Table 2.

Ontogeny of muscle fibre dimensions

SMR fibres CMP fibres
Life history stageFibre diameter (μm)Core diameter (μm)Myofilament area (μm2)Fibre diameter (μm)Core diameter (μm)Myofilament area (μm2)
Hatchling (N=5, n=10)3.5±0.632.6±0.634.2±0.26 (45%)2.7±0.301.2±0.303.7±0.25 (75%)
Juvenile 2 (N=4, n=10)4.4±0.422.9±0.378.6±.26 (56%)3.6±0.891.2±0.368.8±0.94 (89%)
  • Ontogeny of the estimated fibre diameter, mitochondrial core diameter and myofilament area of the circular muscles of the mantle, measured from transmission electron micrographs. Values are means ± s.d.; the percent of the total cross-sectional area of the fibre occupied by myofilaments is listed in parentheses. Within a life history stage, SMR fibre diameter was significantly different from CMP fibre diameter (P<0.05), SMR core diameter was significantly different from CMP core diameter (P<0.005), and SMR myofilament area was significantly different from CMP myofilament area (P≪0.001; one-way ANOVA, Student-Newman-Keuls comparison). With the exception of CMP core diameter, all comparisons between life history stages were significantly different (P<0.05; one-way ANOVA, Student-Newman-Keuls comparison). CMP, central mitochondria-poor circular muscle fibres; SMR, superficial mitochondria-rich circular muscle fibres; N, number of animals; n, number of CMP and SMR cells measured per animal.