4Evolution Mollusks Sipuncula are the sister taxon of Mollusca (2) the two aplacophoran taxa,Neomeniomorpha and Chaetodermomorpha, are monophyletic with a commonneomenioid-like ancestor, and of the two taxa,Chaetodermomorpha are more divided, Aplacophora and Polyplacophora are sister taxa and form a clade, AculiferaAculifera are the sister group of the remainingextant mollusks, ConchiferaAplacophora are progenetic Aculifera.
5Evolution (Cont.) Annelids Some of the earliest animals burrowed in the soft sea-floor mud.They were segmented worms, as shown by fossil worm tunnelling tracks, dated to Ediacaran times.Descendants of these earliest worms can be found today living in the muddy substrate of quiet bays -
7Symmetry of Body Mollusks The body symmetry of Mollusca and Annelida is a figure of the same bilateral appearance when it is cut in half longitudinally.The body symmetry of Mollusca and Annelida when cut in half is the same mirror image of the other half.The body symmetry of Mollusca and Annelida is typically a short soft body with a very small coelom .
9Body cavity for Annelids This is the coelom, found in Mollusks and Annelids
10Structural Support Mollusks The basic body structure, consisting of a foot, visceral mass, and mantle, is similar in most mollusks.The foot is located below the visceral mass.The external shell consists of three layers. The thin outer layer, called the periostracum, is made of a tough hornlike material and serves to protect the lower layers.
11Structural Support (Cont.) AnnelidsElongate body usually round.For polychaetes and clitellidae, head has prostomium and peristomium (which usually has the mouth); anus is in pygidium.Trunk segmentation reflected in external annuli, internally by series of coelomic compartments separated by septae (mostly in oligochaetes, less so in others).Some are homonomous, with body segments mostly similar, others are heterononmous, with specialized segments.
12Nutrition and Digestion MollusksProcess and Structuresmacrophagy (predation and herbivory) – use either radula to scrape food or harpoon-like poisoned teethmicrophagy (filter feeding)- modifications of gills, which are covered by sheets of mucus which trap food, then are passed into the stomachA Mollusk has food brought in through a siphon system and then to its mouth. It then goes to a digestive gland and to its intestine. Wastes leave via the anus.NutritionThey eat plants, animals, and dead thingsMany cephalopods eat fishBivalves usually eat phytoplankton
14Nutrition and Digestion (Cont.) AnnelidsStructures and ProcessThey have either a straight or coiled gut.Some have no known digestive system.Some use a raptorial method by capturing and swallowing preyDeposit feeders ingest sand/dirt and extract nutrients from it.Suspension feeders use tentacles or mucus webs to filter nutrients from fluid environment.The sediment is ingested and any digestible organic material is assimilated as it passes through the alimentary canalNutritionMany eat sedimentUses non-selective deposit feeding
16Transportation and Circulation MollusksStructures3-chambered heartCirculatory system (except for cephalopods) is openCephalopods have a closed circulatory system and an extra pair of powerful gill hearts.Uses one large foot muscleProcessBlood from the paired gills enters the atria, leaves the ventricle.the artery from the ventricle opens and releases blood into tissue-bathing sinuses, eventually draining back into gills.
18Transportation and circulation (Cont.) AnnelidsStructuresWell-developed and closed in most annelidsSome have some vessels capable of functioning as "hearts".Some have no mesodermally derived blood vessels, but have blood "channels”The nervous system has a solid, ventral nerve cord from which lateral nerves arise in each segment. This controls movement.ProcessCarries blood from the dorsal to the ventral vessel in the head region.Every segment has an autonomy; however, they unite to perform as a single body for functions such as locomotion
20Respiration Mollusks Annelids Structures and Process Molluscs use true gills, with extensive capillary network and countercurrent flow for gas exchange.A Mollusk has tubes called siphons that bring water in and out of their bodies so that they can get oxygen and give off carbon dioxide. They have gills that help with this.AnnelidsStructures and processRespiration may occur through gillsIn other types, the cilia are the most likely site for respiration.Many also respire through the skin
21Annelid Reproduction Annelids may reproduce asexually or sexually. Most annelids can regenerate in many different ways. Certain species, such as Dodecaceria can regenerate an entire individual from a single segment.Asexual reproduction is usually by fragmentation.Most polychaetes, chiurans, and pogonophorans are gonochoristic.Gonochorism is the differentiation of male and females of a species by their reproductive organs. For example, most mammals are gonochoristic
23Mollusk reproductionMollusks come in hermaphroditic and gonochoristic forms. Gastropods can be either.When a Gastropod is Hermaphroditic, they usually have only one kind of gonad, and are protandrous.Protandrous means that the male sex organs are produced before female organs.Most bivalves are gonochoristic; though a few are hermaphroditic, like oysters.
25Nervous systemIn mollusks, the brain and one or two large ventral nerve cords, are connected by commissures (which is a ladder form).Cephalopods can be said to have a true brain, capable of learning and complex behavior.
26Nervous system (cont.)All annelids show a degree of cephalization. A well-developed circumesophageal ganglion in the head region leads to paired ventral nerves with ganglia in each segment controlling the activity of that segment via lateral nerves and coordinating with other segments. Many use giant axons (e.g., Lumbricus) for escape reactions.
27Unique characteristics of Mollusks Mollusks have a soft body that is protected by a hard shellMollusks are bilaterally symmetrical.Mollusks are capable of living on either land or in water.They have lungs that can function in both water and air.
28Unique characteristics of Annelids Like mollusks, annelids are bilaterally symmetrical.The Annelid moves by alternating circular and longitudinal muscles.The circular muscles surround the body wall and contractions cause the body to become long and thin.The longitudinal muscles run the length of the body, and cause the body to become shorter and fatter.The body cavity is a true coelom, divided by internal septa.Body possesses 3 separate sections, a prosomium, a trunk and a pygidium.They live in most environments.
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