''Callichirus major sensu lato'' is a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

of ghost shrimp in the infraorder

Axiidea Axiidea is an infraorder of decapod crustaceans. They are colloquially known as mud shrimp, ghost shrimp, or burrowing shrimp; however, these decapods are only distantly related to true shrimp. Axiidea and Gebiidea are divergent infraorders of t ...

, found in flat sandy beaches across the

Pan-American Pan-American, Pan American, Panamerican, Pan-America, Pan America or Panamerica may refer to: * Collectively, the Americas: North America, Central America, South America and the Caribbean * Something of, from, or related to the Americas * Pan-Amer ...

coastline. Originally described as a single species, genetic studies eventually classified it as at least four almost morphologically indistinguishable species, one of which was given the binomial denomination ''Callichirus macrotelsonis'' (Peiró, 2012). The complex is distinguished by

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

, distinctly separated coxae and bases in the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

and

gonochorism In biology, gonochorism is a sexual system where there are two Sex, sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism con ...

, despite vestigial signs of ancestral

hermaphroditism A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

in ''C. macrotelsonis''. The widespread extraction of individuals for living

fishing bait Fishing bait is any bait (luring substance), luring substance used specifically to attract and fishing, catch fish, typically when angling with a fish hook, hook and fishing line, line. There are generally two types of baits used in angling: '' ...

has endangered both its conservation and that of their respective

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

Taxonomy

''Callichirus major'' was first described as ''Callianassa major'' by

Thomas Say Thomas Say (June 27, 1787 – October 10, 1834) was an American entomologist, conchologist, and Herpetology, herpetologist. His studies of insects and shells, numerous contributions to scientific journals, and scientific expeditions to Florida, Ge ...

in 1818, specifically in the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

and East

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

. Its genus was renamed ''Callichirus'' in 1866 by

William Stimpson William Stimpson (February 14, 1832 – May 26, 1872) was an American scientist. He was interested particularly in marine biology. Stimpson became an important early contributor to the work of the Smithsonian Institution and later, director o ...

. It used to be classified in the

infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...

Thalassinidea Thalassinidea is the former infraorder classification of decapod crustaceans that live in burrows in muddy bottoms of the world's oceans. In Australian English, the littoral thalassinidean '' Trypaea australiensis'' is referred to as the ''yabby'' ...

(ghost shrimp) of

decapod The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and p ...

crustaceans Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of Arthropod, arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquat ...

until this infraorder was proven to be

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

in 2009, after which the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Callianassidae Callianassidae is a family of ghost shrimp crustaceans belonging to the infraorder Axiidea, within the order Decapoda. Phylogeny The cladogram below shows Callianassidae's placement within Axiidea, from analysis by Wolfe ''et al.'', 2019. Gene ...

, in which ''C. major'' is included, was definitely placed in the infraorder

Axiidae Axiidae is a family of crustaceans belonging to the infraorder Axiidea, within the order Decapoda. Phylogeny The cladogram below shows Axiidae's placement within Axiidea, from analysis by Wolfe ''et al.'', 2019. Genera Axiidae includes the fo ...

. A supposed

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

ian species described as ''Anomalocaris macrotelsonis'' Ortmann, 1893 was eventually discovered in 1974 to be the fourth larval stage of ''C. major''. In 1995, the results of

genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

published by Staton and Felder concluded that

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

n populations described as ''C. major'' could not belong to the same species as those found in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

. Among those in the United States, although there were minor morphological differences between the populations of the East Coast (from

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

Georgia Georgia most commonly refers to: * Georgia (country), a country in the South Caucasus * Georgia (U.S. state), a state in the southeastern United States Georgia may also refer to: People and fictional characters * Georgia (name), a list of pe ...

) and those of the Gulf of Mexico (from

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

), the overall internal diversity of each population made them genetically indistinguishable. Samples of

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

Mexican Mexican may refer to: Mexico and its culture *Being related to, from, or connected to the country of Mexico, in North America ** People *** Mexicans, inhabitants of the country Mexico and their descendants *** Mexica, ancient indigenous people ...

ghost shrimps also later suggested a species not identical, but close to ''C. major s.s.'' Further testing by Peiró confirmed that populations of the East Coast and the Gulf of Mexico belonged to the same species, which was in turn different from the Colombian ones, but ''C. major'' was definitely described not as only two, but four distinct species with a

origin. Apart from ''C. major'' ''

stricto sensu ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

'' in the

, the Colombian populations were found to belong to a different species than those of Pacific Mexico and

Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...

. Those were described simply as ''C. aff. major'' sp. 2 and ''C. aff. major'' sp. 1, still pending binomial naming. The Brazilian populations was designated as ''C. macrotelsonis''. The relative genetical proximity between Caribbean and Pacific populations implies a separation posterior to the uplift of the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

. Rio confirmed Peiró's tests at a morphological level, suggesting that the absolute lack of information on

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

signs of

in ''C. major s.s.'' might indicate that this feature could be exclusive of the Brazilian species, which she denominated ''C. brasiliensis''. Based on descriptions by Sakai and Türkay in 2012, Felder and Dworschak suggested that the formers' denomination ''C. santarosaensis'' might be ascribed to populations formerly designated as ''C. major'' in the northern Gulf of Mexico, although pending further genetic analysis and casting doubt on the validity of Sakai's and Türkay's description of a damaged juvenile specimen, prejudicing the validity of the

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

Description

The great morphological similarities between all species of the ''C. major'' complex has proven to be a difficulty for the distinction of its closely related species. The ''C. major'' has a

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

with a rigid anterior margin, turning backwards to the ''linea thalassinica'' (an uncalcified membranous groove, in the complex's case distinctly parallel to the longitudinal axis of the body) and forwards to the rounded angles of the

branchiostegal lung A branchiostegal lung is a respiration organ used by some air-breathing arthropods. It is one of the most significant adaptations of some crabs and hermit crabs such as the coconut crab to their terrestrial habitats. The branchiostegal (gill) tis ...

. The

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

is inconspicuous between the first and third pairs of

pereopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these ma ...

s. The complex has a flanked

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

, with characteristically obtuse angles near the base of the

eyestalk In anatomy, an eyestalk (sometimes spelled eye stalk and also known as an ommatophore) is a protrusion that extends an eye away from the body, giving the eye a better field of view. It is a common feature in nature and frequently appears in fict ...

s, which in turn almost reach the basal segment of the antennules' peduncles. The antennules have a third segments 1.5 to 2.5 times as longer as the first and second together. The

has distinctly separated coxae and bases. The first pair of pereopods is very unequal in size, especially in adult males, presenting a uniquely bold instance

in the genus. The second pair is well

chelated Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

, but the fourth and fifth have rather imperfect chelae. The first and second segments of the abdomen are membranous and soft, the latter being longer than the first, and almost twice as long as the third, fourth and sixth segments. The third, fourth and sixth segments have approximately the same length, although the fifth is slightly longer than its adjacent segments. Distinctly for its genus, ''C. major'' is

gonochoristic In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism contras ...

. The

signs of ancestral

(namely, the production of unused

ovaries The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...

by males and additional

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects, have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female, it is ...

s in females) in ''C. macrotelsonis'' and the fully functional hermaphroditism in

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

such as '' C. seilacheri'', however, implies that the genus ''Callichirus'' may have a unique case of

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

basal, but not universal, hermaphroditism.

Habitat

''C. major s.l.'' occurs in open, dissipative and flat sandy beaches, mostly in deep galleries in the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

, but also in shallow

subtidal 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-illuminate ...

depths of 2–3 m. It has a very large geographic distribution across

coastlines. In the Atlantic coastline, the distribution occurs from North Carolina to Santa Catarina, although with a large hiatus from Southern Texas to

Pará Pará () is a Federative units of Brazil, state of Brazil, located in northern Brazil and traversed by the lower Amazon River. It borders the Brazilian states of Amapá, Maranhão, Tocantins (state), Tocantins, Mato Grosso, Amazonas (Brazilian st ...

, being therein only sporadically found in Colombia and

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

. In the Pacific coastline, the complex has been identified in both

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

and Costa Rica. ''C. major s.l.'' is widely employed as living

by many human coastal populations, including those in the

and

, due to its easy availability. Ghost shrimp mass extraction, both specifically regarding ''C. major'' and generically, has been described as ecologically harmful not only for their own

ecological stability In ecology, an ecosystem is said to possess ecological stability (or equilibrium) if it is capable of returning to its equilibrium state after a perturbation (a capacity known as Ecological resilience, resilience) or does not experience unexpecte ...

, but also to different animals that are killed in the procedure. The complex's

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 ...

status has been suggested as

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

, although it has not been officially reviewed by the IUCN.

References

Citations

Sources