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The Vestimentifera and the Pogonophora have complex taxonomic histories, reviewed in Rouse (2001a). However, the roughly 150 species are clearly members of the phylum Annelida and jointly form the family Siboglinidae (Rouse 2001a, b). The consequence of this devaluation in standing is that a complex superstructure of classes, orders, and families has lost its taxonomic value entirely. Both pogonophorans and vestimentiferans are tubicolous , mostly very elongated worms with relatively few highly differentiated segments, few and highly specialized chaetae, and (perhaps most characteristically) with a digestive tract that lacks both anterior and posterior openings . The endodermally derived material is hypertrophied and filled with commensal bacteriae. The chemotrophic activity of these bacteriae is the energy source for the worms, and ultimately hydrogen sulfide in the surrounding waters yields the energy source for production of organic compounds by the bacteriae. The circulatory system is well developed and anteriorly forms a branchial structure, varying in complexity from a single, elongated structure to complex tentacular crowns somewhat resembling the sabellid tentacular crown (especially in pogonophorans ) or forming a uniquely complex structure (especially in the vestimentiferans) (Rouse 2001b). An excellent overview of the morphology is found in Rouse (2001a). A detailed microscopical anatomy of the pogonophorans was presented by Southward (1993) and for the vestimentiferans by Gardiner and Jones (1993). Pogonophorans are very slender, often less than 1 mm in diameter and very elongated, and have been reported from muddy sediments all over the globe. The first species reported were from abyssal depths, but pogonophorans have since been reported also from shelf depths in appropriate sediments. There are no published records of the taxa traditionally considered as pogonophorans from the Gulf of Mexico (GMx), but the MAFLA (MississippiAlabama -Florida) collections contain currently unpublished records of unidentified pogonophorans; that more material will turn up in a careful examination of slender tubicolous sabellids or chaetopterid material from muddy bottoms in the Gulf is anticipated. Most vestimentiferans are linked to hot vents, which are associated with areas of seafloor spreading such as the Mid-Atlantic Ridge and the Eastern Pacific Rise, and associated geological structures (Jones 1985a and papers therein). Most hot vents are in deep water, but at least 793 39 Vestimentifera and Pogonophora (Annelida) of the Gulf of Mexico Kristian Fauchald  Pogonophora. After Hyman 1955, modified by F. Moretzsohn. 794 ~ Vestimentifera and Pogonophora (Annelida) Microscopic Anatomy of Invertebrates 12: Onychophora, Chilopoda and Lesser Protostomes. Wiley-Liss, New York. 3. Gardiner, S. L., E. R. McMullin, and C. R. Fisher. 2001. Seepiophila jonesi, a new genus and species of vestimentiferan tube worm (Annelida: Pogonophora) from hydrocarbon seep communities in the Gulf of Mexico. Proceedings of the Biological Society of Washington 114: 694–707. 4. Jones, M. L. (editor) 1985a. Hydrothermal Vents of the Eastern Pacific: An Overview. Bulletin of the Biological Society of Washington 6: i–vii + 1–547. 5. Jones, M. L. 1985b. On the Vestimentifera, new phylum: six new species and other taxa from hydrothermal vents and elsewhere. Pp. 117–158 in M. L. Jones, ed. Hydrothermal Vents of the Eastern Pacific: An Overview. Bulletin of the Biological Society of Washington 6. 6. Miura, T., J. Tsukahara, and J. Hashimoto. 1997. Lamellibrachia satsuma, a new species of vestimentiferan worms (Annelida: Pogonophora) from a shallow hydrothermal vent in Kagoshima Bay, Japan. Proceedings of the Biological Society of Washington 110: 447–456. 7. Rouse, G. W. 2001a. A cladistic analysis of Siboglinidae Caullery 1914 (Polychaeta, Annelida): formerly the phyla Pogonophora and Vestimentifera. Zoological Journal of the Linnaean Society 132: 55–80. 8. Rouse, G. W. 2001b. Chapter 51. Siboglinidae Caullery 1914. Pp. 202–205 in G. W. Rouse and F. Pleijel, eds. Polychaetes. Oxford University Press, London, U.K. 9. Southward, E. C. 1993. Chapter 8. Pogonophora. Pp. 327–369 in F. W. Harrison and M. E. Rice, eds. Microscopic Anatomy of Invertebrates 12: Onychophora, Chilopoda and Lesser Protostomes. Wiley-Liss, New York. 10. Van der Land, J., and A. Nørrevang. 1975. The systematic position of Lamellibrachia [sic] (Annelida, Vestimentifera). Pp. 86–101 in A. Nørrevang, ed. The Phylogeny and Systematic Position of Pogonophora. Zeitschrift für zoologische Systematik und Evolutionsforschung, Sonderheft 1. 11. Webb, M. 1969. Lamellibrachia barhami, gen nov, sp. nov. (Pogonophora) from the northeast Pacific. Bulletin of Marine Science 19: 18–47. one is known from shallow water near Kagoshima, Japan (Miura, Tsukahara, and Hashimoto 1997). Certain species are associated with cold seeps, including the first recognized species (Webb 1969). All three species reported from the Gulf of Mexico are linked to...

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