What types of modifications to the basic crustacean biramous appendages appear i
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What types of modifications to the basic crustacean biramous appendages appear in the crayfish? Give specific examples. STRUCTURE OF SELECTED REPRESENTATIVES OF PHYLUM ARTHROPODA Cambarus (crayfish) Kingdom: Animalia Phylum: Arthropoda -Crustacea Class: Malacostraca (lobsters, crayfishes, crabs) Genus: Cambarus YOU MUST WEAR PROTECTIVE SAFETY GLASSES WHEN MANIPULATING THE CRAYFISH. a) External Anatomy Examine the external anatomy of the crayfish, noting the hard exoskeleton. The body is divided into a cephalothorax (which is covered by the carapace) and an abdomen. The cervical groove subdivides the carapace into the head and thoracic regions. Locate the rostrum, eyes and telson. The lateral portion of the carapace covers the gill chamber. Cut away the carapace on one side to observe the gills. Often the somites of arthropods are fused together, particularly in the head region, thus making it difficult to count the number of somites. However, counting the number of pairs of appendages often provides a close approximation, as only one pair of jointed appendages is ever attached to a single somite; note though that in some crustaceans, certain somites may lack appendages. The following table lists the typical crustacean appendages: Table 6.1: Typical crustacean appendages On head (6 somites) Embryonic (no appendages) Antennules Antennae Mandibles 1" maxillae IV VI 2d maxillae 1 maxillipeds On thorax (8 somites) VII 2d maxillipeds 48Explanation / Answer
Chelae of decapod crustaceans like crayfish are massive structures. Although chelae perform various other functions like capture of prey, defense against predators etc, reproductive activities are also one of their prime functions. Males have a longer and heavier chelae than females.
In sexual encounters, males use their chelae to grasp and hold the females during copulation.
The term " biramous " means " two branches . So the appendags which have two 'branches ' will be called biramous.
The body of crayfish is made up of twenty body segments grouped into two main body parts-- the cephalothorax and the abdomen. Each segment may possess one pair of appendages. Observations are--
a] The telson is the last segment and does not have any appendages
b] The second last segment has a broad flat, two part structure, the uropod.
c] The other abdominal segments ,each, bear a pair of appendages called swimmerets.
d] The swimmerets of the first two abdominal segments i.e 13 and 14 are larger in males than in females. They are also used for sperm transfer. These are specialised swimmerets and are also referred as 'gonopods'.
e] In females, the first two pairs of swimmerets are smaller and look like the other three pairs.
f] The walking legs are the appendages present on segments 8 to 12. They have two tipped ends.
g] The opening of the female's oviduct is located at the bases of the third pair of walking legs [ on segment 10]
h] On the males, the openings of the vasa deferentia are located by the bases of the fifth pair of walking legs [ segment 12]
i] On the segments 5,6 and 7 at the front of the thorax , are appendages associatd with the mouth. These are called maxillipedes and are smaller than the walking legs. These are biramous too.
j] On segments 3 and 4 of the head are the first and second maxillae.
k] On segment 2 are a pair of heavy grinding structures associated with the mouth. These are the mandibles.
l] The appendage on segment 1 and the prostomium are the antennae and the antennules. These are uniramous.
[ all other appendages are biramous in crayfish]
m] Notice that gills are attached to the walls of the thorax as well as some gills are attached to the bases of the appendages.
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