Siphonostomatoida is an order of copepods, containing around 75% of all the copepods that parasitise fishes. Their success has been linked to their possession of siphon-like mandibles and of a "frontal filament" to aid attachment to their hosts. Most are marine, but a few live in fresh water. There are 40 recognised families:
- Archidactylinidae <small>Izawa, 1996</small>
- Artotrogidae <small>Brady, 1880</small>
- Asterocheridae <small>Giesbrecht, 1899</small>
- Brychiopontiidae <small>Humes, 1974</small>
- Caligidae <small>Burmeister, 1835</small>
- Calverocheridae <small>Stock, 1968</small>
- Cancerillidae <small>Giesbrecht, 1897</small>
- Codobidae <small>Boxshall & Ohtsuka, 2001</small>
- Coralliomyzontidae <small>Humes & Stock, 1991</small>
- Dichelesthiidae <small>Milne-Edwards, 1840</small>
- Dichelinidae <small>Boxshall & Ohtsuka, 2001</small>
- Dinopontiidae <small>Murnane, 1967</small>
- Dirivultidae <small>Humes & Dojiri, 1980</small>
- Dissonidae <small>Yamaguti, 1963</small>
- Ecbathyriontidae <small>Humes, 1987</small>
- Entomolepididae <small>Brady, 1899</small>
- Eudactylinidae <small>C. B. Wilson, 1932</small>
- Hatschekiidae <small>Kabata, 1979</small>
- Hyponeoidae <small>Heegaard, 1962</small>
- Kroyeriidae <small>Kabata, 1979</small>
- Lernaeopodidae <small>Milne-Edwards, 1840</small>
- Lernanthropidae <small>Kabata, 1979</small>
- Megapontiidae <small>Heptner, 1968</small>
- Micropontiidae <small>Gooding, 1957</small>
- Nanaspididae <small>Humes & Cressey, 1959</small>
- Nicothoidae <small>Dana, 1852</small>
- Pandaridae <small>Milne Edwards, 1840</small>
- Pennellidae <small>Burmeister, 1835</small>
- Pontoeciellidae <small>Giesbrecht, 1895</small>
- Pseudocycnidae <small>C. B. Wilson, 1922</small>
- Pseudohatschekiidae <small>Tang et al., 2010</small>
- Rataniidae <small>Giesbrecht, 1897</small>
- Samarusidae <small>Lee J. & I.H. Kim, 2018</small>
- Scottomyzontidae <small>Ivanenko et al., 2001</small>
- Sphyriidae <small>C. B. Wilson, 1919</small>
- Sponginticolidae <small>Topsent, 1928</small>
- Spongiocnizontidae <small>Stock & Kleeton, 1964</small>
- Stellicomitidae <small>Humes & Cressey, 1958</small>
- Tanypleuridae <small>Kabata, 1969</small>
- Trebiidae <small>C. B. Wilson, 1905</small>