diameter of 12 mm (Figs. 9.5g and 9.7c). Each giant basal spicule is made up of
lamellae: Surprisingly, the siliceous lamellae composing the spicules from
Monorhaphis contain not only a bio-silica matrix but also a proteinaceous scaffold.
Initially, Schulze (1904) proposed that the proteinaceous material surrounds the
lamellae as fibers. For our initial light microscopic experiments (M€ uller et al.
2007a, 2008d), all loosely attached organic material was removed from a comitalia
by ultrasonication. A distinction between the axial cylinder and the surrounding
lamellar zone is possible even by light microscopic inspection in a cross section,
using Nomarsky DIC (differential interference contrast) imaging (Fig. 9.7d, e). The
axial cylinder occupies about half of the diameter of the comitalia, usually 150 mm.
When a sample is further subjected to HF dissolution after about 1 min of exposure,
the lamellar zone begins to dissolve. Dissolution starts from cracks in the spicule,
primarily following the gaps between the lamellae, thus forming sawtooth edges.
The dissolution of the axial cylinder proceeds from the periphery without revealing
individual lamellae and the siliceous material is completely dissolved after 90 min.
Within the axial canal, the axial filament is located (Fig. 9.7g). Application of
different dyes allows visualization of the proteinaceous components in the two
zones surrounding the axial canal. Addition of Coomassie Brilliant blue to the HF
solution immediately stains the proteins released from the lamellar zone. During the
initial phase of dissolution, a proteinaceous coating (lamellar coating) is uncovered
which remains only transiently intact until the organized sheets disintegrate to
irregular clumps/aggregates. Prior to this disintegration, the lamellar coating
blisters. A second tube/sheath is formed from proteins of the axial cylinder. This
structure is termed here axial barrel. In contrast to the lamellar coating, the axial
barrel is composed of individual ropelike filaments. These can be stained besides by
Coomassie Brilliant blue also with Sirius Red; the latter stain does not color
proteins from the lamellar zone or from the axial canal. In addition, the axial barrel
can be stained with the fluorescent dye Rhodamine 123 (M€ uller et al. 2008d).
SEM analysis of a broken comitalia (large spicules existing in the body around
the atrial openings) shows also the lamellar-wise organization of the silica mantel
(Fig. 9.7i) and the perfectly concentrically arranged lamellae around the central
axial cylinder (Fig. 9.7f); the central cylinder remains almost intact, while the
peripheral lamellar zone undergoes fracturing into concentric piles of chipped
lamellae (Wang et al. 2008; M€ uller et al. 2007a) In center of the spicules lies the
axial canal, a structural unit that is often circular in hexactinellids (Pisera 2003;
Sandford 2003; Uriz et al. 2003; Uriz 2006); however, toward the tips of the
spicules, the axial canal changes its profile and appears square. The axial canal
is surrounded by a region of electron-dense homogeneous silica constituting
the axial cylinder of a diameter of 100–150 mm. The third and major part of the
spicules is composed of 300–800 regularly and concentrically arranged lamellae
(each 3–10 mm thick; Fig. 9.7f, h–k). The in average 0.1–0.2 mm wide inter-lamellar
space of the spicules does surprisingly not constitute a continuous open slit (M€ uller
et al. 2008a) but is composed of fusion zones and open holes; apparently, the fusion
zones allow a continuum between two silica lamellae. The lamellar organization
becomes also apparent in longitudinal cuts of the spicules (Fig. 9.7d, e). A closer
266
W.E.G. M€ uller et al.
lamellae: Surprisingly, the siliceous lamellae composing the spicules from
Monorhaphis contain not only a bio-silica matrix but also a proteinaceous scaffold.
Initially, Schulze (1904) proposed that the proteinaceous material surrounds the
lamellae as fibers. For our initial light microscopic experiments (M€ uller et al.
2007a, 2008d), all loosely attached organic material was removed from a comitalia
by ultrasonication. A distinction between the axial cylinder and the surrounding
lamellar zone is possible even by light microscopic inspection in a cross section,
using Nomarsky DIC (differential interference contrast) imaging (Fig. 9.7d, e). The
axial cylinder occupies about half of the diameter of the comitalia, usually 150 mm.
When a sample is further subjected to HF dissolution after about 1 min of exposure,
the lamellar zone begins to dissolve. Dissolution starts from cracks in the spicule,
primarily following the gaps between the lamellae, thus forming sawtooth edges.
The dissolution of the axial cylinder proceeds from the periphery without revealing
individual lamellae and the siliceous material is completely dissolved after 90 min.
Within the axial canal, the axial filament is located (Fig. 9.7g). Application of
different dyes allows visualization of the proteinaceous components in the two
zones surrounding the axial canal. Addition of Coomassie Brilliant blue to the HF
solution immediately stains the proteins released from the lamellar zone. During the
initial phase of dissolution, a proteinaceous coating (lamellar coating) is uncovered
which remains only transiently intact until the organized sheets disintegrate to
irregular clumps/aggregates. Prior to this disintegration, the lamellar coating
blisters. A second tube/sheath is formed from proteins of the axial cylinder. This
structure is termed here axial barrel. In contrast to the lamellar coating, the axial
barrel is composed of individual ropelike filaments. These can be stained besides by
Coomassie Brilliant blue also with Sirius Red; the latter stain does not color
proteins from the lamellar zone or from the axial canal. In addition, the axial barrel
can be stained with the fluorescent dye Rhodamine 123 (M€ uller et al. 2008d).
SEM analysis of a broken comitalia (large spicules existing in the body around
the atrial openings) shows also the lamellar-wise organization of the silica mantel
(Fig. 9.7i) and the perfectly concentrically arranged lamellae around the central
axial cylinder (Fig. 9.7f); the central cylinder remains almost intact, while the
peripheral lamellar zone undergoes fracturing into concentric piles of chipped
lamellae (Wang et al. 2008; M€ uller et al. 2007a) In center of the spicules lies the
axial canal, a structural unit that is often circular in hexactinellids (Pisera 2003;
Sandford 2003; Uriz et al. 2003; Uriz 2006); however, toward the tips of the
spicules, the axial canal changes its profile and appears square. The axial canal
is surrounded by a region of electron-dense homogeneous silica constituting
the axial cylinder of a diameter of 100–150 mm. The third and major part of the
spicules is composed of 300–800 regularly and concentrically arranged lamellae
(each 3–10 mm thick; Fig. 9.7f, h–k). The in average 0.1–0.2 mm wide inter-lamellar
space of the spicules does surprisingly not constitute a continuous open slit (M€ uller
et al. 2008a) but is composed of fusion zones and open holes; apparently, the fusion
zones allow a continuum between two silica lamellae. The lamellar organization
becomes also apparent in longitudinal cuts of the spicules (Fig. 9.7d, e). A closer
266
W.E.G. M€ uller et al.