| Lasiognathus | |
|---|---|
 | |
| Lasiognathus amphirhamphus | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Lophiiformes |
| Family: | Oneirodidae |
| Genus: | Lasiognathus Regan, 1925 |
| Type species | |
| Lasiognathus saccostoma Regan, 1925 | |
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| Occurrences ofLasiognathus | |
Lasiognathus, thewolftrap anglerfish, is agenus of deep-seaanglerfish in the familyOneirodidae, with sixspecies known from theAtlantic andPacific Oceans.
It is distinct from otheranglerfish for an enormousupper jaw withpremaxillaries that can be folded down to enclose the much shorterlower jaw.[1] Its lure apparatus appears to consist of a "complete"fishing rod; the projectingbasal bone or pteropterygium being the rod itself; theillicium, a modifieddorsal fin ray) being the fishing line; thebioluminescent esca as bait; and hook-likeenlarged dermal denticles on the esca.
Lasiognathus comes from theAncient Greeklasios, meaning "hairy", andgnathos, meaning "jaw".[2] The common names seems toallude to jaw traps; the hinged premaxillae ofLasiognathus resemble the linked jaw-traps employed bytrappers to capture large fur-bearing mammals, such aswolves.[3] The genus may also be referred to as thewolftrap seadevils,trapjaw seadevils,snaggletooth seadevils[4]: 369 (with sea devil being a term used for deep sea anglerfish across families), orwonderfish (though this last name is a translationThaumatichthys' scientific name).
Onlymetamorphosed femaleLasiognathus have been collected and described; there is presumably extremesexual dimorphism in size and shape, as with other deep-sea anglerfishes. These fishes have a slenderbody with a large, slenderhead measuring over 60% of thestandard length. Themouth is huge, with thepremaxillaries of theupper jaw enlarged and extending well beyond the shortlower jaw. The premaxillaries are separatedanteriorly and connected by a broad elasticmembrane, and are hinged with the upper jaw so that they are able to flip up and down. When in the latter position, the premaxillaries completely enclose the lower jaw. There are numerous long, hookedteeth placed in roughly oblique rows on the premaxillaries.[5]
The pterygiophore (the basal bone supporting the illicium) ofLasiognathus is unusually long amongst anglerfish, measuring some 85% of the standard length. This bone inserts dorsally on the head and is capable of sliding forwards and backwards within a trough that extends the full length of thecranium and between theepaxialmusculature on the front half of the body.[6] The illicium is also long, with a terminal esca and 2-3 bony hook-shaped denticles mounted on an appendage at the tip. The escal bulb is equipped with a flap of skin that allows adjustment of the emitted light. The sphenotic spines (above the eyes) are well-developed, as are the two articular spines (at the rear end of the lower jaw). Theoperculum is divided into two parts, with the dorsal part split into two (rarely three) branches.[5]
Thepectoral fin lobe is small, short, and broad; thefin rays number 5 in thedorsal fin, 5 in theanal fin, 14–20 in the pectoral fins, and 9 in thecaudal fin.[7] Theskin is entirely naked, without spines or denticles. The coloration is a deep chocolate brown.[5] AllLasiognathus are small fishes;L. amphirhamphus is the largest known species at 15.7 cmstandard length.[8]L. beebei attains a maximum length of 11.5 cm,[9]L. dinema 9.5 cm,[10]L. intermedius 12.9 cm,[11]L. saccostoma 7.7 cm,[12] andL. waltoni 9.4 cm.[13]
Lasiognathus was originally placed in the family Thaumatichthyidae due to morphological similarities withThaumatichthys, such as enlarged hinged premaxillaries, escal denticles, and a branched operculum. However, differences between these genera, including features shared with oneirodids but absent inThaumatichthys, suggested thatLasiognathus may belong elsewhere. Bertelsen and Struhsaker (1977) noted that family placement was somewhat subjective given the unclear cladistics of the Oneirodidae.[7]
While the 5th edition ofFishes of the World still recognizes Thaumatichthyidae as a valid family within Ceratioidei, more recent phylogenetic work using morphological and molecular data (mitochondrial sequences and ultra-conserved elements) has recoveredLasiognathus nested within the Oneirodidae, as sister toPuck + (Chirophryne +Leptacanthichthys).[14]
There are currently 6 recognized species in this genus, which are onlydistinguishable by themorphology of the esca. This genus was previously considered part of the family Thaumatichthyidae, but is now placed in the Oneirodidae:[14]
This species is characterized by having only two (as opposed to three) bony hooks on its esca, which are lightly pigmented. The distal escal appendage is elongated and cylindrical with a long, compressed prolongation at the tip as inL. saccostoma. The prolongation has six tiny filaments at the tip and no lateral serrations. Theposterior escal appendage is broad and laterally compressed.[6]
This species is distinguishable by its hooks being placed on a short, transverse, fan-shaped distal escal appendage as opposed to the elongated, cylindrical appendage of all other species.[6]
This species is similar to any of the five previously described members of the genus, these species is unique in having a cylindrical, internally pigmented, anterior escal appendage and a pair of elongate distal escal appendages.[10]
This species has an elongated, cylindrical distal appendage with a short, cylindrical prolongation at the tip without any lateral serrations or filaments. The posterior escal appendage is cylindrical in shape. Its species name refers to its esca being intermediate in shape between those ofL. beebei and those ofL. saccostoma andL. waltoni.[5]
This species has a slender, compressed prolongation at the tip of its elongated, cylindrical distal escal appendage, with numerous lateral serrations and distal filaments. Unlike inL. amphirhamphus, there are three escal hooks and they are darkly pigmented. The posterior escal appendage is broad and laterally compressed, and relatively larger than inL. amphirhamphus.[6]
This species is characterized by a membranous anterior crest on its escal bulb, and an elongated, cylindrical distal escal appendage without a prolongation at the tip.[1]
Lasiognathus species have been collected from widely scattered localities in theAtlantic andPacific Oceans.L. beebei is known from the north Atlantic and offOahu inHawaiian Islands.L. waltoni is known from the central Pacific, just north of Oahu.L. dinema is known from the northernGulf of Mexico.[10]L. intermedius is known from the western north Atlantic, the eastern south Pacific, and from offCape Town, South Africa.L. saccostoma is known from the north Atlantic and off the Hawaiian Islands.[5]L. amphirhamphus is known from off theMadeira Islands in the eastern north Atlantic.[6]Lasiognathus specimens of uncertain species are also known from the north Pacific and theSouth China Sea.[1] They arepelagic in nature, occurring to a depth of 4,000 m.[5]
Little is known of the life habits ofLasiognathus.William Beebe speculated in 1930 that the fishing apparatus ofLasiognathus might "be cast swiftly ahead, when then the hooks and the lights would so frighten any pursued fish that they would hesitate long enough to be engulfed in the onrushing maw," thoughRichard Ellis considered this scenario unlikely. Nolan and Rosenblatt (1975) echoed Beebe's skepticism that the hooks were actually used to hook prey, though they proposed that "squidtentacles could conceivably be impaled on the hooks and the prey thus secured". It has also been proposed thatLasiognathus might form its mouth into a sort ofsieve forfilter feeding. More likely, prey is simply attracted by the glowing esca to within range of the jaws.[15]
Stomach contents reveal thatLasiognathus feeds primarily onbony fishes, such aslanternfishes andbristlemouths, and occasionally takesinvertebrates includingcopepods,amphipods,mysid shrimps,siphonophores,salps,pteropods, andchaetognaths.[1] It is not known whether the males areparasitic; neither males nor larvae have yet been collected.[16]
