166
(Petit et al. 1978; McElwain and Bullard 2014). In Lampsilini (Unionidae) the mantle forms mimetic flaps—lures (attracting fish for transmission of the glochidia;
Zanatta and Murphy 2006, Barnhart et al. 2008). Within the mantle cavity, the gills
(two paired demibranchs; in females modified into marsupia) are placed on each
side of the visceral mass and a large foot. Adult Unionida use the foot for burrowing
or for locomotion over short distances (Amyot and Downing 1998; Schwalb and
Push 2007), while juveniles also use their ciliated foot for food collection (Gatenby
et al. 1996; Schartum et al. 2017; Araujo et al. 2018). Adult unionoids are considered filter feeders. Their eulamellibranch gills are ciliated—the activity of these
cilia results in water currents. The food particles that are suspended in the water are
captured on the gills, trapped in the mucus to be later sorted and transported by
labial palps to the mouth of animal (Allen 1921; Galbraith et al. 2009). The esophagus connects the mouth with the stomach and digestive gland, which surrounds the
stomach in a visceral mass (McElwain and Bullard 2014). Food is transported into
the blind-ended ciliated tubules of the digestive diverticulum where it is digested,
then the non-digested particles pass through the stomach, are compacted by the
crystalline style sac, and removed through the intestine (Owen 1955; McElwain and
Bullard 2014). Particles not ingested by the digestive system are removed as “pseudofeces”. Ciliary activity draws fresh water through incurrent aperture into the
mantle cavity and then into the watertubes of the gills. Next, the water comes to the
suprabranchial chamber and leaves the mantle cavity with the waste materials and
“pseudofeces” throughout the excurrent aperture. During this passage through the
gills haemolymph is oxygenated and carbon dioxide is released. Gills of the females
serve as brooding chambers—the marsupium. Unionoids are usually dioecious,
only some species are hermaphroditic, or occasionally hermaphroditic (Bauer
2001b; Watters 2007; Patterson 2018). Males release sperm into the water as spermatozoa, which can survive there up to 48 h (Ishibashi et al. 2000). The female
draws the spermatozoa with the water to the mantle cavity and to the suprabranchial
chamber, where fertilization occurs. The embryos and larvae are then brooded in the
marsupium. The brooding negatively influences females’ respiration (Richard et al.
1991; Tankersley and Dimock 1993a) and also filtration rate—due to functional
changes in the ciliature of the marsupial demibranchs (Tankersley and Dimock
1993b; Tankersley 1996). Most species have marsupia in the outer demibranchs
(species-rich family Unionidae), but e.g. Margaritiferidae and several species of
Unionidae are tetragenous (which is interpreted as a derived condition; Graf and
O’Foighil 2000), and members of families Hyriidae, Iridinidae, Mycetopodidae and
Etheriidae are endobranchous (Graf and O’Foighil 2000; Bauer 2001b; Graf and
Cummings 2006; Fig. 5.3). The larvae are numerous, small (0.06–0.4 mm), and
must parasitize fish (with some exceptions) to complete metamorphosis (Kat 1984;
Bauer 2001a; Watters and O’Dee 1998; Wächtler et al. 2001; Barnhart et al. 2008).
The nervous system consists of four ganglia, each with several nerve fibers
extending throughout the body. Bilobed pedal ganglion innervates both the ventral
pedal foot musculature and the lateral portions of the visceral mass. Paired cerebral
ganglia are responsible for innervation of anterior adductor, retractor, foot and mantle edge, thus are required for complex motor functions. Visceral ganglion fibers
A. Skawina
(Petit et al. 1978; McElwain and Bullard 2014). In Lampsilini (Unionidae) the mantle forms mimetic flaps—lures (attracting fish for transmission of the glochidia;
Zanatta and Murphy 2006, Barnhart et al. 2008). Within the mantle cavity, the gills
(two paired demibranchs; in females modified into marsupia) are placed on each
side of the visceral mass and a large foot. Adult Unionida use the foot for burrowing
or for locomotion over short distances (Amyot and Downing 1998; Schwalb and
Push 2007), while juveniles also use their ciliated foot for food collection (Gatenby
et al. 1996; Schartum et al. 2017; Araujo et al. 2018). Adult unionoids are considered filter feeders. Their eulamellibranch gills are ciliated—the activity of these
cilia results in water currents. The food particles that are suspended in the water are
captured on the gills, trapped in the mucus to be later sorted and transported by
labial palps to the mouth of animal (Allen 1921; Galbraith et al. 2009). The esophagus connects the mouth with the stomach and digestive gland, which surrounds the
stomach in a visceral mass (McElwain and Bullard 2014). Food is transported into
the blind-ended ciliated tubules of the digestive diverticulum where it is digested,
then the non-digested particles pass through the stomach, are compacted by the
crystalline style sac, and removed through the intestine (Owen 1955; McElwain and
Bullard 2014). Particles not ingested by the digestive system are removed as “pseudofeces”. Ciliary activity draws fresh water through incurrent aperture into the
mantle cavity and then into the watertubes of the gills. Next, the water comes to the
suprabranchial chamber and leaves the mantle cavity with the waste materials and
“pseudofeces” throughout the excurrent aperture. During this passage through the
gills haemolymph is oxygenated and carbon dioxide is released. Gills of the females
serve as brooding chambers—the marsupium. Unionoids are usually dioecious,
only some species are hermaphroditic, or occasionally hermaphroditic (Bauer
2001b; Watters 2007; Patterson 2018). Males release sperm into the water as spermatozoa, which can survive there up to 48 h (Ishibashi et al. 2000). The female
draws the spermatozoa with the water to the mantle cavity and to the suprabranchial
chamber, where fertilization occurs. The embryos and larvae are then brooded in the
marsupium. The brooding negatively influences females’ respiration (Richard et al.
1991; Tankersley and Dimock 1993a) and also filtration rate—due to functional
changes in the ciliature of the marsupial demibranchs (Tankersley and Dimock
1993b; Tankersley 1996). Most species have marsupia in the outer demibranchs
(species-rich family Unionidae), but e.g. Margaritiferidae and several species of
Unionidae are tetragenous (which is interpreted as a derived condition; Graf and
O’Foighil 2000), and members of families Hyriidae, Iridinidae, Mycetopodidae and
Etheriidae are endobranchous (Graf and O’Foighil 2000; Bauer 2001b; Graf and
Cummings 2006; Fig. 5.3). The larvae are numerous, small (0.06–0.4 mm), and
must parasitize fish (with some exceptions) to complete metamorphosis (Kat 1984;
Bauer 2001a; Watters and O’Dee 1998; Wächtler et al. 2001; Barnhart et al. 2008).
The nervous system consists of four ganglia, each with several nerve fibers
extending throughout the body. Bilobed pedal ganglion innervates both the ventral
pedal foot musculature and the lateral portions of the visceral mass. Paired cerebral
ganglia are responsible for innervation of anterior adductor, retractor, foot and mantle edge, thus are required for complex motor functions. Visceral ganglion fibers
A. Skawina