Chapter 5

Marine Protozoans and Invertebrates

Marine Protozoans and Invertebrates

The nonphotosynthetic protistans and the invertebrates in the world ocean dominate most marine communities and monopolize energy flow within them.

Copyright © 2004 Jones and Bartlett Publishers

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Table 5.1 continued

Animal Beginnings: The Protozoans

•Kingdom Protista is an artificial catch-all category for many fundamentally different taxa clearly lacking a common ancestral form, which just happen to be unicellular and heterotrophic.

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Animal Beginnings: The Protozoans

•Fig. 5.2, A planktonic foraminiferan, Globigerina. (a) Drawing of an intact animal emphasizing extended pseudopodia. From Brady 1884. (b) Photograph of Globigerina test.

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Animal Beginnings: The Protozoans• 5.3 The pattern of ciliary movement appearing as waves of alternating

recovery and power strokes sweeping over the cell surface.

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Defining Animals

•Members of kingdom Animalia are typically distinguished from the Protista by

• the presence of contractile muscles,

• signal-conducting neurons,

• and multicellular bodies

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Defining Animals

•Sponges are loose federations of cells that interact sufficiently to allow more efficient handling of food, protection, and other sophisticated survival tasks.

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Defining Animals

•Fig. 5.6 A group of marine finger sponges and several of the specialized cell types that make up the sponge wall.

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Radial Symmetry

•Cnidarians are a large, diverse, and well-known

assemblage of relatively primitive yet versatile

marine invertebrates, including jellyfishes, sea

anemones, corals, and hydroids.

•They are distinguished by their characteristic

nematocyst containing stinging cells (cnidocytes),

some of which are painful and even deadly to

humans.

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Radial Symmetry

•Fig. 5.9 (Top) Undischarged nematocyst; (Bottom) Discharged penetrant nematocyst.

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Fig. 5.8 Planes of symmetry in a radially symmetrical animal.

Marine Acoelomates and Pseudocoelomates

•All remaining animal phyla, except the echinoderms, are bilaterally symmetric and possess an anterior cephalization.

•The most primitive of these are small often-overlooked inhabitants of soft sediments that either lack an internal body cavity (the acoelomates) or have one that is very poorly developed (the pseudocoelomates).

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Marine Acoelomates and Pseudocoelomates

•Fig. 5.14 Plane of symmetry in a bilaterally symmetrical animal.

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Marine Acoelomates and Pseudocoelomates

•Fig. 5.15 Some simple wormlike animal phyla: (a) flatworm, (b) nemertean, (c) gastrotrich, (d) kinorhynch, and (e) nematode.

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Marine Coelomates•Higher animals possess a true coelom, an embryonic development that separates the digestive tract from the body wall, and are separated into two fundamentally different lineages, – the protostomes – and the deuterostomes,

•which are distinguished by a number of developmental factors.

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Marine Coelomates

•Fig. 5.17 Comparison of some early developmental features of protostomes and deuterostomes.

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Marine Coelomates

•Protostomes– The lophophorate phyla, Bryozoa, Phoronida,

and Brachiopoda, all possess a crown of ciliated feeding tentacles, or lophophore.

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Marine Coelomates

•Protostomes—Mollusca– The snails, clams, mussels, oysters,

scallops, octopus, and squid of phylum Mollusca are among the most abundant, easily observable, and best known marine invertebrates.

– The various groups of mollusks are distinguished by their type, number, and location of shell elements.

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Marine Coelomates

•Protostomes

•Mollusca

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Fig. 5.20 Representatives of the common classes of mollusks: (a) Amphineura, (b) Bivalvia, (c) Gastropoda, (d) Scaphopoda, and (e) Cephalopoda.

Marine Coelomates

•Protostomes—Annelida– The 7800 species of polychaete annelids feed

in an impressive variety of ways, including • ingesting organicrich sediments, • preying on other animals,• and using a complex system of tentacles to

function as filter or suspension feeders.

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Marine Coelomates

•Protostomes

•Annelida

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Fig. 5.28 The filtering structures of a tube-dwelling polychaete worm. (Courtesy of T. Phillipp)

Marine Coelomates•Protostomes—Arthropoda– About two thirds of all known organisms are

segmented arthropods, which possess a characteristic exoskeleton of chitin that is molted periodically during growth.

– Many larval and adult arthropods are tiny and important members of the zooplankton, whereas others, such as lobsters and horseshoe crabs, can grow to a weight of several kilograms.

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Marine Coelomates

•Protostomes•Arthropoda

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Fig. 5.32 A variety of marine crustaceans: (a) mysid, (b) cladoceran, (c) euphausiid, (d) copepod, (e) amphipod, (f) crab, and (g) barnacle.

Marine Coelomates•Deuterostomes Echinodermata– Echinoderms, the familiar sea stars, sea

urchins, sand dollars, and sea cucumbers, possess

• a body plan that is secondarily radial, • a unique water-vascular system (which

hydraulically operates numerous tube feet),• and the ability to regenerate significant

portions of their anatomy that have been lost to predators or injury.

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Marine Coelomates

•Deuterostomes•Echinodermata

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Fig. 5.37 Representatives of the six living echinoderm classes: (a) Echinoidea, (b) Asteroidea, (c) Ophiuroidea (d) Holothuroidea, (e) Crinoidea, and (f) Concentricycloidea.

Marine Coelomates•Deuterostomes—Chordata– All chordates, including the vertebrate

subphylum, possess a dorsal hollow nerve cord, a longitudinal stiffening notochord of cartilage, pharyngeal gill slits, and a postanal tail during at least some portion of their life.

– Primitive nonvertebrate chordates are small filter-feeding members of most shorelines and the open sea.

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Marine Coelomates

•Deuterostomes•Chordata

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Fig. 5.38 Nearly transparent sea squirts, each with a small incurrent and a large excurrent opening for circulating water through its body cavity. (Courtesy of T. Phillipp)