Lamprey larva: a jawless vertebrate
Lampreys are jawless aquatic vertebrates. The best-known examples are parasites that use their toothed oral suckers to attach to fish and suck their blood. Although lampreys are sometimes referred to as fish, they are actually quite different from fish and all other vertebrates, beginning with their lack of jaws.
In this lab, you'll look only at the larvae of lampreys; we don't have any specimens of adults. For more information on lampreys, see the links at the bottom of this page.
Lamprey ammocoetes larva
Lamprey larvae are called ammocoetes. The larvae look very different from the adults, and originally they were described as different species -- that's why they have a latin-sounding name. While an adult lampreys may range in size from 10 to 100 cm long, the ammocoetes is only 1-2 cm long. The larvae are anatomically quite simple; eventually they undergo a metamorphosis, reorganizing their bodies and developing into the more-complex adult forms.
The ammocoetes larva microscope slides bear a strong resemblance to those of Branchiostoma; it would be easy to confuse one with the other. Keep in mind, though, that with Branchiostoma, you're looking at a juvenile or adult organism -- what you see on that slide is as big as the organism will get. This is they key take-home point of the ammocoetes slide: the larva of this vertebrate is similar to the adult of the cephalochordate Branchiostoma.
Note these essential chordate characteristics:
- The notochord is a large, pale structure running along the dorsal part of the animal. It's pale because it is cartilage, which is a connective tissue with a low density of cells.
- The dorsal nerve cord, above the notochord, is a darker pink structure. At the animal's anterior end, the nerve cord is expanded to form a brain.
- The pharyngeal bars (gill bars) and pharyngeal slits (gill slits) make up the pharynx.