''Synalpheus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of snapping shrimp of the
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Alpheidae
Alpheidae is a family of caridean snapping shrimp, characterized by having asymmetrical claws, the larger of which is typically capable of producing a loud snapping sound. Other common names for animals in the group are pistol shrimp or alpheid s ...
, presently containing more than 100
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
; new ones are described on a regular basis, and the exact number even of described species is disputed.
''Zuzalpheus''
The genus ''Zuzalpheus'' was established for ''S. gambarelloides'', ''S. brooksi'', and their closest relatives,
which contain several notably
eusocial
Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping gen ...
species.
While these do seem to form a
clade, it is not fully resolved whether or not they are indeed the
sister taxon
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 ...
of all the remaining ''Synalpheus''.
However, a detailed
cladistic
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
study of morphological characters found well marked differences between the proposed two genera and concluded that the supposed species groups around ''S. biunguiculatus''/''S. coutierei'', ''S. brevicarpus'' and ''S. neomeris'' are neither clearly defined nor, as it seems,
monophyletic, while the group separated in ''Zuzalpheus'' was clearly distinct in characters of the minor first walking legs (
pereiopods), and usually distinct in some others; in all ''Synalpheus sensu stricto'' checked to date, the transverse
seta
In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
l comb on the back of the minor first pereopod
dactyl
Dactyl may refer to:
* Dactyl (mythology), a legendary being
* Dactyl (poetry), a metrical unit of verse
* Dactyl Foundation, an arts organization
* Finger, a part of the hand
* Dactylus, part of a decapod crustacean
* "-dactyl", a suffix used ...
is missing, and the
carpus
In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...
is plump (about as wide as it is long or slightly wider) and small (not longer than half the length of the palm).
Moreover, their
stylocerite clearly extends beyond the whole first segment of the first
antennae, their
scaphocerite blade is never missing, the fixed finger of the major first pereopod is about the same length as the dactyl and the
uropod
Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion.
Definition
Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...
al
exopod always has one tooth only; these traits however may be also present in some of the species separated in ''Zuzalpheus'' though as far as can be told, most of these differ. While the authors of the 2008 analysis made no explicit comment on the status of the newly proposed genus, they thus found the ''S. gambarelloides'' species group to be well-marked, and their results certainly harden the case for recognition of ''Zuzalpheus'' at least as a subgenus.
However, this analysis only included 2 species from the ''S. gambarelloides'' species group, and none from the Caribbean, where the vast majority of the group resides. Opinion is still divided, however, and recently ''Zuzalpheus'' was synonymised with ''Synalpheus''.
Distribution
In the narrower sense, ''Synalpheus'' occur in the
East Pacific where they are most plentiful and probably originated, and to a lesser extent in the
Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
and the
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...
; the species placed in ''Zuzalpheus'' occur mainly in the western
Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
where their lineage probably originated, and to a lesser extent in the eastern Atlantic and
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...
, and the
East Pacific. It may thus be that the closure of the
Isthmus of Panama in the
Piacenzian (about 3
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...
) was a key factor in separating the two lineages, as species referred to ''Synalpheus sensu stricto'' are most plentiful in the western Pacific.
Snapping
The snapping behaviour of ''Synalpheus'' is rather well studied. In ''Synalpheus parneomeris'',
peak to peak
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
source levels of 185–190 dB re 1 μPa at 1 m were measured, depending on the size of the claw.
Eusociality
The only known
eusocial
Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping gen ...
aquatic species occur within the genus ''Synalpheus''. The species known to be eusocial are ''S. brooksi'', ''S. chacei'', ''S. elizabethae'', ''S. filidigitus'', ''S. rathbunae'', ''S. regalis'',
[ ''S. microneptunus'',][ Eusociality is thought to have arisen due to competition for space, because among the species that host ''Synalpheus'', empty sponges are rarely found.]kin selection
Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin altruism can look like altruistic behaviour whose evolution i ...
was necessary for this evolution to occur because the only species in which eusociality has appeared are non-dispersing shrimp that hatch directly into crawling individuals.
Species
''Synalpheus'' contains the following species:
References
Further reading
*
External links
{{Taxonbar, from=Q3934246
Alpheidae
Decapod genera
Taxa named by Charles Spence Bate