{'fraction_non_alphanumeric': 0.04285714285714286, 'fraction_numerical': 0.010476190476190476, 'mean_word_length': 5.218934911242603, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
microRNAs revive old views about jawless vertebrate divergence and evolution

Most living vertebrates are jawed vertebrates or gnathostomes, like sharks or mammals. However, two small fish groups, hagfishes (67 species) and lampreys (about 40 species), are devoid of jaws and are either ignored by the public or regarded as pests. Both are eel-shaped, cartilaginous, and scale-less, and their overall anatomy is roughly similar to that of other fishes, with a brain, spinal cord, and sensory capsule, although more simple than that of gnathostomes (Fig. 1). First regarded as intestinal worms or degenerate jawed vertebrates (1) and then gathered into a group, the cyclostomes (rounded mouth), on the basis of basic anatomical characteristics (horny teeth, pouch-shaped gills, single nostril, and lack of paired fins) (2), these fishes became finally considered in evolutionary times as a monophyletic offshoot of primitive vertebrates, sister group to jawed vertebrates (3), and this became the received view for most of the of the 20th century (4).