Bio 105 Lab 4: MARINE VERTEBRATES
Vertebrates (animals with backbones) include fishes, amphibians, reptiles, birds and
mammals. The vertebrates only constitute a sub-phylum in phylum Chordata. Chordates also
include animals without backbones like sea squirts and lancelets in addition to vertebrates.
Hagfish, while technically invertebrates, have traditionally been classified with all other types of
fishes amongst the vertebrates.
The majority of vertebrates in the sea are, of course, fishes, which will be the main focus of this
lab. There are 4 classes of fishes: the jawless (yet toothed!) hagfishes and lampreys and the
jawed cartilaginous fishes and bony fishes.
There are marine reptiles, birds and mammals, but there are no saltwater amphibians – perhaps
with one exception: the Crab-eating Frog (Fejervarya cancrivora) in Southeast Asia. Do you
have a hypothesis of why amphibians are poor candidates to adapt to saltwater? Discuss it with a
lab partner.
It is recommended to bring your notes and textbook to this lab for reference, and add
labeled sketches showing important characteristics.
Station 1: SEA SQUIRTS AND LANCELETS
Sea squirts (tunicates) and lancelets are invertebrate Chordates, and they each occupy a
subphylum in phylum Chordata, along with subphylum Vertebrata.
Tunicates are sessile marine filter feeders covered by a tunic composed of a polysaccharide
similar to cellulose. They filter-feed by means of their pharyngeal basket, drawing water in
through an incurrent siphon and expelling filtered water through an excurrent siphon. When
disturbed, tunicates eject a jet of water through their excurrent siphon, thus, their common
name: sea squirts. Look at the preserved specimens and photos. Tunicates can be very colorful
and many form colonies on rocks, pilings, and in sea caves.
Lancelets (meaning “little blade”) are small and laterally flattened. They live buried in sand,
and filter-feed. Lancelets can swim, but poorly; usually only to re-bury themselves, tail first, a
short distance away. Although they are rare globally, their populations can be very dense
where they are found. For example, in coastal Florida, they can reach densities of over
5,000/m2.
Station 2: HAGFISH
Hagfish are marine jawless fish with a cartilaginous skeleton. They do not have vertebrae but
retain the notochord which acts as a stiffening rod. The eel-shaped body terminates in a caudal
(tail) fin at the posterior end.
Depending on the species, there may be 1-15 round external gill slits on the side behind the
head. The row of small holes along the side of the hagfish are openings to the slime sacs.
Hagfish can quickly produce several liters of slime if attacked by a predator. The slime can coat
the gills of predatory fish, sending it into retreat and even suffocating it.
Hagfish are scavengers (feeders on dead and decaying matter) and have mouthparts highly
modified for sucking. Open the mouth to find two rows of teeth embedded on horny plates.
Note the sensory barbels surrounding the mouth. Find the anus on the ventral side just anterior
to the caudal fin.
Do hagfish have eyes? ____
Do they have dorsal (on back) fins? ____
Do they have paired (left and right) fins? ____
Do they have teeth? ____
Do they have jaws? ____
Hagfish live buried in mud or sand and eat polychaetes or other invertebrates and scavenge on
dead fish. They also burrow into the bodies of dead or dying fish. They typically enter the
mouth of their prey and eat out the contents of the body leaving a sac of skin and bones.
Station 3: LAMPREY
Lampreys are jawless fish with an oral disc - a toothed, funnel-like sucking mouth, with which
they bore into the flesh of other fishes to suck their blood. They live as external parasites. Find
the following structures on the lamprey: eyes, oral disc, the single nostril, gill slits, anterior
dorsal fin, posterior dorsal fin, caudal fin, cloaca.
Is the tail dorsally-ventrally flattened or laterally flattened?
Look in the mouth and see the teeth, and at the bottom of the funnel, the tongue. Are there
any jaws?
The number of external gill slits is constant. How many are there?
.
At the junction of the trunk and tail on the ventral (belly) side is the cloaca.
Station 4: SHARK
This dogfish is a type of shark. Its body is covered with minute placoid scales a.k.a. denticles
(tiny, tooth-like scales), each of which bears a tiny spine. Pass your hand over the skin and note
the rough feeling caused by the spines. Although shark skin feels rough, the spines on the
scales actually reduce hydrodynamic drag.
A whitish line, the lateral line, extends along each side of the body; it overlies the lateral-line
canal which contains sensory cells serving to detect water vibrations.
The head is triangular and somewhat flattened; its pointed extremity is known as the rostrum.
On the ventral side is the mouth with the upper and lower jaws, both of which bear a number
of teeth arranged in diagonal rows. The head further bears the three pairs of sense organs
characteristic of vertebrates – the olfactory (smell) organs, the eyes, and the ears.
The nostrils are a pair of openings on the ventral side of the rostrum. They lead to the olfactory
sac where smell is sensed. Note that in fish, the nostrils have nothing to do with respiration!
On either side of the head are the oval eyes with immovable upper and lower lids. Behind each
eye is a slight prominence, best perceived by feeling with the finger, inside of which the
internal ear is located. There is no external ear or ear opening, but the ears are connected to
the surface of the head by two canals that open by a pair of small pores in the center of the
dorsal surface of the head just back of the level of the eyes.
The rostrum and adjacent parts of the head are punctured by many pores that connect to
mucus glands. Located behind each eye is a circular opening, the first gill slit or spiracle; and a
short distance posterior to this, a row of five elongated slits, the second to sixth gill slits. Water
enters the mouth and spiracle, flows over the gills for oxygen uptake and exits via the gill slits.
In addition the structures named above, identify the following fins: anterior dorsal fin,
posterior dorsal fin, heterocercal caudal fin, pectoral (shoulder) fins and pelvic (hip) fins. The
dorsal fins have spines at their anterior ends. A heterocercal tail has two lobes of unequal size
and shape. Which tail lobe is longer in the shark, the upper or the lower? _____________
Note the sexual difference in pelvic fins; in males the medial side of each pelvic fin is modified
into a stout process directed backward, called the clasper, which is used in mating. On the
upper surface of the clasper is a sperm-conducting groove formed by the in-rolled edges of the
clasper. Near the rear end of the groove is a spine on the outer side and a hook on the inner
side. Between the bases of the pelvic fins is a large opening, the cloaca.
In the dissected dogfish note the following structures: liver, gall bladder, stomach, intestine,
heart, kidneys, spleen, gonads (ovaries/oviducts in females, or testes/sperm ducts in males).
Station 5: SKATE
Skates and rays are cartilaginous fishes closely related to sharks. Identify the following external
structures: rostrum, anterior dorsal fin, posterior dorsal fin, tail, pectoral fins (enormously
enlarged), pelvic fins (immediately posterior to the pectoral fins, often consisting of two lobes),
claspers (in males), eyes, spiracle (behind each eye), mouth, nostrils (in front of the mouth), gill
slits (posterior to the mouth), cloaca.
Station 6: BONY FISH EXTERNAL ANATOMY
Based on the model of a bony fish and diagrams provided, add a sketch and label structures in
bold: operculum (gill cover), dorsal fin(s), homocercal (symmetrical) caudal fin, adipose fin
(small fin posterior to dorsal fins, consisting of fatty tissue, without bony rays), anal fin,
pectoral fin, pelvic fin, lateral line and caudal peduncle (junction between trunk and caudal
fin). Most bony fish have a homocercal tail. If there is an upper and a lower lobe, they are of
equal size and shape. The gills are covered by a flap, the operculum, supported by thin bones.
Look at the gills and gill rakers.
Gills of fishes are the sites where oxygen is absorbed and carbon dioxide is removed. Gill rakers
are bony or cartilaginous projections which point forward and inward from the gill arches. They
aid in the fish's feeding. Their shape and number are a good indication of the diet of the fish.
Fishes which eat large prey such as other fishes and molluscs have short, widely spaced gill
rakers. This type of gill raker prevents the prey item from escaping between the gills.
Fishes which eat smaller prey have longer, thinner and more numerous gill rakers. Species
which feed on plankton and other tiny suspended matter have the longest, thinnest and most
numerous gill rakers.
Station 7: FISH MEASUREMENTS
Practice the following commonly used fish measurements (these are straight-line
measurements, not measured over the curve of the body):
•
Standard length (SL): the length from the tip of the snout (mouth closed) to the
posterior end of the last vertebra, i.e. to the lateral insertion of the caudal fin on the
caudal peduncle (effectively excluding the tail fin). Typically used for most bony fish.
SL = __________________
•
Total length (TL): the length from the tip of the snout (mouth closed) to the tip of the
longer lobe of the caudal fin, usually measured with the lobes compressed along the
midline. Typically used for jawless and cartilaginous fishes.
TL = __________________
•
Fork length (FL): the length from the tip of the snout to the end of the middle caudal fin
rays, i.e. external center of the tail fork. Typically used in fishes with forked tails in which
it is difficult to tell where the vertebral column ends.
FL = __________________
Station 8: BONY FISH INTERNAL ANATOMY
Look at the model fish and available demonstration dissections and diagrams and identify the
following: liver, heart, spleen, kidney, esophagus, stomach and intestine. Try to determine the
sex of the fish based on the gonads: ovaries (female) or testes (male). Note the pyloric caeca,
peculiar to bony fishes, encircling the duodenum (first part of the small intestine). The function
of the pyloric caeca is not fully understood, but it is known to aid in digestion and absorption.
The entire dorsal wall of the body cavity is occupied by a large gas-filled sac, the swim bladder,
a structure also not found in cartilaginous fishes. The function of the swim bladder is similar to
a buoyancy compensator in SCUBA diving. Bony fishes can add or withdraw gases, and thus
obtain neutral buoyancy in the water column.
Station 9: SCALES
Most fish are protected by scales, overlapping plates that cover all or part of the body.
There are several types of scales and numerous variations of each kind. The most common
types are shown below.
1. Placoid - Placoid scales are found in sharks and rays, and can vary greatly in external
appearance. They do not increase in size as the fish grows; instead, new scales are
added. Placoid scales are often referred to as denticles and have the same microscopic
structure as the dentine of teeth. Placoid scales consist of a flattened rectangular basal
plate which is embedded in the fish, and variously developed structures, such as spines.
The spines can be felt on the skin of the dog fish. Do the spines project anteriorly or
posteriorly?
Similar to teeth, placoid scales are composed of a
vascularized (supplied with blood) inner core of pulp, a middle layer of dentine and a
hard enamel-like outer layer.
Use a compound microscope to look at slides of placoid scales. By careful focusing, you
should be able to see the basal plate, spine and the blood vessels in the pulp.
2. Ganoid - Ganoid scales are found in fishes such as gars and sturgeons . Ganoid scales are
usually rhomboid in shape, connected by peg and socket joints. The peg (spine) on each
scale fits into a socket on the adjacent scale. Look at the ganoid scales on the preserved
gar.
3. Leptoid - Leptoid scales are found in the majority of bony fishes. The anterior part of
each scale is usually overlapped by the posterior portion of the scale in front. This
arrangement of overlapping scales gives the fish greater flexibility. Leptoid scales come
in two forms: ctenoid and cycloid. Ctenoid scales have a variously developed spiny
posterior margin (the word "ctenoid" comes from the Greek "cteno", meaning comb,
and refers to the comb-like ctenii on the margin of the scale).
Cycloid scales have a smooth posterior margin lacking ctenii. The word "cycloid" comes
from the Greek "cyclo", meaning circle. The scales of a fish with cycloid scales feels
smooth to the touch.
Look at both kinds of scales under the compound microscope. By using the iris diaphram lever
on the condenser you can increase contrast to see the ctenii on the ctenoid scales. Ctenoid
scales are essentially cycloid scales with teeth at their posterior edges. It is thought that these
teeth help to reduce hydrodynamic drag during swimming. Growth rings can be seen on both
kinds of scales.
Fish age and growth determination. As cycloid and ctenoid scales increase in size, growth rings
called circuli become visible. These rings look a little like the growth rings in the trunk of a tree.
During the cooler months of the year the scale grows more slowly and the circuli are closer
together leaving a dark band called an annulus. By counting the annuli, it is possible (if not
always easy!) to estimate the age of the fish. This technique is extensively used by fisheries
biologists. Look at the slide of trout scales under the compound microscope to see annuli on a
cycloid scale.
Station 10 – SKELETAL ANATOMY
Find these bones on the fish skeleton: vertebrae of the vertebral column, ribs, dorsal fin rays,
operculum (flat bony plate covering the gills).
Station 11: SALMON
As you probably already know, there are 5 species of Pacific salmon found in B.C.: Chinook,
Chum, Coho, Pink and Sockeye. In addition to these native species, the Atlantic salmon can be
found in BC. This species is raised commercially, and occasionally escapes occur.
Look at the posters of the life cycles of Pacific salmon species. As you can see, these fish
undergo dramatic changes in form as they pass from one stage to the next. List the stages from
egg to adult:
Egg adult
Which salmon species grows the largest? ___________________________
Which salmon species has/have spots? ____________________________________
Which salmon species has/have very small or absent teeth? ___________________________
Which salmon species has/have the smallest scales? ______________________________
Which salmon species has/have males that develop a large dorsal hump during spawning?
____________________________
Station 12 – MARINE REPTILES
There are sea snakes, saltwater crocodiles sea turtles and – only in the Galapagos Island - even
a marine iguana. All breathe by means of lungs, and must come up for air at intervals. The
nostrils of marine air breathers are often placed high on the skull’s upper surface. The American
crocodile (see skull) can remain mostly submerged, while continuing to breathe air.
Both the leatherback turtle and the green sea turtle venture into BC waters. Note that a
turtle’s shell is fused with its vertebrae, ribs and shoulder and pelvic girdles.
Station 12 – MARINE BIRDS
Birds, including all marine birds, are technically reptiles from an evolutionary perspective.
Feathers are modified scales adapted to flight. Where on a bird can you usually still find scales?
_________________Many sea birds have webbed toes and some use modified wings to propel
themselves underwater (e.g. penguins or cormorants). Special salt glands excrete excess salt
from ingesting saltwater. Where are these located? _______________________
You should be able to recognize the following species (by common name):
(Add sketches, notes on distinguishing characteristics and/or photos to help you remember)
Belted Kingfisher (Ceryle alcyon)
Black Oystercatcher (Haematopus bachmani)
Canada Goose (Branta canadensis)
Common Loon (Gavia immer)
Double-crested Cormorant (Phalacrocorax auritus)
Glaucous-winged Gull (Larus glaucescens)
Great Blue Heron (Ardea herodias)
Mallard (Anas platyrhynchos)
Northern Pintail (Anas acuta)
American Wigeon (Anas americana)
Station 13: MARINE MAMMALS
Local marine mammals include pinnipeds (seals, sea lions, walrus) as well as cetaceans (whales,
dolphins, porpoises) and the sea otter.
You should be able to recognize the following species (by common name):
(Add sketches, notes on distinguishing characteristics and/or photos to help you remember)
Order Carnivora:
Sea Otter (Enhydra lutris)
Order Pinnipedia or suborder Pinnipedia in order Carnivora):
Northern or Steller Sea Lion (Eumetopias jubatus)
California Sea Lion (Zalophus californianus)
Harbour Seal (Phoca vitulina)
Walrus (Odobenus rosmarus)
Order Cetacea:
Suborder Odontoceti (toothed whales)
Harbor Porpoise (Phocoena phocoena)
Dall’s Porpoise (Phocoenoides dalli)
Pacific White-sided Dolphin (Lagenorhynchus obliquidens)
Orca/Killer Whale (Orcinus orca)
Sperm Whale (Physeter macrocephalus)
Suborder Mysticeti (baleen whales)
Humpback Whale (Megaptera novaeangliae)
Grey Whale (Eschrichtius robustus)
Minke Whale (Balaenoptera acutorostrata)
Blue Whale (Balaenoptera musculus)