The saccopharyngiformes are a derived lineage of unusual eels within the order
Anguilliformes, and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae.
Most of the fish in this group are deep-dwelling and rarely seen, typically known from only a handful of specimens. Species include recognizable fish such as
pelican eels,
bobtail eel
The bobtail snipe eels are two species of deep-sea eels in the family Cyematidae, one only in each of two genera. They are small elongate fishes, growing up to 16cm (6 in) in length.
The family Cyematidae is characterized by thin, short bodies w ...
s, and gulper eels. Some can live deep in the ocean, well into the
aphotic zone, approximately 500–1800 meters deep. Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae.
All families except for the exceptionally rare individuals of proposed family Neoceymatidae (known only from the
Atlantic Ocean) are found in all major oceans.
Description
They have multiple internal differences from the rest of Anguilliformes. Notably, they have no
symplectic bone
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
,
opercular bones, ribs, or
swim bladders
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth wi ...
. Like many other eels, they lack scales and
pelvic fin
Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods.
Structure and function Structure
In actinopterygians, the pelvic fin consists of two en ...
s. Their
myomeres (muscle segments) are V shaped instead of W shaped as in all other fishes, and their
lateral lines
Lateral is a geometric term of location which may refer to:
Healthcare
*Lateral (anatomy), an anatomical direction
*Lateral cricoarytenoid muscle
*Lateral release (surgery), a surgical procedure on the side of a kneecap
Phonetics
*Lateral cons ...
have no pores, instead being modified to groups of elevated tubules. The jaws are quite large, lined with small teeth, and several types are notable for being able to consume fish larger than themselves. Some species in families Eurypharyngidae and Saccopharyngidae are
bioluminescent
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...
.
Like other eels, saccopharyngids have leptocephalus larvae. However, these larvae also have a number of unusual characteristics, such as remarkably deep bodies in the Cyematidae, long lower jaws in the Eurypharyngidae, and unique pigmented swellings at the ends of the gut in Saccopharyngidae and Eurypharyngidae.
The three established families of the suborder Saccopharyngoidei (Eupharyngidae, Monognathidae, Saccopharyngidae) all exhibit
sexual dimorphism.
Taxonomy
Until recently, the order "Saccopharyngiformes" was accepted as a separate order from Anguilliformes, based on their distinct morphological differences from the rest of the "true eels". Genetic work over the past few years has shown that it is instead a derived lineage within the Anguilliformes.
The four (proposed five) families in two suborders are:
* Suborder Cyematoidei
**
Cyematidae
The bobtail snipe eels are two species of deep-sea eels in the family Cyematidae, one only in each of two genera. They are small elongate fishes, growing up to 16cm (6 in) in length.
The family Cyematidae is characterized by thin, short bodies w ...
(bobtail snipe eels)
* Suborder
Saccopharyngoidei
**
Eurypharyngidae (gulpers)
**
Monognathidae (one-jaws)
**
Saccopharyngidae (swallowers)
**
Neocyematidae
Neocyematidae is a family of fishes in the order Saccopharyngiforms. This family, established from five described adult specimens of the species ''Neocyema erythrosoma'', was originally thought to be a part of the family Cyematidae, until genomi ...
(proposed)
References
External links
Rarely-seen deep sea gulper eel (''Eurypharynx pelecanoides'') in the first time ever video of its massive jaws November 2020.
{{Taxonbar, from=Q621582
Bioluminescent fish
Deep sea fish
Eels