. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 322 S. Q. IRVINE ET AL Setiger Bl has dorsally extended aliform notopodia, which secrete and support a mucous net. This net is gathered by the accessory feeding organ of setiger B2. which is located dorsal to a convoluted portion of the gut. From this organ, a ciliated groove on the dorsal midline carries food particles anteriorly to the mouth. Setiger B2 is much longer than other segments, but derives from a single larval segment, as demonstrated below. The posterior three segments of this region consist of highly modified
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 322 S. Q. IRVINE ET AL Setiger Bl has dorsally extended aliform notopodia, which secrete and support a mucous net. This net is gathered by the accessory feeding organ of setiger B2. which is located dorsal to a convoluted portion of the gut. From this organ, a ciliated groove on the dorsal midline carries food particles anteriorly to the mouth. Setiger B2 is much longer than other segments, but derives from a single larval segment, as demonstrated below. The posterior three segments of this region consist of highly modified neuropodia forming fans termed palettes that pump water through the animal's tube by a metachronal, rhythmic movement (MacGinitie, 1939; Barnes, 1965). Each of the five segments in this middle region has a neuropodial torus bearing uncinal plates. Tori are flattened ridgelike parapodia. and uncini are dentate deeply imbedded setae with platelike bases (Fauchald, 1977). The posterior tagma (region C) has an indeterminate number of gametogenic segments of a uniform morphology, tapering in size towards the posterior. Each segment bears a crescent-shaped notopodium and bilohed neuropodium. The small pygidium bears two pairs of cirri surrounding the anus. Larval stages The following stage-numbering system begins with the earliest pelagic larva. Although embryonic development prior to gastrulation and production of the swimming larva have been described (Malakhov, 1984; Henry, 1986), no complete staging scheme has been previously devised for Chaetoptems larvae. Developmental times are postfertiliza- tion ages based on laboratory culture at room temperature of 21°-23°C. Sizes listed are in micrometers, anterior-poste- rior length (excluding apical tuft and posterior papilla) by maximum lateral width (excluding setae). The numbering of segments is as shown in Figure 1. Stage LI—18-36 hours (Fig. 2a): Protrochophore Size: 125 x 100 /urn Ciliary structures: apical tuft present; one p
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
