WHY animal and not plant

[desiredbard]

Hi There

Recently got this great fishindentificatiuon book that makes reading as well, for brittish waters.
However found out that Sponges, and the sea-pens are not plants but animals

Now I know that about corrals, loads of little critters in one corral all independent....
But this does not seem to be the case for sponges and the seapens.

Why are they classified as Animal, (sponges were clasified as plant begore 1960 I think)

Same goes for Anemones, although not all anemone's are static....I mean a Venus Flytrap (meat Eating Plant) is still a plant as well is it not?

Oh and am not looking for a laymans term only explanation here, bit more indepth please, there must be a bored marine biologist around here somewhere

 

[archman]

The defining feature of all *plants* is light-based autotrophy... they photosynthesize. Narrower definitions for *plant* may include:
-multicellular adult form
-vascular tissues (xylem, phloem)
-"true" roots, stems, leaves
-chlorophyll type-b pigments

Sponges have been classified as animals for over 150 years, if I recall correctly.

Carnivorous plants still derive most of their nutrition from photosynthesis. They tend to live in areas that are nutrient-poor; eating bugs is the equivalent of getting a vitamin/mineral shot.

 

[Mako Mark]

sponges have a digestive system, plants dont as far as I can recall. There is also the photosynthisis thing although not all plants do that.

 

[archman]

sponges have a digestive system, plants dont as far as I can recall. There is also the photosynthisis thing although not all plants do that.

Mark, sponges not only lack a digestive system, but any type of organ system. They don't even have basic tissues, just some crummy meso-matrix stuff. The lack of true cellular tissues in the sponges places this group in the Parazoa taxon, which is only shared with Placozoans. All other multicellular *animals* are placed in the Metazoa.

Except for a few highly derived forms that live buried in dirt, all *plants* are photoautotrophic. Protist taxa that comprise both photosynthetic and non-photosynthetic members (i.e. dinophytes, euglenoids) usually aren't referred to as *plants* unless they are a photosynthesis-capable type. Thus, heterotropic dinophytes like Noctiluca aren't called plants, even though the dinophyte grouping as a whole is generally thought of as an "algal" group (by phycologists).

There's a second school of thought that argues that *plants* not only include photosynthetic organisms (of varying sorts), but derived a-photosynthetics that have lost their chlorophyll (and photoautotrophy) secondarily. The trick is figuring out which protozoan lines never had photoautotrophy in the first place, vs. the ones that had it but got rid of the capability at a later time.

 

[Bretagne]

It is at the cell level that the difference is defined, if i remember correctly.

mitochondria versus chloroplasts (I simplify a lot).

 

[Mo2vation]

I thought dude was referring to Pizza.

I'm a plant pizza kinda guy, myself.

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Ken