Invertebrates Flashcards
what is an alternative phylogeny for ecdyzoans?
One problem with the previous phylogeny of the protostomes is that it places the tardigrades as the sister
group to the nematodes, which complicates our understanding of the evolution of segmentation and other characters associated with arthropods (paired limbs with claws).
• Telford et al. (2008) proposed an alternative phylogeny of the Ecdysozoa which places the tardigrades + onychophorans as the sister group to the Arthropods
(Eurarthropods).
describe the external anatomy of an insect
insects all have exoskeletons, a hard outer layer made mostly of chitin which protects and supports the body. The insect body is divided into three parts: the head, thorax, and abdomen. The head is specialized for sensory input and food intake; the thorax, which is the anchor point for the legs and wings (if present), is specialized for locomotion; and the abdomen for digestion, respiration, excretion, and reproduction
the exoskeleton is made up of two layers; the epicuticle, which is a thin, waxy, water-resistant outer layer and contains no chitin, and the layer under it called the procuticle. This is chitinous and much thicker than the epicuticle and has two layers, the outer is the exocuticle while the inner is the endocuticle. the exoskeleton is greatly reduced in the larval stages of insects however (caterpillars for example)
The head in most insects is enclosed in a hard exoskeletal head capsule, or epicranium. the epicranium bears most of the main sensory organs, including the antennae, ocelli, and the compound eyes. It also bears the mouthparts
Most insects have one pair of large, prominent compound eyes composed of units called ommatidia which gives less resolution than vertebrate eyes but better movement perception
insects have antenna covered in setae which allow it to sense smell, and detect the environment around it
insects have mandibles which are used to cut up food The mouthparts vary greatly between insects of different orders, but the two main functional groups are mandibulate and haustellate. Haustellate mouthparts are used for sucking liquids and mandibulates are for chewing and cutting.
The insect thorax has three segments: the prothorax, mesothorax, and metathorax. The anterior segment, closest to the head, is the prothorax; its major features are the first pair of legs and the pronotum. The middle segment is the mesothorax; its major features are the second pair of legs and the anterior wings, if any. The third, the posterior, thoracic segment, abutting the abdomen, is the metathorax, which bears the third pair of legs and the posterior wings
The typical and usual segments of the insect leg are divided into the coxa, one trochanter, the femur, the tibia, the tarsus, and the metatarsus.
The abdomen of an adult insect typically consists of 11–12 segments and is less strongly sclerotized than the head or thorax.
describe Solifugae and their key features
camel spiders, wind scorpions, and sun spiders
The most distinctive feature of Solifugae is their large chelicerae. Each of the two chelicerae are composed of two articles forming a powerful pincer; each article bears a variable number of teeth. Males in all families but Eremobatidae possess a flagellum on the basal article of the chelicera. Solifugae also have long pedipalps, which function as sense organs similar to insects’ antennae and give the appearance of the two extra legs. Pedipalps terminate in reversible adhesive organs.
what are the distinguishing features of molluscs?
The three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system. Other than these things, molluscs express great morphological diversity, so many textbooks base their descriptions on a “hypothetical ancestral mollusc”
Although molluscs are coelomates, the coelom tends to be small, and the main body cavity is a hemocoel through which blood circulates; their circulatory systems are mainly open.
A striking feature of molluscs is the use of the same organ for multiple functions. For example, the heart and nephridia (“kidneys”) are important parts of the reproductive system, as well as the circulatory and excretory systems; in bivalves, the gills both “breathe” and produce a water current in the mantle cavity, which is important for excretion and reproduction. In reproduction, molluscs may change gender to accommodate the other breeding partner.
what are the similarities of annelids and arthopods to infer an evolutionary relationship between them?
Characteristics shared with the Arthropoda include serial
arranged body segmentation (metamerism), double ventral nerve cord, dorsal and ventral longitudinal muscles, and a dorsal blood vessel with forward-going peristalsis.
Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share similar traits to arthropoda
describe sporpiones and their key features
Scorpions are characterised by a metasoma (tail) comprising six segments, the last containing the scorpion’s anus and bearing the telson (the sting). The telson, in turn, consists of the vesicle, which holds a pair of venom glands
the mesosoma, is made up of six segments. The first segment contains the sexual organs as well as a pair of vestigial and genital operculum.
The second segment bears a pair of featherlike sensory organs known as the “pectines”; the final four segments each contain a pair of book lungs. The mesosoma is armored with chitinous plates, or tergites.
Unlike the majority of Arachnida species, scorpions are viviparous. The young are born one by one, and the brood is carried about on its mother’s back until the young have undergone at least one moult
what do you think is the most basal metazoan and why?
A group of extinct metazoans, possibly the most basal of all metazoans, possibly not, are the Ediacaran fauna, a group of quilted mattress and bag-like organisms that lived an extremely long time in the past, during the Ediacaran period, between about 600 and 542 million years ago. These animals have been classified by some workers in their own group, Vendobiota, on the basis of their similar “quilted” appearance, although there is great controversy over this. The Ediacaran fauna has been described as an “early failed experiment in animals.”
what are opliomes and describe their key features
Opiliones are daddy long legs and harvestmen.
known for their exceptionally long walking legs, compared to their body size.
The difference between harvestmen and spiders is that in harvestmen the two main body sections (the abdomen or opisthosoma with ten segments and the cephalothorax or prosoma) are nearly joined, so that they appear to be one oval structure. In more advanced species, the first five abdominal segments are often fused into a dorsal shield called the scutum, which is normally fused with the carapace. Sometimes this shield is only present in males
second pair of legs is longer than the others and works as antennae. They have a single pair of eyes in the middle of their heads, oriented sideways. They have a pair of prosomatic scent glands
what is a basal metazoan?
metazoans are multicellular animals, basal metazoans refer to animals at the base of the evolutionary tree
basal refers to a region at the base or root of a phylogenetic tree. Thus, referring to an extant taxon or species as basal, or as more basal than another, can be misleading.
describe the evolutionary relationships between the invertebrate phyla
introduction section
The basic evolutionary relationships between the various marine invertbrate groups were determined in the 19th century by compariing the developmental (growth) stages of individual organisms. On the basis of the patterns of cell division and early structural development of the bastula[*] stage in development, two major evolutionary lines were seen, the Deuterostomes and the Proterostomes
The evolutionary relationships are based on assumptions about how the embryos develop and the similarity in their molecular structure. The many complex structures, such as gills, lungs, digestive systems, muscles, and flight structures, that had to evolve did so without a known mechanism.
as these organisms continued to evolve, they invaded the land and had to overcome the many challenges that they faced there. Competition for resources, both in the sea and on land, caused a wide variety of body plans to develop.
Annelids, arthropods and mollusks are all protostomes. Echinoderms and chordates are deuterostomes.
what features do cnidarians have that distinguish them from ctenophores? what are the differences between the two?
Cnidarians are distinguished from all other animals by having cnidocytes that fire like harpoons and are used mainly to capture prey. In some species, cnidocytes can also be used as anchors.
ctenophores: Most species have two opposing retractable tentacles before the mouth opening, which spring from each sheath to catch prey. On the side they often bear a row of fibrous filaments, which unlike cnidaria do not contain stinging cells, but colloblasts or “lasso cells.”
Cnidocyte is also called the “stinging cell”. Cnidae are used for prey capture and defense from predators.
There are also morphological differences between the groups. Ctenophores are called comb jellies because many of them have 8 rows of stiffened cilia that function as paddles to propel the animal through the water. Cnidarians do not have comb rows; medusae swim by contracting and releasing the bell, in a sort of gentle jet propulsion. So while ctenophores glide smoothly through the water, medusae (cnidarians) swim with a more jerky pulse-glide-pulse-glide motion.
Radial symmetry is considered an adaptation for living in the open waters of the seas because it allows the animal to encounter its environment in all directions. Although medusae and ctenophores appear to have the same kind of radial symmetry, a closer look at their respective anatomies reveals differences. Medusae have more or less truly radial symmetry. On the other hand, ctenophores such as Pleurobrachia have bi-radial symmetry. The pharynx of the animal is an elongate slit, which creates one plane of bilateral symmetry, and the plane of the two tentacles is at right angles to that of the pharynx. The pharyngeal and tentacular planes of bilateral symmetry are both superimposed over the radial symmetry produced by the 8 comb rows, hence the term “bi- radial symmetry.”
ctenophores do not have true muscle tissue unlike cnidarians, ctenophore muscles are Mostly myoepithelial whereas cnidarians are Mostly epitheliomuscular.
cnidarians also have Two cell layers that sandwich a middle layer of jelly-like material, which is called the mesoglea and ctenophores tend to have Two or Three suggesting they can be tripoblastic. cnidarians have been said to have evolved from tripoblastic ancestors.
Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa.[14] In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks.[15] For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.
describe the adaptations to parasitism in worms
flatworms/plateminthes
+/- relationship, good for worm bad for host
- hooks on the mouth to allow feeding whilst securely attached to host, In adult flatworms, in the upper half of the body, acetabulum is present which act as anchoring structure e.g. Fasciola.
- no digestive (tropic organs) development necessary for for free living. this is due to eating food the host has already digested, the alimentary canal has either totally disappeared (e.g. Taenia solium) or exhibit fair degree of degeneration (e.g. Fasciola, Ascaris).
- development of teguments around the body to protect against digestive fluids - the cuticle is resistant to host’s digestive enzymes, antitoxin and abrasive action of the food and roughage passing through the digestive tract.
- easily colonise a hosts body via sexual reproduction with other flatworms or lay eggs via aexual reproduction if alone
- flat body shape allows life without a circulatory system as the cells are close enough to the surface to receive oxygen and eliminate waste
Important organs in which degeneration have occured are –
locomotory -Since the parasite reside in the host body where they live well protected and nourishment readily available, there is no need to move. Hence, the locomotary organelles are completely lost. However, in cases where the larval forms are free l.ving, the locomotary organs in the form of cilia reappears
nervous system - The endoparasite live in a well protected and more or less stable enviornment inside host’s body in perpetual darkness, there is no need of complex form of nervous system, consequently the photoreceptor organs (eyes) and other sense organs have completely lost. The central and peripheral nervous system have also reduced considerably as compared to the other free living species of the same phylum
why are blood worms and sludge worms more successful at surviving pollution than stone and mayflies
bloodworms and sludge worms are red because they contain haemoglobin. They take in oxygen by diffusion over the whole of their body surface. This allows them to survive in water with lower oxygen concentrations than other similar organisms. Mayfly and stonefly nymphs breathe using external gills. They have no haemoglobin, so the oxygen circulates in their bodies in simple solution. This means they need a higher concentration of oxygen to survive than bloodworms and sludge worms. In unpolluted water, with a high concentration of oxygen, nymphs are more mobile than worms and compete more successfully for food than the worms.
why are riverflies important bio indicators?
Riverflies, along with other freshwater invertebrates, are at the heart of the freshwater ecosystem and are a vital link in the aquatic food chain. Riverfly populations are affected by many factors, predominately water quality, habitat diversity, water level and flow rate. Their common characteristics of limited mobility, relatively long life cycle, presence throughout the year and specific tolerances to changes in environmental conditions make them powerful biological indicators to monitor water quality, and are commonly referred to as ‘the canary of our rivers.’
why is Edicaran fauna not a basal metazoan? or what are the arguments against it being classified as one for definite
The Ediacaran fauna has been described as an “early failed experiment in animals.” Since this group is long-extinct, we’ll never get our hands on its genetic material, and are limited to making guesses based exclusively on crude morphology.
it is extinct and cannot be scientifically tested.
how have parasitic worms adapted to avoid being digested by the host
(a) Strong impermeable cuticle has developed around the parasite.
(b) The parasite stimulates the host gut to secrete huge amount of mucous that surrounds the parasite and protect it from the digestive juice of the host.
(c) Most of the parasites produce antienzymes which protect them from the gastric juice and digestive enzymes of the host.
(d) It has been reported that the lime cells present in the body wall of the tapeworms neutralizes the acidic effect of the gastric juice.
what do phylogenetic studies suggest on the evolutionary relationships between invertebrates
Recent phylogenetic analysis based on
molecular characters (Dunn et al 2008)
suggest two major lineages within the
Protostoma: 1) the superphylum Lophotrochozoa, which
include the molluscs, the annelids several other
phyla, and 2) the Ecdysozoa, which include the
Arthropoda, Onychophora, Tardigrada and
Nematoda.
• The lophotrochozans are split into two groups
those that have lophophores, a fan of ciliated
tentacles surrounding the mouth (bryozoans,
brachiopods, ectoprocts, and phoronids) and
those that have trochophore larvae (molluscs
and annelids, and several other worm-like
groups). There is debate on whether these
subgroups are monophyletic, or even whether
the lophophorates are protostomes!
• The ecdysozoans all share a three-layered
cuticle composed of organic material, which is
periodically molted as the animal grows, hence
the name. There is still controversy over
whether this group is monophyletic and some
researchers still place the annelids as the sister
group to the arthropods or the panarthropods
(arthropods + onychophorans
what are the four main classes of cnidarians?
Scyphozoa (jellyfish)
Anthozoa, (sea anemones, corals)
Hydrozoa (portugease man o war, fresh water jellyfish, hydra,
Cubozoa (box jellyfish)
how did nemotode parasites likely evolve?
nemodermata likely made the parasitic shift by epithelial feeding to blood feeding suggesting they were sucessfully opportunistic leading to an eventual obligate parasite lifestyle
describe the life cycle of a crustacean
At its most complete, a crustacean’s life cycle begins with an egg, which is usually fertilised, but may instead be produced by parthenogenesis. This egg hatches into a pre-larva or pre-zoea. Through a series of moults, the young animal then passes through various zoea stages, followed by a megalopa or post-larva. This is followed by metamorphosis into an immature form, which broadly resembles the adult, and after further moults, the adult form is finally reached. Some crustaceans continue to moult as adults, while for others, the development of gonads signals the final moult.
Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the vestige of the fourth pereiopod in the larvae of Lucifer, and some pleopods in certain Anomura and crabs.
what are the differences between echinoderm and poferia reproduction
echinoderms synchronise sexual reproduction to lunar cycles while others aggregate during the reproductive season to maximise chances of fertilisation.
Some echinoderms brood their eggs. This is especially common in cold water species where planktonic larvae might not be able to find sufficient food. These retained eggs are usually few in number and are supplied with large yolks to nourish the developing embryos. e.g. In starfish, the female may carry the eggs in special pouches, under her arms, under her arched body or even in her cardiac stomach
One species of seastar, Ophidiaster granifer, reproduces asexually by parthenogenesis (growth and development of embryos occur without fertilization)
what is the order Amblypygi and describe its key features
Amblypygi are whip scorpions (tailess), Their bodies are broad and highly flattened and the first pair of legs (the first walking legs in most arachnid orders) are modified to act as sensory organs
These very thin modified legs can extend several times the length of body. They have no silk glands or venomous fangs, but can have prominent pincer-like pedipalps. Amblypygids often move about sideways on their six walking legs, with one “whip” pointed in the direction of travel while the other probes on either side of them. Prey are located with these “whips”, captured with pedipalps, then torn to pieces with chelicerae
what is the evolutionary relationship of echinoderms in invertebrates
Echinoderms evolved over 650 million years ago. Based on deuterostome development pattern, echinoderms share a recent common ancestor with vertebrates
what are the main phylums of invertebrates
Protozoa (like the worms, an arbitrary grouping of convenience; link to their article for details)
Sponges (Porifera)
Stinging jellyfish (Cnidaria)
Comb jellies (Ctenophora)
Flatworms (Platyhelminthes)
Round- or threadworms (Nematoda)
segmented worms (Annelida)
Insects, spiders, crabs and their kin (Arthropoda)
Cuttlefish, snails, mussels and their kin (Mollusca)
Starfish, sea-cucumbers and their kin (Echinodermata)
what are the two types of metamorphosis in crustaceans
Two strategies are followed by various groups of crustaceans. A group is either “direct developers” that emerge from the egg fully formed and only increase in size as they mature, or they exhibit anamorphic growth. In anamorphic growth the morphology of the individual that emerges from the egg changes with each molt. Usually the changes involve adding segments and appendages as well as increasing in overall size. Some animals show much more dramatic changes as they metamorphose, like those seen in the stomatopod . In anamorphic growth, the larvae often look nothing like the adult.
what two species are useful for indicating clean water?
stone fly
fresh water shrimp
describe some reasons for or methods of polluting water
more fossil fuels being burnt for heat and power
more food being grown
land taken over for industry and housing.
As a result there has been an increase in levels of water pollution.
Nitrate fertilisers are very soluble in water and are easily washed off fields by the rain and then into rivers and reservoirs. Because nitrates are all soluble they cannot easily be removed from the water.
Pesticides used by farmers to kill weeds or insects may be washed or blown into streams and rivers.
Sulfur dioxide in the air can dissolve in water to form an acidic solution
eutrophication:
A major problem with the use of fertilisers occurs when they’re washed off the land by rainwater into rivers and lakes. The resulting increase of nitrate or phosphate in the water encourages algae growth, which forms a bloom over the water surface. This prevents sunlight reaching other water plants, which then die. Bacteria break down the dead plants and use up the oxygen in the water so the lake may be left completely lifeless.
what are the 6 major classes of mollusca
gastropoda (snails and slugs)
Cephalopoda ( octopuses, squid, and cuttlefish; and Nautiloidea)
Polyplacophora (chitins)
Bivalvia (clams, oysters, cockles, musssels, scallops)
why are invertebrates important for or used as bio indicators for pollution and water quality
Different species of aquatic invertebrates can survive in polluted water, while others cannot. As such, scientists often take a sample of the invertebrates living in a water source and use the species in the sample to assess the level of pollution in the water. A sample with invertebrates like fresh water shrimp and mayfly larva indicates clean water, because these species have very low tolerance for any pollution. If scientists find water with many rat-tailed maggots (aquatic larvae of droneflies found throughout the uk) or sludge worms, however, they can be sure that the water is highly polluted because these species survive well in polluted waters.
what inverts are uk freshwater habitats usually made up of?
The orders Ephemoptera (mayflies), Plectoptera (stoneflies), and Trichoptera (caddisflies) are important bio indicators for clean water as they are highly pollution sensitive
blood worms, rat tail worms, sludge worms are important polluted water indicators
reasons for ctenophores as basal metazoans
Ctenophores are the sister group of all other animals
- Nervous system components are like those of sponges- sponges
might have the structural components for a nervous system but
lost these cell types…so secondarily without a nervous system!
- Genes for mesodermal cells present but lack other animal
mesodermal gene components- may be independently evolved
what features do cnidarians have that distinguish them from ctenophores? what are the differences between the two?
Cnidarians are distinguished from all other animals by having cnidocytes that fire like harpoons and are used mainly to capture prey. In some species, cnidocytes can also be used as anchors.
ctenophores: have colloblasts instead.
Cnidocyte is also called the “stinging cell”. Cnidae are used for prey capture and defense from predators.
There are also morphological differences between the groups. Ctenophores are called comb jellies because many of them have 8 rows of stiffened cilia that function as paddles to propel the animal through the water.
Cnidarians do not have comb rows; medusae swim by contracting and releasing the bell, in a sort of gentle jet propulsion. So while ctenophores glide smoothly through the water, medusae (cnidarians) swim with a more jerky pulse-glide-pulse-glide motion.
Radial symmetry is considered an adaptation for living in the open waters of the seas because it allows the animal to encounter its environment in all directions.
Although medusae and ctenophores appear to have the same kind of radial symmetry, a closer look at their respective anatomies reveals differences.
Medusae have more or less truly radial symmetry. On the other hand, ctenophores such as Pleurobrachia have bi-radial symmetry.
The pharynx of the animal is an elongate slit, which creates one plane of bilateral symmetry, and the plane of the two tentacles is at right angles to that of the pharynx.
The pharyngeal and tentacular planes of bilateral symmetry are both superimposed over the radial symmetry produced by the 8 comb rows, hence the term “bi- radial symmetry.”
ctenophores do not have true muscle tissue unlike cnidarians, ctenophore muscles are Mostly myoepithelial whereas cnidarians are Mostly epitheliomuscular.
cnidarians also have Two cell layers that sandwich a middle layer of jelly-like material, which is called the mesoglea and ctenophores tend to have Two or Three suggesting they can be tripoblastic. cnidarians have been said to have evolved from tripoblastic ancestors.
Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa.
In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks.[15] For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.
describe the internal anatomy of a typical insect
Circulatory System An insect’s blood does not flow through veins and arteries as ours does. Blood fills the whole cavity of the insect’s body, and bathes all the organs and muscles. The blood is circulated by a long tube that lies just under the exoskeleton of the back. This tube extends almost the entire length of the body. The pumping part of the tube lies in the abdomen, and is called the heart. The front part of the tube extends into the head, and is called the aorta. Blood enters the tube through little openings, called ostia, along the sides. The openings have valves that allow blood to enter the tube, but not to flow out. As the heart contracts, the blood is forced along the tube and out through the aorta. The blood first bathes the brain, and then flows to other parts of the body. It then re-enters the tube through the ostia.
Unlike our blood, an insect’s blood has little to do with bringing oxygen to the cells. Insect blood is greenish, yellowish, or colorless. Few insects have red blood.
Respiratory System An insect breathes by means of tiny holes, called spiracles, along the sides of its body. Each hole leads into a large tube called a trachea. The large tubes divide into small tubes, which, in turn, divide into still smaller tubes that branch out to all the cells of the body. This system of tubes carries oxygen to the cells and takes away carbon dioxide.
Nervous System consists of a brain, located in the head, and two nerve cords that lie side by side along the floor of the thorax and abdomen. The brain receives information from the eyes and antennae, and controls the insect’s body activities as a whole. Another nerve center in the head is connected to the brain and controls the insect’s mouth parts. Each of the two nerve cords contains a cluster of nerve cells, called a ganglion, in each segment of the thorax and abdomen. The two ganglia in each segment are fused and form a sort of little brain that controls the activities of that segment. The ganglia often can work without the brain. For example, many insects that have had their heads cut off can still walk, mate, and lay eggs. In some insects, the three pairs of ganglia in the thorax are fused into one. Various pairs of ganglia in the abdomen are also fused in many insects.
Muscular System is made up of several hundred to a few thousand small but very strong muscles. Grasshoppers have about 900 muscles, and caterpillars have from 2,000 to 4,000. By contrast, man has fewer than 700 muscles. Many insects can lift or pull an object 20 or more times heavier than the weight of their bodies. Few men can lift a weight heavier than the weight of their bodies.
Digestive System of an insect consists basically of a long tube that extends from the mouth to the anus. The tube has three main divisions: (1) the foregut; (2) the midgut, or stomach; (3) the hindgut, or intestine.
After food has been chewed or sucked up by the mouth parts, it enters the foregut through the mouth. The food moves along the tube until it reaches an enlarged area called the crop, where it is temporarily stored and partly digested. Then the food passes into the gizzard, which has thick muscular walls that contract and grind the food into small bits. The gizzard of some insects has teeth that help break up and grind the food. The food next passes into the midgut, where most digestion takes place. Nourishing parts of the food are absorbed into the blood, and wastes and undigested parts move into the hindgut.
Insects have a system of 2 to over 150 malpighian tubes attached to the digestive system where the midgut and hindgut join. The tubes float in the blood and absorb waste materials, which then pass through the tubes into the hindgut. All wastes and extra water that enter the hindgut leave the body through the anus.
Reproductive System Most insects reproduce sexually. That is, a new individual can be created only after a female sex cell (egg) has united with a male sex cell (sperm). The reproductive organs are in the abdomen. Females have two organs, called ovaries, in which eggs develop. A tube called an oviduct carries the eggs away from each ovary. The two oviducts join and form a single tube that opens near the tip of the abdomen. Male insects have two organs, called testes, that produce sperm. A tube carries the sperm from each testis. The two tubes unite and form a single tube that extends to the outside of the abdomen.
