HOME

TheInfoList



OR:

''Callorhinchus'', the plough-nosed chimaeras or elephantfish, are the only living
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
in the family Callorhinchidae (sometimes spelled ''Callorhynchidae''). A few extinct genera only known from
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
remains are recognized. ''Callorhinchus'' spp. are similar in form and habits to other
chimaera Chimaeras are Chondrichthyes, cartilaginous fish in the order (biology), order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to B ...
s, but are distinguished by the presence of an elongated, flexible, fleshy snout, with a vague resemblance to a ploughshare. They are only found in the oceans of the Southern Hemisphere along the ocean bottom on muddy and sandy substrates. They filter feed, with small shellfish making up the bulk of their diet. The plough-nosed chimaera lays eggs on the ocean floor that hatch at around 8 months. They are currently not a target of conservation efforts; however, they may be susceptible to overfishing and trawling. Plough-nose chimaeras are the only extant chimaeras that still inhabit relatively shallow
neritic The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...
habitats, which are thought to have been the ancestral habitats for chimaeriforms up until the beginning of the
Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...
. All other chimaera groups have since shifted their habitats into deeper waters.


Morphology

Plough-nose chimaeras range from about in total length. Their usual color is black or brown, and, often a mixture between the two. While the club-like snout makes elephantfish easy to recognize, they have several other distinctive features. They possess large pectoral fins, believed to aid in moving swiftly through the water. They also have two dorsal fins spaced widely apart, which help identify the species in the open ocean. In front of each pectoral fin is one single gill opening. Between the two dorsal fins is a spine, and the second dorsal fin is significantly smaller than the more anterior one. The caudal fin is divided into two lobes, the top one being larger. The eyes, set high on the head, are often green in color. The snout is used to probe the sea bottom in search of the invertebrates and small fishes on which it preys. The remainder of the body is flat and compressed, often described as elongated. The mouth is just under this snout and the eyes are located high on top of the head. They have broad, flat teeth that have adapted for this eating habit, two pairs that reside in the upper jaw and one pair in the lower jaw. In addition to its use for feeding, the "trunks" of the ''Callorhinchus'' fish can sense movement and electric fields, allowing them to locate their prey.


Phylogeny

Phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
, they are the oldest group of living jawed
chondrichthyes Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...
. They possess the same
cartilaginous Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
skeleton seen in sharks, but are considered holocephalans to distinguish them from elasmobranchs, containing sharks and rays. Because of this, they provide a useful research organism for studying the early development of the jawed characteristic. Among the chondrichthyans, ''Callorhinchus'' has the smallest
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
. Because of this, it has been proposed to be used for entire
genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing or just genome sequencing, is the process of determining the entirety of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's ...
to represent the cartilaginous fish class. Their name comes from the fact that they share traits of both sharks and rays. They can be distinguished from sharks because they possess an operculum over their gill slits. Additionally, their skin is smooth, not covered in tough scales, characteristic of the shark. While the shark's jaw is loosely attached to the skull, the family Callorhinchidae differ in that their jaws are fused to their skulls.


Distribution

Members of this genus are all found in subtropical and temperate waters in the Southern Hemisphere: * '' Callorhinchus callorynchus'' resides off southern South American waters, ranging from
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan. The archipelago consists of the main is ...
north to Peru (in the Pacific) and southern Brazil (in the Atlantic). It is fished for year-round in the waters off of Brazil and Argentina. * '' Callorhinchus capensis'' is found in the oceans off southern Africa, including Namibia and South Africa.Branch, G.M., Branch, M.L, Griffiths, C.L. and Beckley, L.E. 2010. ''Two Oceans: a guide to the marine life of southern Africa'' * '' Callorhinchus milii'' is found in the southwestern Pacific Ocean near the coasts of Australia and New Zealand in warmer, more temperate waters. Still, in these temperate waters, the elephantfish reside in the cooler continental shelf. During the spring and summer, ''C. milii'' migrates to
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...
and inshore bays to mate.


Physiology

The
encephalization quotient Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed and predicted brain mass for an animal of a given size, based on nonlinear regre ...
is 1.1, compared to 6 in humans. Compared to humans, it has a larger
cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...
than
forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain controls body temperature, reproductive functions, eating, sleeping, and the display of emotions. Ve ...
. Its vision is very poor and the electrical sensing capabilities of the snout are predominantly used to find food. Both its circulatory and endocrine systems are similar to similar vertebrates, likely due to the early homologous structures the Callorhinchidae possess relative to the other Chondrichthyes.


Diet

The Callorhinchidae are predominantly filter feeders, feeding on the sandy sediment of the ocean bottoms or continental shelves. The large protrusion of the snout aids in this task. Their diet consists of molluscs, more specifically, clams. Besides this, the Callorhinchidae have been shown to also feed on invertebrates such as jellyfish or small octopuses. They are considered to be incapable of eating bony fish, in that they cannot keep up with the
teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...
s' speed.


Reproduction

The Callorhinchidae are
oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...
. Mating and spawning happen during the spring and early summer. Males possess the characteristic claspers near the pelvic fin that are seen in sharks, and these are used to transport the
gametes A gamete ( ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the Ge ...
. They migrate to more shallow waters to spawn. Also, a club-like protrusion from the head is used to hold onto the female during mating. The keratinous eggs are released onto the muddy sediment of the ocean bottom, usually in shallower water. At first, the egg is a golden yellow color, but this transforms into brown, and finally, black right before hatching. The average time in the egg is 8 months, and the embryo uses the yolk for all nourishment. Once hatched, the young instinctively move to deeper water. The egg cases are long and flat, and resemble pieces of seaweed.


Species

The family contains three
extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...
species, all in the same genus: * '' Callorhinchus callorynchus''
Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
,
1758 Events January–March * January 1 – Swedish biologist Carl Linnaeus (Carl von Linné) publishes in Stockholm the first volume (''Animalia'') of the 10th edition of ''Systema Naturae'', the starting point of modern zoologic ...
(Ploughnose chimaera, American elephantfish, or cockfish) * '' Callorhinchus capensis'' A. H. A. Duméril, 1865 (Cape elephantfish) * '' Callorhinchus milii''
Bory de Saint-Vincent Jean-Baptiste Geneviève Marcellin Bory de Saint-Vincent was a French naturalist, officer and politician. He was born on 6 July 1778 in Agen (Lot-et-Garonne) and died on 22 December 1846 in Paris. Biologist and geographer, he was particularly int ...
, 1823
(Australian ghostshark) A number of fossil species are also known, extending back into the mid-
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
(
Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...
).


Fishery and conservation effort

Currently, no effort is being made to conserve the family Callorhinchidae, but the species are heavily fished for food in South America. Because of this, they are extremely susceptible to being overfished. The greatest risk to this species is trawling or net fishing. Using this method, large numbers are caught quickly. Once caught, the fish are sold as whitefish or silver trumpeter fillets. The most common location of export is Australia. Under the
IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
, two of the three extant species of Callorhinchidae are listed as
least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...
, as they remain common. ''Callorhinchus callorynchus'' is listed as Vulnerable. While fishing quotas are in place in Australia and New Zealand, this is the furthest that the conservation effort spans. Rarely, they are caught to be placed in aquaria, but this is much less common than fishery for food.


References

{{Taxonbar, from1=Q675505, from2=Q2084323 Taxa named by Samuel Garman Taxonomy articles created by Polbot Extant Albian first appearances