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BIOLOGY 03050, INVERTEBRATE ZOOLOGY WEEK 4: FORMS OF LIFE; SPONGES

Dr. W. Crone (303 FTZ, 270-7439, cronewil@hvcc.edu, www.hvcc.edu/academ/faculty/crone/index.html) 9/21/98

Text (7th ed.): Ch. 1, pp. 18-20; Ch. 2, p. 26; Ch. 6, p. 139; Ch. 15, pp. 351-360; Ch. 17

possible web site: http://www.ucmp.berkeley.edu/porifera/porifera.html (sponges)

OVERVIEW OF OTHER TYPES OF LIVING ORGANISMS:

There are many more forms of living organisms than animals or protists, and so briefly:

eukaryotic cells:

those with membrane-bound nuclei, organelles; in animals, plants, fungi

animal:

multicellular organism without cell walls that eats for a living

plant:

multicellular organism with cell walls that synthesizes its own food

fungus:

multicellular organism with cell walls that absorbs food for a living

 

prokaryotic cells:

those without membrane bound organelles and nuclei (with cell walls)

archaebacteria:

bacteria-appearing organisms that live in extremes, e.g., hot, cold, salty

bacteria:

simple, incredibly common organisms, main decomposers of the world (includes cyanobacteria or blue-green"algae")

 

Today, there is a realization that there are three major domains of life: Archaea, Bacteria, and Eukarya (Eucarya).

OVERVIEW OF INVERTEBRATE BODY FORMS:

Unicellular:

the animal-like protists

Multicellular cell aggregates without germ layers:

sponges

(germ layer: ectoderm, mesoderm, endoderm, from which tissues and organs arise)

Multicellular, two main germ layers (and jelly-like mesoglea):

cnidarians and comb jellies

Multicellular, three main germ layers:

no internal body cavity:

flatworms

pseudocoelom (false internal body cavity):

roundworms and rotifers

eucoelom (true body cavity):

other invertebrate phyla; chordates

  1. Phylum Porifera ("pore bearing") (5,000 species): the sponges. These animals have neither true tissues, true organs, nor (often) true symmetry. They are stationary as adults, and consist of flagellate-lined pores for feeding. Thin pinacocytes or covering cells line the sponge. In primitive sponges, porocytes or pore cells make up the ostia (pores). In other sponges, contractile pinacocytes (myocytes) surround the ostia and control their opening size. Choanocytes or collar cells with the flagella create a water current in the sponge. The collar filters catch food particles as they flow past. Water flows through these pores and then out a main hole or osculum. The chambers of the sponge can run from simple (asconoid), intermediate (synconoid), to complex (leuconoid), depending on the folding and branching of the chambers lined by the collar cells. A middle gelatinous layer or mesohyl has wandering archaeocytes or amoeboid cells that assist in food digestion (along with the collar cells; hence, digestion is intracellular) and distribution. Some archaeocytes may secrete supportive structures found in sponges, e.g., sharp spicules in the glass sponges or spongin in the horn ("bath") sponges. As a result of all this, a sponge seems more like a collection of different cell types working together rather than a fully integrated, complex animal. Sponges may reproduce asexually by forming buds or sexually by gametes. A sexually produced free-swimming larva swims before settling down to adulthood.

 

|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|

 

Please send comments and questions to: cronewil@hvcc.edu

 

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