Tunicate facts: no backbone here | Animal Fact Files

Summary

Tunicates, often mistaken for sponges, are actually more closely related to vertebrates like humans and cats, belonging to the phylum Chordata. They possess a notochord in their larval stage but are not vertebrates due to lacking vertebrae. With over 2,000 species, tunicates, also known as sea squirts, exhibit unique traits like green blood and cellulose in their protective tunic. They filter feed, reproduce sexually and asexually, and have defense mechanisms against predators, including light production and jet propulsion.

Takeaways

• 🧬 Tunicates are more closely related to vertebrates like humans and cats than to sponges, as they belong to the phylum Chordata.
• 🌟 Chordates possess a notochord at some point in their lives, which is a key characteristic distinguishing them from other animals.
• 🔍 Tunicates, despite having a notochord in their larval stage, are not vertebrates because they never develop vertebrae.
• 💚 Tunicates have green-colored blood and can circulate it in a unique manner, unlike other animals.
• 🐠 Also known as sea squirts, tunicates are a diverse group with over 2,000 known species.
• 🌊 Tunicates are divided into three groups: the sessile 'cecil' types, and two types of pelagic tunicates, one resembling cecil tunicates and the other tadpole-like.
• 🏠 The 'cecil' tunicates attach to surfaces like rocks or ship hulls for their entire lives, while pelagic tunicates live freely in the open ocean.
• 🌿 Tunicates have a unique tunic made partly of cellulose, a substance more common in plants than in animals.
• 🍽 Tunicates filter food from the water, consuming small particles like plankton, and some have specialized methods for capturing food or live in symbiosis with algae.
• 👶 Tunicates have a short adult lifespan and are typically hermaphroditic, releasing sperm and eggs into the water for external fertilization.
• 🌱 Some tunicates reproduce asexually through budding, leading to the formation of tunicate colonies.

Q & A

Why are tunicates not considered vertebrates despite having a notochord?

Tunicates are not considered vertebrates because they do not possess vertebrae at any point in their lives. The notochord is present only during their larval stage and is eventually lost as they metamorphose into adults.

What is the significance of the notochord in chordates?

The notochord is a flexible rod-like structure found in chordates that provides support during early stages of development. In vertebrates, it eventually forms the spine.

How does the blood of tunicates differ from that of humans?

Tunicates have green-colored blood, which is different from the red blood found in humans and other vertebrates.

What is unique about the way tunicates circulate their blood?

Tunicates can pump their blood in reverse throughout their bodies, a capability that humans and most other animals do not possess.

What is the common name for tunicates and why are they called that?

Tunicates are commonly known as 'sea squirts' because they expel water forcefully, which resembles squirting. Their name also comes from the leathery tunic that protects their barrel-shaped bodies.

What is special about the composition of the tunicate's tunic?

The tunicate's tunic is partially composed of cellulose, a substance typically found in plants rather than animals, which makes it somewhat like an external skeleton.

How do tunicates feed and what do they eat?

Tunicates feed by filtering water through their bodies, consuming small particles like plankton. Some species use their tails to draw in water and food particles, which then get trapped in mucus.

What are the three groups of tunicates and how do they differ?

Tunicates are divided into three groups: the sessile ones that attach to a surface, the pelagic ones that live in the open ocean and resemble the sessile tunicates, and the other pelagic group that looks like tadpole-like tunicate larvae.

How do tunicates reproduce and what is unique about their reproductive process?

Tunicates reproduce both sexually and asexually. Sexually, they release sperm into the water column and then take in water to fertilize eggs internally. Asexually, they reproduce by budding, forming colonies.

What is the lifespan of tunicates and how do they develop from larvae to adults?

Most tunicates live for a single year as adults. After hatching, the larval stage may last only a few days before they find a place to settle and metamorphose into adults, sometimes within 24 hours.

How do tunicates protect themselves from predators?

Tunicates have chemicals that make them distasteful to predators. Some can produce light to confuse attackers, and the pelagic forms can eject water as a form of jet propulsion to escape.