Peltospiridae

Diversity

Peltospiridae is a family of deep-sea gastropods within the order Neomphalida that contains 13 genera and 21 species. They are adapted to the extreme conditions around hydrothermal vents which include high water temperatures, little oxygen, no light, and high acidity. Two species of peltospirid snail have lost the ability to eat entirely, instead relying on chemosynthetic bacteria stored in a modified oesophageal gland. A species called Chrysomallon squamiferum , commonly known as the scaly-foot gastropod or volcano snail, is the only known animal in the world that makes its shell out of mineralized iron. This group has only been found around deep-sea vent localities, which makes them vulnerable to deep-sea mining operations. Valuable minerals are often found in high quantities near these sites.

Geographic Range

Members of Peltospiridae are found in hydrothermal vent fields scattered around the world, although individual species often have limited ranges with little to no migration. According to genetic data, the origin of the family was likely the Pacific Ocean. Modern Pacific species can be found in volcanic fields off the west coast of North America, the East Pacific Rise, and the western Pacific near Australia and New Zealand. In the Indian Ocean, peltospirid snails were found at the Longqi and Kairei vent fields on the Southwest and Central Indian Ridges, as well as a vent location further south towards the Southern Ocean. In the Atlantic, this family is scattered along vent fields that extend up the Mid-Atlantic Ridge as far north as Europe.

• Biogeographic Regions
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Species in the family Peltospiridae are found exclusively around deep-sea hydrothermal vents, along with other invertebrates such as polychaete worms, crabs, shrimp, and bivalves. The adult snails are often densely clustered in areas only a few square meters in diameter at each site. Although the snails can survive high temperatures, they are more often found in cold mineral seeps at the bottom of the vents that can support their chemosynthetic endosymbionts. The larval form of these gastropods has never been identified, but they are thought to be planktonic like many other larval gastropods. This planktonic form is the most likely reason for their global distribution as adult snails move very slowly and are not likely to migrate far from their location.

• Habitat Regions
• saltwater or marine saltwater or marine

• Aquatic Biomes
• oceanic vent oceanic vent

Systematic and Taxonomic History

Peltospiridae is a family of deep-sea hydrothermal vent gastropods in the order Neomphalida . Two other families are found in order Neomphalida , Melanodrymiidae and Neomphalidae . Neomphalida is monophyletic when it includes these three families, but the exact relationship between them is still poorly understood. According to researchers, Melanodrymiidae may be sister to Peltospiridae + Neomphalidae , or Peltospiridae may be sister to Melanodrymiidae + Neomphalidae . In either case, an eastern Pacific origin is most likely for the order Neomphalida . Peltospiridae radiated outwards from here, colonizing locations in the western Pacific Ocean, Indian Ocean, and Atlantic Ocean. Peltospiridae contains 13 genera with 21 known species. The genera are, in alphabetical order, Chrysomallon , Ctenopelta , Depressigyra , Dracogyra , Echinopelta , Gigantopelta , Hirtopelta , Lirapex , Nodopelta , Pachydermia , Peltospira , Rhynchopelta , and Symmetriapelta .

Physical Description

Peltospiridae are characterized by a tapering snout, no eyes, an epipodium (groove between mantle and foot) with modified tentacles, a deep mantle cavity, a single left gill, separate sexes, no copulatory organ, and a mantle edge with two folds. Peltospirid snails also have paired oesophageal pouches that form the largest cavities in the body, and are modified to house chemosynthetic bacterial symbiotes in two species ( Chrysomallon squamiferum and Gigantopelta chessoia ). Other species in this group are grazers and filter feeders with primitive digestive systems. Shell shapes in this group range from un-whorled limpet-like shells to whorled snail-like shells. The shells are made out of aragonite coated in a layer of sulfides. The scaly-foot gastropod Chrysomallon squamiferum has a shell coated in iron sulfide (pyrite) unique to the animal kingdom, and shell color ranges from black to white between different populations. Although peltospirids have separate sexes, sexual dimorphism is not significant. Peltospiridae has a planktonic dispersal stage.

• Other Physical Features
• heterothermic heterothermic

• Sexual Dimorphism
• sexes alike

Reproduction

Members of Peltospiridae live gregariously on hydrothermal vent structures where multiple males may inseminate a single female by inserting spermatophores through a modified cephalic tentacle. The female transfers these spermatophores to the ovary through a specialized duct. This group is not known to display any specialized mating behaviors or means of attracting a mate.

• Mating System
• polyandrous polyandrous

Although Peltospiridae has separate sexes, sexual dimorphism is not significant. Females carry spermatophores inserted by the male which she then uses to inseminate the eggs over time.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• sperm-storing sperm-storing

Peltospiridae are not known to display any parental involvement. Females release fertilized eggs with negative buoyancy into the water where they hatch into a planktonic form.

• Parental Investment
• no parental involvement
• altricial altricial

Lifespan/Longevity

Due to the extreme difficulty of doing long-term ecological studies in deep-sea locations, very little is currently known about the lifespan of species in the family Peltospiridae . Live specimens of Chrysomallon squamiferum , the best studied species in Peltospiridae , survived for two weeks in a collection tank before perishing.

Behavior

Individuals in the family Peltospiridae live in large colonial groups alongside communities of other invertebrate species at deep sea hydrothermal vent locations. A research group from Hokkaido University discovered a colony of Chrysomallon squamiferum that had thousands of individuals clustered within a few square meters. These snails are blind and move slowly which means they do not migrate far from their origin. Enough genetic similarity has been found between two populations of Chrysomallon squamiferum living at different vent locations in the Indian Ocean that researchers believe there may be gene flow across longer distances. This is likely due to their planktonic larval stage that is able to spread long distances on ocean currents. The behavior of species of Peltospiridae is mostly determined by their primary diet. Grazers and filter feeders inhabit areas where bacterial mats and nutrient rich seawater are prevalent, while species with chemosynthetic symbiotes inhabit cold mineral seeps to obtain enough nutrients to survive.

• Key Behaviors
• motile motile
• sedentary sedentary
• colonial colonial

Communication and Perception

Species in Peltospiridae do not display any complex communication, but their sensory organs are well adapted to the complete darkness of the deep sea. All species are characterized by a tapering snout and tentacles that protrude from the edge of the mantle. The snout and tentacles are covered in sensory cilia which allow the snails to feel their way around their environment and find suitable mates. This group has no eyes.

• Communication Channels
• tactile tactile

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

Species in Peltospiridae are mainly grazers that feed on detritus and organic deposits that collect on and around hydrothermal vent structures. They possess a radula, or scraping-tooth, like that of many other gastropods. However, in two species ( Chrysomallon squamiferum and Gigantopelta chessoia ) the radula is weak and reduced. Instead, these species have an enlarged esophageal pouch surrounded by many blood vessels that contains chemosynthetic gamma-proteobacteria. These bacteria feed on the sulfur-rich water seeping from the bottom of the vents and produce carbohydrates that are absorbed by the snail's vascular system. Chrysomallon squamiferum and Gigantopelta chessoia are some of the only known animals in the world that derive all of their nutrition from chemoautotrophy.

• Primary Diet
• detritivore detritivore

Predation

Peltospiridae use their limpet-like shells as a defense against predators. Several species also have mineralized sclerites, or scales, protruding from the foot. Predatory gastropods like Phymorhynchus have a dart-like radula that they use to inject venom into their prey, and the sclerites may serve as a defense against this style of hunting.

Ecosystem Roles

Species in Peltospiridae often form dominant communities on the outside of hydrothermal vent structures that they share with many other invertebrates. By living in dense groups, they decrease their chances of predation and increase their chances for mating in a dark and extreme environment. Several species of Peltospirid snail have developed a symbiosis with chemosynthetic bacteria that are found nowhere else naturally. Snails in Peltospiridae are occasionally preyed upon by the predatory gastropod Phymorhynchus .

• Ecosystem Impact
• biodegradation biodegradation

Economic Importance for Humans: Positive

Peltospirid snails live in the complete darkness of the deep ocean, so they are very rarely encountered by humans. However, these gastropods have indirect benefits for humans as an integral part of the nutrient cycling that occurs in the deep ocean. Many fisheries are dependent on the upwelling of nutrients and planktonic blooms that originate from the deep sea. These snails also have much to teach us about alternative mechanisms of nutrition in the animal kingdom, and could inform us about how life could survive on other planets with hydrothermal features.

• Positive Impacts
• ecotourism ecotourism
• research and education
• produces fertilizer

Economic Importance for Humans: Negative

Species in Peltospiridae do not harm humans, and injuries or fatalities from peltospirid snails have never been recorded. However, these snails live in delicate hydrothermal environments that are prime targets for deep-sea mining operations. Valuable minerals such as magnesium, nickel, copper, zinc, and cobalt are found in high concentrations at these sites. Several of these sites are protected as biodiversity hotspots, which may force mining companies to turn to exploitative operations on land. However, the wealth of knowledge that these snails provide for us about deep-sea ecosystems may prove to be more valuable in the long term, and could encourage us to rethink the ways our own species affect the others that we share our planet with.

Conservation Status

Due to how difficult it is to measure population size of these snails, little is known about their conservation status. The only species listed under the IUCN Red List for Threatened Species in the entire family is Chrysomallon squamiferum which has an Endangered status. This is due to the fact that two of the three vent sites that this species has been found are in international waters, and have been leased out to several countries for mining rights. As of writing, no protections for these endangered populations have been proposed.

Other Comments

" Peltospiridae " means "shield-spire" after the limpet-like shells of some members of the family. No unequivocal fossils of Peltospiridae have been found, but McLean (1989) suggests that a fossil of a Triassic snail called Phryx resembles the species Rhynchopelta concentrica . Another group discovered fossils of a neomphalid gastropod from Cretaceous cold-seep carbonate formations in California. This discovery suggests that there may have been a radiation within Neomphalida during the Mesozoic. Chrysomallon squamiferum is the only animal known that incorporates iron in its shell construction. The chemosynthetic species within Peltospiridae represent some of the only complex animals that get the whole of their nutrition from chemosyntheis.

Additional Links

Encyclopedia of Life

Contributors

Robert Perschau (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Chen, C., Y. Zhou, W. Chunshen, J. Copley. 2017. Two New Hot-Vent Peltospirid Snails (Gastropoda: Neomphalina) from Longqi Hydrothermal Field, Southwest Indian Ridge. Frontiers in Marine Science , 4: 392. Accessed January 28, 2024 at https://www.frontiersin.org/articles/10.3389/fmars.2017.00392/full .

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