Chapter 12: Sponges and Placozoans

Question-and-answer flashcards covering the evolution, structure, reproduction, taxonomy, and unique traits of sponges (Phylum Porifera) and Placozoa.

What major advantage does multicellularity confer in terms of surface area to volume ratio?

It lowers the surface area to volume ratio, allowing individual cells to be more efficient.

Which group is considered the first branch of metazoans?

Sponges (Phylum Porifera).

To which protistan group are animals (including sponges) sister?

Choanoflagellates.

What specialized flagellated cell is shared by choanoflagellates and sponges and is important for filter feeding?

The choanocyte (collar cell).

What is one piece of evidence AGAINST a colonial choanoflagellate-like ancestor for all metazoans?

Choanocytes are present only in adult sponges, not in their larvae or in other animal phyla.

What does the Latin name 'Porifera' literally mean?

'Pore-bearing.'

How large can sponges range in size?

From about 2 mm to 2 m across.

Name three general characteristics of sponges regarding symmetry, tissues, and digestion.

Radial symmetry, no true tissues or organs, and intracellular digestion.

What are spicules and spongin primarily used for in sponges?

They provide structural support.

Through which cellular processes do sponges ingest large versus small food particles?

Phagocytosis for larger particles and pinocytosis for dissolved proteins.

Which sponge class possesses six-rayed siliceous spicules?

Class Hexactinellida.

What are the three main water-flow openings in a sponge from entry to exit?

Ostia → Spongocoel → Osculum.

Which sponge cell type functions most like an epithelium and lines the exterior?

Pinacocytes.

What do archaeocytes do inside the mesohyl?

They are amoeboid cells that can differentiate into sclerocytes (spicules), spongocytes (spongin), collencytes or lophocytes (collagen).

Which contractile sponge cells regulate water flow by constricting pores?

Myocytes.

List the three basic sponge body plans in increasing order of complexity.

Asconoid → Syconoid → Leuconoid.

What larval stage is typical of sexually reproducing sponges?

The parenchymula, a free-swimming larva.

How do gemmules help sponges reproduce?

They are internal asexual buds that can survive harsh conditions and regenerate a new sponge.

What unusual embryonic process occurs in Calcarea and some Demospongiae?

Inversion, where the blastula turns inside-out to place flagellated cells on the exterior.

State one advantage and one disadvantage of asexual reproduction in sponges.

Advantage: No dilution of gene pool (clonal). Disadvantage: Limited dispersal and accumulation of deleterious mutations (Muller’s ratchet).

State one advantage and one disadvantage of sexual reproduction in sponges.

Advantage: Generates genetic variation for natural selection. Disadvantage: Not all individuals are reproductive and many gametes are wasted.

Which sponge class is characterized by calcium carbonate spicules and can possess any of the three body forms?

Class Calcarea.

What structural feature distinguishes glass sponges (Hexactinellida) at the cellular level?

A syncytial tissue organization with many nuclei in a continuous cytoplasm.

Which sponge class includes about 95 % of all sponge species and the only freshwater representatives?

Class Demospongiae.

What is the only described species in Phylum Placozoa?

Trichoplax adhaerens.

Describe the feeding strategy of Trichoplax adhaerens.

It glides over food particles, secretes digestive enzymes externally, and absorbs the digested nutrients.

How does Trichoplax reproduce asexually?

By budding and binary fission.

Why is the discovery of eggs in captive Placozoa significant?

It suggests that the group is capable of sexual reproduction as well as asexual reproduction.

Define 'somatic embryogenesis' in the context of sponge biology.

Regeneration of a whole sponge from somatic cells released during asexual budding.

What is Muller’s ratchet and how does it relate to asexual lineages?

The irreversible accumulation of deleterious mutations in asexual populations, potentially reducing fitness over time.

Which two collagen-secreting cell types are found in the sponge mesohyl?

Collencytes and lophocytes.

What term describes sponges that possess both male and female gametes within the same individual?

Monoecious.

Which sponge body plan contains the greatest internal surface area for choanocytes and is found in the most diverse taxa?

Leuconoid.