MARINE FLORA AND FAUNA OF THE 



NORTHEASTERN UNITED STATES 



Annelida: Oligochaeta 



DAVID G. COOK^ and RALPH 0. BRINKHURST" 

 ABSTRACT 



The manual includes an introduction on the general biology, an illustrated key, an an- 

 notated systematic list, a selected bibliography, and an index to the marine Oligochaeta of 

 the East Coast of North America. The Families Naididae, Tubificidae, Enchytraeidae, and 

 Megascolecidae are treated. 



INTRODUCTION 



The Oligochaeta, a group of predominantly 

 terrestrial and freshwater annelids, includes a 

 number of species which have adapted well to the 

 marine benthic environment. Despite the fact 

 that these organisms may occur in great num- 

 bers in the sea (densities of up to a million per 

 m- have been reported) the information on their 

 ecology and taxonomy is comparatively sparse. 

 The available data do suggest, however, that 

 the intertidal zone, the subtidal zone, the con- 

 tinental shelf, and even the abyssal plain, all have 

 characteristic oligochaetes associated with them. 



Four families of oligochaetes occur along the 

 east coast of North America, namely, the Mega- 

 scolecidae (with 2 species), Naididae (8 spe- 

 cies), Enchytraeidae (13 species), and Tubifici- 

 dae (22 species) ; members of the first named 

 family are known as megadriles and the last 

 three as microdriles (to which much of the fol- 

 lowing discussion applies). 



Definition and Diagnostic Characters 



Oligochaeta are typically vermiform, cylindri- 

 cal, segmented, bilaterally symmetrical, her- 



' National Museum of Natural Science, Ottawa, 

 Canada, and Systematics-Ecology Program; present 

 address: Great Lakes Biolimnology Laboratory Canada 

 Centre for Inland Waters, 867 Lakeshore Road Burling- 

 ton, Ontario, Canada L7R 4A6. 



- Department of Zoology, University of Toronto, 

 Toronto 5, Ontario, Canada, and Systematics-Ecology 

 Program; present address: Fisheries Research Board 

 of Canada, Biological Station, St. Andrews, New Bruns- 

 wick, Canada. 



maphroditic annelids with a spacious coelom, a 

 prostomium, an anterior ventral mouth, and a 

 posterior anus. Conventionally segments are 

 numbered in Roman numerals, beginning at the 

 anterior end with the peristomium as segment I. 

 Each segment, except the persistomium, usually 

 bears four bundles of setae, two dorsolateral, 

 and two ventrolateral (shortened to dorsal and 

 ventral in the key) which are implanted directly 

 in the body wall; parapodia are absent. There 

 are two basic types of setae whose number and 

 morphology in the various body regions are 

 taxonomically important: (a) crochets, which 

 can be straight, curved or sigmoid, may or may 

 not possess a more or less median thickening 

 (the node or nodulus) and which may have 

 rounded, simple-pointed or bifid (forked) distal 

 ends; crochets are found in all oligochaete fam- 

 ilies; (b) hair setae, which are elongate, simple- 

 IJointed structures, without a node, and whose 

 surface may be smooth, finely serrated, or in- 

 vested with a number of very fine lateral hair- 

 lets; hair setae are found only in the dorsal 

 bundles of some Naididae and Tubificidae among 

 the families with marine species. At sexual ma- 

 turity the epidermis of a few anterior segments 

 is thickened, forming a dorsolateral or annular 

 clitellum which secretes the cocoon containing 

 one to several eggs. Oligochaetes do not have a 

 larval stage, and juveniles resembling small 

 adults emerge from the cocoons after a few 

 weeks or months of development. A double 

 ganglionated ventral nerve cord extends through 

 the length of the body: anteriorly it divides 



