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While dismembering it, perhaps you might have noted the modular design and admired the great variety of body appendages (figure 1.9). There are several aspects to lobster construction that reflect the general themes of modularity and serial homology. First, the body is organized into a head (with the eyes and mouthparts), a thorax (with walking legs), and a long tail (yum!). Second, different sections of the body possess numbers of specific appendages (antennae, claws, walking legs, swimmerets). And third, each jointed appendage is itself segmented, and different kinds of appendages have different numbers of segments overall (compare a claw with a walking leg). If you were feeling adventuresome and dissected an insect or a crab, youβd see some general similarities in body organization, segmentation, and appendages but, again, differences in the number and kind of serially homologous structures. FIG. 1.9 The diversity of the serially repeated appendages of a lobster. The antennae, claws, walking legs, swimmerets, and tail structures are all modifications of a common limb design. DRAWING BY
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Sean B. Carroll (Endless Forms Most Beautiful: The New Science of Evo Devo)