The siphonal canal is an anatomical feature of the shells of certain groups of sea snails within the clade Neogastropoda. Some sea marine gastropods have a soft tubular anterior extension of the mantle called a siphon through which water is drawn into the mantle cavity and over the gill and which serves as a chemoreceptor to locate food. [1] Siphonal canals allow for active transport of water to sensory organs inside the shell. Organisms without siphonal canals in their shells rely on passive or diffuse transport or water into their shell. Those with siphonal canals have a direct inhalant stream of water that interacts with sensory organs to detect concentration and direction of a stimulus, such as food or mates. [2] In certain groups of carnivorous snails, where the siphon is particularly long, the structure of the shell has been modified in order to house and protect the soft structure of the siphon. Thus the siphonal canal is a semi-tubular extension of the aperture of the shell through which the siphon is extended when the animal is active.
The size and shape of the siphonal canal are important in taxonomic identification of mollusks. Sealed siphonal canals are a morphological feature of Muricidae subfamilies Ocenebrinae and Typhinae, a feature not found in other subfamilies from this taxonomic group. [3] One gastropod whose shell has an exceptionally long siphonal canal is the Venus comb murex. Some gastropods have a simplified siphonal notch at the edge of the aperture instead of a canal. For example, high intertidal gastropods often have a very short siphonal canal or a greatly reduced siphonal notch. [4]
There are close parallels between shell shape and presence of a siphonal canal. A study done by Vermeij found that shells that have a steep angle of their generating curve relative to their base axis (E) not do not have siphonal canals. [1] Specifically, all shells examined with an E angle greater than 30% did not have siphonal canals, but shells with lower angles often did. [1]
A short siphonal canal is preferred by some species of obligate commensal bivalves. Curvemysella paula is specially adapted to live inside snail shells occupied by hermit crabs. The crescent shaped shell of C. paula facilitates entry into the narrow space inside snail shells where they attach to the columellae and siphonal canal via byssal threads. The position and location of attachment anteriorly near the final whorls of the shell is an evolutionary behavior of adult individuals which prevents removal by the host. [5]
Siphonal indentations have evolved multiple times in gastropods and are widespread among many clades. Euomphanilae gastropods in the genus Scalites developed siphons in the early Ordovician period (448-443 MYA); however, they are not observed in any other members of the clade. 22 of an estimated >23 instances of siphonal indentations evolved in Murchosinoniinae gastropods - the two major clades in this group are Vetigastropoda (1 siphonate group: Tylozone) and Apogastropoda. Apodastropoda contains Caenogastropoda (14 instances of siphon evolution) and Heterobranchia (3 instances of siphon evolution). [6]
The evolution of siphonal indentations and related parts are not associated with species diversification and thus are likely not key innovations. Diversification is observed in only 17% of siphonate clades and primarily occurred during the Ordovician, late Paleozoic, and Mesozoic eras and was restricted to clades with few genera. Active predation only occurs in 1 siphonate clade (~4.5%) and is not considered a driver of evolution. [6] Further, the evolution of the siphonal canal did not coincide with a change in feeding style as the basal ancestor was nonpredatory. [2] One hypothesis is that the evolution of the siphonal canal was due to locomotion, because species without siphonal canals are largely sedentary, whereas siphonal families can move around the benthos. [2] However, due to the widespread ecological contexts of gastropods with a siphonal canal, there is no consensus hypothesis or unified driver which can explain the evolution or loss of this structure. [6]
The siphonal canal arose independently in the fossil record 23 times, and was subsequently lost 17 times. [6] Secondary loss was associated with miniaturization, the adoption of a sessile lifestyle, and non-marine habits. [6] A possible driver for these losses may have been species no longer relying on distance chemoreception, common in non-marine gastropods. [6] During the Cretaceous and Cenozoic periods, some species evolved long or closed siphonal canals. [6] This was the earliest instance of long canal and closed canal evolution, which subsequently arose approximately 15 times. [6] Closed canals in particular helped prevent predation by armoring the gastropod. [6] More generally, the siphonal canal protects gastropods by allowing their shells to be fully closed, with their mantle protected, while still sensing cues from the environment. [6]
The gastropods, commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda.
Neogastropoda is an order of sea snails, both freshwater and marine gastropod molluscs.
Heterobranchia, the heterobranchs, is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks.
A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda.
Strombidae, commonly known as the true conchs, is a taxonomic family of medium-sized to very large sea snails in the superfamily Stromboidea, and the Epifamily Neostromboidae. The term true conchs, being a common name, does not have an exact meaning. It may generally refer to any of the Strombidae but sometimes is used more specifically to include only Strombus and Lambis. The family currently includes 26 extant, and 10 extinct genera.
Aliger gigas, originally known as Strombus gigas or more recently as Lobatus gigas, commonly known as the queen conch, is a species of large sea snail, a marine gastropod mollusc in the family of true conches, the Strombidae. This species is one of the largest molluscs native to the Caribbean Sea, and tropical northwestern Atlantic, from Bermuda to Brazil, reaching up to 35.2 centimetres (13.9 in) in shell length. A. gigas is closely related to the goliath conch, Lobatus goliath, a species endemic to Brazil, as well as the rooster conch, Aliger gallus.
Strombus is a genus of medium to large sea snails, marine gastropod molluscs in the family Strombidae, which comprises the true conchs and their immediate relatives. The genus Strombus was named by Swedish Naturalist Carl Linnaeus in 1758. Around 50 living species were recognized, which vary in size from fairly small to very large. Six species live in the greater Caribbean region, including the queen conch, Strombus gigas, and the West Indian fighting conch, Strombus pugilis. However, since 2006, many species have been assigned to discrete genera. These new genera are, however, not yet found in most textbooks and collector's guides.
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails, but also including some freshwater snails and land snails.
Olive snails, also known as olive shells and olives, scientific name Olividae, are a taxonomic family of medium to large predatory sea snails with smooth, shiny, elongated oval-shaped shells.
The Stromboidea, originally named the Strombacea by Rafinesque in 1815, is a superfamily of medium-sized to very large sea snails in the clade Littorinimorpha.
The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some gastropods appear shell-less (slugs) but may have a remnant within the mantle, or in some cases the shell is reduced such that the body cannot be retracted within it (semi-slug). Some snails also possess an operculum that seals the opening of the shell, known as the aperture, which provides further protection. The study of mollusc shells is known as conchology. The biological study of gastropods, and other molluscs in general, is malacology. Shell morphology terms vary by species group.
Cystiscinae are a taxonomic subfamily of minute sea snails. These are marine gastropod mollusks or micromollusks in the family Cystiscidae, and the clade Neogastropoda.
Persiculinae is a taxonomic subfamily of minute to small predatory sea snails, marine gastropod mollusks. This subfamily includes several species which are micromollusks.
Olivellinae, are a subfamily of small predatory sea snails with smooth, shiny, elongated oval-shaped shells, in the family Olividae. The shells sometimes show muted but attractive colors, and may have some patterning.
Laevistrombus canarium is a species of edible sea snail, a marine gastropod mollusc in the family Strombidae. Known from illustrations in books dating from the late 17th century, L. canarium is an Indo-Pacific species occurring from India and Sri Lanka to Melanesia, Australia and southern Japan. The shell of adult individuals is coloured from light yellowish-brown to golden to grey. It has a characteristic inflated body whorl, a flared, thick outer lip, and a shallow stromboid notch. The shell is valued as an ornament, and because it is heavy and compact, it is also often used as a sinker for fishing nets.
A siphonal notch is a feature of the shell anatomy in some sea snails, marine gastropod mollusks.
The stromboid notch is an anatomical feature which is found in the shell of one taxonomic family of medium-sized to large sea snails, the conches.
Titanostrombus goliath, previously known as Lobatus goliath and Strombus goliath, common name the goliath conch, is a species of very large edible sea snail, a marine gastropod mollusk in the family Strombidae, the true conchs. T. goliath is one of the largest mollusks of the Western Atlantic Ocean, and also one of the largest species among the Strombidae. It was once considered endemic to Brazil, but specimens have also been recently found in the waters of Barbados. Brazilian common names for this species include búzio de chapéu or búzio, and búzio de aba or buzo in. Some phylogenetic hypotheses consider T. goliath as closely related to the queen conch, Aliger gigas.
Scabrotrophon densilamellatus is a species of sea snail, a marine gastropod mollusk in the family Muricidae, the murex snails or rock snails.
Trochia is a genus of sea snails, marine gastropod mollusks in the family Muricidae, the murex snails or rock snails.