Chapter 22 – Chaetognaths, Echinoderms & Hemichordates

Fifty fill-in-the-blank flashcards covering major terminology, anatomy, physiology, development, and ecology of Chaetognaths, Xenoturbellids, Echinoderms (including all five classes), and Hemichordates.

The name Chaetognatha comes from the Greek words meaning “long flowing hair” and “.”

jaw

Chaetognaths are all predators that drift in the plankton.

marine

A chaetognath body is unsegmented and divided into a head, trunk, and tail.

postanal

The depression beneath the chaetognath head is the , which leads to the mouth.

vestibule

Chaetognaths are the only invertebrates whose body is covered by a epidermis.

many-layered

Chaetognaths lack both and excretory systems.

respiratory

Most chaetognaths are , capable of self- or cross-fertilization.

hermaphroditic

Although probably deuterostomes, the phylogenetic position of remains uncertain.

chaetognaths

Phylum Xenoturbellida, first described in 1949, contains only species.

two

Xenoturbella feeds mainly on and their eggs.

bivalves

In Xenoturbella the mouth opens into a gut with no structured gonads.

blind

Echinoderms possess a unique vascular system derived from the coelom.

water

Adult echinoderms show pentaradial symmetry, whereas their larvae are .

bilateral

The echinoderm endoskeleton consists of dermal calcareous .

ossicles

Echinoderms can regenerate lost parts, and some reproduce asexually by .

fragmentation

Echinoderms have no specialized organs for balance (they cannot osmoregulate).

osmotic

Class Asteroidea contains about species of sea stars.

1,500

On the oral side of a sea star, each arm bears an open groove bordered by tube feet.

ambulacral

Soft, delicate projections of the coelom that act as gills on sea stars are called .

papulae

The tiny opening on the aboral surface that connects to the water vascular system is the .

madreporite

Connective tissue in echinoderms that can switch from liquid to solid is known as “ collagen.”

catch

The meshwork between ossicles in echinoderms is called the .

stereom

Water in a sea star flows from the madreporite → stone canal → ring canal → radial canal → lateral canal → .

tube feet (ampullae + suckers)

During feeding, a sea star can evert its stomach through the mouth.

cardiac

The oral (ectoneural) and deep (hyponeural) systems in sea stars are connected by an epidermal .

nerve plexus (nerve net)

Sea-star larvae are first called and later brachiolaria.

bipinnaria

Sea daisies are tiny (

arms

One sea daisy species lacks a digestive tract and absorbs nutrients with a membranous .

velum

Brittle stars (Class Ophiuroidea) have tube feet without .

suckers

In brittle stars the is located on the oral surface, unlike in sea stars.

madreporite

Brittle stars possess five that function in gas exchange and house the gonads.

bursae

The free-swimming larva of brittle stars is called an .

ophiopluteus

Sea urchins have a compact endoskeleton known as a .

test

The five-toothed rasping structure inside sea urchins is called lantern.

Aristotle’s

Respiratory tube feet of many urchins are arranged in petal-like fields called .

petaloids

Sea urchin larvae with long arms are termed .

echinopluteus

Sea cucumbers have a ventral ambulacral region forming a used for movement.

sole

In holothuroids, paired trees connect to the cloaca for gas exchange.

respiratory

The free-swimming larva of sea cucumbers is the .

auricularia

In crinoids, the cup-shaped body disc is the , covered by a tegmen.

calyx

The combined calyx and arms of a crinoid form the .

crown

Crinoid food is carried to the mouth by open, ciliated grooves.

ambulacral

The crinoid larval stage following the embryo is called a .

doliolarium

Hemichordates possess a supportive buccal diverticulum known as a .

stomochord

Enteropneusts have a body divided into proboscis, collar, and .

trunk

Respiration in enteropneusts occurs through U-shaped slits opening to the outside by gill pores.

gill

Some enteropneusts develop into a free-swimming larva called a .

tornaria

Pterobranchs live in secreted tubes and extend tentacular crowns for filter feeding.

collagenous

Certain pterobranch species reproduce asexually by , forming colonies.

budding

Chaetognaths perform diel vertical migration, rising at and sinking by day.

night

Chaetognaths typically range from to 12 cm in length.

1

Echinoderms probably evolved radial symmetry due to a largely /sessile lifestyle.

slow

Sand dollars are echinoids that are bilateral rather than radial.

secondarily