2.
What is the difference between?
a.
Brachiopod and Bivalve.
b.
Graptolite and Anthozoa (coral)
Model
Answer
a.
Brachiopod and Bivalve.
Brachiopods are a phylum
of marine animals that have hard "valves" (shells) on the upper and
lower surfaces. Most species of brachiopod went extinct during the P–T extinction over 250 million
years ago, but many survive today.
Brachiopod valves are hinged at
the rear end, while the front can be opened for feeding or closed for
protection. Articulate brachiopods have toothed hinges
and simple opening and closing muscles, while inarticulate brachiopods have
untoothed hinges and more complex muscles. In a typical brachiopod a stalk-like
pedicle projects from an opening in the hinge or
from a hole in the larger valve, attaching the animal to the sea bed but clear
of silt that would obstruct the opening.
Brachiopods have a mantle that secretes and
lines the shell, and encloses the internal organs. The body occupies typically
about one-third of the internal space inside the shell, nearest the hinge. The
rest of the mantle encloses a water-filled space containing the lophophore, a crown of
tentacles that filters food particles out of the water. In all
species the lophophore is supported by cartilage and by a hydrostatic skeleton.
The lophophore filters
food, mostly phytoplankton,
out of the water. From there the food is transported in succession to: the
grooves along the bases of the lophophore's tentacles; the mouth; pharynx; oesophagus;
and finally the stomach,
where the food is digested. Nutrients are transported from the stomach
throughout the coelom (main
body cavity), including the mantle lobes, by cilia. The wastes produced by metabolism are broken into ammonia, which is eliminated by
diffusion through the
mantle and lophophore.
The lophophore and mantle are the
only surfaces that absorb oxygen
and eliminate carbon
dioxide. Oxygen seems to be distributed by the fluid of the coelom. The
heart is above the stomach, and the blood vessels connect it to the major
organs. However, the main function of the blood may be to deliver nutrients.
The maximum oxygen consumption of brachiopods is low, and their minimum
requirement is not measurable.
The "brain" of adult
articulates consists of two ganglia, one above and the other below the oesophagus. Adult
inarticulates have only the lower ganglion. Nerves run to the lophophore, the
mantle lobes and the muscles that operate the valves. Many brachiopods close
their valves if shadows appear above them, but the cells responsible for this
are unknown. Some brachiopods have statocysts
which detect changes in the animals' balance.
Lifespans range from 3 to over 30
years. Ripe gametes
(ova or sperm) float from the gonads into the main
coelom and then exit into the mantle cavity. The larvae of inarticulate
brachiopods are miniature adults, with lophophores that enable the larvae to
feed and swim for months, until the animals become heavy enough to settle to
the seabed. Larvae of articulate species are different from the adult forms,
live only on yolk,
and remain among the plankton for only a few days before metamorphosing.
The traditional classification
into inarticulate and articulate brachiopods has been supplemented by two
refinements that appeared in the 1990s. One refinement groups the inarticulate Craniida with
articulate brachiopods, as both used the same material in the mineral layers of the shell.
The other segregates the Craniida into a third group, as their outer organic
layer is different from that of either the others. However, some taxonomists
believe it is premature to define the higher levels of classification such as order,
and recommend instead a bottom-up approach that identifies genera and then
groups these into intermediate groups. Traditionally brachiopods have been
regarded as members of or as a sister
group to the deuterostomes, a super-phylum which includes chordates and echinoderms.
One type of analysis of brachiopods' evolutionary relationships has always
placed brachiopods as protostomes, while another type has split between placing
brachiopods among the protostomes or the deuterostomes.
In 2003 it was suggested that
brachiopods evolved from an ancestor similar to Halkieria, a slug-like animal with "chain mail"
on its back and a shell at the front and rear end, and that the ancestral
brachiopod converted its shells into a pair of valves by folding the rear part
of its body under its front. However, new fossils found in 2007 to 2008 suggest
that brachiopods evolved from tommotiids: the tommotiids' "chain mail" formed
the tube of a sessile animal resembling brachiopods. Lineages
that have both fossil and extant brachiopods appeared in the early Cambrian, Ordovician and Carboniferous periods.
Other lineages have arisen and then become extinct, sometimes during severe mass
extinctions. At their peak in the Paleozoic era
the brachiopods were among the most abundant filter-feeders and reef-builders,
and occupied other ecological niches, including swimming in the
jet-propulsion style of scallops. Brachiopod fossils have been useful indicators of
climate changes during the Paleozoic
era. However, after the Permian–Triassic
extinction event, brachiopods recovered only a third of their former
diversity. A study in 2007 concluded that brachiopods were especially
vulnerable to the Permian–Triassic extinction, as they built calcareous hard
parts (made of calcium
carbonate) and had low metabolic rates and weak respiratory systems. It was
often thought that brachiopods were in decline after the Permian–Triassic
extinction, and were out-competed by bivalves. However, a study in 1980
concluded that both brachiopods and bivalves increased all the way from the
Paleozoic to modern times, but bivalves increased faster; after the
Permian–Triassic extinction, brachiopods for the first time were less diverse
than bivalves.
Brachiopods live only in the sea,
and most species avoid locations with strong currents or waves. Articulate
species have larvae that settle quickly and form dense populations in well-defined areas,
while inarticulate larvae swim for up to a month and have wide ranges.
Brachiopods now live mainly in cold and low-light conditions. Fish and
crustaceans seem to find brachiopod flesh distasteful and seldom attack them.
Among brachiopods only the lingulids have been fished commercially, on a very
small scale. One brachiopod species may be a measure of environmental
conditions around an oil terminal being built in Russia
on the shore of the Sea of
Japan.
The fossil brachiopod genera have great diversity
but only a few skeletal
characteristics, while the modern genera have much lower diversity but provide
soft-bodied characteristics as well as skeletal ones – and both sets of specimens
have limitations that make it difficult to produce a comprehensive
classification of brachiopods. The phylum also has experienced significant convergent evolution
and reversals (in which a more recent group seems to have lost a characteristic
that is seen in an intermediate group, reverting to a characteristic last seen
in an older group). Hence some brachiopod taxonomists
believe it is premature to define higher levels of classification such as order,
and recommend instead a bottom-up approach that identifies genera and then
groups these into intermediate groups.[19]
However, other taxonomists
believe that some patterns of characteristics are sufficiently stable to make
higher-level classifications worthwhile, although there are different views
about what the higher-level classifications should be.[19]
The "traditional" classification was defined in 1869;[20]
two further approaches were established in the 1990s:[6]
- In the "traditional"
classification, the Articulata have toothed hinges between the valves,
while the hinges of the Inarticulata are held together only by muscles.[4][6]
- A classification devised in the 1990s, based
on the materials of which the shells are based, united the Craniida
and the "articulate" brachiopods in the Calciata, which have calcite shells. The Lingulida and Discinida, combined in the Lingulata, have shells
made of chitin and calcium phosphate.[6]
- A three-part scheme, also from the 1990s,
places the Craniida in a separate group of its own, the Craniformea.
The Lingulida and Discinida are grouped as Linguliformea, and
the Rhynchonellida and Terebratulida as Rhynchonelliformea.[21][22]
Bivalvia is a class of marine and freshwater mollusks known
for some time as Pelecypoda, but now commonly referred to simply as bivalves.
As with Gastropoda and Cephalopoda,
the term Pelecypoda is in reference to the animal itself while Bivalvia simply
describes the shell. Other names for the class include Acephala, Bivalva, and
Lamellibranchia. The total number of bivalves currenty amounts to 9,200 species in 1,260 genera and 106
families. The global marine bivalves (including brackish water and estuarine
species) contain about 8,000 species, combined in 4 subclasses and 99 families
with 1,100 genera. The largest recent families are Veneridae with more than 680
species or Tellinidae and
Lucinidae with over 500
species. The freshwater bivalves have 7 additional families, of which the Unionidae contain about 700
species [3].
Bivalves have a shell
consisting of two asymmetrically rounded halves called valves that are
mirror images of each other, joined at one edge by a flexible ligament called the hinge.
The shell is typically bilaterally symmetrical, with the hinge lying in
the sagittal plane. Recent Bivalves
cover a large range of shell sizes from 0.52 mm in Condylonucula maya to
1,532 mm in Kuphus polythalamia
Bivalves are unique among the
molluscs, having lost their odontophore and radula
in their transition to filter feeding.
Some bivalves are epifaunal; they attach to surfaces. Others are infaunal; they bury themselves in sediment. These
forms typically have a strong digging foot. Some bivalves such as scallops can swim.
The term bivalve is
derived from the Latin bis,
meaning 'two', and valvae, meaning leaves of a door[4]
Other bivalved animals include brachiopods,
ostracodes,
and conchostrachans
Taxonomy
No consensus exists on bivalve
phylogeny. Many conflicts exist due to taxonomies
based on single organ systems and conflicting naming schemes. More
recent taxonomies use multiple organ systems, fossil
records, as well as molecular
phylogenetics to draw more robust phylogenies. Due to the numerous fossil lineages, DNA
sequence data is of limited use should the subclasses
turn out to be paraphyletic.
In his 1935 work Handbuch der
systematischen Weichtierkunde (Handbook of Systematic Malacology), Johannes Thiele
introduced a mollusc taxonomy based upon the 1909 work by Cossmann and Peyrot.
Thiele's system divided the bivalves into three orders:
- Taxodonta – taxodont dentition
- Anisomyaria – either a single adductor muscle or
one adductor muscle much larger than the other
- Eulamellibranchiata – all forms with lamellibranch ctenidia
The last was divided into four
sub-orders: Schizodonta, Heterodonta, Adapedonta and Anomalodesmata.[5][6]
The systematic layout presented
here follows Norman D.
Newell's 1965 classification based on hinge tooth morphology:[7]
Anthozoa is a class within the phylum Cnidaria that contains the sea
anemones and corals.
Unlike other cnidarians, anthozoans do not have a medusa
stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some
substrate on which the cnidarian grows.
Some anthozoans can also reproduce asexually through budding.
Biology
and anatomy
Like those of other cnidarians,
the individual polyps have a cylindrical body crowned by a ring of tentacles
surrounding the mouth. The mouth leads into a tubular pharynx which
descends for some distance into the body before opening into the gastrovascular
cavity that fills the interior of the body and tentacles. Unlike other
cnidarians, however, the cavity is subdivided by a number of radiating
partitions, or mesenteries. The gonads are also
located within the cavity walls.[1]
All cnidarian species can feed by
catching prey with nematocysts; sea anemones are capable of catching fish and
corals of catching plankton.
Some of the species also harbour a type of algae, dinoflagellates
called zooxanthellae,
in a symbiotic
relationship; the reef building corals known as hermatypic corals rely on this
symbiotic relationship particularly. The zooxanthellae benefit by using
nitrogenous waste and carbon dioxide produced by the host or , and the
cnidarian gains photosynthetic capability and increased calcium carbonate
production in hermatypic corals.[2]
Anemones and certain species of
coral live in isolation, however most corals form colonies of genetically identical
polyps; these polyps closely resemble anemonies in structure, although are
generally considerably smaller. Most kinds of stony
coral live in all parts of the underwater world.
b.
Graptolite and Anthozoa (coral)
Graptolites (Graptolithina) are fossil colonial animals known
chiefly from the Upper Cambrian
through the Lower Carboniferous
(Mississippian). A
possible early graptolite, Chaunograptus, is known from the Middle
Cambrian.
The name graptolite comes from
the Greek
graptos, meaning "written", and lithos, meaning
"rock", as many graptolite fossils resemble hieroglyphs
written on the rock. Linnaeus originally regarded them as 'pictures resembling
fossils rather than true fossils', though later workers, supposed them to be
related to the hydrozoans.[citation needed] More recent
work places them near the pterobranchs, possibly within.
Taxonomy
The name originates from the
genus Graptolithus, which was used by Linnaeus in
1735 for inorganic mineralizations and crustations which
resembled actual fossils. In 1768, in the 12th volume of Systema Naturae, he
included G. sagittarius and G. scalaris, respectively a possible plant fossil and a possible
graptolite. In his 1751 Skånska Resa, he included a figure of a
"fossil or graptolite of a strange kind" currently thought to be a
type of Climacograptus (a genus
of biserial graptolites). Later workers used the name to refer to a specific
group of organisms. Graptolithus was officially abandoned in 1954 by the
ICZN, partly because
of its original purpose as a grouping for inorganic mimicries of fossils.
(Bulman, 1970: V 6)
Since the 1970s, as a result of
advances in electron microscopy, graptolites have generally
been thought to be most closely allied to the pterobranchs,
a rare group of modern marine animals belonging to the phylum Hemichordata (hemichordates).
Comparisons are drawn with the modern hemichordates Cephalodiscus and Rhabdopleura.[1]
Cephalodiscus numbers about 18 species, and was first discovered in
1882.
Graptolites
as Index fossils
Graptolites are common fossils
and have a worldwide distribution. The preservation, quantity and gradual
change over a geologic
time scale of graptolites allows the fossils to be used to date strata of rocks
throughout the world.[1]
They are important index fossils for dating Palaeozoic
rocks as they evolved rapidly with time and formed many different species. British
geologists can divide the rocks of the Ordovician and Silurian periods into
graptolite biozones; these are generally less than one million years in
duration. A worldwide ice age
at the end of the Ordovician eliminated the majority of the then-living
graptolite; species present during the Silurian period were the result of
diversification from only a one or two species that survived the Ordovician glaciation.[1]
Graptolites are also used to
estimate water depth and temperature during the
graptolites lifetimes.
Write the correct word for the
sketches:
1) Phylum:
Echinodermata
Class: Echinoidae
2) Phylum:
Colentrata
Class: Anthozoa
3) Phylum:
Mollusca
Class: Bivalvia
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