. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 98 A. OKUSU. Figure 25. Three types of larval spicules right after metamorphosis, (a) Dorsal view. Two types of spicules are equally abundant over the entire body of the juvenile: hollow upright spicules (Spl) lie against the body, while bladelike solid spicules (Sp2) project outwards from the body, (b) The third type of larval spicule (Sp3) is broad and solid, forming a single row on each side of the pedal groove, (c) Ventral view, (d) Anteriormost region covered with Sp2-type spicules. A. anterior; EP; epidermal papilla; P
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 98 A. OKUSU. Figure 25. Three types of larval spicules right after metamorphosis, (a) Dorsal view. Two types of spicules are equally abundant over the entire body of the juvenile: hollow upright spicules (Spl) lie against the body, while bladelike solid spicules (Sp2) project outwards from the body, (b) The third type of larval spicule (Sp3) is broad and solid, forming a single row on each side of the pedal groove, (c) Ventral view, (d) Anteriormost region covered with Sp2-type spicules. A. anterior; EP; epidermal papilla; P. posterior, PGr. pedal groove; Spl. spicule type 1; Sp2, spicule type 2; Sp3, spicule type 3. pericalymma tests, whereas the lamellibranch bivalve ve- lum also functions in feeding, and the homology is not certain. Polyplacophorans (Grave, 1932; Eernisse and Reynolds, 1994), archaegastropods (Patten. 1886; Kessel. 1964). and chaetodenn aplacophorans (Nielsen. 2001) have tro- chophore larvae with a ciliated circular velum. Polypla- cophoran vela are composed of one to three rows of pro- totrochal bands (Grave. 1932; pers. obs.). The ventral side of the ciliated apical region of polyplacophorans becomes absorbed at metamorphosis, while the dorsal side of the apical region gives rise to adult features such as the anterior- most shell valve and spicules (Grave, 1932). The archae- gastropod vela also have three rows of prototrochal bands. which function in both locomotion and feeding. There seem to be several rows of ciliary bands on the chaetoderm aplacophoran vela; however, lack of complete developmen- tal descriptions of the group limits speculation. The question of the ancestral larval type among molluscs has been important in many discussions of their origin and diversification. The pericalymma of neomenioid apla- cophorans and protobranch bivalves has been regarded as plesiomorphic by some authors (, Drew, 1901; Thomp- son, 1960; Salvini-Plawen, 1972. 1973, 1980), althoug
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
