Description
The body of the long-toed salamander is dusky black with a dorsal stripe of tan, yellow or olive-green. This stripe can also be broken up into a series of spots. The side of the body can have fine white or pale blue flecks. The belly is dark-brown or sooty in color with white flecks. Root tubercles are present, but they are not quite as developed as other species such as the Tiger Salamander.
The eggs of this species look similar to those of its cousins, the northwestern salamander (Ambystoma gracile) and the tiger salamander (Ambystoma tigrinum). Like many amphibians, the eggs of the long-toed salamander are surrounded by a gelatinous capsule. This capsule is transparent, making the embryo visible during development. Unlike A. gracile eggs, there are no visible signs of green algae, which makes egg jellies green in color. When in its egg, the long-toed salamander embryo is darker on top and whiter below compared to a tiger salamander embryo that is light brown to grey above and cream-colored on the bottom. The eggs are about 2 mm (0.08 in) or greater in diameter with a wide outer jelly layer. Prior to hatching—both in the egg and as newborn larvae—they have balancers, which are thin skin protrusions sticking out the sides and supporting the head. The balancers eventually fall off and their external gills grow larger. Once the balancers are lost the larvae are distinguished by the sharply pointed flaring of the gills. As the larvae mature and metamorphose, their limbs with digits become visible and the gills are absorbed.
The skin of a larva is mottled with black, brown, and yellow pigmentation. Skin color changes as the larvae develop and pigment cells migrate and concentrate in different regions of the body. The pigment cells are called chromatophores, which are derived from the neural crest. There are three types of pigment chromatophores in salamanders, including yellow xanthophores, black melanophores, and silvery iridiophores (or guanophores). As the larvae mature the melanophores concentrate along the body and provide the darker background. The yellow xanthophores arrange along the spine and on top of the limbs. The rest of the body is flecked with reflective iridiophores along the sides and underneath.
As larvae metamorphose, they develop digits out of their limb bud protrusions. A fully metamorphosed long-toed salamander has four digits on the front hands and five digits on the rear feet. Its head is longer than it is wide, and the long outer fourth toe on the hind limb of mature larvae and adults distinguishes this species from others and is also the etymological origin of its specific epithet: macrodactylum (Gr. makros = long and Gr. daktylos = toe). The adult skin has a dark brown, dark grey, to black background with a yellow, green, or dull red blotchy stripe with dots and spots along the sides. Underneath the limbs, head, and body the salamander is white, pinkish, to brown with larger flecks of white and smaller flecks of yellow. Adults are typically 3.8–7.6 cm (1.5–3.0 in) long.
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