. Bulletin of the Natural History Museum Zoology. . Fig. 4 Bracts of Bargmannia elongata. Scale bar = 1 mm. This thickening diminishes in the region of the thrust block, but there is still a shallow median gutter that enfolds the nectosomal stem in the region of attachment of the nectophore (Figure 2 B). In the preserved nectophores, the nectosac is a dorso-ventrally undulating tube (Figure 2B, n; 2C), with prominent dorso-lateral extensions in the mid region, and ventro-lateral ones both apically and basally. However, this arrangement is not apparent in the nectophores of the living animal (F
. Bulletin of the Natural History Museum Zoology. . Fig. 4 Bracts of Bargmannia elongata. Scale bar = 1 mm. This thickening diminishes in the region of the thrust block, but there is still a shallow median gutter that enfolds the nectosomal stem in the region of attachment of the nectophore (Figure 2 B). In the preserved nectophores, the nectosac is a dorso-ventrally undulating tube (Figure 2B, n; 2C), with prominent dorso-lateral extensions in the mid region, and ventro-lateral ones both apically and basally. However, this arrangement is not apparent in the nectophores of the living animal (Figure 1 ).The nectosac is broadest at about two-thirds its length, narrowing slightly towards its apex. It has a distinct apical emargination; U-shaped in the younger nectophores (Figure 3 A). Typically, the ventral, adaxial region towards the apex of the nectosac is distinctly undercut and, from a level just basal to the point of insertion of the pedicular canal, its wall is devoid of musculature (Figure 2 B). The musculature of the remainder of the nectosac appears well developed and gives it a distinctly opaque appearance. The ostium, in the preserved material, opens onto the dorso-basal (abaxial) surface (Figure 2C, o) and is roughly rhomboidal in shape. However, this probably is distortion due to preservation (see Figure 1). In the Alvin specimens it has a large velum, with a relatively small central opening, but in net collected material often the velum is destroyed. The lateral walls of the ostium extend out to form lateral processes (Figure 3C) that, typically, are covered by patches of ectodermal cells of varied size. Further such patches are present on the ventral margin of the velum, but not on the dorsal margin, except for the youngest nectophores. Some, if not all, of these cells probably produce bioluminescent material since this has been found to be the case in another Bargmannia spp. (Dr S. Haddock, personal communication). The long pallial canal (Figure 2B, pc)
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