By: Christian Jay Rayon Nob

History of Systematics of Gastropods

Biodiversity

Diversity-Species of Gastropods-Worker of Gastropods Systematics

History

The first gastropods were exclusively marine, with the earliest representatives of the group appearing in the late Cambrian.

Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive.

By the Carboneferous period many of the shapes seen in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms.

During the Mesozoic era that the ancestors of many of the living gastropods evolved.

In Cenozoic era , yield very large numbers of gastropod fossils, many of these fossils being closely related to modern living forms. The diversity of the gastropods increased markedly at the beginning of this era, along with the bivalves.

This gastropod is called Neptunacontraria because the spiral goes anti-clockwise - the opposite way to most gastropods. It is from the Pliocene period (Cenozoic), about 3 million years old.

Biodiversity There are more than 65,000 species. about 30,000 are marine 30,000 live on land 5,000 live in fresh water Some of the more familiar and better-known gastropods are terrestrial

gastropods (the land snails and slugs) and some live in freshwater, but more than two thirds of all named species live in a marine environment.

Gastropods have a worldwide distribution from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized every medium available except the air.

DiversityAt all taxonomic levels, gastropods are second only to the

insects in terms of their diversity. Gastropods have the greatest numbers of named

molluscs species.Different estimates for aquatic gastropods (based on

different sources) give about 30,000 species of marine gastropods, and about 5,000 species of freshwater and brackish gastropods. The total number of recently discovered species of freshwater snails is about 4,000.

There are 444 recently extinct species of gastropods (extinct since the year 1500), 18 species that are now extinct in the wild (but still existing in captivity) and 69 "possibly extinct" species.

Species of Gastropods

Sub-class Prosobranchia

Sub-class Opisthobranchia

Sub-class Pulmonates

Worker of Gastropods Systematics

Winston Ponder and David R. Lindberg they revised the ‘’taxonomy of the Gastropods’’

- an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs.

Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.

assigns the various Gastropods into ranked categories- such as sub-orders and families- classification scheme is based on the molluscs' internal and

external shapes and forms. but did not take into account any analysis of their DNA or RNA.

Evolutionary Trees and Roots

Characters- Morphological Character

Evaluation of Trees

Anatomy -External-Internal

CharactersSensory organs and nervous system

include olfactory organs, eyes, statocysts and mechanoreceptors.Gastropods have no hearing.In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the 4 tentacles, are the most important sensory organ. The chemosensory organs of opisthobranch marine gastropods are called rhinophores.The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes, and even to lens eyes.In land snails and slugs, vision is not the most important sense, because they are mainly nocturnal animals.The nervous system of gastropods includes the peripheral nervous system and the central nervous system. The central nervous system consist of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia.

Digestive systemThe radula of a gastropod is usually adapted to the

food that a species eats. The simplest gastropods are the limpets and abalones, herbivores that use their hard radula to rasp at seaweeds on rocks.Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over the gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers.Respiratory system

Almost all marine gastropods breathe with a gill, but many freshwater species, and the majority of terrestrial species, have a pallial lung. Gastropods with a lung belong to one group with common descent, the Pulmonata, however, gastropods with gills are paraphyletic. The respiratory protein in almost all gastropods is hemocyanin, but a pulmonate family Planorbidae have hemoglobin as respiratory protein.

Circulatory systemGastropods have open circulatory

system and the transport fluid is hemolymph. Hemocyanin is present in the hemolymph as the respiratory pigment.

Excretory systemThe primary organs of excretion in

gastropods are nephridia, which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in the body cavity, and digestive glands opening into the stomach.

Reproductive systemCourtship is a part of mating behavior in some gastropods

including some of the Helicidae. Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts.

In many marine gastropods other than the opisthobranchs, there are separate sexes; most land gastropods however are hermaphrodites.

Feeding behaviorMarine gastropods include some that

are herbivores, detritus feeders, predatory carnivores, scavengers, parasites, and also a few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the sea floor. In some species that have evolved into endoparasites, such as the eulimid Thyonicoladoglieli, many of the standard gastropod features are strongly reduced or absent.

Evaluation of Trees

Kingdom Animalia

Phylum Molluska

Class Gastropoda

Family Lymnaeidae

Family Physidae

Family Thiaridae

Family Viviparidae

Family Neritidae

Subclass Pulmonata Subclass Prosobranchia

Subclass Opisthobranchia

Family Sacoglossa

Anatomy

External Anatomy

Internal Anatomy

Molecular Systematics

•Historical Context

•Basic Techniques

•Impact on Phylogenetics

•Limitations of Molecular Phylogenetics

Historical Context

- The freshwater snail family Lymnaeidae has a long and controversial systematic history. About 1,800 species and 34 genera of lymnaeids have been named in the past. Recent classifications have variously recognised a single genus. In particular, relationships inferred solely from morphological similarities of the shell, radula, and prostate gland have been found to be questionable when these data were tested against karyological and biochemical methods. Some emphasis has been placed on chromosome numbers in recent years; however, there are few character states among lymnaeids and thus little systematic resolution.

Basic Techniques

Scientist uses the method Genomic DNA isolation

Polymerase chain reaction (PCR) , DNA sequencing , and Sequence alignment.

Compared to the other large groups like insects and vertebrates, cladistic methodology into systematic and evolutionary studies of Mollusca has been a slow process.- this maybe due to the numbers of the workers of those groups. And also the traditional approach of many practicing malacologists that mollusks are unsuited for cladistic analysis.

Impact on Phylogenetics

Limitations of Molecular Phylogenetics

Many workers try to clarify gastropod molecular evolution but still many aspects of gastropod phylogeny remain unclear just like heterobranchia, the present study did not provide a robust phylogenetic hypothesis for the relationships among different lineages of Heterobranchia based on H3-Genesequences.

Molecular investigations of Gastropoda have been made difficult.- due to lack of slowly evolving of thier genes.

Morphological Case Studies

The hydrobiid gastropods comprise the largest group of freshwater mollusks, with more than 1,000 species and more than 400 Recent and fossil genera. This compilation is a prelude to the first rigorous phylogenetic analysis of the higher taxa of this cosmopolitan, yet poorly understood, group, for which at least 70 family-group taxa have been proposed. It also was prepared to fulfill a need for standardization of terminology and interpretation of characters used in taxonomic descriptions of these small, often morphologically simple, snails. Given that taxonomic study of these animals has long been hampered by reliance on a limited number of morphological features, all aspects of the shell and the soft-part anatomy are reviewed as part of this treatment, and attempt to be maximally inclusive in listing characters.

Many characters are extensively annotated, and in some cases new concepts of homology and/or division of characters are proposed.

Hydrobiid Snail

Molecular Case StudiesThe hermaphroditic freshwater snail Bulinus forskalii acts as

intermediate host for the trematode Schistosoma guineensis, an agent of human intestinal schistosomiasis. Despite the medical importance of this snail, little is known about its mating system, even though this influences the epidemiology of schistosomiasis. Therefore, a parent-offspring analysis was carried out to elucidate its mating system. Eleven highly polymorphic microsatellites generated multilocus genotypes, enabling parentage assignment to all of the 432 offspring reared from 28 pairs of laboratory-bred B. forskalii. Ninety percentof progeny were of uniparental origin, and only six pairs produced mixed clutches of crossed and selfed progeny. No pair reproduced exclusively by outcrossing. These results provide compelling evidence that B. forskalii has a mixed mating system dominated by uniparental reproduction, in agreement with indirect assessments from studies of population genetic structure and inbreeding effects. This reproductive strategy may be pivotal to the persistence of B. forskalii in its patchy, temporally unstable habitats, as well as helping it to cope with its parasitic burden.

Schistosomiasis

Conclusion

In general, the body of a gastropod consists of four main parts: the visceral mass, mantle, head and foot.  The head is highly developed and bilaterally symmetrical.  It contains a pair (sometimes two) of tentacles, a mouth, and eyes.  The eyes are often located on the tips of the tentacles.  The mouth contains an important device called the radula that functions in food processing, but has also adapted to serve many different purposes.  The radula may contain up to a quarter of a million individual teeth that grind up food before it is passed to an esophagus and stomach.