AplacBase
Welcome to AplacBase!
AplacBase is a resource for all information surrounding aplacophoran molluscs! Check here for accepted aplacophoran taxa, distribution, identification guides, and more! The goal of AplacBase is to provide information for both experts and non-experts alike to aid in identification and general knowledge on this understudied group.
What are aplacophorans?
Aplacophora (Solenogastres + Caudofoveata) are weird marine molluscs. As small, shell-less, and worm-shaped, these animals have challenged malacologists with their generally rather uniform morphology since their discovery 150 years ago. By now, there are 319 officially named species of Solenogastres (also Neomeniomorpha), and roughly 170 Caudofoveata (Chaetodermomorpha) (see our species database). However, estimates suggest that these numbers represent only a fraction of the true aplacophoran diversity.
In competing phylogenetic hypothesis, Apalcophora are either regarded as the first two offshoots of the molluscan tree and interpreted to represent the ancestral condition of molluscs, or they are placed together with chitons (Polyplacophora) in a clade called Aculifera as the sister taxon to all other molluscs. Despite their key role in the understanding of mollusc evolution, they are one of the lesser known groups among Mollusca.
Although common in the global benthic malacofauna, aplacophorans often go unnoticed, are left unidentified, or are simply discarded for research as their identification requires a combination of complex and time-consuming methods and is inaccessible for the untrained (see below for detailed explanations on how to study aplacophorans). As a consequence, less than 500 species have been described so far. Most Aplacophora from remote locations constitute new taxa, but even from well-studied areas new species are still being routinely discovered.
Aplacophora (Solenogastres + Caudofoveata) are weird marine molluscs. As small, shell-less, and worm-shaped, these animals have challenged malacologists with their generally rather uniform morphology since their discovery 150 years ago. By now, there are 319 officially named species of Solenogastres (also Neomeniomorpha), and roughly 170 Caudofoveata (Chaetodermomorpha) (see our species database). However, estimates suggest that these numbers represent only a fraction of the true aplacophoran diversity.
In competing phylogenetic hypothesis, Apalcophora are either regarded as the first two offshoots of the molluscan tree and interpreted to represent the ancestral condition of molluscs, or they are placed together with chitons (Polyplacophora) in a clade called Aculifera as the sister taxon to all other molluscs. Despite their key role in the understanding of mollusc evolution, they are one of the lesser known groups among Mollusca.
Although common in the global benthic malacofauna, aplacophorans often go unnoticed, are left unidentified, or are simply discarded for research as their identification requires a combination of complex and time-consuming methods and is inaccessible for the untrained (see below for detailed explanations on how to study aplacophorans). As a consequence, less than 500 species have been described so far. Most Aplacophora from remote locations constitute new taxa, but even from well-studied areas new species are still being routinely discovered.
AplacBase is a continuously expanding online database about Aplacophora!
Our aims are: to provide 1) an up-to-date species list of Solenogastres and Caudofoveata and their known distribution ranges; 2) a compilation of 150 years’ worth of aplacophoran literature; and 3) a photo database and keys for fast and efficient identification of animals to at least higher taxonomic levels.
We hope AplacBase will not just support and facilitate future aplacophoran biodiversity research, but also contribute to make scientific progress (especially taxonomy and biodiversity research) more accessible to the general public, as a resource to raise awareness and public participation in biodiversity and nature conservation.
Our aims are: to provide 1) an up-to-date species list of Solenogastres and Caudofoveata and their known distribution ranges; 2) a compilation of 150 years’ worth of aplacophoran literature; and 3) a photo database and keys for fast and efficient identification of animals to at least higher taxonomic levels.
We hope AplacBase will not just support and facilitate future aplacophoran biodiversity research, but also contribute to make scientific progress (especially taxonomy and biodiversity research) more accessible to the general public, as a resource to raise awareness and public participation in biodiversity and nature conservation.
Solenogastres
We can find Solenogastres (=Neomeniomorpha) all over the world: from the shallow intertidal zone, down to the deepest parts of our oceans at the bottom of deep-sea trenches. They inhabit tropical coral reefs as well as the cold waters surrounding the North and South Pole (have a look at our distribution map). In the late second half of the 20th century, a lot of work was conducted on the diversity of Antarctic Solenogastres, which is why so many species are described from this area. Most species are only a couple of millimeters long. The smallest animals are Solenogastres that live within the ‘interstitial’, the tiny pore spaces between sand grains, and might be even smaller than a millimeter. The largest animals belong to the genera Epimenia and Neomenia. Many species are closely associated with hydroids and corals and one species has been found inside a hexactinellid sponge. So far they have been found to live on different types of sediment, like sand, mud, or silt. Species of the genus Helicoradomenia even live on hydrothermal vent sites.
Traditional taxonomy of Solenogastres is notoriously time-consuming and complex and involves the study of the fragile and small sclerites that cover their body and the study of internal anatomy (commonly using histology). The advent of molecular barcoding (i.e. sequencing specific parts of an animal’s genetic code) has really been a game-changer in the identification of animal groups that might otherwise require specialist equipment and knowledge as well as a lot of time. In theory, an animal can be easily identified by comparing its unique “DNA barcode” to databases, like GenBank (https://www.ncbi.nlm.nih.gov/genbank/), where such barcodes are stored for thousands of species. However, we do not yet have such a reference library of molecular barcodes for most solenogaster species. So while we can use their DNA as an additional character to differentiate between solenogaster species, for the time being it is not yet possible to identify them based on their DNA barcodes.
We can find Solenogastres (=Neomeniomorpha) all over the world: from the shallow intertidal zone, down to the deepest parts of our oceans at the bottom of deep-sea trenches. They inhabit tropical coral reefs as well as the cold waters surrounding the North and South Pole (have a look at our distribution map). In the late second half of the 20th century, a lot of work was conducted on the diversity of Antarctic Solenogastres, which is why so many species are described from this area. Most species are only a couple of millimeters long. The smallest animals are Solenogastres that live within the ‘interstitial’, the tiny pore spaces between sand grains, and might be even smaller than a millimeter. The largest animals belong to the genera Epimenia and Neomenia. Many species are closely associated with hydroids and corals and one species has been found inside a hexactinellid sponge. So far they have been found to live on different types of sediment, like sand, mud, or silt. Species of the genus Helicoradomenia even live on hydrothermal vent sites.
Traditional taxonomy of Solenogastres is notoriously time-consuming and complex and involves the study of the fragile and small sclerites that cover their body and the study of internal anatomy (commonly using histology). The advent of molecular barcoding (i.e. sequencing specific parts of an animal’s genetic code) has really been a game-changer in the identification of animal groups that might otherwise require specialist equipment and knowledge as well as a lot of time. In theory, an animal can be easily identified by comparing its unique “DNA barcode” to databases, like GenBank (https://www.ncbi.nlm.nih.gov/genbank/), where such barcodes are stored for thousands of species. However, we do not yet have such a reference library of molecular barcodes for most solenogaster species. So while we can use their DNA as an additional character to differentiate between solenogaster species, for the time being it is not yet possible to identify them based on their DNA barcodes.
Caudofoveata
Caudofoveata (=Chaetodermomorpha) is distinguished from Solenogastres by a suite of morphological characters, the most obvious of which are the complete absence of a foot, the presence of an oral shield (an anterior, muscular structure used in burrowing and feeding), and a small mantle cavity restricted to the posterior-most part of the body that contains one pair of true ctenidia (gills). Adult caudofoveates range in size from around 1 mm (many prochaetodermatids; Scheltema, 1985) to over 40 cm (Chaetoderma felderi) in length, although most described species are on the order of 2 mm to 5 cm. Caudofoveates commonly inhabit muddy substrata in calm, coastal waters but they are also common and, in some places, relatively abundant in the deep sea. For example, Prochaetoderma yongei can reach densities of 400 individuals / m2 in the north Atlantic although such densities are exceptional. Because of the obvious difficulties in studying these animals in their natural habitat, little is known about the behavior of caudofoveates in situ. At least some species appear to form horizontal burrows keeping their mantle cavity near the surface of the substratum. Although without a typical molluscan foot, caudofoveates are able to burrow efficiently in a peristaltic fashion using their circular and longitudinal musculature. Caudofoveates are thought to feed on microorganisms such as foraminiferans and/or detritus. Examination of transcriptome data from Falcidens caudatus suggests that nematodes may also be on the menu. Within Caudofoveata, classification is based primarily on characteristics of the sclerites and radula. Three families are generally recognized.
Caudofoveata (=Chaetodermomorpha) is distinguished from Solenogastres by a suite of morphological characters, the most obvious of which are the complete absence of a foot, the presence of an oral shield (an anterior, muscular structure used in burrowing and feeding), and a small mantle cavity restricted to the posterior-most part of the body that contains one pair of true ctenidia (gills). Adult caudofoveates range in size from around 1 mm (many prochaetodermatids; Scheltema, 1985) to over 40 cm (Chaetoderma felderi) in length, although most described species are on the order of 2 mm to 5 cm. Caudofoveates commonly inhabit muddy substrata in calm, coastal waters but they are also common and, in some places, relatively abundant in the deep sea. For example, Prochaetoderma yongei can reach densities of 400 individuals / m2 in the north Atlantic although such densities are exceptional. Because of the obvious difficulties in studying these animals in their natural habitat, little is known about the behavior of caudofoveates in situ. At least some species appear to form horizontal burrows keeping their mantle cavity near the surface of the substratum. Although without a typical molluscan foot, caudofoveates are able to burrow efficiently in a peristaltic fashion using their circular and longitudinal musculature. Caudofoveates are thought to feed on microorganisms such as foraminiferans and/or detritus. Examination of transcriptome data from Falcidens caudatus suggests that nematodes may also be on the menu. Within Caudofoveata, classification is based primarily on characteristics of the sclerites and radula. Three families are generally recognized.
Funding and Institutions
|
This work is supported in part by funding from the National Science Foundation:
NSF DEB 1846174. CAREER: Revolutionizing Biodiversity and Systematics Research on Aplacophora (Mollusca) and Training the Next Generation of Invertebrate Systematists. NSF ICB 2001601. Digitization TCN: Collaborative Research: Documenting Marine Biodiversity through Digitization of Invertebrate Collections (DigIn). |
|
