Section II—External Anatomy

Perhaps the mudpuppy’s (Figure 5.9) most striking larval feature is the presence of three pairs of external gills, located just posterior to the flattened head. Also retained are two pairs of pharyngeal slits, one between the first and second gills, the other between the second and third gills.

The slits may be probed but will be observed later (Figure 5.10). Note the prominent transverse gular fold.

FIGURE 5.6 Caudal vertebra of the mudpuppy in (a) dorsal, (b) ventral, and (c) posterior views.

The mouth is large and bounded by lips. The lidless eyes are small, as are the widely separated nares, which communicate with the oral cavity (see below). A short neck is present between the head and the long trunk. Posteriorly, the large, flattened tail bears a small, marginal fin, which, however, lacks the supporting rays present in fishes.

Paired pectoral and pelvic limbs are small, but bear the three segments typical of terrestrial tetrapods. The cloaca, marking the posterior end of the trunk, lies ventrally between the pelvic limbs. In males the cloacal aperture is surrounded by small projections or papillae. The region around the cloaca is swollen due to the presence of the cloacal gland. Lastly, note the smooth, scaleless skin, which has an important respiratory function. A lateral line system is present as well, but is not obvious.