Figure 1.
Chiton articulatus and Chiton albolineatus preserved.
Chiton articulatus (left) and Chiton albolineatus (right) preserved, showing some of the several sizes here studied.
Figure 2.
Diagram of Chiton articulatus illustrating the location and orientation of the cutting planes.
(A) Dorsoventral orientation to permit the cutting of sagittal sections. (B) Lateral orientation to permit the cutting of frontal sections. (C) Dorsoventral orientation to permit the cutting of several transverse sections.
Figure 3.
Allometric relationships during the early life of Chiton articulatus and Chiton albolineatus.
Relationships between measurements (total weight “TW”, and total length “TL”) and body weight (BW) pooled for both sexes of Chiton articulatus (0.007 to 4.400 g BW) and Chiton albolineatus (0.004 to 3.632 g BW) during the range of early life here studied. Continuous line indicates equation tendency.
Figure 4.
Ontogenesis and maturity of gonads through the early life of Chiton articulatus and Chiton albolineatus.
Relation among total length (mm) and the periods of the gonadal sac formation (Pw: without gonad, Pe: gonadal emergence, Pf: gonadal sac formed), and the stages of gonad development (S0: gametocytogenesis, S1: gametogenesis, and S2: mature) in males and females from Chiton articulatus and Chiton albolineatus. The arrowhead indicates the sexual differentiation, and the arrow indicates the onset of the first sexual maturity. Number of data (n).
Figure 5.
Chiton through the period without gonad.
Chiton articulatus (0.074 g BW, 11 mm TL, and 7 mm TW) during the period without gonads. (A) Composite digital image in transverse section of the entire specimen showing the general histological anatomy. (B) Close-up of the dorsal part of a whole specimen. Abbreviations: a, articulamentum; af, accessory fold; c, cuticle; ct, ctenidium; da, dorsal aorta; f, foot; go, girdle ornamentations; k, kidney; lm, longitudinal muscle; ln, lateral “visceral” nerve cord; mg, mantle girdle; oe, oesophagus; pg, pharyngeal gland; pn, pedal nerve cord; r, radula; tm, transversal muscle; v, valve; vc, visceral cavity “hemocoel”.
Figure 6.
Chiton through the starting period of gonad emergence.
Chiton articulatus (0.053 g BW, 9 mm TL, and 6 mm TW) through the starting period of gonad emergence, showing the projection of the squamous epithelium that extends along the wall of the dorsal aorta and is thrown toward the visceral cavity. (A) Composite digital image in transverse section of the whole specimen showing the general histological anatomy. (B) Close-up of the dorsal part from the whole specimen. Abbreviations: a, articulamentum; af, accessory fold; c, cuticle; ct, ctenidium; da, dorsal aorta; dg, digestive gland; ds, dorsal aorta sinus; f, foot; go, girdle ornamentations; gr, gonadal ridge (i.e., the precursor to the gonad); gs, gonadal sinus (i.e., cavity formed by a bending or curving from the gonadal ridge and containing chiefly blood); i, intestine; k, kidney; lm, longitudinal muscle; ln, lateral “visceral” nerve cord; mg, mantle girdle; ms, muscle sinus; pn, pedal nerve cord; st, stomach; tm, transversal muscle; v, valve; vc, visceral cavity “hemocoel”.
Figure 7.
Chiton through the formation of the gonadal lobes.
Chiton articulatus (0.382 g BW, 21 mm TL, and 12.5 mm TW) through the middle period of gonad emergence, showing the formation of two oval lobes. (A) Composite digital image in transverse section of the whole specimen showing the general histological anatomy. (B) Close-up of the dorsal part of the whole specimen. Abbreviations: a, articulamentum; af, accessory fold; c, cuticle; ct, ctenidium; da, dorsal aorta; dg, digestive gland; f, foot; go, girdle ornamentation; gs, gonadal sinus (i.e., cavity formed by a bending or curving from the gonadal ridge and containing chiefly blood); k, kidney; lm, longitudinal muscle; ln, lateral “visceral” nerve cord; mg, mantle girdle; pn, pedal nerve cord; st, stomach; tm, transversal muscle.
Figure 8.
Chiton through the merging of the gonadal lobes.
Chiton articulatus (0.185 g BW, 16 mm TL, and mm 9 TW) through the last period of gonad emergence, showing the ciliated cuboidal epithelial cells and the beginning of the merging of the lobes of the gonad sac. (A) Composite digital image in transverse section of the dorsal part of the whole specimen showing the general histological anatomy. (B) Close-up of the ventral right side of the gonad sac without tissue plates but showing the rise of the early oogonia with basophilic granular cytoplasm and one nucleolus, as well as the development of the early cells that constitute the tissue plates on the ventral wall of the gonad sac. Abbreviations: da, dorsal aorta; ds, dorsal aorta sinus; gl, gonadal lumen (i.e., an inner open space or cavity of the gonad), lm, longitudinal muscle; ms, muscle sinus; v, valve; vc, visceral cavity “hemocoel”; vw, ventral wall of gonad sac.
Figure 9.
Chiton articulatus (0.347 g BW, 21 mm TL, and 12 mm TW) through the last period of gonad emergence, showing the ciliated cuboidal epithelial cells, the merged lobes, the rise of the tissue plates and, in turn, development toward the gonad sac formed. (A) Composite digital image in transverse section of the whole specimen showing the general histological anatomy. (B) Close-up of the dorsal part of the whole specimen. Abbreviations: a, articulamentum; af, accessory fold; ct, ctenidium; da, dorsal aorta; dg, digestive gland; ds, dorsal aorta sinus; f, foot; go, girdle ornamentation; i, intestine; k, kidney; lm, longitudinal muscle; mg, mantle girdle; ms, muscle sinus; pn, pedal nerve cord; rs, residual gonadal sinus; v, valve; vc, visceral cavity “hemocoel”.
Figure 10.
Gametocytogenesis in a Chiton female.
Composite digital image in frontal section of the anterior dorsal part of a Chiton articulatus female (1.161 g BW, 29 mm TL, and 16.5 mm TW) with the ovary in the gametocytogenesis stage (S0) showing the formation of the primary oocytes.
Figure 11.
Gametocytogenesis in a Chiton male.
Composite digital image in transverse section of a Chiton albolineatus male (0.596 g BW, 27.5 mm TL, and 13 mm TW) through the gametocytogenesis stage (S0), showing the general histological anatomy of the gonad sac wholly expanded forming a gonadal lumen and with several tissue plates occurring above the ventral wall. Early spermatocytes occur around the tissue plates. Abbreviations: da, dorsal aorta; gl, gonadal lumen, lm, longitudinal muscle; st, stomach; vc, visceral cavity “hemocoel”.
Figure 12.
Gametogenesis in a Chiton articulatus female.
Composite digital image in frontal section of the anterior dorsal part of a Chiton articulatus female (2.469 g BW, 35 mm TL, and 22 mm TW) with the ovary in the gametogenesis stage (S1) showing asynchronous groups of oocytes, i.e., primary oocytes, secondary oocytes, and mature ova without a dominant group. Abbreviations: po, primary oocytes; so, secondary oocytes; mo, mature ova.
Figure 13.
Gametogenesis in a Chiton albolineatus female.
Composite digital image in transverse section of the dorsal part of a Chiton albolineatus female (0.953 g BW, 28 mm TL, and 14 mm TW) with the ovary in the gametogenesis stage (S1) showing only a synchronous group of secondary oocytes without replenishment by earlier oocytes. Abbreviations: da, dorsal aorta; k, kidney; gl, gonadal lumen; lm, longitudinal muscle; st, stomach; tm, transversal muscle; vc, visceral cavity “hemocoel”.
Figure 14.
Gametogenesis in a Chiton male.
Composite digital image in transverse section of a Chiton albolineatus male (0.434 g BW, 21 mm TL, and 11 mm TW) with testis in the gametogenesis stage (S1) showing spermatocytes and spermatids occurring around the tissue plates and forming groups, and some spermatozoa beginning to replenish the gonadal lumen. Abbreviations: da, dorsal aorta; gl, gonadal lumen, lm, longitudinal muscle; st, stomach; vc, visceral cavity “hemocoel”.
Figure 15.
Composite digital image in transverse section of an ovary of Chiton articulatus (2.228 g BW, 32 mm TL, and 22 mm TW) in mature stage (S2) showing only a synchronous group of mature ova without replenishment by earlier oocytes.
Figure 16.
Composite digital images in transverse section (A) of the posterior dorsal part and (B) of the anterior dorsal part from mature Chiton albolineatus males (A: 0.648 g BW, 25 mm TL, and 13 mm TW, and B: 1.365 g BW, 29.5 mm TL, and 16 mm TW) showing the gonadal lumen fully replenished with sperm. Abbreviations: da, dorsal aorta; dg, digestive gland; i, intestine; k, kidney; lm, longitudinal muscle; s, spermatozoa; tm, transversal muscle; vc, visceral cavity “hemocoel”.
Figure 17.
Early life stages for Chiton spp.
Ranges in total length proposed to distinguish growth sequences or “early life stages” in the studied chitons, Chiton articulatus and Chiton albolineatus.