1. CRUSTACEA is a subphylum consisting of primarily aquatic arthropods
they constitute the remotest group of arthropods to man.
They are the most popular group as food item.
They show the highest variation in
size and
forms of appendages
They derive their name from the quality of their cuticle which is hard and stony described by the latin word ‘crusta’.
is a large group with about species.

2. Diagnostic features
Body has two tagmata, i.e. Cephalothorax and Abdomen.
Number of segments on the cephalothorax and abdomen vary and so are the number, forms and functions of the appendages they carry.
Each segment bear one pair of biramous appendages
Cephalothorax has two pairs of anteniform pre oral appendages, i.e. Antennule and antenna.
They utilize gills and general body surface for gaseous exchange
Coelomoducts, i.e. green glands occurring on the antenna or maxilla are used for excretion
Sexes are separate, a few species are however hermaphrodites.
Development is usually indirect with a Nauplius larval stage, with very few segments and four distinct pairs of appendages (Fig 3b)

3. Examples

4. Examples

5. Examples

6. Examples

7. Gross structure of a typical crustacean
A typical crustacean has two tagmata, i.e. Cephalothora and Abdomen
Both or cephalothorax may covered dorsally by a hard carapace with a pair of groove that allow the emergence of the pair of stalked compound eye anteriorly on the cephalothorax.
The conspicuous stalked compound eye inform the numerous yoruba descriptions and adages such as “ Oju Ede”, “iseju akan”, “Oju ni alakan fi so ori” etc.
On the ventral side of the cepalothorax are series of paired appendages usually in the order
antennule,
antenna,
mouthparts - mandible maxilla 2nd maxilla surrounding the mouth and
maxillipeds,
walking legs,
swimmerets.

8. External morphology

11. Gross structure of a typical crustacean
The structure, size and number of appendages vary extensively but
They depend largely on the
number of segments retained by the animal and
functional need and use the animal.
Some of the basic functional need include
locomotion,
feeding,
sensory
Respiration and
reproductive uses.
The number of abdominal segment may be reduced drastically but when intact are usually simple without or with similar pair of appendage per segment (Pleopods) and a caudal ramus/telson and Uropod on the last segment.

12. The typical crustacean appendage
A typical crustacean appendage is ‘Y’ shaped (Fig 3a) and described as biramous
The proximal basal portion known as the protopodite has three segments named: precoxa, coxopodite and basipodite.
Two terminal fingerlike rami, i.e. exopodite (exterior) and endopodite (medial), radiate from each protopodite hence the description biramous.
Each endopodite has five segments, named Itchyopodite, meropodite, coxopodite, propodite dactylopodite, (I must come properly dressed) respectively.
Additional medial and exterior lobes developed on the limbs are known as endites and exites, respectively.
The exites and are usually flat lobed and used as gills and sometimes described as epipodites.

13. The typical crustacean appendage cont’d
Appendages are collectively modified for so many functions
These include:
swimming,
respiration,
creation of water current for feeding and ventilation
food filtration
reproductive and
sensory functions.
Hence they are usually phyllopodous, i.e. flat with wide surface area
In the more advance crustaceans, however, appendage on each segment is selectively modified for one or two of the listed functions and so may not be phyllopodous but stenopodous.
each segment therefore carry specialized appendage that is morphologically and functionally unique in its propodite, endopodite exopodite, epipodite or endites morphology
Evolution in crustaceans therefore involves limb specialization and
since each segment carry an appendage crustaceans showcase the highest degree of appendage variation
Thus appendage is the greatest asset of crustaceans.

14. CRUSTACEA DIVERSITY Brahiopoda (fairy shrimps), Ostracoda
The sub phylum consist of six major subclasses,namely,
Brahiopoda (fairy shrimps),
Ostracoda
Copepoda (cyclops)
Brachiura (fish louse)
Cirripedia (barnacles)
Malacostraca (shrimps, crabs etc..

16. Branchiopoda The subclass contains primitive and tiny crustaceans.
The major distinguishing feature of the group is the undifferentiated series of appendages modified for respiration hence the name Branchiopoda which literarily means “gill foot”
Members of the group present
variable number of segments
abdomen lacking appendages.
Examples include:
water fleas e.g. Daphnia sp
fairy shrimps e.g. Artemia sp
Tadpole shrimps, e.g. Apus sp etc.

17. Daphnia sp.
is laterally compressed and covered by a bivalve carapace that ends posteriorly in a spine.

18. Daphnia morphology The carapace spares few anterior segments on the
cephalothorax
opens ventrally to reveal the
Appendages and has neither a hinge
nor adductor muscle.
The body is highly shortened with
very few segments representing
the cephalothorax and
the abdomen completely lost and
represented by one segment or
Reduced to one segment the is curved
ventrally.
Daphnia with left carapace removed

19. Daphnia morphology On the cephalothorax is
a single sessile compound eye
a pair of reduced antennules
a pair of well developed antenna
radiating forward or anteriorly used
mfor swimming
mandible and maxillae around the
mouth are lost and
5 to 6 pairs of foliaceous limbs with
conspicuous setae at their margins
used for filtering food
Filtered food particles are transferred to
the food groove leading to the mouth.
The abdomen is flexed ventrally bearing
the anus and a terminal spine.
They are freeliving and a prominent
component of fresh water planktons.

20. Daphnia with right carapace removed

21. Artemia sp
is dorsoventrally compressed without a carapace.

22. Artemia morphology The cephalothorax has
a single median dorsal eye and a
pair of lateral compound eye
a pair of small antennules
well developed paired antenna
reduced mandible, maxillae (1 &2)
numerous similar foliaceous
Paired limbs used for locomotion &
respiration in an upside down posture and.
the last pair being modified into
copulatory organ
Abdomen has 6 segments that lacks
appendages but end in caudal rami.

24. They :
Are freeliving
do not feature in tropical waters.
Farmed for fish diet

25. Ostracoda The subclass include crustaceans : that are microscopic
bottom dwelling
whose entire body is covered by a carapace that is
calcium carbonate impregnated
hinged
bivalved.

26. Thus ostracods e.g. Cypris have extensive fossil records
Body shows no obvious sign of segmentation
but the cephalothoracic appendages are barely noticeable,
while abdomen is greatly reduced and devoid of appendages,
e.g. Cypris

27. Cypris is a minute crustacean whose total length is less than 2mm
Its entire body is covered by a bivalve carapace that opens ventrally and is controlled by adductor muscle that functions on a hinge dorsally.

28. Cypris morphology The enclosed cephalothorax bear an eye,
Large antennules
Large antenna,
mandible,
first maxilla and
second maxilla and
2 to 4 pairs of
setaceous limbs.

30. Cypris morphology cont’d
The large paired antennules and antenna project out of the carapace ventrally and are used for locomotion,
The two pairs of maxillae are large and follaceous with conspicuous setae to effect food filtration since Cypris is a filter feeder and to enhance gaseous exchange.
The abdomen is
greatly shortened thus the bulk of the body length is cephalothorax.
lacks appendages but bear a telson that ends in a caudal rami.

31. Copepoda This is a subclass of minute crustaceans
Most of them are free living but some are parasitic
The free living forms form the bulk of zooplanktons in marine and freshwater environments

32. Copepoda They E.g. Cyclops generally lack carapace
present improved no of visible segments
Have a with a complement of varied appendages.
play a significant trophic role as primary consumers that feed on phytoplanktons.
exhibit vertical migration an interesting phenomenon where they migrate to top of water during the day and bottom at night.
E.g. Cyclops

33. Copepods

34. Cyclop Is a copepod that Is clubbed shaped Is about 5mm long
Is free living.
has no carapace.

35. Cyclop

36. Cyclop morphology Cephalothorax has Abdomen a dorsal median eye,
uniramous well developed antennules
well developed antenna
mandible
1st maxilla
2nd maxilla
a pair of maxillipede
four pairs of oarlike biramous appendages
Abdomen
is narrow and cylindrical
has four segments
lacks appendages and
ends in a forked caudal rami

37. Cyclop morphology cont’d
antennules and antenna used for locomotion
1st and 2nd maxilla used for filter feeding due to their numerous setae,
four pairs of oarlike biramous appendages and a last pair of uniramous oar like appendage used for swimming and generating water current.
The oarlike appendage inform the name copepoda, i.e. oar foot.

38. Brachiura Members of this subclass are crutaceans that are
minute and
parasitic.
They are ectoparasites of both marine and fresh water fishes.
They dwell on the skin and gill
Thus their body is modified for this unique mode of life as they are
flattened dorsoventrally
Short Abdomen hence the name Brachiura
equipped with appendages for
sucking blood and
attaching to host
e.g. Argulus

39. Argulus is a parasitic crustacean. Its body is Shortened
dorsoventrally flattened
covered with a carapace restricted to the cephalothorax
show no obvious sign of segmentation ventrally

40. Brachiurans

41. Argulus morphology Cephalothorax has Abdomen is A pair of compound eye
reduced antennules
modified antenna
spiny mandible
1st maxilla with base modified into suckers
setaceous 2nd maxilla carrying claws and
four pairs of appendages fringed with setae
Abdomen is
small
Not covered by carapace
Not segmented
Not carrying appendages
bilobed representing the caudal rami.

42. Argulus morphology cont’d
The antenna is modified for attachment
The mandible is spiny for sucking,
The base of 1st maxilla modified into suckers for attachment,
The 2nd maxilla is setaceous and carrying carrying claws and the four pairs of appendages are fringed with setae. All used for swimming and they ensure the success of this organism as a intermittent blood sucking ectoparasite that require to move around.

43. Cirripedia These are commonly referred to as barnacles.
They are unique crustaceans that spend their adult life attached to a surface.
They attach to floating inanimate objects in the sea.
They frequently attach to the hulls of ship and large vessels on the high seas and render them less streamline and slow.
Unfortunately their bodies, for protective reasons, are enclosed in calcareous shell plates equitable to a carapace that are very difficult to scrape.
Barnacles therefore constitute a major problem in the maritime industry.

47. Cirripedia They are sessile
They are ones described by Agasis, a famous French zoologist as “a shrimp-like animal, standing on its head and lying on its back in a lime stone house and kicking food into its mouth”.
Eg Lepas and Balanus

48. Morphology
As expected the number of segments and the quality of appendages are drastically reduced to cope with their sedentary life.

49. Lepas is a stalked barnacle,
The main body , i.e. capitulum is suspended by a muscular peduncle attached to the hard substratum by a cement gland.
The duct of the cement gland opens on the vestigial antenule thus confirming that the peduncle must have originated from the antennule
The capitulum which represent the remaining part of the body is covered by a soft carapace in form of a mantle dorsally.

50. The mantle or carapace secretes five calcareous shell plates,
A carina, which is dorsal and medial acting as the hinge and two pairs,of Tergum and Scutum located latero-anteriorly and latero-posteriorly respectively on the capitulum

51. Lepas morphology
A preoral adductor muscle connect the two sides in the anterior region of the capitulum between the scutum mantle.
The animal is attached at the antennules region, and lie on its back leaning on the dorsal carina and extending to the space between the tergums within the mantle cavity.

52. Lepas morphology cont’d
Lepas body consist of the cephalothorax and a virtually obliterated abdomen without appendages.
The body segments are indistinct
The appendages include:
non existent eye
Antennule
antenna,
vestigial mandible,
1st and 2nd maxilla which form oral appendages around the mouth, and
six pairs of biramous feathery appendages (cirri) curled forward towards the mouth.

53. Lepas morphology cont’d
Each cirri is an elongated and segmented endopodite or exopodite af the appendage fringed by numerous setae and used for filter feeding.
The cirri effect this by unrolling, and curling towards each other and collecting or trapping food particles in the water and transferring them to the mouth.
Anus opens on the last segment within the mantle cavity.

54. Balanus Is a sessile barnacle.
It lacks peduncle instead it is attached directly by means of a flat calcareous base.
Its carapace secretes six plates, i.e.
a dorsal carina,
a ventral rostrum and
two pairs of lateral plates (lateral and caprolateral) that form a circular wall around the animal.
The dorsal aperture left behind by the circular wall is sealed by two pairs of movable valve-like lids, i.e. tergum and scutum,

55. Balanus
The opening created by the tergum and scutum allow appendages to emerge and food filtration
The animal lies within the mantle with its ventral side facing the terum and scutum and its anterior end attached to the mantle base.
The appendages are similar to those of Lepas and mode of action are the same.

56. Malacostraca
This is the largest subclass of crustaceans and it includes the very familiar ones like crayfishes, prawns, lobsters and crabs.
They show impressive and most developed structural and appendage variation amongst crustaceans
The may or may not be covered by carapace. When covered however only the cephalothorax is involved.
Segmentation in them is quite discernible and it usually 20 segments, 14 of which represent the cephalothorax and 6 the abdomen.
They have well developed a biramous antennule and a full complement of abdominal appendages.
The subclass include three major orders, namely:
Isopoda,
Amphipoda and
Decapoda

61. Isopoda
The order include marine, freshwater, terrestrial and parasitic representatives.
They posses dorsoventrally flattened body with undifferentiated tagmata in terms of dimension.
they lack carapace and show clearly mapped out segments both dorsally and ventrally, e.g. Ligia

63. Ligia morphology On the cephalothorax is on the abdomen
a pair of sessile compound eyes
a pair of short antennules
a pair of well developed long antenna
mandible
maxilla
maxillule,
maxillipede and
seven pair of walking legs radiating beyond the body laterally and used for crawling.
on the abdomen
The first five segments bear pleopods which are broad platelike plates restricted to the ventral surface and used for gaseous exchange.
The last segment bear biramous paired rod like uropod.

64. Amphipoda This is the smallest order of malacostraca
they include mainly marine forms. Some of them, however, occur in freshwater and along the edges of lakes and seas.
They are quite similar to the isopods, as they lack carapace and abdomen is not visibly distinguishable from cephalothorax.
They are however laterally compressed with posterior end that could easily be taken for anterior and hence the name Amphipoda
e.g. Gammarus

66. Gammarus The cephalothorax have On thee abdominal
paired sessile compound eye
well developed and long antennules
well developed and long antenna,
Mandible
1st and 2nd maxilla,
maxillipede and
seven pairs of legs
the first two pairs being modified for prehensile purpose and hence referred to as gnathopods.
The coxopodites of each of the seven pairs of limbs are flattened and form plates that enlarges the animal lateral view.
On thee abdominal
the first three segments carry pleopods fringed by setae and used for swimming
while the last two carry elongated pleopods that points backwards giving the same impression as the antennule and antenna anterioirly, and hence the similarity.
The last abdominal segment bear paired rod like uropod.

71. Decapoda This is the largest and the most familiar order of Crustacea.
They occur in marine, fresh water and some are amphibious.
They are Malacostracans with
three pairs of maxillipedes on the 7th, 8th and 9th segments
Five pairs of walking legs (Hence the name decapoda) on the segments 10 to 14 of the cephalothorax and
Carapace cover dorsally on the cephalothorax
Two suborders are recognized, i.e.
Natantia
Reptantia

72. Natantia are adapted to swimming and so their
body is laterally compressed
Legs are emasculated and too fragile to carry their body,
Leg arrangement and disposition favor streamline posture
cephalothorax is extended anteriorly to form a rostrum that acts as keel,
pleopods bear extended surfaces in form of setae on the fringes and hence function better as swimming paddles and
the antenna bear large scale that serve as rudders.
Common examples include prawn and shrimps.

75. Reptantia are adapted for crawling hence
their body is dorsoventrally flattened
They have heavy and well developed legs
They have small pleopods and
They have small antenna.
Most Decapods belong to this group
Some of these are the
crayfish
crab
lobsters and
hermit crab.

76. Crayfish externals show two tagmata: Cephalothorax and abdomen.
The former bear the following
a paired stalked compound eyes,
antennule for balance and olfactory functions,
antenna for tactile sensation and excretory functions,
paired mandible,
paired maxilla
paired maxillule
3 pairs of maxillipedes for crushing, mincing and handling food and
five pairs of walking leg with the first pair, great chela, being modified for food capture and defense.
The coxopodite of the fifth walking legs bear the genital openings of the female and the male crayfish.
The abdomen carry
five pairs of pleopods,
the first two of which are modified into copulatory appendages in males.
On the last segment of the abdomen is the tail fan which comprises of flat plates representing a median telson and a pair of uropods, each presenting two plate correspond to the exopodite and the endopodite of the appendage.

77. Crayfish

79. Crab has a very short body it is dorsoventrally flattened.
Dorsally only the shortened cephalothorax is observed.
The abdomen is reduced and flexed beneath the cephalothorax.
Tail fan is lacking and the pleopods are reduced to hairy structures that are used for egg brooding by the females and modified for copulation in males
Since they dwell relatively longer on land, the limbs are large, equipped with heavy muscles and squeezed, within the narrow span of the cephalothorax thus disabling forward movement

80. Crab

82. They are particularly popular because they are edible