Which Of The Following Animals In Not An Example Of A Member Of Clade Lophotrochozoa?

Identify the common characteristics of superphylum Lophotrochozoa

There are five phyla in the superphylum Lophotrochozoa (too known as the crest or cycle animals): Platyhelminthes, Rotifera, Nemertea, Mollusca, and Annelida. These phyla include animals from flatworms to squids. While these may seem like very different creatures, they share characteristics that place them together in the tree of life. Let'due south figure out just what makes these animals part of the aforementioned superphylum.

Learning Objectives

• Identify common structural and organization characteristics of the superphylum Lophotrochozoa
• Depict the unique anatomical and morphological features of flatworms
• Draw the unique anatomical and morphological features of rotifers
• Describe the unique anatomical and morphological features of Nemertea
• Describe the unique anatomical and morphological features of mollusks
• Draw the features of animals classified in phylum Annelida

Characteristics of Superphylum Lophotrochozoa

Figure one. The Caribbean area reef squid (Sepioteuthis sepioidea) is a circuitous lophotrochozoan.

Animals belonging to superphylum Lophotrochozoa are protostomes, in which the blastopore, or the indicate of involution of the ectoderm or outer germ layer, becomes the mouth opening to the alimentary canal. This is chosen protostomy or "commencement mouth." In protostomy, solid groups of cells split up from the endoderm or inner germ layer to course a fundamental mesodermal layer of cells. This layer multiplies into a band and and so splits internally to course the coelom; this protostomic coelom is hence termedschizocoelom.

Equally lophotrochozoans, the organisms in this superphylum possess either a lophophore or trochophore larvae. The lophophores include groups that are united by the presence of the lophophore, a set of ciliated tentacles surrounding the rima oris. Lophophorata include the flatworms and several other phyla. These clades are upheld when RNA sequences are compared. Trochophore larvae are characterized past 2 bands of cilia around the body.

The lophotrochozoans are triploblastic and possess an embryonic mesoderm sandwiched between the ectoderm and endoderm plant in the diploblastic cnidarians. These phyla are likewise bilaterally symmetrical, meaning that a longitudinal section will divide them into right and left sides that are symmetrical. Information technology as well means the kickoff of cephalization, the evolution of a concentration of nervous tissues and sensory organs in the caput of the organism, which is where it first encounters its environment.

Phylum Platyhelminthes

The flatworms are acoelomate organisms that include many gratis-living and parasitic forms. Nigh of the flatworms are classified in the superphylum Lophotrochozoa, which also includes the mollusks and annelids. The Platyhelminthes consist of ii lineages: the Catenulida and the Rhabditophora. The Catenulida, or "concatenation worms" is a small clade of merely over 100 species. These worms typically reproduce asexually past budding. Notwithstanding, the offspring do not fully disassemble from the parents and therefore resemble a chain in appearance. All of the remaining flatworms discussed here are role of the Rhabditophora. Many flatworms are parasitic, including important parasites of humans. Flatworms have three embryonic tissue layers that give rise to surfaces that encompass tissues (from ectoderm), internal tissues (from mesoderm), and line the digestive arrangement (from endoderm). The epidermal tissue is a single layer cells or a layer of fused cells (syncytium) that covers a layer of circular muscle above a layer of longitudinal muscle. The mesodermal tissues include mesenchymal cells that contain collagen and support secretory cells that secrete mucus and other materials at the surface. The flatworms are acoelomates, so their bodies are solid betwixt the outer surface and the cavity of the digestive arrangement.

Physiological Processes of Flatworms

The free-living species of flatworms are predators or scavengers. Parasitic forms feed on the tissues of their hosts. Most flatworms, such as the planarian shown in Figure 2, have a gastrovascular cavity rather than a consummate digestive system. In such animals, the "mouth" is likewise used to expel waste product materials from the digestive system. Some species too take an anal opening. The gut may exist a uncomplicated sac or highly branched. Digestion is extracellular, with digested materials taken in to the cells of the gut lining past phagocytosis. One grouping, the cestodes, lacks a digestive system. Flatworms have an excretory system with a network of tubules throughout the torso with openings to the environment and nearby flame cells, whose cilia crush to directly waste fluids concentrated in the tubules out of the body. The system is responsible for the regulation of dissolved salts and the excretion of nitrogenous wastes. The nervous organisation consists of a pair of nerve cords running the length of the torso with connections between them and a large ganglion or concentration of fretfulness at the anterior end of the worm, where there may also exist a concentration of photosensory and chemosensory cells.

Figure 2. The planarian is a flatworm that has a gastrovascular crenel with one opening that serves as both oral fissure and anus. The excretory system is fabricated upwards of tubules continued to excretory pores on both sides of the body. The nervous organization is composed of two interconnected nervus cords running the length of the body, with cognitive ganglia and eyespots at the anterior finish.

In that location is neither a circulatory nor respiratory system, with gas and food substitution dependent on diffusion and jail cell-cell junctions. This necessarily limits the thickness of the body in these organisms, constraining them to exist "flat" worms.

Most flatworm species are monoecious, and fertilization is typically internal. Asexual reproduction is common in some groups.

Diversity of Flatworms

Platyhelminthes are traditionally divided into 4 classes: Turbellaria, Monogenea, Trematoda, and Cestoda (Effigy 3). Every bit discussed in a higher place, the relationships among members of these classes is being reassessed, with the turbellarians in particular at present viewed equally a paraphyletic grouping, a grouping that does not have a single common ancestor.

Figure 3. Phylum Platyhelminthes is divided into four classes. (a) Form Turbellaria includes the Bedford's flatworm (Pseudobiceros bedfordi), which is about 8–10 cm in length. (b) The parasitic class Monogenea includesDactylogyrus spp. Dactylogyrus, unremarkably chosen a gill fluke, is about 0.2 mm in length and has 2 anchors, indicated past arrows, that information technology uses to latch onto the gills of host fish. (c) The Trematoda class includesFascioloides magna (correct) andFasciaola hepatica (two specimens of left, too known as the mutual liver fluke). (d) Class Cestoda includes tapeworms such as thisTaenia saginata.T. saginata, which infects both cattle and humans, can attain four–10 meters in length; the specimen shown hither is almost 4 meters. (credit a: modification of work by Jan Derk; credit d: modification of work past CDC)

The class Turbellaria includes mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments. The ventral epidermis of turbellarians is ciliated and facilitates their locomotion. Some turbellarians are capable of remarkable feats of regeneration in which they may regrow the body, even from a small fragment.

The monogeneans are ectoparasites, generally of fish, with simple lifecycles that consist of a free-pond larva that attaches to a fish to begin transformation to the parasitic developed class. The parasite has only one host and that host is normally merely one species. The worms may produce enzymes that assimilate the host tissues or just graze on surface mucus and peel particles. Most monogeneans are hermaphroditic, but the male person gametes develop commencement and and then cross-fertilization is quite mutual.

The trematodes, or flukes, are internal parasites of mollusks and many other groups, including humans. Trematodes have complex lifecycles that involve a chief host in which sexual reproduction occurs, and one or more than secondary hosts in which asexual reproduction occurs. The primary host is almost always a clam. Trematodes are responsible for serious human diseases including schistosomiasis, a blood fluke. The disease infects an estimated 200 million people in the tropics, leading to organ impairment and chronic symptoms like fatigue. Infection occurs when the human enters the water and a larva, released from the primary snail host, locates and penetrates the skin. The parasite infects various organs in the trunk and feeds on carmine blood cells before reproducing. Many of the eggs are released in feces and find their way into a waterway, where they are able to reinfect the main snail host.

The cestodes, or tapeworms, are likewise internal parasites, mainly of vertebrates (Effigy four). Tapeworms live in the abdominal tract of the primary host and remain fixed using a sucker on the anterior end, or scolex, of the tapeworm torso. The remaining body of the tapeworm is fabricated up of a long serial of units called proglottids, each of which may contain an excretory system with flame cells, but contain reproductive structures, both male and female person. Tapeworms do not possess a digestive system; instead, they blot nutrients from the food matter passing them in the host'southward intestine.

Effigy 4. Tapeworm (Taenia spp.) infections occur when humans consume raw or undercooked infected meat. (credit: modification of work by CDC)

Proglottids are produced at the scolex and gradually migrate to the end of the tapeworm; at this betoken, they are "mature" and all structures except fertilized eggs accept degenerated. Most reproduction occurs by cross-fertilization. The proglottid detaches from the body of the worm and is released into the feces of the organism. The eggs are eaten by an intermediate host. The juvenile worm infects the intermediate host and takes up residence, ordinarily in muscle tissue. When the muscle tissue is eaten by the master host, the cycle is completed. There are several tapeworm parasites of humans that are transmitted by eating uncooked or poorly cooked pork, beefiness, and fish.

Phylum Rotifera

The rotifers are a microscopic (about 100 µm to 30 mm) group of by and large aquatic organisms that get their proper noun from thecorona, a rotating, wheel-similar structure that is covered with cilia at their anterior end (Figure 5). Although their taxonomy is currently in flux, i treatment places the rotifers in three classes: Bdelloidea, Monogononta, and Seisonidea. The classification of the group is currently under revision, however, as more phylogenetic show becomes available. It is possible that the "spiny headed worms" currently in phylum Acanthocephala volition exist incorporated into this group in the time to come.

The torso course of rotifers consists of a caput (which contains the corona), a trunk (which contains the organs), and the human foot. Rotifers are typically free-pond and truly planktonic organisms, but the toes or extensions of the human foot can secrete a gummy material forming a holdfast to help them attach to surfaces. The caput contains sensory organs in the class of a bi-lobed brain and small eyespots near the corona.

Figure 5. Shown are examples from two of the three classes of rotifer. (a) Species from the form Bdelloidea are characterized by a large corona, shown separately from the whole animals in the centre of this scanning electron micrograph. (b) Polyarthra, from the grade Monogononta, has a smaller corona than Bdelloid rotifers, and a single gonad, which give the course its proper name. (credit a: modification of work by Diego Fontaneto; credit b: modification of work by U.South. EPA; scale-bar data from Cory Zanker)

The rotifers are filter feeders that will eat dead cloth, algae, and other microscopic living organisms, and are therefore very important components of aquatic food webs. Rotifers obtain food that is directed toward the oral cavity by the current created from the movement of the corona. The nutrient particles enter the mouth and travel to themastax (pharynx with jaw-like structures). Food and so passes by digestive and salivary glands, and into the stomach, then onto the intestines. Digestive and excretory wastes are collected in a cloacal float earlier being released out the anus.

Watch the video beneath to see rotifers feeding. Notation that this video has no audio.

Figure 6. This illustration shows the beefcake of a bdelloid rotifer.

Rotifers are pseudocoelomates commonly found in fresh water and some salt water environments throughout the world. Figure 6 shows the anatomy of a rotifer belonging to class Bdelloidea. Most ii,200 species of rotifers have been identified. Rotifers are dioecious organisms (having either male or female person genitalia) and exhibit sexual dimorphism (males and females have different forms). Many species are parthenogenic and exhibit haplodiploidy, a method of gender determination in which a fertilized egg develops into a female and an unfertilized egg develops into a male. In many dioecious species, males are short-lived and smaller with no digestive system and a single testis. Females can produce eggs that are capable of dormancy for protection during harsh environmental conditions.

Phylum Nemertea

The Nemertea are colloquially known as ribbon worms. Near species of phylumNemertea are marine, predominantly benthic or bottom dwellers, with an estimated 900 species known. Withal, nemertini have been recorded in freshwater and terrestrial habitats as well. Most nemerteans are carnivores, feeding on worms, clams, and crustaceans. Some species are scavengers, and some nemertini species, similarMalacobdella grossa, take also evolved commensalistic relationships with some mollusks. Some species have devastated commercial fishing of clams and crabs. Nemerteans accept almost no predators and 2 species are sold as fish bait.

Morphology

Figure 7. The proboscis worm (Parborlasia corrugatus) is a scavenger that combs the body of water flooring for food. The species is a fellow member of the phylum Nemertea. The specimen shown here was photographed in the Ross Sea, Antarctica. (credit: Henry Kaiser, National Scientific discipline Foundation)

Ribbon worms vary in size from ane cm to several meters. They show bilateral symmetry and remarkable contractile properties. Because of their contractility, they tin change their morphological presentation in response to environmental cues. Animals in phylum Nemertea show a flattened morphology, that is, they are flat from front end to back, like a flattened tube. Nemertea are soft and unsegmented animals (Effigy vii).

A unique characteristic of this phylum is the presence of a proboscis enclosed in arhynchocoel. The proboscis serves to capture food and may be ornamented with barbs in some species. The rhynchocoel is a fluid-filled cavity that extends from the head to well-nigh ii-thirds of the length of the gut in these animals (Figure 8). The proboscis may be extended or retracted by the retractor muscle attached to the wall of the rhynchocoel.

Effigy viii. The anatomy of a Nemertean is shown.

Watch the video beneath to run across a nemertean set on a polychaete with its proboscis.

Digestive System

The nemertini show a very well-developed digestive organisation. A mouth opening that is ventral to the rhynchocoel leads into the foregut, followed by the intestine. The intestine is present in the course of diverticular pouches and ends in a rectum that opens via an anus. Gonads are interspersed with the intestinal diverticular pouches and open up outwards via genital pores. A circulatory arrangement consists of a closed loop of a pair of lateral claret vessels. The circulatory system is derived from the coelomic cavity of the embryo. Some animals may also accept cantankerous-connecting vessels in addition to lateral ones. Although these are chosen blood vessels, since they are of coelomic origin, the circulatory fluid is colorless. Some species comport hemoglobin as well as other xanthous or greenish pigments. The claret vessels are connected to the rhynchocoel. The menses of fluid in these vessels is facilitated by the contraction of muscles in the body wall. A pair of protonephridia, or primitive kidneys, is nowadays in these animals to facilitate osmoregulation. Gaseous exchange occurs through the skin in the nemertini.

Nervous Organisation

Nemertini have a ganglion or "encephalon" situated at the anterior end between the mouth and the foregut, surrounding the digestive system likewise every bit the rhynchocoel. A ring of iv nerve masses chosen "ganglia" composes the encephalon in these animals. Paired longitudinal nerve cords emerge from the brain ganglia and extend to the posterior stop. Ocelli or eyespots are present in pairs, in multiples of two in the anterior portion of the body. It is speculated that the eyespots originate from neural tissue and not from the epidermis.

Reproduction

Animals in phylum Nemertea show sexual dimorphism, although freshwater species may be hermaphroditic. Eggs and sperm are released into the water, and fertilization occurs externally. The zygote then develops into aplanuliform larva. In some nemertine species, apilidium larva may develop within the young worm, from a serial of imaginal discs. This larval form, characteristically shaped like a deerstalker cap, devours tissues from the young worm for survival before metamorphosing into the adult-like morphology.

Phylum Mollusca

PhylumMollusca is the predominant phylum in marine environments. It is estimated that 23 per centum of all known marine species are mollusks; there are over 75,000 described species, making them the second most diverse phylum of animals. The name "mollusca" signifies a soft trunk, since the earliest descriptions of mollusks came from observations of unshelled cuttlefish. Mollusks are predominantly a marine group of animals; however, they are known to inhabit freshwater likewise every bit terrestrial habitats. Mollusks display a broad range of morphologies in each class and subclass, but share a few central characteristics, including a muscular pes, a visceral mass containing internal organs, and a mantle that may or may non secrete a beat out of calcium carbonate (Figure nine).

Effigy 9. There are many species and variations of mollusks; this illustration shows the anatomy of an aquatic gastropod.

Practise Questions

Which of the following statements nearly the anatomy of a mollusk is faux?

1. Mollusks have a radula for grinding nutrient.
2. A digestive gland is connected to the stomach.
3. The tissue below the shell is called the mantle.
4. The digestive arrangement includes a gizzard, a tum, a digestive gland, and the intestine.

Testify Answer

Statement d is imitation

Mollusks take a muscular foot, which is used for locomotion and anchorage, and varies in shape and office, depending on the type of clam nether study. In shelled mollusks, this foot is unremarkably the same size as the opening of the shell. The human foot is a retractable as well as an extendable organ. The human foot is the ventral-nigh organ, whereas the drape is the limiting dorsal organ. Mollusks are eucoelomate, but the coelomic crenel is restricted to a crenel around the heart in developed animals. The mantle cavity develops independently of the coelomic cavity.

The visceral mass is present higher up the foot, in the visceral hump. This includes digestive, nervous, excretory, reproductive, and respiratory systems. Mollusk species that are exclusively aquatic take gills for respiration, whereas some terrestrial species have lungs for respiration. Additionally, a tongue-like organ called aradula, which bears chitinous tooth-like decoration, is nowadays in many species, and serves to shred or scrape nutrient. Themantle (also known as the pallium) is the dorsal epidermis in mollusks; shelled mollusks are specialized to secrete a chitinous and hard calcareous shell.

About mollusks are dioecious animals and fertilization occurs externally, although this is not the case in terrestrial mollusks, such as snails and slugs, or in cephalopods. In some mollusks, the zygote hatches and undergoes two larval stages—trochophore andveliger—before condign a young adult; bivalves may exhibit a third larval phase, glochidia.

Classification of Phylum Mollusca

Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Mollusks have a dramatic diversity of grade, ranging from big predatory squids and octopus, some of which show a high degree of intelligence, to grazing forms with elaborately sculpted and colored shells. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda.

Figure 10. This chiton from the class Polyplacaphora has the eight-plated shell that is indicative of its course. (credit: Jerry Kirkhart)

Class Aplacophora ("bearing no plates") includes worm-like animals primarily establish in benthic marine habitats. These animals lack a calcareous shell but possess aragonite spicules on their epidermis. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia (excretory organs). Members of course Monoplacophora ("begetting ane plate") posses a single, cap-like shell that encloses the body. The morphology of the shell and the underlying beast can vary from circular to ovate. A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. The monoplacophorans were believed extinct and simply known via fossil records until the discovery ofNeopilina galathaeain 1952. Today, scientists have identified about ii dozen extant species.

Animals in the grade Polyplacophora ("bearing many plates") are unremarkably known every bit "chitons" and bear an armor-like 8-plated shell (Figure 10). These animals have a broad, ventral human foot that is adapted for suction to rocks and other substrates, and a mantle that extends across the beat out in the form of a girdle. Calcareous spines may be present on the girdle to offer protection from predators. Respiration is facilitated byctenidia (gills) that are nowadays ventrally. These animals possess a radula that is modified for scraping. The nervous system is rudimentary with simply buccal or "cheek" ganglia nowadays at the inductive end. Eyespots are absent in these animals. A single pair of nephridia for excretion is present.

Figure 11. These mussels, found in the intertidal zone in Cornwall, England, are bivalves. (credit: Mark A. Wilson)

Class Bivalvia ("two shells") includes clams, oysters, mussels, scallops, and geoducks. Members of this course are found in marine as well as freshwater habitats. Every bit the name suggests, bivalves are enclosed in a pair of shells (valves are unremarkably called "shells") that are hinged at the dorsal end by shell ligaments as well as shell teeth (Figure xi). The overall morphology is laterally flattened, and the head region is poorly developed. Eyespots and statocysts may be absent in some species. These animals are suspension feeders—they eat material, such as plankton, that is suspended in the water effectually them. Due to their diet, this grade of mollusks lacks a radula. Respiration is facilitated by a pair of ctenidia, whereas excretion and osmoregulation are brought about by a pair of nephridia. Bivalves often possess a large curtain cavity. In some species, the posterior edges of the mantle may fuse to course 2 siphons that serve to take in and exude water.

One of the functions of the mantle is to secrete the shell. Some bivalves like oysters and mussels possess the unique ability to secrete and eolith a calcareousnacre or "female parent of pearl" effectually foreign particles that may enter the mantle cavity. This property has been commercially exploited to produce pearls.

Scout this animation of mussels feeding.

Animals in class Gastropoda ("tum foot") include well-known mollusks like snails, slugs, conchs, ocean hares, and body of water collywobbles. Gastropoda includes trounce-bearing species as well as species with a reduced beat. These animals are asymmetrical and usually present a coiled shell (Effigy 12). Shells may beplanospiral (like a garden hose wound up), commonly seen in garden snails, orconispiral, (similar a spiral staircase), commonly seen in marine conches.

Figure 12. (a) Snails and (b) slugs are both gastropods, merely slugs lack a beat out. (credit a: modification of work by Murray Stevenson; credit b: modification of piece of work by Rosendahl)

The visceral mass in the shelled species displays torsion around the perpendicular axis on the middle of the foot, which is the key characteristic of this group, forth with a foot that is modified for crawling (Effigy 13). Almost gastropods bear a caput with tentacles, eyes, and a fashion. A complex radula is used past the digestive organisation and aids in the ingestion of food. Eyes may be absent in some gastropods species. The mantle cavity encloses the ctenidia besides every bit a pair of nephridia.

Figure xiii. During embryonic evolution of gastropods, the visceral mass undergoes torsion, or counterclockwise rotation of anatomical features. As a result, the anus of the adult fauna is located over the caput. Torsion is an contained process from coiling of the shell.

Can Snail Venom Exist Used as a Pharmacological Painkiller?

Figure 14. Members of the genus Conus produce neurotoxins that may one day take medical uses. (credit: David Burdick, NOAA)

Marine snails of the genusConus (Figure 14) attack prey with a venomous sting. The toxin released, known every bit conotoxin, is a peptide with internal disulfide linkages. Conotoxins tin can bring about paralysis in humans, indicating that this toxin attacks neurological targets. Some conotoxins have been shown to block neuronal ion channels. These findings accept led researchers to study conotoxins for possible medical applications.

Conotoxins are an exciting surface area of potential pharmacological evolution, since these peptides may exist maybe modified and used in specific medical conditions to inhibit the activity of specific neurons. For instance, these toxins may be used to induce paralysis in muscles in specific health applications, like to the use of botulinum toxin. Since the entire spectrum of conotoxins, as well every bit their mechanisms of action, are not completely known, the report of their potential applications is still in its infancy. Almost inquiry to engagement has focused on their employ to treat neurological diseases. They have also shown some efficacy in relieving chronic pain, and the pain associated with atmospheric condition like sciatica and shingles. The study and use of biotoxins—toxins derived from living organisms—are an excellent example of the application of biological science to modern medicine.

Grade Cephalopoda ("caput foot" animals), include octopi, squids, cuttlefish, and nautilus. Cephalopods are a class of shell-bearing animals every bit well as mollusks with a reduced crush. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. All animals in this grade are cannibal predators and have beak-like jaws at the anterior terminate. All cephalopods show the presence of a very well-adult nervous system along with eyes, as well as a closed circulatory system. The foot is lobed and adult into tentacles, and a funnel, which is used as their mode of locomotion. Suckers are present on the tentacles in octopi and squid. Ctenidia are enclosed in a large mantle cavity and are serviced past large blood vessels, each with its own heart associated with information technology; the mantle has siphonophores that facilitate exchange of water.

Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion. This is chosen "jet" propulsion. A pair of nephridia is present inside the mantle cavity. Sexual dimorphism is seen in this class of animals. Members of a species mate, and the female then lays the eggs in a secluded and protected niche. Females of some species care for the eggs for an extended menstruation of time and may end up dying during that fourth dimension flow. Cephalopods such as squids and octopi also produce sepia or a nighttime ink, which is squirted upon a predator to aid in a quick getaway.

Reproduction in cephalopods is unlike from other mollusks in that the egg hatches to produce a juvenile adult without undergoing the trochophore and veliger larval stages.

In the shell-bearingNautilusspp., the spiral trounce is multi-chambered. These chambers are filled with gas or water to regulate buoyancy. The crush structure in squids and cuttlefish is reduced and is present internally in the form of a squid pen and cuttlefish bone, respectively. Examples are shown in Figure 15.

Figure 15. The (a) nautilus, (b) giant cuttlefish, (c) reef squid, and (d) blueish-ring octopus are all members of the class Cephalopoda. (credit a: modification of work by J. Baecker; credit b: modification of work by Adrian Mohedano; credit c: modification of work past Silke Baron; credit d: modification of work by Angell Williams)

Figure xvi. Antalis vulgaris shows the archetype Dentaliidae shape that gives these animals their common proper noun of "tusk shell." (credit: Georges Jansoone)

Members of class Scaphopoda ("gunkhole feet") are known colloquially as "tusk shells" or "tooth shells," as axiomatic when examiningDentalium, one of the few remaining scaphopod genera (Figure xvi).

Scaphopods are unremarkably buried in sand with the anterior opening exposed to water. These animals bear a single conical shell, which has both ends open. The head is rudimentary and protrudes out of the posterior end of the shell. These animals do not possess eyes, but they take a radula, equally well as a foot modified into tentacles with a bulbous end, known equallycaptaculae. Captaculae serve to catch and dispense prey. Ctenidia are absent in these animals.

Phylum Annelida

PhylumAnnelida includes segmented worms. These animals are constitute in marine, terrestrial, and freshwater habitats, but a presence of h2o or humidity is a critical factor for their survival, especially in terrestrial habitats. The name of the phylum is derived from the Latin discussionannellus, which means a minor band. Animals in this phylum show parasitic and commensal symbioses with other species in their habitat. Approximately xvi,500 species take been described in phylum Annelida. The phylum includes earthworms, polychaete worms, and leeches. Annelids bear witness protostomic development in embryonic stages and are oft called "segmented worms" due to their primal feature ofmetamerism, or true segmentation.

Morphology

Figure 17. The clitellum, seen here as a protruding segment with different coloration than the rest of the body, is a structure that aids in annelid reproduction. (credit: Rob Hille)

Annelids brandish bilateral symmetry and are worm-like in overall morphology. Annelids have a segmented body plan wherein the internal and external morphological features are repeated in each body segment. Metamerism allows animals to become bigger by calculation "compartments" while making their movement more efficient. This metamerism is thought to arise from identical teloblast cells in the embryonic stage, which give rise to identical mesodermal structures. The overall torso tin be divided into head, body, and pygidium (or tail). Theclitellum is a reproductive structure that generates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs; information technology appears equally a fused band in the inductive 3rd of the animal (Figure 17).

Anatomy

The epidermis is protected past an acellular, external cuticle, but this is much thinner than the cuticle found in the ecdysozoans and does not require periodic shedding for growth. Circular besides as longitudinal muscles are located interior to the epidermis. Chitinous hairlike extensions, anchored in the epidermis and projecting from the cuticle, chosensetae/chaetae are present in every segment. Annelids show the presence of a true coelom, derived from embryonic mesoderm and protostomy. Hence, they are the nearly advanced worms. A well-adult and complete digestive system is nowadays in earthworms (oligochaetes) with a mouth, muscular pharynx, esophagus, crop, and gizzard beingness present. The gizzard leads to the intestine and ends in an anal opening. A cantankerous-sectional view of a body segment of an earthworm (a terrestrial blazon of annelid) is shown in Figure 18; each segment is limited by a membranous septum that divides the coelomic crenel into a series of compartments.

Figure 18. This schematic drawing shows the bones beefcake of annelids in a cross-sectional view.

Annelids possess a closed circulatory organisation of dorsal and ventral blood vessels that run parallel to the gastrointestinal tract also as capillaries that service private tissues. In addition, these vessels are connected by transverse loops in every segment. These animals lack a well-developed respiratory system, and gas substitution occurs across the moist body surface. Excretion is facilitated by a pair of metanephridia (a type of primitive "kidney" that consists of a convoluted tubule and an open up, ciliated funnel) that is present in every segment towards the ventral side. Annelids show well-developed nervous systems with a nerve ring of fused ganglia present around the pharynx. The nerve cord is ventral in position and bears enlarged nodes or ganglia in each segment.

Annelids may be either monoecious with permanent gonads (as in earthworms and leeches) or dioecious with temporary or seasonal gonads that develop (every bit in polychaetes). However, cross-fertilization is preferred in hermaphroditic animals. These animals may also show simultaneous hermaphroditism and participate in simultaneous sperm commutation when they are aligned for copulation.

This combination video and blitheness provides a closeup await at annelid anatomy.

Classification of Phylum Annelida

Phylum Annelida contains the form Polychaeta (the polychaetes) and the course Oligochaeta (the earthworms, leeches and their relatives).

Earthworms are the most abundant members of the class Oligochaeta, distinguished past the presence of the clitellum as well as few, reduced chaetae (oligo– = "few"; –chaetae = "hairs"). The number and size of chaetae are greatly diminished in Oligochaeta compared to the polychaetes (poly=many,chaetae = hairs). The many chetae of polychaetes are also arranged inside fleshy, flat, paired appendages that protrude from each segment calledparapodia, which may be specialized for unlike functions in the polychates. The subclass Hirudinea includes leeches such asHirudo medicinalis andHemiclepsis marginata. The class Oligochaeta includes the subclass Hirudinia and the bracket Brachiobdella. A significant difference betwixt leeches and other annelids is the development of suckers at the inductive and posterior ends and a lack of chaetae. Additionally, the division of the body wall may not correspond to the internal segmentation of the coelomic cavity. This adaptation possibly helps the leeches to elongate when they ingest copious quantities of blood from host vertebrates. The subclass Brachiobdella includes species likeBranchiobdella balcanica sketi andBranchiobdella astaci, worms that prove similarity with leeches besides every bit oligochaetes.

Figure xix. The (a) earthworm, (b) leech, and (c) featherduster are all annelids. (credit a: modification of work by S. Shepherd; credit b: modification of work past "Sarah Thou…"/Flickr; credit c: modification of work by Chris Gotschalk, NOAA)

In Summary: Superphylum Lophotrochozoa

Flatworms are acoelomate, triploblastic animals. They lack circulatory and respiratory systems, and have a rudimentary excretory system. This digestive system is incomplete in near species. There are four traditional classes of flatworms, the largely free-living turbellarians, the ectoparasitic monogeneans, and the endoparasitic trematodes and cestodes. Trematodes have complex lifecycles involving a molluscan secondary host and a principal host in which sexual reproduction takes place. Cestodes, or tapeworms, infect the digestive systems of primary vertebrate hosts.

The rotifers are microscopic, multicellular, mostly aquatic organisms that are currently under taxonomic revision. The group is characterized by the rotating, ciliated, wheel-like structure, the corona, on their head. The mastax or jawed pharynx is some other construction unique to this grouping of organisms.

The nemertini are the simplest eucoelomates. These ribbon-shaped animals comport a specialized proboscis enclosed within a rhynchocoel. The development of a closed circulatory arrangement derived from the coelom is a significant difference seen in this species compared to other pseudocoelomate phyla. Alimentary, nervous, and excretory systems are more developed in the nemertini than in less advanced phyla. Embryonic development of nemertine worms gain via a planuliform larval stage.

Phylum Mollusca is a large, marine group of invertebrates. Mollusks testify a variety of morphological variations within the phylum. This phylum is also singled-out in that some members showroom a calcareous shell as an external means of protection. Some mollusks take evolved a reduced vanquish. Mollusks are protostomes. The dorsal epidermis in mollusks is modified to grade the curtain, which encloses the drape cavity and visceral organs. This crenel is quite singled-out from the coelomic cavity, which in the adult animate being surrounds the heart. Respiration is facilitated by gills known as ctenidia. A chitinous-toothed tongue chosen the radula is present in most mollusks. Early evolution in some species occurs via two larval stages: trochophore and veliger. Sexual dimorphism is the predominant sexual strategy in this phylum. Mollusks can be divided into 7 classes, each with distinct morphological characteristics

Phylum Annelida includes vermiform, segmented animals. Segmentation is seen in internal anatomy likewise, which is called metamerism. Annelids are protostomes. These animals take well-developed neuronal and digestive systems. Some species conduct a specialized band of segments known every bit a clitellum. Annelids testify the presence numerous chitinous projections termed chaetae, and polychaetes possess parapodia. Suckers are seen in order Hirudinea. Reproductive strategies include sexual dimorphism, hermaphroditism, and serial hermaphroditism. Internal division is absent in course Hirudinea.

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Source: https://courses.lumenlearning.com/suny-wmopen-biology2/chapter/superphylum-lophotrochozoa/

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