Chapter 14 Key Concepts

Protists are neither animals nor plants; they are free- living, one-celled organisms.
Amoeboid forms include naked amoebas, Foraminifera with calcium carbonate skeletons, and Radiolaria with silica skeletons.
Ciliates are elongate, and their outer body is covered with cilia, which are used for locomotion.
Flagellates also are elongate, but they are propelled by one or a few flagellae instead of by many cilia.
Members of the phylum Porifera possess structures consisting of groups of flagellated cells, which move water and food particles into open chambers.
The cnidarians are all built around a common, cup-shaped polyp body plan, which has a ring of tentacles and a digestive tract with one opening.
Cnidarians are divided into Hydrozoa, Scyphozoa (true jellyfish), and Anthozoa (corals and anemones).
Flatworms are truly bilaterally symmetrical, with anterior-posterior differentiation. They also have distinct organs.
Ribbon worms have a proboscis and a complete gut and are mobile carnivores that burrow through the sand.
Many nematodes live free in all marine environments, using longitudinal muscles that work antagonistically against a fluid-filled body with a rigid wall. Free-living nematodes may be carnivorous or plant eating; some consume organic matter from sediment.
Annelids are worms divided into segments, with a tubular gut from mouth to anus and three distinct embryonic tissue layers.
The annelids are divided into the Polychaeta, Oligochaeta, and Hirudinea.
Annelid locomotion depends on layers of longitudinal and circular muscles working against a rigid fluid, compartmentalized among many segments.
Annelids adopt a wide range of living positions and include free burrowers, infaunal tube dwellers, and epifaunal tube constructors. They may be carnivores, deposit feeders, and suspension feeders.
Peanut worms live in burrows in soft sediment and in rock crevices. They gather food by means of an introvert that has branched tentacles.
The members of the phylum Pogonophora are generally deep-sea species that lack a gut and depend on symbiotic bacteria.
Mollusks have a head-foot complex, a mantle that usually secretes a calcium carbonate shell, and a gill, suspended in a mantle cavity, which is used for respiration and commonly for suspension feeding.
Members of the class Bivalvia are distinguished by two symmetrical shells connected in a hinge region. The mantle secretes the shell, and a gill, or ctenidium, usually helps in respiration and collects phytoplankton on ciliated tracts.
Members of the class Gastropoda have a flattened foot, usually a cap-shaped or coiled shell, and a mouth apparatus known as a radula. They are characterized by a twisting of the body, known as torsion. Many species lack a shell.
Members of the class Polyplacophora (chitons) have a flattened foot, a radula, and eight dorsal articulated plates.
Members of the class Monoplacophora include simple animals with a cap-shaped shell, posterior gill, flattened foot, and radula.
Members of the class Cephalopoda are distinguished by elaborate nervous and muscular coordination, the presence of grasping arms, and a carnivorous feeding mode.
Members of the class Scaphopoda (tusk shells) have an elongate conical shell and live buried within the sediment, feeding on foraminiferans and other small animals.
Arthropods are characterized by an external cuticle of chitin as well as by segmentation and jointed appendages.
The Trilobita (subphylum Trilobitomorpha) are an extinct class whose members had relatively unspecialized appendages and a compact body.
The subphylum Chelicerata includes the horseshoe crabs, spiders, terrestrial scorpions, and pycnogonids (sea spiders). These animals are characterized by a first pair of movable claws and a division of the body into two general sections.
The subphylum Crustacea is the largest marine arthropod group. Its members are characterized by a head with two pairs of antennae, three pairs of mouthpart appendages, and a trunk with several specialized appendages. The trunk is sometimes divided into a thorax and a posterior abdomen.
The lophophorate phyla include the Bryozoa, Brachiopoda, and Phoronida. They are united by the presence of a looped feeding and respiring structure known as a lophophore.
Bryozoans are abundant on hard surfaces and consist of colonies of small (<1 mm in width) individuals known as zooids.
Bryozoan colonies can occur as sheets, erect colonies, or units connected by runners, known as stolons.
Brachiopods have two shells and use a pedicle to attach to the bottom; a lophophore allows them to feed on suspended matter.
Phoronids are wormlike, with a lophophore that protrudes above the substratum.
Echinoderms are exclusively marine and have an outer skin that encloses a skeleton of interlocking ossicles.
Both locomotion and feeding in echinoderms are based on the water vascular system, which uses water pressure to operate many tube feet.
Sea stars (Asteroidea) are usually carnivorous, and many feed by extruding the stomach and digesting prey, mostly outside the body.
Echinoids (Echinoidea) are usually covered with spines and may live on the surface, using the teeth of a structure called an Aristotle’s lantern to scrape algae, or burrowing in the sand, feeding on sediment or suspended matter.
Sea lilies and feather stars (Class Crinoidea) are characterized by a cup-shaped body, with upward- reaching arms that catch zooplankton on specialized tube feet.
Sea cucumbers (Class Holothuroidea) are tubular and have a crown of tentacles, which either feed on sediment or are directed upward to feed on zooplankton.
Brittle stars and basket stars have a central disk and distinct, separate, flexible arms that move the animal along the bottom without the use of tube feet.
Sea squirts are barrel-shaped animals that filter water through a mucus sheet. A tadpole-shaped larva relates them to the vertebrates.