Invertebrate Anatomy OnLine
Balanus eburneus ©
Copyright 2001 by
is one of many exercises available from Invertebrate
Anatomy OnLine , an
Internet laboratory manual for courses in Invertebrate Zoology. Additional
exercises can be accessed by clicking on the links on the left. A
glossary and chapters on supplies and laboratory techniques are also available. Terminology
and phylogeny used in these exercises correspond to usage in the Invertebrate
Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated
figure callouts refer to figures in the textbook. Callouts
that are not hyphenated refer to figures embedded in the exercise. The glossary
includes terms from this textbook as well as the laboratory exercises.
Mandibulata, Crustacea sP,
Eucrustacea, Maxillopoda SC,
Progonomorpha, Thecostracomorpha, Thecostraca, Cirripedia C,
Thoracica O, Balanomorpha sO,
Balanoidea SF, Balanidae F, (Fig
16-15, 19-89, 19-90)
by far the largest and most diverse animal taxon, includes chelicerates,
insects, myriapods, and crustaceans as well as many extinct taxa such as
segmented body primitively bears a pair of jointed appendages on each segment. The
epidermis secretes a complex cuticular exoskeleton which must be molted to
permit increase in size. Extant
arthropods exhibit regional specialization in the structure and function of
segments and appendages but the ancestor probably had similar appendages on all
segments. The body is typically divided into a head and trunk, of which the
trunk is often further divided into thorax and abdomen.
gut consists of foregut, midgut, and hindgut and extends the length of the body
from anterior mouth to posterior anus. Foregut
and hindgut are epidermal invaginations, being derived from the embryonic
stomodeum and proctodeum respectively, and are lined by cuticle, as are all
epidermal surfaces of arthropods. The
midgut is endodermal and is responsible for most enzyme secretion, hydrolysis,
coelom is reduced to small spaces associated with the gonads and kidney. The
functional body cavity is a spacious hemocoel divided by a horizontal diaphragm
into a dorsal pericardial sinus and a much larger perivisceral sinus. Sometimes
there is a small ventral perineural sinus surrounding the ventral nerve cord.
hemal system includes a dorsal, contractile, tubular, ostiate heart that pumps
blood to the hemocoel. Excretory
organs vary with taxon and include Malpighian tubules, saccate nephridia, and
organs also vary with taxon and include many types of gills, book lungs, and
nervous system consists of a dorsal, anterior brain of two or three pairs of
ganglia, circumenteric connectives, and a paired ventral nerve cord with
segmental ganglia and segmental peripheral nerves. Various
degrees of condensation and cephalization are found in different taxa.
is derived with centrolecithal eggs and superficial cleavage. There
is frequently a larva although development is direct in many. Juveniles pass
through a series of instars separated by molts until reaching the adult size and
reproductive condition. At
this time molting and growth may cease or continue, depending on taxon.
is the sister taxon of Chelicerata and in contrast has antennae on the first
head segment, mandibles on the third, and maxillae on the fourth. The
brain is a syncerebrum with three pairs of ganglia rather than the two of
chelicerates. The ancestral mandibulate probably had biramous appendages and a
J-shaped gut, posterior-facing mouth, and a ventral food groove. The two highest
level mandibulate taxa are Crustacea and Tracheata.
is the sister taxon of Tracheata and is different in having antennae on the
second head segment resulting in a total of 2 pairs, which is unique. The
original crustacean appendages were biramous but uniramous limbs are common in
derived taxa. The
original tagmata were head but this has been replaced by head, thorax, and
abdomen or cephalothorax and abdomen in many taxa. Excretion is via one,
sometimes two, pairs of saccate nephridia and respiration is accomplished by a
wide variety of gills, sometimes by the body surface. The nauplius is the
earliest hatching stage and the naupliar eye consists of three or four median
includes all Recent crustaceans except the remipedes. The taxon is characterized
by a primary tagmosis consisting of heat, thorax, and abdomen although the
derived condition of cephalothorax and abdomen is more common. Eight is the
maximum number of thoracic segments.
are “short” crustaceans with 10 of fewer trunk segments including a maximum of
seven thoracic segments. The abdomen consists of three segments, none of which
have appendages. The
naupliar eye has three, instead of four, pigment cups. Maxillopoda
includes such well known taxa as copepods, barnacles, ostracods, and
branchiurans as well as more obscure groups like tantulocaridans and
are a diverse taxon including free-living and parasitic groups. Barnacles
are sessile and most are hermaphroditic. Most
are suspension feeders but many are parasites and some are predators. The
exoskeleton usually secretes heavy calcareous plates which grow with the animal
and are not molted, although the rest of the exoskeleton is.
barnacles are typically sessile, non-parasitic, suspension feeders although some
are also predators. Most
live attached to hard substrata in coastal waters where they use their setose
thoracic appendages to filter particulate food or capture prey from the water.
The dorsolateral body wall is evaginated and folded to form a bilobed carapace
similar to the mantle of bivalve molluscs and brachiopods, and accordingly known
as the mantle. The
mantle encloses a mantle cavity and the body and also secretes a calcareous,
body consists of a head, thorax, and vestigial abdomen. There
is no cephalothorax and no maxillipeds although the carapace (mantle) encloses
the entire body including the complete thorax. The head is divided into a
preoral region anterior to the mouth and a postoral region behind it and bears
little resemblance to the heads of other crustaceans. The
preoral region is much enlarged and elaborated to form an attachment organ by
which the animal adheres permanently to its substratum. The
rest of the body is postoral and consists of the remainder of the head, the
thorax, and a tiny abdomen. In
lepadomorph, or stalked, barnacles, the preoral region of the head is a
flexible, muscular stalk. The
postoral region is enclosed in the mantle, mantle cavity, and shell. The
preoral head of balanomorph, or acorn, barnacles does not form a stalk and
instead attaches directly to the substratum.
exercise is written specifically for the ivory barnacle, Balanus
eburneus, but applies equally
well to any balanid and with minor modification to most acorn (balanomorph)
living or preserved specimens can be used. The
study should be conducted with a dissecting microscope.
your animal is alive, place it in a dish of isotonic magnesium chloride or,
better, use a specimen which has already been in the relaxant for about an hour. Arthropods
are notoriously slow to succumb to the effects of magnesium chloride. A
1-2 cm barnacle requires 30-60 minutes to relax.
a toothbrush to scrub the fouling organisms from the surface of your barnacle. Place
the cleaned animal in a dish of isotonic magnesium chloride if it is living or
in tapwater if preserved. Your
specimen may be attached to a substratum, such as an oyster shell, or it may
have been removed from the substratum.
the external anatomy in a dissecting pan on the stage of a dissecting
barnacle body consists of an anterior head with four pairs of appendages, and a
thorax with six pairs. The
second antennae are absent. The
abdomen is vestigial. A
large carapace, known as the mantle, extends posteriorly from the head and
encloses the entire animal. No
cephalothorax is present and there are no maxillipeds.
Carapace and Mantle Cavity
the exterior of the animal. It
is completely enclosed by the carapace, or mantle,
which is a double fold of the body wall (Fig 1). Barnacles, of course, are
arthropods and as such secrete an exoskeleton to enclose the body. In
acorn barnacles the outer surface of the double layered mantle is calcified to
form a rigid box which contains a soft animal. The
remaining exoskeleton, including the inner surface of the mantle, is not
sclerotized or calcified and is flexible and thin.
Figure 1. A simplified sagittal section of an acorn
barnacle showing the spatial relationships between the body, mantle, and mantle
cavity. The animal is upside down with its feet in the “air” and its head stuck
to the ground. Barnacle30L.gif
you can see at present is the heavily calcified part of the exoskeleton. It
is underlain by the epidermis of the outer layer of mantle, which secreted it. It
is composed of a series of more or less vertically-oriented, overlapping,
immovable, calcareous mural
plates (= wall plates),
which form a ring around the animal, and four movable opercular
plates (Fig 2, 19-78B,C).
barnacles had eight wall plates but modern barnacles have six. The wall plates
slope inward and together form a truncated cone resembling a volcano. An
opening, theaperture, is at the apex of the cone but it is
probably covered by the four opercular plates which form a door, or operculum,
to close the aperture. These
plates are movable and are operated by specialized muscles.
an additional calcareous plate, the basis,
which forms the base of the cone and is glued firmly to the substratum (Fig 4,
19-78A). The basis is the floor of the calcareous box inhabited by the barnacle. (Not
all acorn barnacles have a calcareous basis. Sometimes
it is membranous.) If
your specimen has been removed from the substratum, you may be able to see the
the basis remains with the substratum when the barnacle is removed. Often
it remains with the barnacle but is cracked or otherwise damaged. If
your barnacle is still attached to the substratum, you will not see the basis at
Figure 2. The
exterior of a generalized balanomorph barnacle. Barnacle18L.gif
is a good time to orient the animal and determine the major body axes. Acorn
barnacles lie on their backs with the dorsal surface attached to the substratum
(Fig 1). The
base then is dorsal. Look
at the aperture and
find the four plates forming the operculum. The
aperture and operculum are ventral. A
long straight cleft, the aperture, divides the operculum into right and left
halves, each half being composed of two plates. This
line corresponds to the antero-posterior
axis, which is the axis
of symmetry. Two
of the opercular plates are easier to see because their largely horizontal
orientation results in a broad exposed surface. These
are the scuta, or
scutal plates (Fig 2). The
scuta are at the anterior end
and there is one on the right and one on the left. The
other two opercular plates are the terga,
or tergal plates. They
are posterior. Their
orientation is more vertical and consequently you see less of them than of the
scuta. Determine right and left.
calcareous plates forming the immovable wall of the shell are collectively known
as the mural plates (=
wall plates). The wall consists of two plates on each side and a single plate at
each end. The
plates on either side are the lateral
plates (Fig 2, 19-78B). Note
how they overlap each other. The
single plate at the anterior end is the rostrum. It
is adjacent to the scuta, of course, and in the genus Balanus,
it overlaps the two lateral plates adjacent to it. The carina is
the unpaired plate at the posterior end. It
is adjacent to the terga and, unlike the rostrum, is overlapped by its adjacent
lateral plates (this is not true of all barnacles). The calcareous plates grow
with the barnacle and are not shed at each molt although the flexible chitinous
portions of the exoskeleton are molted.
Mantle and Mantle Cavity
your forceps and/or teasing needles to push the two scutal plates apart and open
the aperture of a relaxed barnacle. With
low magnification of the dissecting microscope, look into the aperture. The
space within the aperture is the mantle
tough, darkly pigmented lining of the mantle cavity is the carapace, known in
barnacles as the mantle. (Even
though we have long known that barnacles are not molluscs, this terminology
remains appropriate since, in both groups, the mantle is a double layer of body
wall, secretes a shell, and encloses a mantle cavity filled with water.)
mantle is derived from the bivalved carapace of the cypris larva (Fig 19-79B). It
is a double fold of the body wall and its inner surface is covered with a thin
chitinous exoskeleton (Fig 1). This
part of the exoskeleton is not calcified but the outer surface is.
you are looking into the aperture you will see the thoracopods, or cirri,
in their retracted position. These
are the thoracic appendages and they are used for suspension feeding. In
this position they look like coiled, setose whips. They
will be studied in more detail later. Find
the cylindrical, transverse scutal
adductor muscle running from
the inside surface of one scutum across the midline to the other scutum. Its
action is to pull the two scuta tightly together and close the aperture. The
terga are attached by connective tissue to the scuta so contractions of the
adductors move them also and the two sets of plates close in unison.
the barnacle from the dish and place it on a towel. Use
a small (2") C-clamp to rack the articulations between adjacent mural plates. Do
this carefully and gently. Place
the jaws of the clamp on opposite sides of the shell and apply gentle pressure
until you feel the plates give slightly then back off the clamp. Do
not apply pressure after the valves move. Inspect
the shell and determine which joints are still firm and reposition the clamp to
apply pressure to a still solid joint. Continue
this until all the plates are loose (The joint between the two left lateral
plates need not be broken).
place the barnacle in a small dissecting pan of isotonic magnesium chloride (or
water, if preserved) and place it on the stage of the dissecting microscope at
low power. Use scalpel, needles, fine scissors, and forceps, as required, to
remove the rostrum, carina, and right lateral plates from the outer surface of
the mantle. Carefully
separate the plates from the underlying soft tissue first using scissors to cut
the tough mantle and then the scalpel to separate the soft tissue from the
not cut into the body of the animal.
that the mantle joins the plates about halfway up their walls. Keep
the animal's orientation in mind as you work (Fig 1). Keep
the two left lateral plates and the opercular plates intact. They
will help support the soft body of the barnacle and also serve as useful
at the left side of the opercular plates. Note
the large tergal spur,
a process on the lateral border of the tergum. It
also makes a useful landmark (Fig 3).
the animal in the pan so that the exposed right side is up and facing you and
the animal's anterior end is to your left. Look
at the soft tissue you have exposed. Organs
will be studied in the order they appear in the dissection rather than in a
standard order or by organ system.
mantle should still be intact after its calcareous plates have been removed. It
is a thin, darkly pigmented in places, layer consisting mostly of epithelium and
a thin chitinized cuticle. The
soft tissue adjacent to the basis is derived from the greatly enlarged preoral,
the remainder of the animal is postoral.
Figure 3. The
opercular plates from the left side of an ivory barnacle, Balanus
eburneus, from Ft. Pierce,
The ovary is
a large, highly branched, yellowish (in life) organ occupying most of the
preoral head along the dorso-lateral length of the animal near the junction of
the lateral plates and the basis (Fig 4, 19-78A). It
consists of numerous narrow lobes. The
other ovary is on the left side but you will not see it now.
a wetmount of a small piece of ovary and use the compound microscope to look for
should be abundant and yolky. <
sets of opercular muscles can
be seen at present. Except
for the scutal adductor, they originate on the immovable plates of the wall and
insert on the movable plates of the operculum. The
muscles are white and fibrous but may be covered with a darker connective
depressor muscles originate
on the anterior basis and dorsal rostrum to insert on the antero-dorsal corner
of the scutum (Fig 4, 19-78A). The scutal
abductor muscleinserts on the posterior lateral edge of the scutum.
powerful tergal depressor muscle extends
from the dorsal posterior edge of the tergum to the posterior basis and dorsal
muscles all work together to move the right scutum and tergum laterally and
dorsally, thus opening the aperture. An
identical set of muscles is present on the left side. These
muscles oppose the unpaired scutal adductor muscle, which you have already seen
and whose action is to move the right and left scutum and tergum medially and
ventrally to close the aperture.
Figure 4. View
of the right side of a dissected Balanus
fine scissors to make a longitudinal cut through the right lateral mantle just
ventral to the ovary (remember that ventral is toward the aperture, dorsal
toward the basis). Extend
this cut from anterior to posterior ends of the barnacle. Cut
only through the translucent mantle. This
will open the mantle cavity from
Reproduction and Development
mantle cavity may be filled with eggs or shelled nauplius larvae enclosed in a
pair of membranous ovisacs secreted by the female system. Eggs
are released into the mantle cavity by the female system where they are
fertilized by sperm from a nearby individual. The
eggs are brooded and naupliar stages are passed in ovisacs in the mantle cavity. Each
nauplius is enclosed in a transparent eggshell from which it will eventually
emerge before leaving the mantle cavity. Some
barnacles retain the larvae in the mantle cavity to the next larval stage, which
is the cypris.
nauplius larva is the characteristic crustacean larva (Fig 5, 19-79A). It
has a large unsegmented head with three pairs of appendages, viz. antenna
1, antenna 2, and mandibles, and a large median naupliar eye. The
barnacle nauplius is easily distinguished from other crustacean nauplii by a
pair of secretory frontal horns on the anterolateral corners of the head.
nauplii are available, either from the mantle cavity of your specimen or from a
plankton tow, make a wholemount and examine one with the compound microscope. Find
the two pairs of antennae, mandibles, and the naupliar
your nauplius of a barnacle it will have frontal
removed from the mantle cavity will be enclosed in the eggshell and the horns
will not be visible. A
few nauplii may have broken from their shells and will be easier to examine. <
Figure 5. The
nauplius of an unidentified barnacle species from a plankton tow made at
Beaufort, North Carolina. Barnacle21L.gif
cypris is the characteristic barnacle larva (Fig 19-79B). It
has a bivalve carapace resembling that of a clam, or more appropriately, an
ostracod (Fig 19-85). As
in other crustaceans, the carapace is an expanded fold of the body wall of the
posterior edge of the head. It
is bivalves and its large valves gape ventrally as do those of a clam, ostracod,
or cladoceran. The
aperture of the adult barnacle develops from the ventral gape of the cypris. Within
the two valves is a small crustacean with two compound eyes, a naupliar eye, the
first antennae, six pairs of thoracic appendages, and a vestigial abdomen.
cypris is a type of zoea larva. (Zoea
are larvae that swim using thoracic appendages whereas nauplii use head
zoea stage follows the nauplius, of course.) The
lecithotrophic cypris does not feed. It
swims for a week or two in the plankton and then settles on a suitable hard
moves over the substratum using its first antennae as legs. When
it finds an acceptable site it attaches using these same antennae and then
secretes an adhesive, again using the first antennae, to attach itself
then undergoes metamorphosis to a miniature barnacle with the shape of the
settled barnacles are known as spat.
living or preserved cypris larvae are available, examine them and find the
structures described above. <
all the reproductive stages and the ovisac from the mantle cavity so you can
clearly see the structures within. Remember
that the mantle cavity is a small pocket of seawater partly enclosed by the
animal but continuous with the sea through the aperture (Fig 1). Don't
let the fact that you exposed it by cutting through the body wall mislead you
into thinking it is an internal cavity. Demonstrate
the continuity between mantle cavity and exterior by passing a needle or probe
through the aperture into the space exposed by your lateral incision.
is easiest to study the thorax first and then move anteriorly to the head. Find
the large bulbous thorax extending
dorsally and posteriorly in the mantle cavity (Fig 4, 19-78A). There
is no abdomen.
your attention to the conspicuous cuticularized (but not calcified) biramous
thoracic appendages (= thoracopods)
arising along the ventral surface of the thorax. Six pairs are present. The
appendages extend ventrally into the mantle cavity and, as you know, can be
extended from the aperture to feed (Fig 19-80B).
six pairs of thoracopods are known as cirri and
are numbered anterior to posterior. The
two similar rami of
each thoracopod are long, multiarticulate, and whiplike. The
rami bear numerous, long, evenly spaced setae along
one edge. The
six pairs of cirri have a total of 24 rami. The
posterior cirri are the longest and the anterior ones are shorter but more
the cirri form a cast net that is extended from the aperture and swept
anteriorly through the water to collect phytoplankton or small zooplankton.
the series of cirri anteriorly from the sixth to the first pair noting that they
decrease in length anteriorly but become stouter. The
rami of the first pair are the shortest of all.
a ramus from one of the posterior cirri and make a wetmount of it. Examine
it with 100X of the compound microscope and confirm that it is composed of many
article bears a fringe of long, evenly spaced setae on
one edge. Do
you think this structure, sweeping through the water in concert with 23 others
like it, would make a good filter? <
a living, unanesthetized barnacle in a dish or aquarium. It may exhibit the
characteristic feeding behavior of barnacles. With
the aperture open the barnacle extends its setose thoracic appendages in the
characteristic "casting" motion barnacles use for feeding. The
six pairs of cirri are swept, posterior to anterior, through the water to remove
>1f. Balanus has
a pair of light sensitive ocelli and usually responds to a shadow by withdrawing
the cirri and closing the aperture. Pass your hand over the living,
unaesthetized, feeding barnacles in an aquarium or dish to block the light. <
The anus lies
at the bottom of a deep pocket on the dorsal midline just dorsal to the bases of
the sixth cirri. The penis also
arises from the body wall ventrally between the bases of the sixth cirri. There
is no mistaking the penis. It
is a long flexible tube capable of achieving impressive lengths when extended. It
must be able to reach to other barnacles and deposit sperm in the mantle cavity. An
8-mm barnacle can extend its penis 50 mm to visit a neighbor.
The head and
its appendages are anterior to the first pair of cirri of the thorax (Fig 4,
is divided into a large preoral region and a much smaller postoral region. The
first antennae are in the preoral region of the head attached to the substratum
and the second antennae are absent. Consequently,
barnacles have only four pairs of head appendages, three of them mouthparts.
6. Mouth cone and mouthparts of the goose barnacle, Pollicipes. barnacle16L.gif.
mouthparts form a mouth cone surrounding
the mouth on the ventral midline. Posteriormost among the head appendages are
the second maxillae (Fig
are closest to the first cirri and are the posterior border of the mouth cone. They
are large and lie closer to the midline than do any other head appendages. Their
bases are fused together across the midline. Distally,
each bears a dense fringe of long setae on its anterior border.
maxillae are smaller than
the second and are anterior to and a little lateral to them (Fig 6). Each
has a row of short, stout spines on its distal end.
The mandibles are
anterior to the first maxillae (Fig 6). Each
consists of a base from which arises a large, setose mandibular palp and a
smaller medial endite. The
endite is tucked out of sight between the palp and the first maxilla. It
bears coarse teeth on its distal edge.
The mouth lies
on the midline between the two mandibular endites. It
is surrounded by the mouthparts and labrum.
cuticularized bilobed fold of the body wall, the labrum,
or upper lip, forms a semicircle around the anterior edge of the mouth (Fig 6). It
is not a segmental appendage.
first antennae are the attachment organs of barnacles and are located on the
dorsal surface in the basis, far removed from the other head appendages. You
will not see them.
scutal adductor muscle, which you saw earlier, lies anterior to the head (Fig 4,
6, 19-78A). A
tiny eye, which you probably will not see, is located near this muscle. You
may have noticed earlier that barnacles are aware of light and dark when you
watched it close the aperture and ceased casting when a shadow passed over it.
of the two ovaries connects to the exterior by a long oviduct, which is
difficult to find. Each
oviduct opens into the mantle cavity via a female
gonopore located laterally at
the base of the first cirri.
oviducal gland (= egg sac gland) is a swollen, secretory, glandular expansion of
the distal end of the oviduct just proximal to the gonopore. It
is manifest externally by a large swelling at the base of the first cirrus. The
oviducal gland secretes the thin, elastic ovisac which encloses the eggs and
embryos in the mantle cavity. The
ovisac prevents developing eggs from becoming caught in the feeding current and
being swept from the mantle cavity. It
gradually deteriorates to allow the escape of the larvae at the appropriate
slit-like female gonopore is at the dorsal end of the swelling and is hidden by
the overhanging cuticle of the exoskeleton.
The gut is
located within the head and thorax and much of it can be seen through the thin
body wall (Fig 4, 19-78A). In
living material much of the digestive system is pale yellow or brownish. It
consists of a mouth, esophagus, stomach, intestine, and anus. You
have already seen the mouth and anus. The
intestine can be seen through the body wall near the surface on the dorsal,
posterior midline of the thorax. It
disappears from view beneath the bases of the posterior cirri. The
stomach occupies most of the anterior thorax and head and is surrounded by the
yellowish digestive ceca,
which can be seen without dissection in living material.
you wish to expose the gut, proceed as follows. Carefully
open the right side of the thorax, using your finest scissors to cut
longitudinally through the thin, transparent body wall from posterior to
not cut deeper than the body wall.
find the short esophagus,
first remove the head appendages on the right side. Insert
the blade of a fine pairs of scissors into the mouth and let it follow the lumen
of the esophagus dorsally. When
you have the blade in place in the esophagus, close the scissors to cut through
the intervening tissue and expose the esophageal lumen. The
esophagus is a short, straight tube extending dorsally from the mouth into the
anterior end of the stomach.
the stomach is
surrounded by the yellowish (in life), lobulated digestive
stomach occupies much of the preoral head and extends into the anterior thorax.
your fine scissors to extend the existing incision and open the stomach. Cut
posteriorly, opening the lumen of the gut as you go. At
first you will cut through yellow digestive
cecum but posteriorly the stomach is surrounded by the white (in life) testes. Try
to avoid cutting the long, curved, bright white (in life) vas deferens.
stomach is a spacious chamber extending posteriorly to the anterior dorsal
corner of the bulge of the thorax (Fig 4). Here
it narrows to become the intestine,
which runs just beneath the surface, along the posterior edge of the thorax to
barnacles, including Balanus,
are hermaphroditic. You
have already seen the penis, ovaries, female gonopores, and maybe the testes. The
paired testes are
whitish, highly branched tubes draining innumerable tiny spherical testicular follicles where
sperm are produced. The
testes occupy the anterior thorax and fill most of the space around the gut in
this region. They can
be seen faintly through the body wall.
testis drains via a vas deferens into a large, bright white (in life) seminal
vesicle which leads to the
base of the penis (Fig 4). It
can be seen through the body wall of living specimens.
seminal vesicle originates on the ventral surface of the stomach as the fine
tubes from the testicular follicles coalesce. It
extends posteriorly on the surface of the stomach, then extends along the bases
of the cirri to the base of the penis. The
right and left seminal vesicles coalesce at the base of the penis to become the
sperm duct. This
duct extends through the penis to open via the male gonopore at the tip of the
most arthropods, barnacles have flagellated sperm, a trait that is taken as
evidence of their primitive condition.
some of the testis and vas deferens from the thorax and make a wetmount using
the preparation with 400X and look for sperm. Their
long flagella are easily seen at the end of a narrow, elongate head. <
to the vicinity of the left tergal spur and note a large, conspicuous,
membranous gill on
the mantle. It is composed of large membranous sacs attached to a long central
extends out into the mantle cavity. There
is one on the right also and you may have noticed it earlier and wondered what
it was. The
entire mantle epithelium is thought to function in gas exchange but the gill is
specialized for that purpose and has thinner walls than the rest of the mantle. It
is hollow and blood circulates through it.
A. 1970. Invertebrate
Zoology, vol. III, Crustacea. Wiley,
New York. 523p.
JH. 1950. Lepas
anatifera, pp 413-418 in Brown FA (ed), Selected Invertebrate Types. Wiley,
New York. 597p.
Ruppert EE, Fox RS,
Barnes RB. 2004.
Invertebrate Zoology, A functional evolutionary approach, 7 th ed.
Brooks Cole Thomson, Belmont CA. 963 pp.
G. 1992. Cirripedia. in
Harrison, F. W. & A.
G. Humes (eds.). Microscopic
Anatomy of Invertebrates vol. 9 Crustacea. Wiley-Liss,
New York. pp249-312.
VA. 1979. Marine
flora and fauna of the northeastern United States. Arthropods: Cirripedia. NOAA
Tech Rep. NMFS Circ 425: 1-28.
Slides and coverslips
Large living (anesthetized) or preserved acorn barnacle
Isotonic magnesium chloride
Small dissecting pan (sardine tin with wax bottom
Living specimens should be placed in isotonic
magnesium chloride about 60 minutes before needed.
If possible living, active specimens should be
available in a dish or aquarium for behavioral observations.