|A new genus of polychaete worm (Family Orbiniidae) from methane seeps in the Gulf of Mexico, with a review of the systematics and phylogenetic interrelationships of the genera of Orbiniidae|
Blake, J.A. (2000). A new genus of polychaete worm (Family Orbiniidae) from methane seeps in the Gulf of Mexico, with a review of the systematics and phylogenetic interrelationships of the genera of Orbiniidae. Cah. Biol. Mar. 41(4): 435-449
In: Cahiers de Biologie Marine. Station Biologique de Roscoff: Paris. ISSN 0007-9723, more
An abundant polychaete Methanoaricia dendrobranchiata gen. nov. et sp. nov., found in association with methane seeps (>500 m) in the Gulf of Mexico, has affiliations with the family Orbiniidae. These seepworms are large, up to 15 cm long, 7-9 mm wide anteriorly, with hundreds of crowded segments. Distinct body regions are absent. Branched branchiae extend over the entire body. The prostomium is narrow, elongate, directed ventrally, and bluntly rounded on the anterior margin. Eyes are absent; eversible nuchal papillae are present. The peristomium is reduced to a single, narrow achaetous ring. Parapodia bear long, laterally directed, cirriform noto- and neuropodial lamellae. Capillary chaetae have transverse rows of bristles. Narrow, pointed notopodial spines have a single subapical spur or secondary tooth. Neurochaetae of anterior chaetigers include a few threadlike capillaries, about 5 simple spines with weakly developed crenulations along their margins, and 3-4 emergent curved aciculae; spines are absent by the middle of the body. The pygidium has a terminal anus surrounded by several long, tapering cirri. The chaetal and branchial structure of these worms allies them most closely to the Orbiniidae despite the lack of distinct body regions. In order to understand the relationship of the seepworm with other orbiniid genera, a phylogenetic (cladistic) analysis was performed. The results of this analysis suggests that the current classification of orbiniid genera into subfamilies is not appropriate and a new classification is proposed that is based on increasing modification of body structure and chaetae. Two clades or subfamilies of Orbiniidae are proposed using these characters rather than the traditional peristomial ring structure. The seepworm appears to be a separate and distinct sister taxon.