Illinois Natural History Survey - University of Illinois

KEY TO GRANIA (ANNELIDA, CLITELLATA, ENCHYTRAEIDAE)
OF NORTH AMERICA, BERMUDA, AND THE CARIBBEAN


 INTRODUCTION

Enchytraeids are characterized morphologically by their setal shapes and reproductive structures. When present, setae are straight, sigmoid or bent, rarely possessing a nodulus and rarely forked. Spermathecae have an anterior location (segment V) and male pores are on segment XII, glandular sperm funnels and a male penial apparatus are also present. Within marine habitats there are only seven known genera (Healy and Coates, 1999); in comparison, there are about 22 genera that occur in terrestrial and freshwater habitats. The genera with marine species are Achaeta Vejdovsky, 1878, Enchytraeus Henle,1837, Lumbricillus Ørsted, 1844, Stephensoniella Cernosvitov, 1934 (amended, Coates, 1983), Marionina Michaelsen, 1889, Grania Southern, 1913, and Randidrilus Coates and Erséus, 1985; all of of these genera have been recorded from the Western Atlantic.


Locke, J.M., and K.A. Coates. 1999. Redescriptions of Grania americana, G. bermudensis and descriptions of two new species of Grania (Annelida: Clitellata: Enchytraeidae) from Bermuda. Proceedings of the Biological Society of Washington 112:598-623.


GRANIA OF THE NORTHWEST ATLANTIC

The coastal habitats of the Western Atlantic have escaped major exploration of the marine enchytraeid Clitellata. Within the cursory taxonomic surveys of marine enchytraeids, the genus Grania has been diverse and relatively abundant (Kennedy, 1966; Lasserre, 1971; Erséus and Lasserre, 1976; Lasserre and Erséus, 1976; Coates and Erséus, 1985). These reports include species found along eastern North American coastlines, on the nearby Atlantic island of Bermuda, and in the Caribbean. It is expected that many new species remain to be discovered in this region as new habitats are explored and taxonomic character information improves.

Grania are infaunal, sometimes interstitial, indistinctly segmented worms. Generally they are found in well sorted medium to coarse sand as well as poorly sorted sandy mud, both intertidally and subtidally. The worms are microscopic, with an average length of approximately 7 mm and diameter of 0.12 mm. Grania are distinguished from other marine enchytraeids by their robust, straight, pointed setae which occur singly both ventrally and laterally. The setae may be lacking completely in some species. The unpigmented body wall of Grania is rigid due to the thick cuticle they possess, thus causing their movements to be stiff and inflexible similar to that observed in nematodes. The diagnostic characteristics for species are the shape and distribution of setae, the spermathecal shape and structure of the male duct system: the sperm funnel, vasa deferentia and penial apparatus. Specimens must be mature to be identified to species.

Grania americana Kennedy, 1966, was the first record of an enchytraeid in a continental shelf habitat of Atlantic North America (Coates and Erséus, 1985). A few years later, an extensive report by Lasserre (1971) (based upon some of his work work at the Marine Biological Laboratories of Woods Hole, Massachusetts) recorded three subtidal enchytraeid species, one of which was Hemigrania postclitellochaeta. The genus Hemigraniahas since been synonymized with Grania (Erséus and Lasserre, 1976), and Grania postclitellochaeta does not occur in North American waters (Coates and Erséus, 1985). However, the area sampled by Lasserre remains the most northern known limit for Grania in eastern North America. In 1976, Erséus and Lasserre made additions to the North Atlantic fauna with records of Grania monospermatheca Erséus and Lasserre, 1976, from Cape Cod, Massachusetts, and Grania bermudensis Erséus and Lasserre, 1976 (Locke and Coates, 1999) from the Atlantic sub-tropical island of Bermuda. Coates and Erséus (1985) described three new species -- Grania reducta, Grania atlantica, and Grania levis -- all from off the coast of northeastern USA. The enchytraeid genus Randidrilus, also described from the North American coast by Coates and Erséus (1985), is quite similar to Grania in morphology and distribution. Due to its common occurrence in samples with Eastern North American Grania, the two Randidrilus species of the region are also included in the key presented here. The most recently reported species from the Western Atlantic region are Grania laxarta and Grania hylae from Bermuda (Locke and Coates, 1999).

Cook and Brinkhurst (1973) published a report on the marine oligochaetes of the Northeastern United States in which they presented information in standard couplet key format for four families, Enchytraeidae, Naididae, Tubificidae, and Megascolecidae (= Acanthodrilidae). Grania was represented within the key by a single species, Hemigrania postclitellochaeta (Knöllner, 1935). As noted above, the taxonomic status of this species has since been amended (Coates and Erséus, 1985). A modern, comprehensive key does not exist for Grania of the northwestern Atlantic nor for any other marine enchytraeids (Milligan, 1996), even though a number of Grania species are now described from this extensive region (Coates and Erséus, 1985; Locke and Coates, 1999). In fact, enchytraeids have been excluded from all keys to aquatic oligochaetes of North America, (Brinkhurst, 1986; Kathman and Brinkhurst, 1998, 1999).  Certainly, there are several more species awaiting discovery beyond the current northern limit for Grania in Eastern North America.

The following key has been designed to assist in the identification of the nine species of Grania and two species of Randidrilus recorded from the eastern coast of North America, Bermuda, and the Caribbean. Information in the key should prove beneficial for distinguishing species already present and enable the recognition of species never before described from the region.

  © Copyright 1999-2017, K.A. Coates; ALL RIGHTS RESERVED



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