Saccopharyngiformes

(vertebrate zoology) Formerly an order of actinopterygian fishes, the gulpers, now included in the Anguilliformes.

(Swallowers and gulpers)

Class: Actinopterygii

Order: Saccopharyngiformes

Number of families: 4

Evolution and systematics

The Saccopharyngiformes are divided into two suborders, the Cyematoidei, with the single family Cyematidae (with two monotypic genera), and the Saccopharyngoidei, which contains the other three families. Of these three families, the Monognathidae is the most diverse, with 14 identified species in the genus Monognathus. The Saccopharyngidae has 11 species in the single genus Saccopharynx; the closely related family Eurypharyngidae is monotypic. There is still controversy over the inclusion of the Cyematidae in this order, but they are placed here on the basis of reduction of skeletal features that are common among all four families. Systematists consider the Saccopharyngiformes to be quite different from anguilliform eels. The order is thought to consist of highly specialized fishes. All four families share numerous common features, most of which have to do with extreme loss of skeletal features, presumably the result of the extremely energy poor environment.

Within the Saccopharyngoidei, the eurypharyngids and saccopharyngids are superficially most similar in appearance and are considered the closest in taxonomic relationship. The Monognathidae represent a more advanced and highly specialized family, as evidenced by even greater reduction in skeletal components, that is, the loss of the upper jaw. The first fossil evidence for this order is reported to be from the Middle Cretaceous.

Physical characteristics

The loss of skeletal structures has resulted in fishes that are among the most unusual and striking in their appearance. Among other characteristics, all are scaleless, lack pelvic fins, and have very long dorsal and anal fins. All are rather "flabby" to the touch and presumably are very poor swimmers. In members of the Saccopharyngoidei, the mouths are very large to enormous, with distensible pharynges and stomachs, to allow for the capture of very large prey. Dentition varies among the families. Well-produced, posteriorly curved teeth are found in the Saccopharyngidae, with the other three families possessing small to minute teeth in the jaws.

Except for the enlarged head and mouth structure, the rest of the body of these fishes is elongated and very slender (filamentous in eurypharyngids and saccopharyngids). The body coloration varies from scattered pigment patches to a light uniform brown in monognathids, with dark brown to solid black in cyematids, eurypharyngids, and saccopharyngids. Thin white lines of unknown function extend from the head to the tail along the upper body in the saccopharyngids and eurypharyngids, and individuals in both families have luminous bulbs at the very tip of the filamentous tail. The filament may constitute 50% or more of the overall length of the fish. Overall lengths of the substantial part of the body in all saccopharyngiforms is small, not exceeding 19.6 in (50 cm).

Distribution

Saccopharyngids are most abundant and diverse in the Atlantic Ocean. Eurypharynx pelecanoides is well known from the Atlantic and central and eastern Pacific Oceans, and the monognathids are about equally diverse in the Atlantic (six species) and Pacific Oceans (seven species). Among the Cyematidae, Cyema atrum is widespread in the Atlantic, Pacific, and Indian Oceans, while Neocyema erythrostoma is only known from the eastern South Atlantic. Saccopharyngiformes have not been reported from the Mediterranean.

Habitat

These are primarily bathypelagic inhabitants, with the majority of adult specimens being collected at depths greater than 3,280 ft (1,000 m). Larvae and juveniles live in shallower waters, even into the upper mesopelagic zone below 656 ft (200 m).

Behavior

Owing to the extreme depths at which these fishes live, there are few reports of any behavior.

Feeding ecology and diet

All saccopharyngiform species are poor swimmers at best. There have been no reports on feeding in the cyematids, but it is thought that eurypharyngids and saccopharyngids draw prey close to them by means of luminescent lures on their tails and then quickly open their mouths to suck food in. Saccopharyngids are piscivorous (eat only other fish); eurypharyngids take a broader range of fish and invertebrate prey. An even more unusual form of feeding has been postulated for monognathids. It is thought that their prey (crustaceans) may be lured by scent released from glands around the mouth; when they come close enough, the fish bite them by means of a hollow fang in the mouth that injects venom, much like a rattlesnake. The fish then swallows the dead or dying shrimp whole. Little is known about the predators that feed in members of this order.

Reproductive biology

Nothing is known about the cyematoids, other than that they have separate sexes that do not appear to exhibit dimorphism. They also have leptocephalus larvae—a thin, largely transparent, ribbonlike stage that is common to several primitive orders of bony fishes (Elopiformes and Anguilliformes), including all saccopharyngiforms. In all three families of saccopharyngoids, sexually mature individuals are dimorphic. Males have greatly enlarged nasal structures and slightly enlarged eyes, and the jaws and stomachs in both males and females atrophy. It is widely believed that males locate their mates by following scent trails of pheromones released by the females and that spawning is a terminal event, with both individuals dying after mating. This reproductive pattern has been found in a number of shallow water eels and other fish species.

Conservation status

There are no known conservation measures specific to these families. No species from either family is listed on the IUCN Red List.

Significance to humans

Owing to their rarity and poorly studied biological characteristics, no significance can be attributed to saccopharyngiforms. They are objects of curiosity because of their extreme body specializations.

Species accounts

Resources

Bertelsen, E., Jørgen Nielsen, and David G. Smith. "Families Saccopharyngidae, Eurypharyngidae, and Monognathidae." In Fishes of the Western North Atlantic, edited by Eugenia B. Böhlke. Part 9. New Haven: Sears Foundation for Marine Research, 1989.

Nelson, Joseph S. Fishes of the World. 3rd edition. New York: John Wiley and Sons, 1994.

Smith, David G. "Order Saccopharyngiformes, Family Cyematidae." In Fishes of the Western North Atlantic, edited by Eugenia B. Böhlke. Vol. 9, Part 1. New Haven: Sears Foundation for Marine Research, 1989. ——. "Families Cyematidae, Saccopharyngidae, Eurypharyngidae, and Monognathidae: Leptocephali." In Fishes of the Western North Atlantic, edited by Eugenia B. Böhlke. Vol. 9, Part 2. New Haven: Sears Foundation for Marine Research, 1989.

Bertelsen, E., and Jørgen G. Nielsen. "The Deep-Sea Eel Family Monognathidae (Pisces, Anguilliformes)." Steenstrupia 13, no. 4 (1987): 141–198.

Gartner, John V. Jr. "Sexual Dimorphism in the Bathypelagic Gulper Eel Eurypharynx pelecanoides (Lyomeri: Eurypharyngidae), with Comments on Reproductive Strategy." Copeia 2 (1983): 446–449.

Nielsen, Jørgen G., and E. Bertelsen. "The Gulper-Eel Family Saccopharyngidae (Pisces, Anguilliformes)." Steenstrupia 11(1985): 157–206.

"FishBase: A Global Information System on Fishes." 7 Nov. 2002 (12 Nov. 2002).

[Article by: John V. Gartner Jr., PhD]

gulper eel
Pelican eel, Eurypharynx pelecanoides. From plate 49 of Oceanic Ichthyology by George Brown Goode and Tarleton Hoffman Bean, published 1896.
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii- Order: Saccopharyngiformes
Families
Cyematidae Eurypharyngidae Monognathidae Saccopharyngidae

Saccopharyngiformes is an order of unusual ray-finned fish superficially similar to eels, but with many internal differences. Most of the fish in this order are deep-sea types known from only a handful of specimens such as the Umbrella Mouth Gulper Eel. Saccopharyngiformes are also bioluminescent in several species. Some, such as the swallowers, can live as deep as 10,000 feet (3,000 m) in the ocean, well into the aphotic zone.

Saccopharyngiforms lack several bones, such as the symplectic bone, the bones of the opercle, and ribs. They also have no scales, pelvic fins, or swim bladder. The jaws are quite large, and several types are notable for being able to consume fish larger than themselves. Their myomeres (muscle segments) are V-shaped instead of W-shaped like in all other fish, and their lateral line has no pores, instead it is modified to groups of elevated tubules.

Classification

There are four families in two suborders in the order:

• Suborder Cyematoidei
  • Cyematidae (bobtail snipe eels)
• Suborder Saccopharyngoidei
  • Eurypharyngidae (pelican eel)
  • Monognathidae
  • Saccopharyngidae (swallowers, gulpers or gulper eels)

Diet

The gulper eel eats fish, copepods, shrimp, and plankton. It uses its mouth like a net by opening its large mouth and swimming at its prey. Due to the gulper eel's specialised body shape, it is a poor swimmer and relies on the luminescent organ at the tip of its tail to attract prey.

External links

• "Saccopharyngiformes". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
• Enchanted Learning Gulper Eel Copyright 1999 - 2006
• The Sea - Gulper Eel J.D. Knight, Copyright 1998
• Small fish takes big bite - Caymanian Compass, 9 October 2007

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