brachio mayu

8/11/2019 Brachio Mayu

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BRACHIOPODS( " Lamp shells " )


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They are often known as"lamp shells", since the

curved shells of the class

Rhynchonellida look ratherlike pottery oil-lamps of

ancient Greece and Rome.


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Characteristics

1)Bilaterally symmetrical.2)Body has more than two cell layers, tissues and

organs.3)Body cavity a true coelom.4)Body possesses a U-shaped gut with or withoutan anus.5)Body enclosed in a pair of shells, one dorsal andthe other ventral.6)Has a nervous system with a ganglionatedcircum-oesophagal ring.7)Has a true open circulatory system with one ormore hearts.8)Has no gaseous exchange organs.

9)Has a lophophore.10)Reproduction normally sexual andgonochoristic, but without true gonads.11)Feed on fine particles in the water.12)All live in marine environments.

13)Aquatic sessile feeders


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Brachiopods are small animals with the largestliving species having a shell length of about 10 cm(4 in) and most species being much smaller thanthis. There are only about 350 living species ofBrachiopods known to science now. However thereare over 30,000 fossil species known showing thatthey were once a much more successful phylumthan they are today.The remainder of Paleozoic could be termed theAgeof Brachiopods


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Brachipods resemble bivalves because they havemantle and two calcified valves. BUT they differ intheir shells. Brachipod shells cover top and bottom of the

organism. It has definite dorsal and ventral half

with ventral shell larger than the dorsal shell. Bivalve shells have left and right halves to their

shells, the two halves of their shells nearlyequal.


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Currently, brachiopods are divided into two or

three major groups:-Class Inarticulata (including lingulids), and

Class Articulata based on the presence or absenceof hinge teeth and sockets.

Articulate brachiopods have toothedhinges and simple opening andclosing muscles, while Inarticulatebrachiopods have untoothed hinges

and more complex muscles.


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BRACHIOPODA-

ClassificationPhylum Brachiopoda (Cambrian-Recent)

Class Inarticulata (Cambrian-Recent)

Class Articulata (Cambrian-Recent)

Order Orthida (Cambrian-Permian)

Order Strophomenida (Ordovician-Jurassic)

Order Pentamerida (Cambrian-Devonian)

Order Rhynchonellida (Ordovician-Recent)

Order Spiriferida (Ordovician-Jurassic)

Order Terebratulida (Devonian-Recent


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Appearance

THE SHELL The most obvious aspect of a Brachiopod is its

shell, this shell is a hard solid object that oftenremains intact long after the animal is dead, andthis is why we have such a good fossil record ofthe Brachiopoda. The shell is composed of about50% calcium carbonate or phosphate which theanimal extracts from the sea water.

The shells grow continually throughout theanimals life, new material is laid down along thelarger rounded edge of the shell (called the'margin') by the cellular epithelium. The outersurface of the shell is covered by the

periostracum. The two halves of the shell are normally not

equal; the larger half being called the ventral orbrachial valve and the smaller half the ventral orpedicle valve.


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External

Each valve is ribbed with the ribsradiating outwards from theumbo, and posses growth lineswhich run concentrically around

the shell, thus crossing the ribs.When closed the two valves ofthe shell meet perfectly, the linewhere they meet is called thecommisure.


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Internal


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The interior of the shell is lined with a mantle, amembranous duplication of the body wall, throughwhich respiration may occur and which secretes

the shells. The shell is closed and opened byadductor and diductor muscles respectively. Thescars of these muscles may be seen on the insideof the valves. The body of the animal occupiesonly about one-third of the interior of the shell.

The rest is taken up by the lophophore, which issupported by a two-limbed, calcareous structure,the brachidium. The brachidium is variable inshape consisting in its simplest form of the loopoftwo short or moderately long, curved structures,

and in its more complex form of two thin, spirallycoiled ribbons or spires. The shape of thebrachidium is very important in determining theclassification of brachiopod types. The brachidiumsupports the brachia, the fleshy arm-like part ofthe lophophore which bear the tentacles or cirri

that sweep food particles into the mouth.


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One of the most distinguishing features ofbrachiopods is the presence of a pedicle, a fleshy

stalk-like structure that aids the animal inburrowing and maintaining stability.

Pedicle


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The lophophore, which is the animals feeding andrespiratory mechanism is supported, except in verysmall species (less than 5mm) by a stiffening rod orcalcareous loop that arises from the inner surface ofthe shell. The lophophore normally has two arms thatrise out spirally into each half of the mantle cavity.

Each arm of the lophophore is comprised of a numberof slender parallel filaments. These filaments aremucous covered and support larger cilia.

FOOD ANDRESPIRATION


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The lophophore captures food particles,

especially phytoplankton (tinyphotosynthetic organisms), and deliverthem to the mouth via the brachial groovesalong the bases of the tentacles. Foodpasses through the mouth, muscular

pharynx ("throat") and oesophagus("gullet"), all of which are lined with ciliaand cells that secrete mucus and digestiveenzymes. The stomach wall has branched

ceca ("pouches") where food is digested,mainly within the cells.


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Nutrients are transported throughout thecoelom, including the mantle lobes, by cilia.The wastes produced by metabolism arebroken into ammonia, which is eliminatedby diffusion through the mantle andlophophore

The Inarticulata, which are the moremodern of the two groups, have an anuswhich directs the wastes into the exhalent

current, the Articulata have a blind endinggut with no anus and wastes are passed outof the mouth.


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Within the body or coelomic cavity there is afluid which contains blood corpuscles. These

blood corpuscles contain a respiratorypigment called hemerythrin, which likehaemoglobin contains iron. These cells carryoxygen to the various parts of the body andtake the carbon dioxide away. There are

canals within the body through which thiscoelomic fluid flows, but it is not a trueblood system and there is only one bloodvessel which has muscular walls and beatsonce every 30 to 40 minutes to keep the

fluid circulating around the body.

d i


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Adults of most species are of one sex

throughout their lives. The gonads aremasses of developing gametes (ovaorsperm), and most species have four gonads,two in each valve. Those of articulates lie inthe channels of the mantle lobes, whilethose of inarticulates lie near the gut. Ripegametes float into the main coelom and thenexit into the mantle cavity via themetanephridia, which open on either side ofthe mouth. Most species release both ovaand sperm into the water, but females of

some species keep the embryos in broodchambers until the larvae hatch.

Reproduction


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The larvae of inarticulates swim as planktonfor months and are like miniature adults,with valves, mantle lobes, a pedicle thatcoils in the mantle cavity, and a smalllophophore, which is used for both feeding

and swimming.


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As the shell becomes heavier, the juvenile sinks tothe bottom and becomes a sessile adult. The larvaeof articulate species live only on yolk, and remainamong the plankton for only a few days. This type oflarva has a ciliated frontmost lobe that becomes thebody and lophophore, a rear lobe that becomes thepedicle, and a mantle like a skirt, with the hemtowards the rear.

On metamorphosing into an adult, the pedicleattaches to a surface, the front lobe develops thelophophore and other organs, and the mantle rolls upover the front lobe and starts to secrete the shell.

NERVOUS AND


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The nervous system is fairly similar in allspecies and consists of ring of nerves whichencircles the oesophagus. From this ring afew other nerves reach out into the mantle,the lophophore and the muscles. There is notrue brain as brachiopods are ancient andrather simple animals.

NERVOUS ANDMUSCULAR SYSTEM


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The two valves of the shell of Brachiopods is opened

and closed by muscles. In the art iculatathere is a

simple arrangement two sets of paired muscles. Theadductor muscles which close the halves of the shell

are the largest. The diductor muscles which have

their point of attachment close to the hinge in the

dorsal valve open the shell so that the animal can

feed. There is also a pair of adjustor muscles which

attached to the Ventral valve and the pedicel. The

pedicel is a stalk of horny material that is normally

glued or cemented to a rock or something similar.

ECOLOGY


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Distribution and habitat

Brachiopods live only in the sea. Most speciesavoid locations with strong currents or waves,

and typical sites include rocky overhangs,crevices and caves, steep slopes of continentalshelves, and in the bottoms of deep oceans.

ECOLOGY


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However, some articulate species attach to

kelp or in exceptionally sheltered sites inintertidal zones. The smallest livingbrachiopod, Gwynia, is only about 1 millimetre(0.039 in) long, and lives in gravel.Rhynchonelliforms (Articulata excludingCraniida), whose larvae consume only theiryolks and settle and develop quickly,specialize in specific areas and form densepopulations that can reach thousands per

meter.


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Young adults often attach to the shells ofmore mature ones. On the other hand,inarticulate brachipods, whose larva swim forup to a month before settling, have wideranges. Members of the discinoid genusPelagodiscus have a cosmopolitandistribution.


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Interactions with other organisms

Brachiopod valves often serve as substratesfor encrusting organisms. Brachiopodmetabolisms are 3 to 10 times slower thanthat of bivalves. While brachiopods wereabundant in warm, shallow seas during theCretaceous period, they have been out-bredby bivalves, and now live mainly in cold andlow-light conditions.

Brachiopod shells occasionally show evidenceof damage by predators, and sometimes ofsubsequent repair. Fish and crustaceans seemto find brachiopod flesh distasteful.


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Among brachiopods only the Lingulids havebeen fished commercially, and only on a verysmall scale. Brachiopods seldom settle onartificial surfaces, probably because they arevulnerable to pollution. This may make the

population of Coptothyrus adamsiuseful as ameasure of environmental conditions aroundan oil terminal being built in Russia on theshore of the Sea of Japan.


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Order Orthida

Shells of orthids are typically strophic(having an elongated hinge line)

The shape is generally semi- or sub-circularin outline.

Valve convexity is usually unequallybiconvex with a slightly inflated pediclevalve.

Orthids are typically covered with finediverging radial costae.


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Orthida

Platystrophia

Late Ordovician


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Strophomenida

The Strophomenida were the largest orderof brachiopods, with about 400 genera.

They were also by far the mostmorphologically diverse group, and included

some very unusual forms, as well as more"normal" forms.

Strophomenids first appeared in theOrdovician and persisted until the middle

Jurassic.


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Strophomenida Strophomenids may be identified by their supra-

apically located pedicle foramen, at least in youngshells.

Adult strophomenids lacked an open pedicle foramen,and usually lived attached to the bottom or to otherobjects by the pedicle valve.

One group of strophomenids, theproductids, were

characterized by very long spines extending from theshell. These are thought to have functioned as a sort of

"snowshoe," supporting and stabilizing the organismon soft muds.

Other strophomenids were attached to the bottom by

a cone-shaped pedicle valve, with the upper valvecovering the cone like a pot lid. The unusual brachiopod Prorichthofeniafrom the

Permian of Texas is one of these unusual conicalforms.
http://www.ucmp.berkeley.edu/brachiopoda/prorichthofenia.gifhttp://www.ucmp.berkeley.edu/brachiopoda/prorichthofenia.gif


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Pror ichthofenia Rugose Coral

This shape is convergent on that of other attachedorganisms, such as Paleozoic rugose corals and livingscleractinian corals, and it is though that, like corals,some strophomenids bore photosynthetic algae insidetheir tissues that helped to supply them with food.
http://www.ucmp.berkeley.edu/brachiopoda/prorichthofenia.gifhttp://www.ucmp.berkeley.edu/brachiopoda/prorichthofenia.gif


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Order Pentamerida

Shells of pentamerids are generallybiconvex.

Pentamerids are typically ovoid, circular,triangular, or more commonly pentameral inoutline.

The interior of the shell is typified by aprominent medial ridge or septa in thebrachial and/or pedicle valve.

Also diagnostic of pentamerids is a spoonshaped structure modified from plates in the

pedicle valve called the spondylium whichsupported muscle tissues


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Pentamerida


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Pentamerids grew to sizes of over 10 cm, and they

represent one of the largest types of dwellers withinSilurian reefs. A thickened beak area served as aweight to stabilize the shell in the sediment, andthere was no fixed attachment. Pentameridbrachiopods often lived as clumps of individuals.


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Rhynchonellida

Rhynchonellids look a bit like little nuts. Their hinges come to a point, a condition

paleontologists call non-strophic.

They are often ridged.

The commisure, the line between the twovalves or shells, is zig-zagged, as can beseen in the somewhat unusual asymmetricrhynchonellid Rhactorhynchia.

The earliest fossil rhynchonellids are from

the Ordovician period. During the Mesozoic Era, rhynchonellids

were the most abundant brachiopods.

A few species still exist today.
http://www.ucmp.berkeley.edu/brachiopoda/rhactorhynchia.jpghttp://www.ucmp.berkeley.edu/brachiopoda/rhactorhynchia.jpg


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Rhynchonellida

Rhactorhynchia
http://www.ucmp.berkeley.edu/brachiopoda/rhactorhynchia.jpghttp://www.ucmp.berkeley.edu/brachiopoda/rhactorhynchia.jpg


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Spiriferida Spiriferids are easy to identify.

They often have an extended hingeline so wide they look winged.

Other prominent characters are thefold and the sulcus that you can

see. The feature that gives the spiriferids

their name ("spiral-bearers") is theinternal support for the lophophore;this support, which is oftenpreserved in fossils, is a thin stripof calcareous material that istypically coiled tightly within theshell.
http://www.ucmp.berkeley.edu/glossary/gloss7/lophophore.htmlhttp://www.ucmp.berkeley.edu/glossary/gloss7/lophophore.html


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Fossil spiriferids first appear in theOrdovician period.

They were extremely diverse during theDevonian period and later went extinctduring the Jurassic period.

Some fossil brachiopods make spectacular

finds, replaced by pyrite


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Terebratulida

Most living brachiopod, arerepresentative of the group;terebratulids.

Terebratulids first appear as fossils inthe Devonian.

Terebratulids are responsible for thename of "lamp shells" forbrachiopods; their shells resembleancient oil lamps, with the pedicleforamen resembling a wick.


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Terebratulida

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