AR-1580 11 MOLLUSCA: BIVALVIA Robert F. McMahon Arthur E. Bogan Department of Biology North Carolina State Museum Box 19498 of Natural Sciences The University of Texas at Arlington Research Laboratory Arlington, TX 76019 4301 Ready Creek Road Raleigh, NC 27607 I. Introduction A. Collecting II. Anatomy and Physiology B. Preparation for Identification A. External Morphology C. Rearing Freshwater Bivalves B. Organ-System Function V. Identification of the Freshwater Bivalves C. Environmental and Comparative of North America Physiology A. Taxonomic Key to the Superfamilies of III. Ecology and Evolution Freshwater Bivalvia A. Diversity and Distribution B. Taxonomic Key to Genera of B. Reproduction and Life History Freshwater Corbiculacea C. Ecological Interactions C. Taxonomic Key to the Genera of D. Evolutionary Relationships Freshwater Unionoidea IV. Collecting, Preparation for Identification, Literature Cited and Rearing I. INTRODUCTION ament uniting the calcareous valves (Fig. 1). The hinge lig- ament is external in all freshwater bivalves. Its elasticity North American (NA) freshwater bivalve molluscs opens the valves while the anterior and posterior shell ad- (class Bivalvia) fall in the subclasses Paleoheterodonta (Su- ductor muscles (Fig. 2) run between the valves and close perfamily Unionoidea) and Heterodonta (Superfamilies them in opposition to the hinge ligament which opens Corbiculoidea and Dreissenoidea). They have enlarged them on adductor muscle relaxation. gills with elongated, ciliated filaments for suspension feed- The mantle lobes and shell completely enclose the ing on plankton, algae, bacteria, and microdetritus. The bivalve body, resulting in cephalic sensory structures be- mantle tissue underlying and secreting the shell forms a coming vestigial or lost. Instead, external sensory struc- pair of lateral, dorsally connected lobes. Mantle and shell tures are concentrated on the mantle margins where they are both single entities. During development, the right and are exposed to the external environment when the valves left mantle lobes extend ventrally from the dorsal visceral open. Compared to other molluscs, the bivalve body is mass to enfold the body. Each lobe secrets a calcareous laterally compressed and dorso-ventrally expanded, shell valve which remains connected by a mid-dorsal isth- adapting them for burrowing in sediments, enclosure by mus (Allen, 1985). Like all molluscs, the shell valves con- shell valves and mantle protecting their soft tissues from sist of outer proteinaceous and inner crystalline calcium abrasion and preventing fine sediments from entering carbonate elements (Wilbur and Saleuddin, 1983). The lat- the mantle cavity where they could interfere with gill eral mantle lobes secrete shell material marked by a high suspension feeding. These adaptations along with a proportion of crystalline calcium carbonate making them highly protrusile, muscular, spadelike foot used for bur- thick, strong and inflexible, while the mantle isthmus se- rowing, have made bivalves the most successful infaunal cretes primarily protein, forming a dorsal elastic hinge lig- suspension feeders in marine and freshwater habitats. Copyright © 2001. Elsevier Science. All rights reserved. © 2001. Elsevier Science. Copyright Ecology and Classification of North American Freshwater Invertebrates. 2nd Edition Copyright © 2001 by Academic Press. All rights of reproduction in any form reserved. 331 Ecology and Classification of North American Freshwater Invertebrates, edited by James H. Thorp, et al., Elsevier Science, 2001. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/pace/detail.action?docID=300657. Created from pace on 2017-11-13 06:08:58. 332 Robert F. McMahon and Arthur E. Bogan FIGURE 1 General morphological features of the shells of (A) corbiculoidean, (B) unionoidean, and (C) dreissenoidean freshwater bivalves. The NA bivalve fauna is the most diverse in the ily Corbiculidae). This species invaded NA freshwaters world, consisting of approximately 308 extent native in the early 1900s and now extends throughout the and seven introduced taxa (Turgeon et al., 1998). The coastal and southern United States and Mexico, be- majority of species fall in the superfamily Unionoidea coming the dominant benthic species in many habitats with 278 native NA and 13 recognized subspecies in 49 (McMahon, 1983a,1999). More recently, two dreis- genera in the family, Unionidae and five species in two senid species, Dreissena polymorpha (zebra mussel) genera in the family, Margaritiferidae. Many species in and Dreissena bugensis (quagga mussel) have invaded this group have unique morphological adaptations and North America. D. polymorpha was discovered in highly endemic, often endangered populations (Neves Lake St. Clair and Lake Erie in 1988 after introduction et al., 1997). In the superfamily, Corbiculoidea, the in 1986. It now extends throughout the Great Lakes, family Sphaeriidae, has 36 native and four introduced St. Lawrence River, and the Mississippi River and most NA species. While falling into only four genera, the of its major tributaries (Mackie and Schloesser, 1996). Sphaeriidae are more cosmopolitan than unionoideans D. bugensis was first found in the Erie-Barge Canal and (note “unionoideans” as used here refers to all species eastern Lake Erie, NY, in 1991 and has since spread within the superfamily, Unionoidea while “unionid” through Lakes Erie and Ontario and the St. Lawrence used later in the chapter refers only to those River (Mills et al., 1996). Both species are likely to unionoidean species in the family, Unionidae), several have been simultaneously introduced as planktonic genera and species having pandemic distributions. veliger larvae released with ballast water from ships en- Copyright © 2001. Elsevier Science. All rights reserved. © 2001. Elsevier Science. Copyright Corbicula fluminea falls within the Corbiculacea (fam- tering the Great Lakes from ports on the Bug and Ecology and Classification of North American Freshwater Invertebrates, edited by James H. Thorp, et al., Elsevier Science, 2001. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/pace/detail.action?docID=300657. Created from pace on 2017-11-13 06:08:58. 11. Mollusca: Bivalvia 333 FIGURE 2 General external anatomy of the soft tissues of (A) corbiculoidean, (B) unionoidean, and (C) dreissenoidean freshwater bivalves. Dnieper rivers in the Black Sea, Ukraine (Marsden but their soft tissue morphologies are relatively similar et al., 1996, Mills et al., 1996). and, thus, will be discussed in general terms below. A. External Morphology II. ANATOMY AND PHYSIOLOGY 1. Shell NA freshwater bivalves fall into three superfamilies: Bivalve shells consist of calcium carbonate Unionoidea, Corbiculoidea, and Dreissenoidea. Exter- (CaCO3) crystals embedded in a proteinaceous matrix, Copyright © 2001. Elsevier Science. All rights reserved. © 2001. Elsevier Science. Copyright nal shell morphology among these groups vary (Fig. 1), both secreted by underlying mantle tissue. In most Ecology and Classification of North American Freshwater Invertebrates, edited by James H. Thorp, et al., Elsevier Science, 2001. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/pace/detail.action?docID=300657. Created from pace on 2017-11-13 06:08:58. 334 Robert F. McMahon and Arthur E. Bogan FIGURE 3 A crosssection through the mantle and shell edges of a typical freshwater unionoidean bivalve displaying the anatomic features of the shell, mantle, and mantle edge. Sphaeriids have a complexed cross-lamellar shell structure and lack nacre, but their mantle edge has a similar structure. bivalves, the shell consists of three parts: an outer pro- ens and strengthens the shell, thus accounting for most teinaceous periostracum secreted from the periostracal of its mass. 2ϩ Ϫ groove in the mantle edge, and underlying, calcareous Calcium (Ca ) and bicarbonate (HCO3 ) neces- prismatic and nacre layers in which CaCO3 crystals are sary for shell CaCO3 crystal deposition are transported embedded within an organic matrix (Fig. 3). The pe- from the external medium across the body epithelium Ϫ riostracum is initially secreted free of the other layers, into the hemolymph (blood). HCO3 ions are also gen- but soon fuses with the underlying prismatic layer se- erated from metabolically released CO2 reacting with ϩ N ϩ ϩ Ϫ creted by a portion of the mantle edge just external to hemolymph water (CO2 H2O H HCO3 ). the periostracal groove (Fig. 3). The prismatic layer These ions are actively transported across the mantle consists of a single layer of elongated CaCO3 crystals into the extrapallial fluid for CaCO3 deposition into oriented 90° to the horizontal shell plane (Fig. 3). The the shell matrix (Wilbur and Saleuddin, 1983). periostracum edge seals the extrapallial space between CaCO3 crystal formation requires release of pro- ϩ 2ϩ ϩ Ϫ N ϩ ϩ mantle and shell, allowing CaCO3 concentrations in tons (H ) (Ca HCO3 CaCO3 H ) which that space to reach saturation levels required for crystal must be removed from the extrapallial fluid in order to deposition (Saleuddin and Petit, 1983). The tanned maintain the high pH required for CaCO3 deposition protein of the periostracum is impermeable to water, (extrapallial fluid pH 7.4–8.3). It is proposed that Hϩ Ϫ preventing shell CaCO3 dissolution. Layers of conchi- combines with HCO3 to form H2CO3, followed by olin (i.e., tanned protein) occurring within unionoidean dissociation into CO2 and H2O which diffuse from the shells, are suggested to