Chapter 31 Protostome Animals

31.1 what is protostome

• Protostome means (first mouth) the first embryonic development opening which is the blastopore becomes the mouth, compared to the deuterostomes

• They’re also bilateral symmetry and have three germ layers making them triploblastic

• Protostomes are monophyletic group broken down into two major lineage lophotrochozoan and Ectozoan

• Protostomes phyla are considered Arthropoda (insects, chelicerates, crustaceans, myriapods), Nematoda, Mollusca, Platyhelminthes, and Annelida which make up 90% of the animal species with insects being 70% alone

• Protostome started in water and transition and adapted to land multiple times coevolving with adaption radiation

• Protostome like mollusks and arthropods have compartmentalized and flexible body parts meaning their bodies are divided into regions with distant function, allowing body regions to evolve independently

31.2 what is lophotrochozoan

• Lophophores make up 13 phyla such as mollusks, rotifers, flatworm, annelids that are a monophyletic group within protostome

• Rotifers are tiny suspension feeders with a ciliated corona,

• Flatworms are acoelomate with various feeding methods including parasitism, without specialized structures for gas exchange and requires moist environments/habitats for gas exchange to occur

  • Turbellaria which are mostly free living found in freshwater or marine environments with blind digestive tract and a tubelike pharynx

  • Cestoda which are endoparasitic tapeworms that absorb nutrients their body wall, usually caught by humans with consumption of raw meat

  • Trematoda are endoparasitic or ectoparasitic flukes that feeds on their host fluids and tissue. Also causing diseases like schistosomiasis in humans

  • Monogenea are tiny ectoparasitic that usually feeds on the skin or gills of fish

• Annelids are segmented worms which distinguish them from flatworms with diverse feeding strategies and movement adaptation. Most annelids contain a coelom and have a fully developed digestive tract with a mouth and anus

  • Polychaeta are diverse marine worms with large parapodia and chaeta for the more mobile species and reduce parapodia and chaeta for sedentary species

  • Oligochaetes are earthworms and other oligochaetes that play an important role in soil aeration and organic matter contribution

  • Hirudinea are half leeches being ectoparasites and the other half are predators or scavengers

• Mollusks play an important role in the freshwater, marine, and terrestrial environment with over 85,000 species, only second to arthropods in diversity. They have a body plan with three main components which are the foot (used for movement), visceral mass (radula which is a feeding structure and gills for gas exchange), and mantle (forms shells, lungs, or siphon for water flow and jet propulsion)

  • Polypalcophora (chitons) have 8 dorsal plates, are grazing herbivores, and move by creeping

  • Bivalvia (clams, mussels, scallops, oysters) are suspension feeders using gills with two-part shells, while others burrow or use jet propulsion

  • Gastropoda (snails, slugs, nudibranchs) have diverse feeding strategies using radula, herbivores, detritivores, and predator while moving by creeping or swimming

  • Cephalopoda (squid, octopuses, nautiluses, cuttle fish) are intelligent predators with modified feet as arms and tenacles and they use jet propulsion or crawling to move

• Lophophores function in suspension feeding in adults

• Trochophore larvae swim and may feed using cilia to do so

• spiral cleavage is unique to lophotrochozoans compared to radial cleavage, for comparison in other animals

• Snails and Chitons use grasping and moving, bivalves use digging appendage, and cephalopods use tenacles

31.3 what is Ectozoan

• Ecdysozan grow by molting, which is shedding the old cuticle, expanding the body with fluid, and forming a new larger cuticle or exoskeleton. Their stiff bodies provide them with muscle attachment and protection but it leaves them vulnerable when they’re molting

• Ecdysoza phyla make up of

Dynamic Study Module Answer

• In bivalves such as clams, the foot is modified as a digging appendage.

• The foot of cephalopods such as squid and octopuses is modified as arms and tentacles: long, muscular extensions with suckers that aid in highly nimble movement and prey capture.

• In sea butterflies (swimming sea snails), the foot forms winglike flaps that enable swimming.

• In most terrestrial snails, the mantle forms an internal lung.

• In bivalves, the mantle is lined with muscle and forms tubes called siphons.

• In cephalopods, the mantle forms a siphon that functions in jet propulsion.

• In incomplete metamorphosis (a form of direct development), juveniles called nymphs look like smaller versions of the adults.

• In complete metamorphosis (a form of indirect development), there is a distinct larval stage; larva can be referred to as grubs, caterpillars, and maggots.

• In insects, complete metamorphosis is 10 times more likely than incomplete. The significance of this is likely due to selective advantage related to feeding behaviors. Because juveniles like maggots, caterpillars, or grubs have different feeding behaviors than their adult forms—flies, moths, and beetles—they do not compete for resources.

• An adaptation that is central to the water-to-land transition made by animals is that insects can close their respiratory passages. Insects evolved a waxy layer to minimize water loss from the body surface, with openings to respiratory passages that can be closed if the environment dries.

• A group that includes trochophore larvae, molting, and repeating segments includes both lophotrochozoans and ecdysozoans. Trochophores are a type of larvae common to marine mollusks, marine annelids, and several other phyla in the Lophotrochozoa. Arthropods have a highly reduced coelom but, like mollusks, possess an extensive body cavity called a hemocoel. All ecdysozoans grow intermittently by molting—that is, by shedding an exoskeleton or external covering. Repeating segments are found in the annelids.

• One of the reasons for protostome success is the fact that the majority of animals have wings. There are more species of animals on the planet today with insect wings than without. According to data in the fossil record, insects were also the first animals that had wings and could fly.

• Wings did not evolve from the jointed limbs of arthropods. Rather, wings occur as unjointed extensions of the dorsal cuticle on the second and third segments of the insect thorax—in addition to the jointed legs on the ventral side.

• The characteristics that have traditionally been used to distinguish a protostome from a deuterostome are the development of the first initial pore and its fate as a mouth rather than an anus; body cavities arise out of mesodermal cells and not out of mesodermal pockets.

• If tetrapods had arisen 50 million years before they actually did, protostome groups might have exhibited less diversity in feeding structures and reproductive strategies because they would have faced competition from tetrapods.

• The bivalve shell is an adaptation that reduces predation

• The 13 phyla of protostome subgroup Lophotrochozoa includes rotifers, mollusks, annelids, and platyhelminthes.