Classification of Arthropod taxa with symbiotic members. Arthropod phylogeny is also included

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ASSIGNMENT No. 1
ARTHROPOD PHYLOGENY AND CLASSIFICATION OF
ARTHROPOD TAXA WITH SYMBIOTIC MEMBERS
SUBMITTED BY : MUZNA KASHAF
ROLL NUMBER : (16261514-030)
SUBMITTED TO : Dr. NOUSHEEN ZAFEER
COUSE TITLE : PRINCIPLES of PARASITOLOGY
SEMESTER : VIII
DEPARTMENT of ZOOLOGY
UNIVERSITY of GUJRAT,
SUB-CAMPUS, RAWALPINDI

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CONTENTS
Pg. number
Arthropod Phylogeny…………………………………………………………………… 3
 Introduction…………………………………………………………………….... 3
 Literature Review………………………………………………………………... 3
Classification Of Arthropodan Taxa With Symbiotic Members ……………………. 4
 Phylum Arthropoda……………………………………………………………... 4
 Comparative Study…………………………………………………………….... 5
 Subphylum Trilobitomorpha (Trilobites)……………………………………… 5
 Subphylum Chelicerata…………………………………………………………. 5
 Class Merostomata………………………………………………………………. 5
 Class Arachnida…………………………………………………………………. 6
 Class Pycnogonida………………………………………………………………. 6
 Sub Phylum Crustacea………………………………………………………….. 6
 Subphylum Myriapoda………………………………………………………….. 6
 Class Chilopoda………………………………………………………………….. 7
 Class Symphyla…………………………………………………………………… 7
 Class Diplopoda…………………………………………………………………... 7
 Class Pauropoda………………………………………………………………….. 7
 Sub Phylum Hexapoda…………………………………………………………... 7
 Class Insecta………………………………………………………………………. 8
 Class Entognatha…………………………………………………………………. 8
 Conclusion………………………………………………………………………… 8
 References ………………………………………………………………………… 9

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ARTHROPOD PHYLOGENY
INTRODUCTION:
As might be expected from arthropods’ long evolutionary history and extreme diversity,
establishment of evolutionary relationships, especially among the more inclusive taxa, is a
challenge that has occupied many scientists ever since Darwin’s time. Exceptionally detailed
comparative anatomical research, especially that focused on homology between body segments
and formation of the head through segment fusion, was the standard approach through much of
this period. Embryological development also has been an important part of phylogenetic research
on arthropods ever since Darwin claimed, based on nauplius structure, that barnacles were
crustaceans rather than mollusks (Fahrbach, 2004).
Within Arthropoda, relationships are now proposed based on a combination of embryological,
morphological, and molecular evidence to establish homologies between body parts, especially
head segments. Although some authors use molecular data to argue that the mandibulate
Myriapoda (centipedes and millipedes) are a sister group to the non-mandibulate Chelicerata
(horseshoe crabs, ticks, mites, etc.), combining them into a taxon called Paradoxopoda or
Myriochelata, we accept the evidence as outlined by Scholtz and Edgecombe that Mandibulata,
which includes Hexapoda (insects), Crustacea, and Myriapoda, is monophyletic (Zhang, 2011).
Crustacea and Hexapoda, somtimes grouped in a clade named Pancrustacea, are now considered
sister taxa within Mandibulata. Embryological evidence, especially that involving brain
development and eye structure, suggests Hexapoda actually are most closely related to
Malacostraca within Crustacea, but 28S + 18S ribosomal RNA sequence data do not necessarily
support this relationship. The position of myriapods remains unresolved, partly because they
have not been studied to the same extent as insects and crustaceans. Finally, Hexapoda does not
include some six-legged arthropods, namely, members of classes Collembola (the exceedingly
abundant springtails), Protura, and Diplura; members of all these classes occur mainly in or on
damp soil or litter (Scholtz and Edgecombe, 2006).
LITERATURE REVIEW:
In recent years, such work has been complemented by molecular techniques, especially those
allowing scientists to study the role of homeobox (Hox) genes. Consequently, our ideas about
who is most closely related to whom have undergone, and may continue to undergo, rather
substantial adjustment. Traditionally, arthropods have been included in a single phylum of
metameric, coelomate animals. Arthropods share many features with annelids, such as
metamerism and a nervous system consisting of supraesophageal ganglia, nerves encircling the
esophagus, and a ventral series of segmental ganglia. Such similarities led to claims that the two
phyla are related and that arthropods likely evolved from annelidlike ancestors, but this idea is
not supported by current research. Lophotrochozoa. Based on 18S ribosomal RNA sequence
data, phylum Arthropoda is considered a member of superphylum Ecdysozoa, i.e., animals that

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molt, along with Nematoda and other smaller phyla such as Nematomorpha Onychophora
(wormlike tropical and subtropical organisms), and Tardigrada (water bears). Recent phylogenies
using “nearly complete 28S + 18S ribosomal RNA gene sequences” show Arthropoda,
Onychophora, and Tardigrada as a monophyletic clade with the other ecdysozoans comprising
the sister group.
CLASSIFICATION OF ARTHROPODAN TAXA WITH SYMBIOTIC MEMBERS
This classification of Crustacea relies heavily on Kabata, Marcotte, Bowman and Abele, and
Martin and Davis. Classification of Arachnida is according to Savory, and diagnoses of the
orders of pterygotes mainly follow Borrer et al., Gillott, and Richards and Davies. Subphylum
Uniramia as traditionally constituted may not be a valid or monophyletic taxon (Borrer et al.,
2009).
PHYLUM ARTHROPODA
Bilaterally symmetrical invertebrates with jointed exoskeleton covering body and appendages;
cilia absent; body segmented, though segmentation commonly reduced as a result of fusion;
appendages typically specialized for different functions; coelom greatly reduced; nervous system
consists of dorsal brain and a double or single (fused) ventral nerve cord; eggs typically rich in
yolk; development highly modified (Martin, 2001).
Fig.1; Classification of Arthropod taxa

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COMPARATIVE STUDY:
SUBPHYLUM TRILOBITOMORPHA (TRILOBITES)
Extinct; head (or cephalon) composed of 5 segments bearing a pair of antennae and compound
eyes; oval, flattened body composed of cephalon, thorax, and pygidium, each segmented; dorsal
surface molded longitudinally into 3 lobes; each segment bears a pair of similar, branched
appendages; marine; Cambrian Period to the end of the Paleozoic Era; more than 4,000 fossil
species known (Borrer et al., 2009).
Fig.2; Trilobitomorpha
SUBPHYLUM CHELICERATA
Body divided into prosoma (cephalothorax) and opisthosoma (abdomen); no antennae; first pair
of appendages consists of chelicerae flanking the mouth; in most chelicerates the other prosomal
appendages are a pair of pedipalps and four pairs of legs (Zhang, 2011).
Fig.3; Spider
CLASS MEROSTOMATA
Large marine chelicerates with book gills on the underside of the opisthosoma; prosoma covered
by a dorsal carapace; opisthosoma bears a long terminal spine; 2 orders, Xiphosura (horseshoe
crabs, 4 species) and Eurypterida (Gigantostraca), which is extinct and includes 200 fossil
species from the Paleozoic Era (Martin, 2001).

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CLASS ARACHNIDA (SCORPIONS, SPIDERS, TICKS, MITES)
Chiefly terrestrial; book lungs and/or tracheae as gas exchange organs; opisthosoma (abdomen)
segmented or unsegmented externally and broadly or narrowly joined to the prosoma; prosomal
appendages consist of 1 pair of chelicerae, 1 pair of pedipalps, and 4 pairs of legs; gonopore
always on the lower side of second abdominal segment; about 70,750 species; 0.25 mm–l8 cm
(Borrer et al., 2009).
CLASS PYCNOGONIDA (SEA SPIDERS)
Marine; narrow trunk of 4 to 6 segments; greatly reduced abdomen; cephalon (head) with
proboscis bearing a pair of chelicerae, palpi, and egg-carrying legs; usually 4 pairs of walking
legs attached to lateral projections of the trunk; tubercle with 4 eyes located dorsally between the
first pair of legs; no gas respiratory organs; commonly found crawling over sessile animals, such
as hydroids and bryozoans; about 1,000 described species; 1 mm–10 cm (Zhang, 2011).
SUBPHYLUM CRUSTACEA
It includes crabs, shrimp, isopods, amphipods, krill, brine shrimp, copepods, barnacles. Chiefly
aquatic; head bearing 2 pairs of antennae, a pair of mandibles, and 2 pairs of maxillae; trunk
highly variable but commonly covered in part or entirely by a posteriorly directed fold of the
head (carapace); paired appendages biramous, often with 1 branch lost; 2 stalked or stalkless
compound eyes present in most; when present, gas exchange organs are gills; mostly marine, but
many freshwater species; some isopods terrestrial; 44,000 described species distributed among 6
subclasses (Marcotte, 1982).
Fig. 4; Carapace of crab
SUBPHYLUM MYRIAPODA
Chiefly terrestrial; segmental appendages primitively unbranched; head appendages comprise a
pair of antennae, a pair of mandibles, and 1 or 2 pairs of maxillae; trunk and appendages
variable; respiratory organs are tracheae (Zhang, 2011).

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Fig.5; Millipede and Centipede
CLASS CHILOPODA (CENTIPEDES)
Elongate; many trunk segments, each with 1 pair of legs; 2 pairs of maxillae covered by a large
pair of poison claws representing the first pair of trunk appendages; eyes, if present, are simple
ocelli; gonopore on last segment; 5 mm to almost 30 cm; about 3,000 living species (Zhang,
2011).
CLASS SYMPHYLA
Mouthparts consist of a pair of mandibles and 2 pairs of maxillae; 12 leg-bearing trunk
segments; terminal segment carries a pair of spinnerets; gonopore on fourth segment; l–8 mm;
about 160 living species (Martin, 2001).
CLASS DIPLOPODA (MILLIPEDES)
Elongate; trunk containing many diplosegments, each bearing 2 pairs of legs and spiracles; single
pair of maxillae fused to form a flattened plate (gnathochilarium); first 4 trunk segments not
diplosegments, and third bears the gonopores; simple eyes (ocelli) present or absent; 2 mm–28
cm; about 10,000 living species (James, 2015).
CLASS PAUROPODA
Antennae branched; a pair of maxillae; 9–11 trunk segments bearing legs; gonopores on third
trunk segment as in diplopods; 0.5–1.5 mm; about 500 described species (Zhang, 2011).
SUBPHYLUM HEXAPODA:
Subphylum Hexapoda includes the most important class Insecta.

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Fig.6; Dragonfly
CLASS INSECTA
Body composed of a head, thorax, and abdomen; head bears simple eyes and usually a pair of
lateral compound eyes; 2 pairs of maxillae, the second pair fused (labium); thorax of 3 segments,
each with a pair of legs, and the second and third usually bearing wings; abdomen of 11
segments without appendages in the adult; gonopore at end of abdomen; 0.25 mm–33 cm; at
least 1 million described species (Martin, 2001).
CLASS ENTOGNATHA
It includes all the wingless insects of the subphulum hexapoda.
CONCLUSION:
Arthropod relationships, both within the phylum and with other animal phyla, are uncertain. For
many years arthropods and annelids were believed to be closely related, with arthropods likely
evolving from annelid ancestors, or vice versa. Modern analyses question that assumption,
suggesting that their similarly segmented body plans would have to have evolved independently
(James, 2015).
Likewise, many relationships within the group are equally unsettled. For example, the terrestrial
arthropods insects and myriapods are commonly believed to be closely related. It is possible that
both groups derived from a common ancestor. On the other hand, accumulating molecular
evidence allies insects more closely with crabs and other crustaceans and links the myriapods
with horseshoe crabs and arachnids (Zhang, 2011).
Furthermore, some groups of animals have been incorporated into the Arthropoda. A group of
parasitic worms known as the pentastomids, for example, are considered to be highly modified
crustaceans at present. In contrast, two other groups of animals, the microscopic water bears
(tardigrades) and the onychophorans (such as Peripatus) are closely related to arthropods but will
probably remain in one or more separate phyla (James, 2015).

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REFERENCES:
 Zhang Z-Q (ed) (2011) Animal biodiversity: an outline of higher-level classification and
survey of taxonomic richness. Magnolia Press, Auckland
 James H. Diaz, in Mandell, Douglas, and Bennett's Principles and Practice of Infectious
Diseases (Eighth Edition), 2015
 Fahrbach, S. E. 2004. What arthropod brains say about arthropod phylogeny. Proc. Nat.
Acad. Sci. 101:3723–3724.
 Marcotte, B. M. 1982. Evolution within the Crustacea, part 2:Copepoda. In L. G. Abele
(Ed.), The biology of Crustacea,vol. 1. Systematics, the fossil record, and biogeography.
New York: Academic Press, Inc., pp. 185–197.
 Martin, J. W., and G. E. Davis. 2001. An updated classification of the recent Crustacea.
Nat. Hist. Mus. Los Angeles Co. Sci. Series. Dec. 14, 2001:i–viii, 1–124.