controlled by the collagen fibrils, the sponges have the capacity of morphogenetic
remodeling. This potential is widely documented both in hexactinellids, e.g., during
regeneration of grafts in Rhabdocalyptus dawsoni (Leys et al. 1999) and also in
demosponges, e.g., in C. reniformis (Francesco et al. 2001). Those reorganization
processes, involving also a temporary plasticisation of the cortex, involve the
highly dynamic arrangement of the functional fibrous elements, especially of
collagen (Hartman and Reiswig 1973; Gaino and Pronzato 1983). Primarily, the
collencytes synthesize the collagen fibers that comprise contractile features
(Harrison and De Vos 1991). Even more, those contractile cells have been
implicated in neuroid signal conductions, interpreted as “promyoneuroid elements”
(Le ´vi 1970; Garrone 1978). In addition, pinacocytes are capable to undergo contractile responses/amoeboid movements in conjunction with collagen and modulate
the water current through the aquiferous canals. The intracellular structural
elements, the “histoskeleton” (formed by associated cytoskeletal elements and
extracellular components), allow a coordinated cell movement and a controlled
contraction/relaxation as well as motility (Pavans de Ceccatty 1986). Within the
cell lattices, the collagen fibrils connect the cells also by direct mechanical contact.
Finally, and despite of their usual sessile behavior/growth plan (Alexander 1979;
Barnes 1987), some sponges have the capacity of active locomotion (Bond and
Harris 1988), based on the flexible interaction between the contractile fibrils and
collagenous internal stroma (Garrone 1978). Linkages between adjacent collagen
fibrils have been identified that are glycoproteins and glycosaminoglycans in nature
(Garrone 1978; Simpson 1984).
9.3 Well-Preserved Fossils in Body Preservation at the
Ediacaran/Lower Cambrian Border: The Siliceous
Sponges from Chengjiang
Equally important as the Burgess Shale fossil sponge fauna is the rank of fossils
from the Cambrian/Precambrian/Neoproterozoic period, excavated in the Cambrian
“Burgess Shale”-type deposits in South China (Rigby and Collins 2004; Zhang
et al. 2008), especially in Chengjiang (Fig. 9.2a). Based on fossil records, the
hexactinellids represent the oldest taxon detected and have been described from
Australia, China, and Mongolia (older than 540 Ma) (Gehling and Rigby 1996;
Brasier et al. 1997; Li et al. 1998). Especially outstanding is the preservation of the
fossil hexactinellids from the Niutitang Formation (Sancha) in Hunan (Early
Cambrian; China; Steiner et al. 1993; Steiner 1994). There, completely preserved
sponge fossils, e.g., Solactiniella plumata, were discovered (Steiner et al. 1993),
displaying large, 15 mm–100 mm, spicules. These spicules still exhibit the characteristic axial canals as shown by Xiao et al. (2005) and the lamellar organization that is known from modern hexactinellids (Wang et al. 2009); Fig. 9.3f, g.
Stratigraphically equivalent are the Chengjiang assemblages found in Yunnan
9 The Unique Invention of the Siliceous Sponges
257
remodeling. This potential is widely documented both in hexactinellids, e.g., during
regeneration of grafts in Rhabdocalyptus dawsoni (Leys et al. 1999) and also in
demosponges, e.g., in C. reniformis (Francesco et al. 2001). Those reorganization
processes, involving also a temporary plasticisation of the cortex, involve the
highly dynamic arrangement of the functional fibrous elements, especially of
collagen (Hartman and Reiswig 1973; Gaino and Pronzato 1983). Primarily, the
collencytes synthesize the collagen fibers that comprise contractile features
(Harrison and De Vos 1991). Even more, those contractile cells have been
implicated in neuroid signal conductions, interpreted as “promyoneuroid elements”
(Le ´vi 1970; Garrone 1978). In addition, pinacocytes are capable to undergo contractile responses/amoeboid movements in conjunction with collagen and modulate
the water current through the aquiferous canals. The intracellular structural
elements, the “histoskeleton” (formed by associated cytoskeletal elements and
extracellular components), allow a coordinated cell movement and a controlled
contraction/relaxation as well as motility (Pavans de Ceccatty 1986). Within the
cell lattices, the collagen fibrils connect the cells also by direct mechanical contact.
Finally, and despite of their usual sessile behavior/growth plan (Alexander 1979;
Barnes 1987), some sponges have the capacity of active locomotion (Bond and
Harris 1988), based on the flexible interaction between the contractile fibrils and
collagenous internal stroma (Garrone 1978). Linkages between adjacent collagen
fibrils have been identified that are glycoproteins and glycosaminoglycans in nature
(Garrone 1978; Simpson 1984).
9.3 Well-Preserved Fossils in Body Preservation at the
Ediacaran/Lower Cambrian Border: The Siliceous
Sponges from Chengjiang
Equally important as the Burgess Shale fossil sponge fauna is the rank of fossils
from the Cambrian/Precambrian/Neoproterozoic period, excavated in the Cambrian
“Burgess Shale”-type deposits in South China (Rigby and Collins 2004; Zhang
et al. 2008), especially in Chengjiang (Fig. 9.2a). Based on fossil records, the
hexactinellids represent the oldest taxon detected and have been described from
Australia, China, and Mongolia (older than 540 Ma) (Gehling and Rigby 1996;
Brasier et al. 1997; Li et al. 1998). Especially outstanding is the preservation of the
fossil hexactinellids from the Niutitang Formation (Sancha) in Hunan (Early
Cambrian; China; Steiner et al. 1993; Steiner 1994). There, completely preserved
sponge fossils, e.g., Solactiniella plumata, were discovered (Steiner et al. 1993),
displaying large, 15 mm–100 mm, spicules. These spicules still exhibit the characteristic axial canals as shown by Xiao et al. (2005) and the lamellar organization that is known from modern hexactinellids (Wang et al. 2009); Fig. 9.3f, g.
Stratigraphically equivalent are the Chengjiang assemblages found in Yunnan
9 The Unique Invention of the Siliceous Sponges
257