External appearance of a lamprey
1 – sucker funnel; 2 – skin folds; 3 – nostril; 4 – parietal organ; 5 – eye; 6 – lateral line; 7 – dorsal fins; 8 – caudal fin; 9 – urogenital papilla; 10 – anal opening; 11 – external gill openings
Lamprey larva – ammocoete
Skull and branchial skeleton of a lamprey
1 – hyoid arch; 2 – olfactory capsule; 3 – auditory capsule; 4 – rudiments of upper vertebral arches; 5 – notochord; 6 – pericardial cartilage; 7 – branchial arches; 8 – hyoid cartilaginous plate; 9 – skeleton of the sucker funnel
Dissected lamprey
1 – unpaired nostril; 2 – olfactory capsule; 3 – integument; 4 – brain; 5 – spinal canal; 6 – notochord; 7 – fibrous tissue cord; 8 – dorsal muscles; 9 – pericardial sac; 10 – ovary; 11 – intestine; 12 – liver; 13 – venous sinus; 14 – atrium; 15 – ventricle; 16 – external gill opening; 17 – gill pouch with dissected upper part; 18 – respiratory tube; 19 – tongue musculature; 20 – oral cavity; 21 – hyoid plate; 22 – oral funnel
Oral funnel and branchial apparatus of a lamprey
1 – skin folds; 2 – oral opening; 3 – respiratory tube; 4 – internal gill opening; 5 – external gill openings; 6 – gill pouch; 7 – interbranchial septum
Circulatory system of cyclostomes
1 – carotid arteries; 2 – dorsal aorta; 3 – anterior cardinal vein; 4 – caudal vein; 5 – posterior cardinal vein; 6 – subintestinal vein; 7 – hepatic vein; 8 – portal vein of the liver; 9 – venous sinus; 10 – atrium; 11 – ventricle; 12 – inferior jugular vein; 13 – ventral aorta; 14 – afferent branchial arteries; 15 – efferent branchial arteries (veins are shown in black, arteries – in white or hatched)
Brain of a lamprey: A – from above; B – from below
1 – cerebral hemispheres of the forebrain; 2 – olfactory lobes; 3 – diencephalon; 4–5 – left and right habenular ganglia; 6 – parietal organ covering the epiphysis; 7 – infundibulum; 8 – optic lobes of the midbrain; 9 – opening in the roof of the midbrain; 10 – floor of the midbrain; 11 – rudimentary cerebellum; 12 – rhomboid fossa; 13 – medulla oblongata (Roman numerals denote cranial nerves)
