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First published online January 19, 2006
Journal of Experimental Biology 209, 433-443 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02017
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Ontogeny of mantle musculature and implications for jet locomotion in oval squid Sepioteuthis lessoniana

Joseph T. Thompson* and William M. Kier

Department of Biology, CB#3280 Coker Hall, University of North Carolina, Chapel Hill, NC 27599-3280, USA


Figure 1
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  		Fig. 1. Schematic of the mantle musculature. CM, circular muscles; CMP, central mitochondria-poor circular muscles; RM, radial muscles; SMR, superficial mitochondria-rich circular muscles. Modified from Kier and Thompson (2003).

 

Figure 2
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  		Fig. 2. Sagittal view of the mantle of a newly hatched Sepioteuthis lessoniana that shows (A) the relative proportions of superficial mitochondria-rich (SMR) and central mitochondria-poor (CMP) circular muscle fibres. Scale bar, 50 µm. A magnified view of SMR fibres is visible in B. Note the large size of the mitochondrial core (Mt) relative to the CMP cells in C. Note also that the cross-sectional area of myofilaments is not substantially different between the SMR (B) and CMP cells (C). The scale in B and C is the same. Scale bar in B, 10 µm. Bright-field microscopy of 1 µm glycol methacrylate sections stained with 1% Toluidine Blue. Mt, mitochondrion; N, nucleus.

 

Figure 3
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  		Fig. 3. Sagittal view of the mantle of a juvenile Sepioteuthis lessoniana that shows (A) the relative proportions of superficial mitochondria-rich (SMR) and central mitochondria-poor (CMP) circular muscle fibres. A nerve (N) and radial muscle fibres (R) are also visible in the micrograph. Compare A with Fig. 2A and note that juveniles have a much larger proportion of CMP to SMR circular muscle fibres. B and C show magnified views of the SMR and CMP cells, respectively. Scale bars in B and C are 10 µm. Bright-field microscopy of 1 µm glycol methacrylate sections stained with 1% Toluidine Blue.

 

Figure 4
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  		Fig. 4. Transmission electron micrographs of transverse sections of the ventral mantle of a newly hatched Sepioteuthis lessoniana showing circular muscle fibres cut parallel to their long axes. (A) View of a superficial mitochondria-rich (SMR) and a central mitochondria-poor (CMP) circular muscle fibre. Note the core of mitochondria (Mt) in each. A radial muscle cell (RM) is also visible. (B) Magnified view of a CMP muscle cell showing a single sarcomere and its thick filaments (TF). Note that the length of the thick filaments is about 1 µm. The scale bar in each panel is 1 µm. DB, dense bodies.

 

Figure 5
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  		Fig. 5. Transmission electron micrographs of transverse sections of the ventral mantle of a juvenile Sepioteuthis lessoniana showing circular muscle fibres cut parallel to their long axes. (A) Portion of a superficial mitochondria-rich (SMR) muscle fibre to illustrate the length of the thick filaments (TF). The approximate dimensions of the sarcomere and the long axis of the thick filaments are indicated by the arrow. Note that the lengths of the longest thick filaments are 4-5 µm. (B) View of a central mitochondria-poor (CMP) cell that shows a portion of one sarcomere. The arrow indicates the approximate length of one sarcomere and the long axis of the thick filaments. Note that the lengths of the longest thick filaments are ~1.5 µm. Scale bars, 1 µm. MT, mitochondria.

 

Figure 6
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  		Fig. 6. Plot showing an ontogenetic change in the maximum rate of mantle contraction. Each point represents the maximum rate of mantle contraction during the escape jet for one individual. H, J1, J2 and Y2 refer to the life history stages of Segawa (1987Go) and correspond to Hatchling, Juvenile 1, Juvenile 2 and Young 2, respectively. See Materials and methods for more detail on the life history stages of Segawa.

 




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