Sponges, Bryozoans, & Tunicates

Sponges are the most primitive of the invertebrates and were probably the Earth’s first multicelled animal, have existed for for than 500 million years. Most sponges found on our beaches are “spongy”, firm yet flexible, but this is where the generalization stops. Sponges exhibit remarkably different colors, textures, and shapes (branched, cup or vase shaped, conical, globular, or encrusting). Precise identification is difficult because there can be more variation within a species than between species due to growth form and color being determined by the water in which they live. Common to all sponges is the collection of individual cells within a spongy skeleton. These cells are specialized to either constantly circulate water through canals within the sponge structure, or to capture tiny food particles from the circulating water.

Moss Animals or Bryozoans are most closely related to mollusks (!), but like the sponges and corals, are colonies of animals (zooids).  Bryozoan colonies are found most commonly as growths or crusts on other objects. They cover seaweeds, form crusts on stones and shells, hang from boulders, or rise from the seabed, readily colonizing submerged surfaces. Bryozoans were originally classified as plants, and some such as the Common and Ambiguous Bryozoans can easily be mistaken for seaweed or algae, hence the name Moss Animal. If you are interested, this post covers my first acquaintance with Bryozoans.

The Rubbery Bryozoans form gray or brown rubbery, gelatinous colonies that encrust sessile (unmoving) objects, and form branching, shrubby masses. This bryozoan is very commonly found on Sea Whips and is considered a fouling organism. I find this bryozoan very frequently on the island, with just a few examples below.

I’m not positive on the identification of this one, but I think it may be Hornwrack, a type of bryozoan frequently mistaken for seaweed.Colonies begin as encrusting mats, producing loose fronds with rounded ends after their first year of growth. They are found washed ashore after storms and apparently smell like lemons. I didn’t think to give this a sniff (that’s a new one for me), but will do so if I find something similar again.

Tunicates include Sea Porks, Livers, and Squirts. The name tunicate comes from the unique outer covering or “tunic”, which is formed from proteins and carbohydrates, and acts as an exoskeleton. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, and stiffSome tunicates live as solitary individuals, but others live as colonies of individual zooids. They are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water.  Most adult tunicates are sessile, and live permanently attached to  hard surfaces on the ocean floor, docks, or pilings.

Sea Pork is not a single animal, but actually a colony of individual zzooids living together within a firm, rubbery tunic. The colonies are beached as white, pink, yellow, green, red, or purple rubbery lumps. They generally have a flattened side and may be composed of lobes. The colony grows attached to a hard surface such as jetty rocks or dock pilings, and they are shaped to some degree by this surface.

Leathery or Pleated Sea Squirts look sort of like small wrinkled potatoes. The basal end (bottom) was formerly attached to a hard surface, while the opposite end is puckered with lobes around a siphon. This siphon squirts water when squeezed, hence the name sea squirt 🙂 They are beached as single animals or in attached groups.

Sandy Skinned Tunicates look (and feel) like soft potatoes rolled in sand. their thin tunic is embedded with mud, sand small bits of shell. They are often beached still attached to rocks or shells.

T11667432_1025990984077654_7403582324055772774_nhis has been a confusing group of critters, and I must confess, that I am at a bit of a loss to classify some of my specimens.  When I first collected the specimen on the right, I thought it was a sponge. It is about 12 inches wide, with a firm texture, but still sponge-like.  But it is formed of interconnecting tubes and is an odd example, indeed.However, while reading to write this page, I found a photo of a Branched Bryozoan that looked very similar, albeit, much smaller, so, maybe?. 0791-1024x768And the next photo? I first thought this was also a sponge, but without the actual colony in hand, appearances now suggest to me that this could be a desiccated Sea Pork. So much more to learn, but oh, what a wonderful adventure it is.

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