Decapoda

1 Milne-Edwards did this when he separated Mysis and Leucifer from the Decapoda, but he himself afterwards saw that this was an error.

2 Shrimp, shrimp, n. a genus of edible crustaceans, of the order Decapoda, allied to lobsters, crayfish, and prawns: a little wizened or dwarfish person.—v.i. to catch shrimps.—ns.

3 In the higher Decapoda the male is generally larger than the female and has stronger chelae.

4 In the Decapoda, where the antennal gland alone is well-developed in the adult, the maxillary gland sometimes precedes it in the larva.

5 Thus, speaking generally, it is one or both of the fourth pair of short arms which are modified in the Decapoda, of the third pair in the Octopoda.

6 In the Decapoda there are also reflecting elements which produce iridescent hues.

7 The Decapoda are more adapted for swimming than the Octopoda, the body being usually provided with fins.

8 These hooks are special modifications of the toothed chitinous ring which covers the sucker-rim in the Decapoda generally.

9 In the oceanic Decapoda the cornea does not completely close, but leaves a central aperture traversed by the optic axis.

10 In the Decapoda the antennal gland is largely developed and is known as the “green gland.”

11 At the base of the inferior antennae in the Decapoda the so-called "green-gland" has its opening; in the Macrura at the end of a conical process.

12 The Cephalopods which have the foot divided into ten of these segments or arms are called the Decapoda, those which have only eight of them are called the Octopoda.

13 The taxonomist notices the fact and distinguishes the two groups of Octopoda and Decapoda.

14 This is seen, for example, in the Brachyura among the Decapoda.

15 In the majority of the Decapoda there is a saccular invagination of the integument in the basal segment of the antennular peduncle having on its inner surface “auditory” setae of the type just described.

16 A gradual reduction of the tentacular arms can be seen in the Decapoda, leading to their total absence in Octopoda; thus in Leachia, Chaunoteuthis and others these arms are reduced to mere stumps.

17 In the Ostracoda and Copepoda the phosphorescence, as already mentioned, is due to glands which produce a luminous secretion, and this is the case also in certain members of the Schizopoda and Decapoda.

18 Phylogeny and Classification.—The order is divided into two sub-orders, Decapoda and Octopoda, by the presence or absence of the tentacular arms.

19 Fins.—In the majority of the Decapoda and in the Cirrhoteuthidae, the mantle is produced into lateral symmetrical expansions which have the function of fins.

20 In the Decapoda three pairs are thus modified, and in the Tanaidacea, Isopoda and Amphipoda only one.

1 十足目

shrimp crab nipper spider crab