Decapoda

“ In other Octopoda, and in nearly all the Oigopsida among the Decapoda, the genital ducts are paired in the female, but only the left is developed in the male. The funnel forms a complete tube in the Dibranchiata, and in the majority of the Decapoda, as in Nautilus, it is provided with an internal valve projecting from its somatic surface, which allows water to pass outwards but prevents it passing inwards. The mantle performs rhythmical respiratory movements of expansion and contraction, the water entering between funnel and mantle and passing out through the funnel. ”

“ These are vestiges of lateral cerebral lobes which degenerate in the course of development.
The coelomic cavity appears as a symmetrical pair of spaces in the mesoderm, right and left of the intestine, and from it grow out the genital ducts and the renal organs. The gonad develops from the wall of the coelom.
Phylogeny and Classification.—The order is divided into two sub-orders, Decapoda and Octopoda, by the presence or absence of the tentacular arms. The Decapoda are more adapted for swimming than the Octopoda, the body being usually provided with fins. ”

“ Phosphorescent Organs.—Many Crustacea belonging to very different groups (Ostracoda, Copepoda, Schizopoda, Decapoda) possess the power of emitting light. 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. In other cases in the last two groups, however, the light-producing organs found on the body and limbs have a complex and remarkable structure, and were formerly described as accessory eyes. ”

“ The visceral sac is often strengthened, and the viscera protected, by an internal non-spiral shell. The ‘arms’ which surround the mouth are modifications of the molluscan foot (p. 200) , and are either eight or ten in number. In the former case (Octopoda) the arms, which are termed ‘sessile,’ are all of similar formation, in the latter (Decapoda) , besides the eight sessile arms there are two much longer ‘tentacular’ arms, which widen at their tips into ‘clubs’ covered with suckers.
Remarks have already been made on the generative organs of Cephalopoda (p. 136 f.) ”

“ One of the most characteristic features of the Dibranchiata are the acetabula, or suckers, with which the arms are furnished. They are usually disposed on the sessile arms in rows (of which there are four in most Sepia, two in Octopus, and one in Eledone) , and become more numerous and smaller at the tip of the arm. They are massed together in large numbers of unequal size on the ‘clubs’ in the Decapoda, particularly in Loligo. In most Octopoda their base is flush with the surface of the arm, but in Decapoda the acetabula are pedunculate, or raised on short stalks. ”

“ The tentacular arms, which are the principal external feature of the Decapoda, are not derived from the same muscular ring as the sessile arms, but arise from the cephalic cartilage, and emerge between the third and fourth arm on each side. In Sepia they can be entirely retracted into a kind of pocket behind the eyes, while in Loligo they are simply folded over one another. In Chiroteuthis the arms are six times as long as the body, and the clubs have four rows of denticulate suckers. ”

“ The Decapoda are abundantly represented in the Secondary formations by the Belemnitidae, whose shell (fig. 19) consists of a straight conical phragmacone covered posteriorly by a very thick rostrum, and produced anteriorly into a thin long proöstracum which is only occasionally preserved. In certain cases remains of the arms provided with hooks, and of the ink-sac, have been recognized. The Belemnitidae appear first in the Upper Trias, attain their maximum development in the Jurassic rocks, and are not continued into the Tertiary period, though represented in the Eocene by a few allied forms. ”

“ The male is very often provided with clasping organs for seizing the female. These may be formed by the modification of almost any of the appendages, often the antennules or antennae or some of the thoracic limbs, or even the mandibular palps (some Ostracoda) . In addition, some of the appendages in the neighbourhood of the genital apertures may be modified for the purpose of transferring the genital products to the female, as, for instance, the first and second abdominal limbs in the Decapoda. In the higher Decapoda the male is generally larger than the female and has stronger chelae. ”

“ Pelagic Crustacea belong chiefly to the Copepoda (Calanidae, Centropagidae, Candacidae, Pontellidae, Corycaeidae) , a few Ostracoda (Halocypridae and Cypridinae) , and among Malacostraca a few Amphipoda (Hyperina) , some “Schizopoda,” and among Decapoda only the Sergestidae, if we except the few special forms which live on the floating weeds of the Sargasso Sea, e.g. the Prawns Virbius acuminatus and Latreutes ensiferus, and the Brachyura Neptunus sayi and Planes minutus. ”

“ In the higher Decapoda, numerous additional centres are developed in the brain and its structure becomes extremely complex.
Eyes.—The eyes of Crustacea are of two kinds, the unpaired, median or “nauplius” eye, and the paired compound eyes. The former is generally present in the earliest larval stages (nauplius) , and in some Entomostraca (e.g. Copepoda) it forms the sole organ of vision in the adult. In the Malacostraca it is absent in the adult, or persists only in a vestigial condition, as in some Decapoda and Schizopoda. ”

“ The important array of characters which separates the Euphausiidae from the other Schizopods and unites them with the Decapoda can no longer be neglected, and the consideration of Anaspides and its allies will further emphasise the extreme difficulty of retaining the Schizopoda as a natural group. In the sequel Calman’s proposed scheme will be adopted.
DIVISION 1. SYNCARIDA. There is no carapace, and all the eight thoracic segments may be free and distinct. Eyes may be pedunculate or sessile. The mandible is without a lacinia mobilis. ”

“ Ir in fig. 14) , and then secondly an outer circular fold grows up like a wall and completely closes over the iridian folds and the axis of the primitive vesicle (fig. 33, C) . This covering is transparent, and is the cornea. In the oceanic Decapoda the cornea does not completely close, but leaves a central aperture traversed by the optic axis. These forms are termed Oigopsidae by C. d’Orbigny, whilst the Decapoda with closed cornea are termed Myopsidae. In the Octopoda the cornea is closed, and there is yet another fold thrown over the eye. ”

“ All the walking legs are chelate, and the animal is quite blind, as are all the Eryonidea, the eye-stalks being fused with the carapace.
Only a single family Eryonidae is recognised.
Tribe 3. Peneidea.—Tribe 4. Caridea. We will now consider the Shrimps and Prawns, since in them occurs the most complete metamorphosis found in the Decapoda. The Peneidea are distinguished from the ordinary Prawns and Shrimps (Caridea) by having the first three instead of the first two pereiopods chelate. The genus Peneus affords several species which are of commercial value as objects of food ”

“ It may assume the form of a bivalve shell entirely enclosing the body and limbs, as in many Phyllopoda (fig. 6) and in the Ostracoda. In the Cirripedia it forms a fleshy “mantle” strengthened by shelly plates or valves which may assume a very complex structure. In many cases, however, the shell-fold coalesces with some of the succeeding somites. In the Decapoda (fig. 3) , this coalescence affects only the dorsal region of the thoracic somites, and the lateral portions of the carapace overhang on each side, enclosing a pair of chambers within which lie the gills. ”

“ These rays are not only used as [Pg 81] feet, but, being highly flexible, are adapted for employment also as prehensile arms, with which their owner captures its prey, and they are rendered more perfect for this purpose by being furnished with suckers which hold firmly to any surface to which they are applied. 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. All of these have two plume-like gills—one on each side—and so are called Dibranchiata ”

“ Of the Decapoda, seven families are typically fresh-water in habitat—the Aegleidae, containing the single species Aeglea laevis, related to the Galatheidae, which inhabits streams in temperate S. America; the Atyidae, a family of Prawns from the tropical rivers and lakes of the New and Old World, and in the Mediterranean region. A number of Palaemonidae are found in fresh water, e.g. Palaemonetes varians in Europe and N. America, while several species of Palaemon occur in lakes, streams, and estuaries of the tropical Old and New World. ”

“ Besides these, a small number of subterranean Decapoda are known which retain the eye-stalks but are without functional ommatidia. These are Troglocaris schmidtii, in Hungary, related to the fresh-water Atyid Xiphocaris of East Indian and East Asiatic fresh waters rather than to the South European Atyephyra; Palaemonetes antrorum, from artesian wells in Texas; and several species of Cambarus from the Eastern United States. A blind species of Cambarus, C. stygius, has been described from the caves of Carniola, and if this determination is correct, is the sole Cambarus occurring outside America. ”

“ Taxonomy, distribution and biomass (Decapoda) ., vol. 61, pp. 125–140 ↑ Tesch, JJ (1917) , Synopsis of the genera Sesarma, Metasesarma, Sarmatium and Clistocoeloma, with a key to the determination of Indo-Pacific species., vol. 3, pp. 127–260 ↑ Holthuis, LB (1953) , Enumeration of the decapod and stomatopod Crustacea from Pacific coral islands., vol. 24, pp. 1–66, Maps 61–62 1 2 3 4 5 Yaldwyn, JC & Wodzicki, K. (1979) , Systematics and ecology of the land crabs (Decapoda: Coenobitidae, Grapsidae and Gecarcinidae) of the Tokelau Islands, central Pacific., vol. ”

“ Two others, A. tubercula, belonging exclusively to the Indian Ocean, and A. baillant, which is met occasionally in the Pacific and Atlantic Oceans.
The nautilus belongs to the section of Octopoda, and the class of Acetabuliferous Cephalopods, having, as the name indicates, eight feet, from ὀκτὼ, eight, and ποῦς, foot; at the same time the body is entirely fleshy, and without fins. The genera of cuttles (Sepia) and Calmars (Loligo) belong to another section of the same class; namely, the Decapoda, because they have ten feet and a sort of internal osselet, with fins, &c. ”

“ This animal has not been found again since Darwin’s discovery, but Hansen [71] describes a number of peculiar Nauplius larvae taken in the plankton of various regions, which he argues probably belong to members of this group. A wide field of work is offered in attempting to find the adults into which various larvae grow.
95 Sub-Order 6. Rhizocephala. [72] These remarkable animals are Cirripedes which have taken to living parasitically on various kinds of Crustacea; the majority infest species of Decapoda, e.g. ”

“ The antennæ are formed according to the type of the Diplopoda, with seven joints. The body is composed of numerous segments. The scuta may be prolonged laterally into laminæ, but afford protection only to the back and flanks; the central part of the abdomen is not covered by a firm, resistant shell. The feet are hidden beneath the broad body. The male genitalia are placed in the seventh segment. In the classification of the families and genera I have followed Mr. Brandt, [26] his arrangement, as far as the two species I have seen enable me to judge, being founded on natural characters. ”

“ Surface markings more generally characterize small groups than individual species, yet are sometimes available even in closely allied forms. The possession of a mucro characterizes groups; whilst its size and its shape are often specific. As in all the other Diplopoda each species has a peculiar and persistent form of the Genitalia, more marked in the male than in the female. Indeed a certain type of arrangement seems in this group to characterize a genus.
Genus IULUS.
Scutum primum magnum, lateribus in femina nonnihil productis. ”

“ He manœuvres with all the delicacy of which he is capable, to make the anemone change its shell; he assists it in detaching itself, and if by chance the new dwelling is not to its taste, it seeks another until the Adamsia is perfectly satisfied. This association is not confined to the union of a decapod with a nereid and an actinia; a curious cirrhipede often establishes itself on the body of the pagurus, and on the outside of the shell we generally find a colony of polyps, of a rose or yellow colour, which extend like a living carpet round this habitation. ”

“ The Octopoda, without tentacles, have eight long arms, united at the base by a web; the suckers in two rows, which are sessile; the eyes fixed; shell, two short stiles enclosed in the mantle; the body united to the head by a broad neck-band; no side-fins; shell internal and rudimentary in the British species; body oval, warty, and without fins, in Octopus; small and oblong, arms tapering and webbed, and suckers in a single row, in Eledone (Fig. 321) . ”

“ The Diplopods depend upon the vegetable kingdom for their sustenance. The body is much more rigid than in the Chilopods, from the close conjunction, or often imbrication, of the segments, and the inflexibility of the segments themselves, caused by the density and thickness of the scuta aud sterna and the absence of lateral membranes. For this reason the Diplopoda possess but little or none of that power of raising and twisting the body, which is so annoying to the collector of tropical Scolopendra. ”

“ The resemblance between the Chilopoda and the Diplopoda is principally superficial and due to the elongation and vermiform shape of the body, which in both is composed of a number of similar or subsimilar somites not differentiated as are those of Insecta, existing Arachnida and most Crustacea, into series or “tagmata” of varying function. Until 1893 no one doubted the correctness of the assumption that the Chilopoda and Diplopoda were orders of a class Myriapoda of the same systematic status as the Arachnida or Hexapoda. ”