Sponge Diagram Unlabeled – Whole Sponge and Body Wall

All 11 parts on the diagram

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The sponge 4

Osculum The large opening where water leaves after passing through the central cavity. It is the way out, not a mouth.
Ostia (pores) The intake pores, where water enters the sponge. They lead through the wall to the cavity inside.
Spongocoel The central cavity of the sponge. In a simple sponge like this one it is lined with collar cells.
Spicules Stiff rods and spikes that make up the skeleton. Long straight ones stand round the osculum, and three-rayed ones lie in the wall.

The body wall 7

Pinacocytes Thin, flat cells packed tightly together in a single layer. They are the skin of the sponge.
Porocyte A cell shaped like a tube. Water passes through its middle, and the cell can tighten to slow the flow.
Mesohyl A jelly-like layer between the outer cells and the collar cells. Spicules and wandering cells lie in it.
Archaeocytes Cells that move about like an amoeba. They carry food to the other cells and can change into any other kind of sponge cell.
Choanocytes (collar cells) Collar cells whose beating flagella drive the water through the sponge. They catch the food it carries.
Collar A ring of tiny finger-like threads, the microvilli. It sits round the base of the flagellum. Food is caught here.
Flagellum A single long whip that rises from the middle of the collar. Its beating pulls water past the cell.

How this list was compiled: Every name checked on 2026-09-30 in two sources. Animal Diversity Web, University of Michigan, Porifera: pores (ostia), osculum, spongocoel, choanocytes (collar cells), mesohyl, spicules, and the simple asconoid sponge, https://animaldiversity.org/accounts/Porifera/. University of California Museum of Paleontology, Porifera, the cells: pinacocytes, choanocytes with their collar and flagellum, mesohyl, archaeocytes and porocytes, https://ucmp.berkeley.edu/porifera/pororg.html. Wikipedia, Sponge, Choanocyte, Pinacocyte, Mesohyl and Osculum, for a second reading of each name, https://en.wikipedia.org/wiki/Sponge. H. S. Pratt, A Course in Invertebrate Zoology (1902, public domain), for the needle-like spicules round the osculum and the three-rayed ones in the wall, https://archive.org/details/courseininverteb00prat. NOAA National Ocean Service, What is a sponge?, https://oceanservice.noaa.gov/facts/sponge.html. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work

How it works

An unlabeled diagram of the sponge, the water animal: a vase-shaped sponge with its right half cut away, and under it a strip of the body wall enlarged to show the cells. Eleven parts wait for a name.

Read the full guide

Label a sponge, fill in the blank: the word list

Four names go on the whole sponge: osculum, ostia, spongocoel and spicules. Seven go on the body wall: pinacocytes, porocyte, mesohyl, archaeocytes, choanocytes, collar and flagellum.

Two names on one cell

The large cell at the right of the wall strip is a single collar cell, drawn bigger than the rest. The ring of upright threads on top of it is the collar, and the one long wavy thread rising from the middle is the flagellum. The tube lying across the wall is the porocyte, and the two star-shaped cells in the middle band are the archaeocytes.

The arrows show the path of the water. None of them takes a name.
Both sponge unlabeled diagrams print on the same sheet of paper, the whole animal above its wall.
A textbook may print pores for ostia and collar cells for choanocytes. The list under the diagram gives both.

Questions and answers

What is the difference between ostia and the osculum?

Ostia are the many small pores in the wall, where water enters. The osculum is the one large opening at the top, where the water leaves. On the sheet the ostia are the holes dotted over the uncut left half of the sponge.

Where are the choanocytes on a sponge diagram?

Lining the central cavity. On the wall strip they are the row of cells down the right side, each with a wavy thread. The flat cells down the left side, facing the water, are the pinacocytes.

Where is the mesohyl on a sponge diagram?

Between the two layers of cells: the wide plain band in the middle of the wall strip, a jelly-like layer in which the spicules and the archaeocytes lie. It is the one part with no line, so the name goes on the band itself.

Is there a sponge diagram unlabeled PDF?

Yes. Press Print this diagram and choose Save as PDF in the print window. Print the answer key saves the same two drawings with every name written in.