Order

Petromyzontiformes

  Class

Cephalaspidomorphi

No. in FishBase

Genera : 8 | Species : 42 Eschmeyer's Catalog of Fishes

  Environment

Fresh : Yes | Brackish : Yes | Marine : Yes

  Division

Peripheral/diadromous

  Aquarium

none

  First Fossil Record

lower   Permian    

  Remark

Distribution: Mainly north hemisphere temperate zones of the world.
Size; larvae max 10 cm, adults max 120 cm.
Habitat and ecology: Marine species anadromous. Parasitic or non-parasitic, the latter restricted to freshwater. Land-locked, lake populations or species are common in the northern hemisphere, which also commonly appear as species pairs, with one species parasitic, and the other non-parasitic.
The larval (ammocoete) stage is filter feeding, whereas the adult uses the sucker shaped mouth to attach to other fishes and feeds off the wound (feed on a variety of bony fishes, right whale Eubalaena glacialis, sharks like Cetorhinus maximus, Prionace glauca, Carcharhinus plumbeus, C. obscurus, Somniosus microcephalus Ref. 58185).
Description: Jawless vertebrates with cartilaginous skeleton and notochord. Eel-like in shape; scales and paired fins absent; adults with well developed eyes; pouch-like gills not supported by gill arches; corneous teeth on the circular oral disk and the tongue; dorsal and ventral nerve roots separated; nasohypophyseal sac has an external opening only; intestinal tract with spiral valve and cilia; members of Petromyzontinae have the highest number of chromosomes (164-174) among vertebrates; 1 (genus Ichthyomyzon) or 2 (all other genera) dorsal fins; cloaca under the anterior half of the second dorsal fin; midgut of ammocoetes (at least in Entosphenus tridentatus, Lampetra fluviatilis, and Petromyzon marinus) does not possess a diverticulum; oral papillae present along the anterior and lateral edges of the oral disc, but absent from the posterior edge; all oral papillae of uniform size; oral fimbriae present around the entire perimeter of the oral disc; one supraoral lamina; labial teeth either pointed or rounded; eyes dorsolateral in immature and mature adults; fins separate in immature adults and contiguous in mature adults of genera with 2 dorsal fins; second dorsal fin/posterior lobe of the single dorsal fin confluent with (= continuous with) the caudal fin in ammocoetes as well as in immature and mature adults; one pair of kidney-shaped buccal glands; gular pouch, when present, small, never extending past the posterior edge of the eye.
Reproduction: Sexes separate; eggs numerous (thousands), small and not yolky, buried in spawning redds excavated in clean, hard bottoms (litophilous broodhiders). Non-parasitic species breed immediately after metamorphosis. Parents die after spawning. The larval (ammocoetes) stage lives for several years in freshwater before undergoing a radical metamorphosis and then as a rule returns to the sea.
Lampreys (together with hagfishes) are the most basal extant vertebrates. Definite fossil records date back to the upper Carboniferous, about 280 million years ago (Ref. 12268). Also from the Cretaceous of China from 125 million years ago and from the Devonian of South Africa from 360 million years ago.
Ammocoetes and adults are used as bait in some areas. A number of species are used as food.
Classification: The classification follows Ref. 89241 based on partial results of Ref. 89370 where Geotria and Mordacia are separated in two other distinct families (Ref. 89241, Ref. 58010). Hence the meaning of the subfamily Petromyzontinae is consequently changed.
Petromyzontidae Petromyzontinae ((Petromyzon, 1 sp., Ichthyomyzon, 6 spp.) Lampetrinae (4 gen., 29 spp.) Geotriidae (Geotria, 1 sp.) Mordaciidae (Mordacia, 3 spp.)
Other previous classifications were:
Ref. 39873 Petromyzontidae Geotriidae (Geotria, 1 sp.; Mordacia, 3 spp.)
Cited in Ref. 39873 Petromyzontidae Petromyzontinae Geotriinae (Geotria, 1 sp.; Mordacia, 3 spp.)

  Etymology

Latin, petra = stone + Greek, myzo = to suckle + Greek, odous, odontos = teeth ( Ref. 45335).

  Reproductive guild

nonguarders

  Typical activity level

  Main Ref

Renaud, C.B. 2011

  Coordinator

  Deep Fin Classification