodial hooks of O. fusiformis are arranged in multiple transversal rows or setal patches on each side of the body from the fourth setiger onwards. The setae are curved distally and consist of two identical spines lying side by side at the same level. Their tips generally point ventrofrontally. Within each patch, the setae lie inside a setal follicle that consists of a basal chaetoblast, at least one follicle cell, and varying numbers of epidermal cells. Each setal patch is basally surrounded by an extracellular matrix that is continuous with the subepidermal basal lamina. An additional discontinuous extracellular matrix lies between the epidermis and the follicle cells. It is of functional significance for the attachment of the epidermal cells and seems to be related to the special organization of the setal patches, because it is absent in juveniles; they have single neuropodial rows of hooked setae per segment. New setae are formed at the dorsal and caudal edges of each patch, whereas the degeneration of setae is observed at the frontal edge of each patch. Microvilli project from the apex of the chaetoblast into canals within the fully differentiated setae. These canals remain when the microvilli are withdrawn from the seta during formation. Each hook is formed by a single large microvillus. The results of the present paper substantiate the hypothesis of a homology of the hooked setae in the Oweniida and other Annelida. These results and data from the literature support the hypothesis that the Oweniida is the sister-group of a monophylum which consists of the Terebellida, Pogonophora, and Sabellida.
Type of Medium:
Online Resource
ISSN:
0008-4301
,
1480-3283
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
1996
detail.hit.zdb_id:
1490831-1
SSG:
12
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