Biology 3B Laboratory Invertebrates II: Annelida, Nematoda ...

Biology 3B Laboratory 

Invertebrates II: Annelida, Nematoda, Arthropoda, Onychophora, Echinodermata 

Objectives 

• To understand the basic differences among the invertebrate animal phyla 

• To investigate and learn the obvious external and internal characteristics of annelids, 

nematodes, arthropods and echinoderms 

• To investigate at the microscopic level the organization and function of selected tissues and 

cells within these groups 

Figure One. Cladogram of the Major Animal Phyla based upon SSU-rRNA 

INTRODUCTION 

In this laboratory, we will continue to survey the remaining four invertebrate phyla: Annelida, 

Nematoda, Arthropoda and Echinodermata (figure 1). We have already studied two of the five major 

protostome phyla. Of the remaining three major phyla of protostomes in which we will study in this 

laboratory, only the arthropods and annelids exhibit metamerism, the division of the body into 

segments. Segmentation is advantageous during development, where greater efficiency is obtained 

by constructing a whole organism out of identical somites or segments. In the adult, locomotor 

activity is enhanced because of the independent nature of each segment and the flexibility afforded 

by a series of segmented parts. Segmentation also gives these phyla a survival advantage. Since 

many segments are similar to other segments in form and function, damage to one or several 

segments does not necessarily compromise body functions. 

Biology 3B Laboratory Invertebrates II Page 1 of 17

PHYLUM ANNELIDA 

Members in the phylum Annelida are often referred to as segmented worms because of their 

segmentation, a distinguishing characteristic that sets them apart form other animals. The most 

recognizable members include the earthworms (terrestrial habitat), leeches (terrestrial and 

freshwater), and marine worms. All annelids are triploblastic, bilaterally symmetrical, and 

eucoelomate. In addition, annelids exhibit a body wall with both longitudinal and circular muscle 

layers (which, along with segmentation mentioned above, allows these animals to be quite mobile). 

They have a complete digestive tract. Their nervous system shows some degree of cephalization 

with a “brain” and two ventral nerve cords that running the entire length of the body. They have a 

closed circulatory system with aortic arches that act as the “heart” to pump blood through muscular 

blood vessels. They also have a well developed excretory system which removes waste from the 

blood and coelom. 

There are three major classes within the phylum Annelida, described below. 

Class Polychaeta - mostly marine worms, such as Nereis (the clamworm) 

Class Hirudinea - the leeches (predominantly freshwater), such as Hirudo 

Class Oligochaeta - mostly freshwater and terrestrial worms, such as Lumbricus (the 

earthworms) 

OBSERVATION OF POLYCHAETA 

CLASS POLYCHAETA 

Polychaete worms are mostly a marine group of worms characterized by many segments with a pair 

of parapodia with numerous setae (figure 2). They have a distinct head with eyes, palps and 

tentacles. 

o Examine a clamworm (Nerius). These 

are the “typical” polychaete worms that 

can be found living in the mud and 

debris of shallow coastal waters. Using 

the dissecting scope, observe the head 

region and find the following: eyes, 

mouth on the ventral side, jaws, and 

tentacles. 

o Examine one of the segments. Locate a 

parapodium on one side a body 

segment. Parapodia function in 

locomotion and respiration for 

polychaetes. Each parapodium is 

comprised of two lobes which bear 

numerous setae (the reason for the 

class name). 

Figure 2: Structure of a clamworm (Nerius) 

OBSERVATION OF OLIGOCHAETA 

CLASS OLIGOCHAETA 

Like polychaete worms, oligochaete worms are also segmented both outside and inside. However, 

oligochaetes do not have parapodia, their head is less developed and they have fewer setae. The 


most noticeable external feature in this group is the clitellum (figure 3). Most members in this class 

are either terrestrial (most) or inhabit freshwater. 

o Obtain an earthworm (Lumbricus) and place the animal in a dissecting tray. You may need a 

dissecting scope to fully appreciate the external anatomy. The first four segments comprise the 

head region. Find the mouth on the first segment (figure 3). The prostomium overhangs the 

mouth. They have a complete digestive tract that terminates on the last segment with the anus. 

o The most obvious external feature is the clitellum, a swollen area in the anterior third of the 

specimen. This region functions in reproduction by secreting a mucous which holds the 

participants together during sperm exchange and cocoon formation around the fertilized eggs. 

o Orient the worm dorso-ventrally by locating the tiny setae (hairs). Run your fingers along the 

animal to feel the rough texture produced by the setae. Four of these structures are found on the 

ventral surface of each metamere. They provide traction during locomotion. 

o Starting with the segment that holds the mouth, locate segment 14. Observe the openings for the 

oviducts (female pore) on the ventral surface. Find the sperm ducts (male pore) on the ventral 

surface of segment 15. 

Figure 3: Structure of an earthworm. 

We will examine the internal structure when we begin the systems. 

OBSERVATION OF HIRUDINEA 

CLASS HIRUDINEA 

The best known member in this class is the freshwater leech. Other members can be found on land 

and the marine environments. Members in this class typically have 33-34 segments with a clitellum. 

Most do not have setae and no members have parapodia. Members have both anterior and posterior 

suckers. 

o Examine representative members in this class. The medicinal leech, Hirudo medicinalis, secretes 

an anticoagulant on the host at they parasitized them. This leech was commonly used in the 

practice of blood-letting. It is still used today to increase circulation to surgical areas, especially 

with finger reattachments. Note the smaller oral sucker and larger posterior sucker. 


PHYLUM NEMATODA 

Triploblastic pseudocoelomates 

The development of a body cavity (coelom) is considered a major evolutionary advantage over those 

animals which do not possess a body cavity (acoelomate). As you have already learned, body 

cavities are advantageous for a number of reasons, such as to provide more room for organ 

development, to provide an increased surface area for diffusion of gases and/or nutrients, and to 

facilitate locomotion by serving as hydrostatic skeleton. 

A body cavity is characteristic of all bilateral animals above the acoelomates. A true coelom is a 

cavity in which the inner body wall and the visceral organs are lined with peritoneum. A 

pseudocoeIom, found in animals to be examined in the present exercise, is defined as a body cavity 

that is lined by mesoderm externally and endoderm internally (figure 4). 

The nematodes are one of several phyla 

usually discussed together as the 

pseudocoelomates because of their shared 

possession of this structure. Except for this 

one common feature, they are a diverse 

group of animals, only distantly related. 

Included in this broad group of animals are 

the Phyla Rotifera, Nematomorpha, 

Gastrotricha, Kinorhyncha, and others. We 

will examine members of the phylum 

Nematoda as a representative 

pseudocoelomate. 

However, nematodes are grouped with 

arthropods as an ectodyzoan due to 

molecular evidence supporting ecdysis, the 

ability to shed the exoskeleton as the 

organism grows. 

Nematodes have a worldwide distribution 

that include, terrestrial, freshwater, marine 

and parasitic forms. They are round worms 

with a tough, flexible cuticle that is non;living. 

Nematodes are important ecologically for 

their recycling and decomposition 

capabilities. 

OBSERVATION OF NEMATODA 

• Examine the male and female intestinal 

roundworm, Ascaris lumbricoides, in 

Figure 4: Comparison of body cavities. dissecting tray. Gloves should be worn, if 

available. If not, handle organism with forceps. 

Do not touch with bare skin. Ascaris is sexually dimorphic and sexes are easily differentiated. 

Male worms are smaller, typically have a hook-shaped sideways bend near their posterior end, 


and may have tiny copulatory spicules protruding slightly from the cloaca. Ascaris is an intestinal 

parasite of vertebrates, with A. lumbricoides infecting up to 64% of individuals living in the 

southeastern United States. The female lays up to 200,000 eggs/day which passes out of the 

host via their feces. The embryo is very resistant, thus be careful handling these worms as you 

could potentially infect yourself. 

o Examine the slide of a trichina worm, Trichinella spiralis. You will be observing calcified cyst of 

the juvenile trichina worm (figure 5) in the muscle of the host. Trichinosis is the disease that is 

caused by the trichina worm. Human infestations are typically due to the ingestion of 

undercooked meats such as pork. Roughly 2% of the population in the US has a light infection 

with trichina worms. Heavy infestations may cause death. Other species that can be infected 

include: hogs, rats, dogs, cats and any other omnivorous or carnivorous species. 

Figure 5: Encysted juvenile Trichinella spiralis 

o Examine the slide of a hookworm, Necator americanus. Note the anterior portion of the worm with 

a hook-like appearance in a tissue section. Infestations results when the juvenile hookworm 

comes in contact with the skin and burrows into the host. The juvenile then travels via the 

bloodstream to the lungs, move up the respiratory tract and then swallowed. In the small 

intestines they will mature. 

o Examine a slide of pinworms, Enterobius vermicularis. These worms live in the large intestines of 

humans and are the most common nematode parasite. These infestations are more 

embarrassing than debilitating. The female will travel to the anus at night to deposit eggs around 

the anus. Scratching contaminates the hands and bedding. The eggs are then swallowed and 

hatch in the duodenum and mature in the large intestines. This is a very common infestation in 

children. 


o Examine the free-living nematode, the vinegar eel (Tubatrix aceti) on a depression slide, if 

available. These worms have a high tolerance to low pH. Describe how the body bends. 

PHYLUM ARTHROPODA 

The phylum Arthropoda is the largest in the animal kingdom. More than 75% of all living organisms 

are arthropods with insects contributing the greatest numbers. Like annelids they are characterized 

by metamerism, i.e. the body is segmented. In addition, they have a chitonous exoskeleton. The 

segmented body is divisible into functional units called tagmata. In some arthropods three tagmata 

are present - a head (involved in feeding and sensory functions), a thorax (involved mostly in 

locomotion), and an abdomen (which performs the visceral functions). In many arthropods the head 

and thorax are fused, forming a cepahalothorax. 

The phylum contains three extant subphyla - Chelicerata, Crustacea, and Uniramia. The subphylum 

Chelicerata contains arthropods in which the first appendages are modified into chelicerae (pincerlike 

feeding structures). Well-known representatives of this subphylum include the class Arachnida 

(scorpions, spiders, ticks, etc.) and the class Merostomata (horseshoe crabs). 

Major Arthropoda subdivisions (you are only responsible the taxonomy down to the class level) 

• Subphylum Trilobita 

• Subphylum Chelicerata 

o Class Merostomata - horsecrab 

o Class Pycnogonida – sea spiders 

o Class Arachnida 

• Order Araneae - spiders 

• Order Scorpionida - scorpions 

• Order Opiliones - harvestmen 

• Order Acari – ticks & mites 

• Subphylum Crustacea 

o Class Branchiopoda 

• Order Cladocera – water fleas 

o Class Maxillopoda 

• Subclass Copepoda - copepods 

• Subclass Cirripedia - barnacles 

o Class Malacostraca 

• Order Isopoda – isopods, pill bugs 

• Order Euphausiacea - krill 

• Order Decapoda – crabs, shrimp, lobster, crayfish, etc. 

• Subphylum Uniramia 

o Class Chilopoda - centipedes 

o Class Diplopoda - millipeds 

o Class Insecta - insects 


OBSERVATION OF ARTHROPODA 

SUBPHYLUM TRILOBITA 

This extinct group has members dating back to the Carboniferous to the Cambrian. The body has 

two longitudinal furrows that run down the entire length. There is three distinct body sections: head, 

thorax, and abdomen. 

o Examine the fossil of a trilobite (Figure 6). Do not get it confuse with chitons. 

SUBPHYLUM CHELICERATA 

Figure 6. Trilobite 

Organisms that you will examine in this group includes: horseshoe crabs, spiders, ticks and scorpions. 

These organisms are grouped here because the first pair of appendages is modified into chelicerae 

for feeding. They also have a pair of pedipalps for capturing prey and four pairs of legs. There are 

two body segments: the cephalothorax and abdomen. 

• CLASS MEROSTOMATA 

This group contains the aquatic chelicerates such as the horseshoe crab and the extincit 

eurypterids. 

o Examine the horseshoe crab (Limulus). On the horseshoe shaped carapace comprises 

the cephalothorax, the simple eye and pair of compound eyes can be found on the 

dorsal surface. Behind the hinge is the abdomen. The telson is the tail. 

o Examine the ventral surface of Limulus (figure 7) Find the mouth. The chelicerae are the 

first pair of appendage used to manipulate food. The pedipalps are the second pair of 

appendages, used to capture prey. The remaining four pairs of appendages are the 

walking legs. On the abdomen, find the six leaf-like structures. The first is the genital 

opercula and the remaining five are the book gills (used for respiration). 

Figure 7: Dorsal and ventral view of Limulus 


• CLASS ARACHNIDA 

This class consists of members that are rather familiar to most. They include spiders, scorpions, 

ticks and mites. All members posses a pair of cherlicera, pedipalps and four pairs of walking legs. 

o Examine the Cephalothorax of the garden spider Argiope (figure 8) Note the number of 

eyes. Identify the chelicerae. They have been modified into fangs for the injection of 

poison. Find the pedipalp. What’s its general function? In males, the pedipalps are 

modified as an intromittent organ to deliver sperm to the female. How many walking do 

spiders have and what body segment (tagmata) are they located? 

o Obtain a dissecting scope and examine the ventral abdominal region of Argiope. Look for 

the lung slit at the anterior portion of the abdomen. Towards the posterior end of the 

abdomen, you will notice three pairs of spinnerets on a raised surface responsible for silk 

production. 

Figure 8: Ventral view of Argiope 

o Examine a scorpion. The pincers are the pedipalps. Note the stinger with venom sac at 

the distal portion of the abdomen. 

o Examine the slide of a tick. These are ectoparasites on various vertebrates. Many can 

transmit diseases such as Lyme disease and Rocky Mountain spotted fever. 

o Examine the slide of a mite. Mites are some of the smallest archnids. 


SUBPHYLUM CRUSTACEA 

In the subphylum Crustacea, mandibles are the primary feeding appendages. All crustacean 

appendages are biramous i.e. they have two processes extending from the base. Gills are used in 

respiration. Shrimp, crabs, lobsters, and many microscopic species are included in this subphylum. 

• CLASS MAXILLOPODA 

You will examine one group of organisms within this class, the barnacles. The body of the 

barnacle is sessile as an adult and is housed within a calcareous shell. We will have the 

opportunity to see living barnacles at the tidepools. When the tide is out (when we’ll be there); 

you will not be able to see the cirri (feeding legs). 

o Examine the shell of the acorn barnacle (Balanus). These are attached directly to the 

substrate. 

o Examine the gooseneck barnacle (Lepas – Figure 9). The main body is attached to the 

substrate via a stalk. 

Figure 9: Lepas 

• CLASS MALACOSTRACA 

We examine members in the order Decapoda only in this class. Decapods, as the name implies, 

have ten walking legs on the Cephalothorax which is covered by a hard carapace. Many have 

the first walking leg modified into a cheliped that is used in capturing prey and defense. 

o Examine the dorsal and ventral surface of a preserved crayfish (Cambarus – figure 10). 

Locate the following paired structures, then carefully remove them from one side and place 

them in the correct sequence on a sheet of paper (figure 11). 

Head 

‣ Antennules – two, short filamentous structures at the tip of the rostrum for touch, 

taste and equilibrium 

‣ Antennae – the long filamentous structure lateral to the antennules for touch and 

taste 

‣ Mandible – bears teeth for crushing food 

Thorax 

‣ First maxilla – for handling food 

‣ Second maxilla – food handling and bailing water from gill chamber 

‣ Maxilliped (1 – 3) – touch taste and food handling 

• 2 nd & 3 rd maxilliped – have gills for respiration 

‣ Cheliped (1 st walking leg) – grasping food, defense and respiration 

‣ Walking legs (2 – 4) – walking and respiration 

Abdomen 

‣ Swimmerets – circulates water 

• Males – 1 st is modified to transfer sperm to female seminal receptacle 

• Females – assists in carrying eggs and young (2 – 5) 

‣ Uropod & Telson – locomotion & protecting eggs (female) 


Figure 10 (above): Dorsal and ventral external crayfish structure 

Figure 11 (below): Crayfish appendages 


o Examine other representative malacostracans (crabs, shrimp, etc.). 

We will examine the internal anatomy when we begin the systems. 

SUBPHYLUM UNIRAMIA 

Organisms in the subphylum Uniramia also have mandibles as the primary feeding appendages, 

however their appendages are uniramous (having only one process extending from the base), and a 

tracheal system is used for respiration. This large subphylum includes the following classes: lnsecta 

(Insects), Diplopoda (millipedes), and Chilopoda (centipedes). 

• CLASS CHILOPODA 

o Examine preserved centipedes. They do 

not have a hundred legs. They do have 

one pair of legs per body segment. The 

maxilliped is modified into a fang for the 

delivery of poison. Centipedes are active 

predators living in moist places. If live 

ones are available, observe their 

locomotion. 

• CLASS DIPLOPODA 

o Examine preserved millipedes. These do 

not have a thousand of legs. They do 

Figure 12: Centipede and millipede 

have two pairs of legs per body segment. 

Like centipedes, millipedes can be found 

living in moist habitats. However, they are herbivores or scavengers feeding on decaying 

wood or leaves. Some millipedes produce cyanide as a chemical defense mechanism. 

Observe the locomotion of live millipedes if available. 

• CLASS INSECTA 

This is by far the largest group of animals with estimates of over one million named species. The 

major characteristics of insects are: three walking legs on the thorax, one pair of antennae, three 

body segments (head, thorax and abdomen). Many insects have either one or two pairs of wings. 

• Examine a preserved grasshopper and observe its external features (figure 13). The 

exoskeleton is divided by sutures into plates called sclerites. 

o HEAD: The head consists of fused sclerites forming a cranium and mouth parts. A pair of 

antennae arise in front of the compound eyes. Three ocelli (simple eyes) can be seen - 

one in the center, between the antennae, and two located above the base of the antennae. 

o THORAX: The thorax consists of three segments. The anterior prothorax bears the first 

pair of legs. The mesothorax (middle segment) bears a pair of legs and a pair of leathery 

wings. The metathorax (third segment) bears a pair of highly modified jumping legs and a 


pair of membranous wings which are extension of the respiratory system. The legs are 

jointed. 

• Examine the wings of a beetle (Orthoptera). The forewing is called the elytra 

which functions to protect the membranous hindwing that’s used for flight. 

• Examine the wings of a cranefly (Diptera). The forewing is for flight and the 

hindwing is reduced and modified for balance. 

o ABDOMEN: The abdomen is simple, devoid of appendages, and made up of 10 to 11 

segments. Note the terminal structures and use them to determine the sex of the specimen. 

Be sure to compare your grasshopper to one of the opposite sex. In the female, the 

ovipositor is for laying the eggs inside the earth. At the tip look for a pair of sensory 

structures known as cerci. 

• Observe the female cricket and notice the long ovipositor for depositing eggs. 

o On either side of the first abdominal segment you might see a thin membrane, called the 

tympanum - a hearing organ. Spiracles are present on either side of most of the segments. 

The spiracles are most prominent in the thorax region. They are the breathing pores of the 

elaborate network of the tracheal system. 

Figure 13: External features of a female grasshopper. 

Insect have mouth parts that are adapted for the type of feeding they specialize in. There are four 

basic mouth parts: sucking mouthparts, sponging/lapping mouthparts, siphoning and 

chewing/biting mouthparts. You want to be able to differentiate these mouthparts for they type of 

feeding (figure 14). 

o Examine the slide of the mosquito head (sucking mouthpart) 

o Examine the slide of the butterfly head (siphoning mouthpart) 

o Examine the slide of the fly head (lapping mouthpart) 

o Examine the slide of the honeybee (chewing) 


Chewing Sponging/Lapping Siphoning Sucking 

Figure 14: Insect mouthparts. 

PHLYUM ONYCHOPHORA 

Members in this group are often referred to as velvet or walking worms. They are an unusual group 

in that they have characteristics of annelids and arthropods. Onychophorans have changed very little 

in the past 500 million years. Aysheaia is a fossil onychophoran from the Burgess shale deposit that 

dates back to the mid-Cambrian. It looks very much like the modern day onychophorans. Some 

have called this the “missing link” between these two phyla. 

Onychophorans are a terrestrial species. They are active at night or when there is very high humidity. 

o Examine the preserved velvet worm (Peripatus). 

PHYLUM ECHINODERMATA 

Echinoderms are a group of animals that arose from bilaterally symmetrical ancestors even though 

the animals show pentaradial symmetry. Many of them have a bilateral larval stage and hence the 

radial feature may be secondarily acquired. As you have already studied, most radially symmetrical 

animals are sessile, however echinoderms are free moving. They are triploblastic and 

eucoelomate. Echinoderms are marine animals and that include: sea stars, sea urchins, sea 

cucumbers, and sea lilies. The body parts are arranged in "fives" around the oral/aboral axis. 

The most noticeable characteristics for echinoderms are the calcareous ossicles for the endoskeleton, 

the water vascular system with tube feet, pedicellariae, dermal branchiae and pentaradial symmetry. 

Major classes of Echinodermata include: 

Asteroidea – sea star 

Ophiuroidea - brittle stars, basket stars 

Echinoidea - sea urchins, sand dollars 

Holothuroidea - sea cucumbers 

Crinoidea - sea lilies, feather stars 


OBSERVATION OF ECHINODERMATA 

CLASS ASTEROIDEA 

Sea stars are found in relatively shallow waters, and range in size from less than an inch to nearly 

three feet in diameter. They feed primarily on bivalves, prying the shell to open with their tube feet, 

everting their stomach into the victim's body cavity, and digesting it. The larvae are known as 

bipinnaria and have bilateral symmetry, whereas the adult form is star shaped with arms not sharply 

marked off from the central disk. Sea stars can perform autotomy (self-amputation) of their arms. 

However, if a small portion of the central disc remains attached to it, the amputated arm can then 

regenerate and form a new individual (a clone). 

o Examine live, preserved or dehydrated sea stars (figure 15). Identify the oral and aboral surfaces. 

Radiating from the central disk are the five arms, noting their spiny texture (from which they get 

the name echinoderm - spiny skin). At the tip of each arm is the eyespot. Note the calcareous 

spines, dermal branchiae (skin gills - little sac-like structures on the skin) and pedicellariae 

(claws - tiny pincer-like structures on some living sea stars that can aid in food capture or keep the 

sea star clean of debris). 

o The madreporite (a light colored, circular, slightly raised structure located on the aboral surface 

near the base of two arms) is the opening, or intake, of the water vascular system. The anus is 

seen as a minute opening at the center of the aboral surface. Ambulacral grooves are the deep 

grooves that extend from the oral surface along the midline of each arm. The tube feet are seen 

as double rows of soft tubular "feet" on each arm, lying along and just inside the ambulacral 

groove. On the dehydrated specimen, the tube feet may or may not be present. 

o Examine the living sea star, if available, observe the madreporite plate, eyespot, sensory 

tentacles (located at the tip of each arm/ray), ambulacral groove, tube feet and pedicellariae 

(if present). 

Figure 15: Dorsal and ventral sea star surfaces 


CLASS OPHIUROIDEA 

Brittle stars are secretive echinoderms found from tidepools to great depths in the ocean. Although 

they are one of the more agile and abundant echinoderm, they are not frequently seen. On our 

tidepool trip, you will need to carefully turn over rocks to find brittle stars. If caught, brittle stars will 

often detach an arm (autotomize) in hopes that the predator is attracted to the wiggling arm as the 

brittle star escapes. Brittle stars differ from sea stars in that brittle star in that their ambulacral 

grooves are closed. Their tube feet are reduced and to do not have suckers. As a result, the tube 

feet are not used for locomotion. Instead, they “walk” with their arms. 

o Examine a preserved brittle (figure 16). Do not handle them roughly. On the oral surface find: 

mouth, five triangular jaws, oral shield located between the arms. Find the oral shield that’s 

modified into the madreporite plate. Note the spines on each arm. 

o Examine the preserved basket star. 

Figure 16: Oral view of the central disk of a brittle star. 

CLASS ECHINOIDEA 

This class includes sea urchins, heart urchins and sand dollars. This group is distinct in that they do 

not have arms and are more or less globular. They have tube feet with suckers and movable spines. 

Their ambulacral grooves are closed and covered by ossicles. 

o Examine the test of sea urchin. On the aboral surface, fine the madreporite plate, anus, 

ambulacral groove with tube feet pores, spine tubercle with or without the spine. On the oral 

surface, find the mouth and tooth. 


Figure 17: External structure of the sea urchin 

o Examine the Aristotle’s lantern from the chewing complex of a sea urchin. 

o Examine a living sea urchin. Note the moveable spines and the tube feet. Do the tube feet have 

suckers? 

o Examine the sand dollar and heart urchin or sea biscuit on display. 

CLASS HOLOTHUROIDEA 

Sea cucumbers are placed into this class and have cucumber shape. There are no arms or spines. 

The ambulacral grooves are closed. Sea cucumbers have soft bodies because their ossicles are 

microscopic and embedded in the thick muscular wall. 

o Examine the sea cucumber (Cucumaria) and find the mouth at one end with the anus at the other. 

The mouth is surrounded by modified tube feet called tentacles. 


CLASS CRINOIDEA 

Most crinoids (seas lilies and feather star) are an ancient group of enchinoderms with few living 

members. The oral end is “up” where as the aboral end has the attachment stalk or cirri. 

o Examine fossil or preserved specimens as available. Note the 10 arms with pinnules. The arms 

radiate from the calyx where the digestive and other organs are located. The calyx and arms are 

collectively called the crown.

Biology 3B Laboratory Invertebrates II: Annelida, Nematoda ...

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