B. balanoides (Stimp.), B. ovularis (Gould), the rock-barnacle. This is perhaps the most conspicuous of the barnacles. It inhabits the whole northern Atlantic coast, and is so abundant that it not only whitens the rocks with a complete incrustation of shells, but the animals are so crowded that many of them lose their normal shapes and become greatly elongated. When the rocks are covered with water they seem alive, on account of the thousands of waving tentacles. This species also incrusts woodwork between tide-marks.
The shell is small, white, and variable in shape; sometimes its height is less than the diameter of its base; again the height is several times greater and the summit broader than the base. In its early stages the valves are smooth, but later the base is scalloped by four or five grooves. The summit of the plates is even and blunt. The aperture is diamond-shaped. Two valves of the operculum are pointed at the tips; two are blunt, making a deep notch in the summit. These valves are the distinctive feature by which to recognize this species, which varies so much in outward form; the species is also distinguished by its membranous base, which does not form a solid plate like that of other species.
B. eburneus, the ivory barnacle. This species, like B. balanoides, is a very common barnacle, and is found on all kinds of submerged woodwork, whether fixed or floating. It is also found on the carapace of [pg256] crabs and Limulus, and on mollusks. It is chiefly found on objects below low-water mark. It ranges from Massachusetts Bay to Florida. It is easily distinguished from the preceding by its low, broad form and shelly base. The shell is smooth and circular at the base, and inclines backward, forming an oblique cone with a triangular opening; the plates terminate in points at the summit and incline backward, the last one forming a kind of beak. The operculum is pyramidal; two of its valves have both transverse and longitudinal lines well defined at the base, and are coarsely toothed at the edges; the posterior valves are slightly grooved across.
B. rugosus (Gould), B. crenatus. Shell white, cylindrical, somewhat conical, rugged, the summit usually as broad as the base; height often greater than diameter; aperture diamond-shaped, plates ending at the summit in acute spreading points, the posterior plate folded and curved like a beak; plates rough, with coarse, irregular ribs; valves of the operculum at the summit acute, with diverging points; the points striated. Found on shells and stones in deep water and also on bottoms of ships.
B. geniculatus. Shell dirty greenish-white, cone-shaped; aperture about the size of base; shell-plates triangular, unequal in breadth, and with alternate large and small ribs; the smaller ribs compressed and roughened on the edges by the conspicuous lines of growth which run across them; depressed areas between the plates marked with fine cross-lines; front valves of the operculum have coarse plated ridges, which incline over one another and are crossed by fine radiating lines; diameter at base one to one and a half inches; height two thirds the diameter. Found on pecten shells, and abundant off the coast of Maine.
B. tintinnabulum. Shell pink to purplish, conical, with six triangular plates, which are grooved, forming unequal ribs, and crossed by distinct lines of growth; spaces between plates crossed by lateral lines; posterior valves of the operculum longer than the others and curved forward, resembling the beak of a bird of prey; diameter at the base one inch; height one and a half inches. Found in warm waters and on vessels from the South.
Suborder RHIZOCEPHALA
These are parasitic forms and very degenerate. Sacculina lives on crabs, and its term of life is about three years, during which period the afflicted crab does not moult. Its shape is that of an ovoid sac on a stalk, which it attaches between two segments of the ventral surface of its host. The stalk divides and ramifies in a root-like manner within the body of the crab, from whose vital elements it absorbs its nourishment. The roots spread like a mycelium through the whole crab, even to the claws.
Peltogaster lives on hermit-crabs. [pg257]
This subclass comprises highly organized Crustacea, usually of considerable size, having the appendages much differentiated, the thorax with eight segments, and the abdomen with seven segments.
ORDER SCHIZOPODA
The name, meaning "cleft-footed," applies to the appendages of the thorax, which are once-branched (biramous). Gills, when present, are attached to these feet, and hang freely in the water. A delicate carapace covers the thorax; the abdomen is proportionately very large, often twice the length of the cephalothorax. In Mysis the eggs are carried in pouches under the thorax, giving the common name of "opossum-shrimp" to this small, transparent, phosphorescent crustacean.
Genus Mysis
M. sternolepis. About one inch in length; translucent; antennæ very long; segments marked at joints with dark spots; the last two segments terminate in a stout spine; telson longer than the sixth segment; the sides are nearly straight and are armed with spines; the extremity is cleft; eyes large and prominent. Found abundantly in winter on the shores of still, muddy bays and sounds, especially among eel-grass.
ORDER DECAPODA ("Ten-footed")
The Decapoda are named from their ten walking-legs. The higher forms of crustaceans belong to this order. All the Decapoda have a similar anatomy, but are placed in two subdivisions [pg258] according to their external form. In Macrura, the first subdivision, belong the lobsters, crawfish, shrimps, prawns, and hermit-crabs, animals having a long and more or less cylindrical body, with the abdomen extended; in Brachyura, the second subdivision, are placed the crabs, animals having the thorax broad and flat, and the abdomen bent under the thorax. The Decapoda have twenty segments, all of which, except the last one, have, at some period of life, a pair of appendages. The first two pairs of appendages, or, in the stalk-eyed forms, the first three pairs, are especially connected with the senses, and are often fringed with hairs, which are also considered to have a sense-function. The antennules, or first pair of appendages after the eye-stalks, are sometimes divided into two or three branches. At the base of the antennules are the ears. The antennæ, or second pair of appendages, are undivided, but are larger than the first pair, and are often very long. At the base of the antennæ are the renal glands. Both the antennules and the antennæ are slender, elongated, movable, and full of joints. In some species they are greatly modified, as in Scyllarus, where they are developed into broad swimming-plates and, perhaps, as shovels for burrowing; in some amphipods they are used as swimming-organs. (Plate LX.)
| PLATE LX. External Anatomy of a Lobster. | |
|---|---|
| C, carapace; e, eye; g, gill; m, metastoma; n, endopodite; p, epipodite; x, exopodite; I-VII, abdominal segments; 1, antennula; 2, antenna; 3, mandibles; 4, 5, maxillæ; 6, 7, 8, maxillipeds; 9, big pincer; 10-13, walking-feet. | |
The next six pairs of appendages are grouped about the mouth. They are the mandibles, the maxillæ, and the maxillipeds. The mandibles are at the mouth-opening, and, being heavy and hard, are adapted to tearing and grinding; they have a jointed attachment, the palpus, whose office is to keep the mandibles clean. The two pairs of maxillæ are delicate and leaf-like. The three pairs of maxillipeds grow gradually larger, the last pair being very prominent and extending over the other mouth-parts. Next come five pairs of walking-feet. One or more pairs of these feet have pincer-like ends, or claws. Some species have the claws immensely developed, as in lobsters. The claws are the chelæ, and the feet which bear the chelæ are termed the chelipeds. The rest of the walking-feet have generally single, hook-like ends, but are variously modified in different species. The abdominal segments have six pairs of appendages, also variously modified. The last segment is without appendages, but often is extended into a tail, [pg259] or fin-like expansion. The next to the last segment, in many forms, has appendages modified into swimming-plates, which extend on each side of the telson, forming a broad, fan-like caudal extremity.
They have, then, to correspond to the twenty segments of the body, two pairs of sensory, six pairs of mouth-, and five pairs of walking-appendages attached to the cephalothorax, and six pairs on the abdomen. The terminal segment, or telson, is without appendages. The exopodite is present on the maxillipeds, but disappears from the walking-feet in the higher forms.
In moulting the Macrura split in the longitudinal line down the back; in the Brachyura the split occurs across the body at the point between the thorax and the abdomen.
Suborder MACRURA SHRIMPS, PRAWNS, LOBSTERS, CRAWFISH, AND HERMIT-CRABS
The characteristic features of the Macrura are an elongated body with the abdomen usually extended; a carapace, somewhat cylindrical; and the last pair of appendages of the abdomen (which are attached to the next to last segment) united with the last segment, or telson, to form a powerful caudal fin, used for swimming backward. The creeping forms in moving walk forward, but swim backward.
FREE-SWIMMING FORMS: SHRIMPS AND PRAWNS
In these animals the body is compressed and the carapace is not hard. The abdomen is very large in proportion to the cephalothorax, and has a peculiar bend. The rostrum is often longer than the thorax. The eye-stalks, antennæ, and legs sometimes attain extraordinary length, and the chelæ (claws) are not always on the first pair of legs. In some species chelæ are on two or three pairs of the legs. Above the antennæ are expanded antennal scales, which, together with the long bases of the antennules and very prominent eye-stalks, make the head a broad and conspicuous feature. The difference between shrimps and prawns is not very well defined, the small individuals seeming to be generally called shrimps, the larger full-grown ones prawns. [pg260] Prawns are known as crevettes in France and as Garnelen in Germany, where they are largely used as food. In the United States the shrimp-fishery is an industry of the South. On the California coast the fisheries are very extensive and are monopolized by the Chinese.
Genus Penæus
P. setiferus. This species is about six inches in length when full-grown. A ridge or crest extends along the center of the carapace, and terminates in a long, pointed, toothed rostrum, the teeth being fringed with hair on the inner side. The antennæ are a foot or more in length; there are chelæ on the first three pairs of thoracic feet; the swimming-feet and lateral margins of the segments of the abdomen are fringed with hair; and the caudal appendages are longer than the telson. It ranges from Virginia southward, and is very abundant on the shores of the Southern States, where it is gathered for the markets. The large ones are known as prawns and the small ones as shrimps.
P. brasiliensis. This species is associated with P. setiferus, and, although not so abundant, forms a part of the shrimp-supply in the fisheries. It differs from the former in having a groove on each side of the ridge which runs through the center and whole length of the carapace. The first three pairs of feet are chelated. This shrimp is found as far north as Long Island, and often in brackish water, or even where the water is quite fresh.
Genus Palæmonetes
P. vulgaris (Palæmon vulgaris). Average size one half of an inch in length; body translucent, almost colorless, irregularly spotted; rostrum as long as carapace and toothed on the upper edge. It is found among eel-grass in brackish water, and also in pools and ditches on muddy shores from Massachusetts Bay to Florida. Commonly known as prawns.
Genus Crangon
C. vulgaris, the common sand-shrimp. It ranges from Labrador to North Carolina on the Atlantic coast and from Alaska to southern California on the Pacific coast. It is found in abundance on sandy shores at low-water mark, and in shallow water below tide-mark; also among rocks and seaweeds. When left by the tide it buries itself in the sand. Its color varies with its location, rendering it inconspicuous. Upon the [pg261] sandy shores it is translucent, pale in color, and often specked, closely resembling the sand, while on dark, muddy bottoms it is much darker. This is an edible shrimp, eagerly devoured by fishes; it is also gathered for the markets. The body of C. vulgaris is broad at the anterior end and tapers to a sharp point at the posterior extremity. A pair of broad, divided appendages on the cylindrical segment, which is next to the last on the abdomen, together with the sharp telson, form a fan-like swimming-tail. As in all shrimps, the antennæ are long and have plate-like antennal scales at the base, which are fringed with hairs. The mandibles are long. The movable finger of the chela is folded across the extremity of the claw.
C. franciscorum, the California shrimp. This species is about three inches in length. It is distinguished from C. vulgaris by its larger size and by the greater length of the movable finger of the chela, which folds parallel to the side of the claw instead of across its extremity. Its color is light or dark yellowish-gray, mottled. This is the shrimp extensively gathered by the Chinese for commercial purposes. The shrimp-meat is dried and cured, and then separated by blowers very much as wheat is cleaned. It is exported to Eastern countries in great quantities, the value of the export being estimated at one hundred thousand dollars per annum.
CREEPING FORMS: LOBSTERS AND CRAWFISH
Family ASTACOIDÆ
Genus Homarus
There are but three species of this genus, which is the most important one of all the Crustacea. They are H. vulgaris of Europe, H. capensis of the Cape of Good Hope, and H. americanus, which occurs on the eastern coast of the United States from Labrador to New Jersey. The lobster-fishery is one of great importance, and of such value that it is governed by stringent laws. The [pg262] annual catch on the Atlantic coast of North America amounts to many millions of lobsters, the money value of which is very large.
H. americanus, the common lobster of the Atlantic coast. The characteristic feature of the lobster is its enormously developed chelæ, or pincer-claws, which are on the first pair of walking-feet. Small claws occur on the next two pairs, and simple hooks on the remaining two pairs. The appendages on the abdomen are divided (biramous). In the female they are used, excepting the last pair, for holding the eggs; in the male they are greatly abridged. The appendages on the next to last segment are divided and broadly flattened, forming with the telson a powerful swimming-paddle. The rostrum is very prominent, and has a long, pointed end, slightly upturned, and several spines.
The lobster belongs to the creeping forms of the order; it walks forward by means of the ten feet, but swims backward by using its caudal fin. It lives in deep water on rocky bottoms, hiding among stones, etc., but frequents sandy shores as well. It lives on dead and decaying animal matter, and it would seem strange that its flesh is so palatable, were it not that we know that chemical combinations which take place in the assimilation of food make one kind as clean, when transformed, as another. All the crustaceans have a similar dietary, being scavengers of the sea; yet fishes find them more acceptable than other animal food, and fishes capable of capturing larger prey subsist largely on the minute entomostracans described elsewhere.
The lobster is so large that it can easily be dissected, and will serve as a type of the structure of Crustacea. In dissecting one can follow the descriptions given of the anatomy of Crustacea on page 246, and will be interested in observing the beautiful arrangement of the parts and their adaptation to the uses they serve. [pg263]
The female lobster carries her eggs on the abdominal legs, to which they are glued by a kind of cement. After the young emerge from the egg, the zoëæ still cling to the mother for a little time. The lobster moults eight times the first year, five times the second, and three times the third year, after which the male moults twice and the female once a year. It retires to some secluded spot for this operation, which is attended with many dangers. The back splits open longitudinally and the animal slowly withdraws, leaving the shell complete. In preparation for moulting, the lime around the contracted joints of the chelæ is absorbed, so that the soft flesh can pass through. Any injury to a limb at the time of moulting, or which results from fighting or from any accident, is repaired at successive moultings, and a lost member is replaced by a new, but not always a perfect, one.
Genus Panulirus
P. interruptus. This is the California spiny lobster, rock-lobster, or salt-water crawfish. It differs from the common lobster Homarus of the Atlantic coast in having no large claws, the first pair of feet being simple like the rest, also in having antennæ which are enormously long and very large at the base. The carapace is beset with spines, and the lateral margins of the abdominal segments end in spines. This species lives among the rocks on the southern California coast.
P. argus or americanus resembles P. interruptus, and is found on the coast of Florida.
Genus Scyllarus
Scyllarus has a broad, almost square carapace, which is uneven and coarsely granulated; the anterior corners are sharp, the posterior ones rounded. The antennæ are curiously modified into broad, flat, double plates reaching quite across the straight anterior end of the carapace. The under scales of these modified antennæ are rounded and leaf-like, the upper ones are pointed. The margins of the abdominal plates on the ventral side are toothed, and on the upper side the first three sections have [pg264] knobs, the third one being the most prominent, and forming the posterior extremity when the abdomen is folded in. The walking-feet are all simple and end in points; the first pair are the longest, and the following ones gradually diminish in size. The ventral surface is rough and spiny. The abdomen is of about the same length as the carapace. These animals are found off the Florida coast and are caught in the fish-traps. They are uncommon. The very peculiar development of the antennæ makes them worthy of examination when opportunity offers.
ANOMALOUS FORMS: ANOMURA
The anomalous forms which are intermediate between the suborders Macrura and Brachyura were, until recently, placed in a suborder, Anomura. The members of this group differ from one another, and some of them resemble in external features members of the other divisions of the suborders, but there is a difference in anatomical structure which separates them in the classification.
Family DROMIDÆ
Genus Hippoconcha
H. arcuata. This curious little crab, found on the Florida coast, carries the half of a bivalve shell over its back. Its fifth pair of thoracic legs are bent over the back, and these, together with the fourth pair of legs and the spiny front edge of the carapace, enable the crab to hold the shell in position. This crab was formerly classed with the hermits, all of which were originally called Bernhardus, after the monk of that name.
Family PAGURIDÆ THE HERMIT-CRABS
In these curious animals the posterior part of the body is not protected by a crustaceous covering, and therefore the animal seeks protection by inserting its soft and defenseless abdomen into some hollow object, usually the shell of a gasteropod mollusk, as the whelk or the periwinkle (Buccinum, Littorina). The hermit-crabs do not always use a shell for this purpose, as they are sometimes found in the tubes of plant-stems or in sponges. Like other organisms in the animal world, they seem [pg265] well fitted to make the best of their surroundings, the body becoming modified to suit the peculiar conditions under which they live. In those which inhabit shells the abdomen becomes spiral, in conformity to the convolutions of the shell. All the abdominal appendages are more or less atrophied; the sixth pair become like hooks, and these fasten to the columella of the shell, keeping the crab securely attached to it. In the female some of the abdominal appendages are hair-like and are adapted to carrying the eggs. The thorax, being protected, is protruded from the shell at will. The first pair of feet are much larger than the others, and are provided with claws (chelæ). The first right foot is usually much larger than the left, and, besides the usual functions of capturing and crushing prey, the claw, or hand, serves as an operculum to close the mouth of the shell when the crab retires completely within it. The small left hand is shaped to fill out the parts of the opening not covered by the right one, thus making a close fit. The next two pairs of feet end in simple hooks, and are used for walking and dragging the crab along when he travels. These crabs move about very fast, and the houses upon their backs seem no encumbrance. [pg266]
In some genera both hands are alike; in others the left one is the larger. In the case of hermits which live in tooth-shells, the right hand is cylindrical in form, fitting the circular opening of the shell. The other extreme is found in the genus Cancellus, where both the chelipeds and the first pair of ambulatory feet are ingeniously shaped, so that when closed they form a round operculum, or door, which closes the way into the compact sponge which this crab has for its carcinœcium, or house. It is interesting to note these differences and observe the perfection with which the feet are formed and jointed to suit the openings of different shells. Some genera show other adaptations to their twisted houses, the eye-stalks being uneven in length and the ambulatory feet unequal on the opposite sides. Besides this, some species are hairy and cover themselves with dirt for further protection. The exposed claws of some hermits have a special armature of spines, which make a fringe of points around the opening of the shell when the crab is withdrawn.
As the hermit grows he is occasionally obliged to find a new or larger shell, and there are amusing anecdotes of the troubles he experiences at these times while house-hunting. Very often he tries several shells before he finds one to fit. There is a tradition, not, however, well authenticated, that if the shell chosen happens to be occupied by its natural owner, the crab tears out and devours the unfortunate occupant. If the desired shell is occupied by another hermit inferior in strength to himself, he proceeds to take possession by violence. He then examines carefully the empty shell, inserting his legs and feelers, and if he decides to occupy it he withdraws his abdomen from the old shell and darts it so quickly into the new one that the act of transference is difficult to follow. After walking about with the new shell it sometimes proves to be unsatisfactory and further search becomes necessary. After it is well domiciled the crab never ventures outside the shell until it is obliged to change again on account of growth, or because some stronger crab dispossesses him. The shells of hermit-crabs serve frequently as the home of other animals which live with them a commensal life. The hydroid Hydractinia polyclina often covers the exterior of such shells with a brown, velvety growth. Some sea-anemones also are commensals [pg267] with hermits. Adamsia palliata is always found on the shell occupied by Eupagurus prideaux, and never on any other. This is a European form. On our own coast a red anemone, the Epizoanthus americanus, found in deep water off the entire eastern shore, fastens on the shell occupied by the hermits Eupagurus pubescens and E. kroyeri. This anemone in time absorbs the shell of its host and itself becomes its protector—an advantage to the hermit, who finds room in the yielding polyp-mass for its increasing size, and feels no longer the necessity for change of domicile. The female hermit holds its eggs in the posterior feet until they are hatched; the young are then released, pass into the water, and soon find shells for themselves.
Genus Pagurus
P. bernhardus. This is a large species, bright red in color, rough and hairy. It inhabits the shells of Fulgur carica or of Polynices heros. It ranges from Cape Cod northward, and is replaced on the northern California coast by P. alaskensis and P. aleuticus.
P. pollicaris. This hermit inhabits shells similar to those occupied by the last, but is pale red in color, and its surface is granulated and not hairy. The short joint of the chela has a broad angle. It ranges from Massachusetts to Florida, and occurs at low-water mark on rocky and shelly bottoms of bays and sounds.
P. longicarpus. A quick-moving little hermit with long chelipeds, found in small shells at the water's edge in quiet places. They exist in great numbers and are eaten, shell and all, by fish. This species can be distinguished from all others by its very light color and metallic luster.
Genus Clibanarius
C. vittatus. This hermit is found from North Carolina southward along the edge of the water and in tide-pools. It cannot be mistaken [pg268] for any other hermit common on our coast, since it has the very distinctive feature of white longitudinal stripes on the ambulatory feet. The chelipeds are about equal, rough with tubercles, and the tips have smooth black edges. Body and feet are quite hairy. The color is brown and white.
Genus Pylopagurus
This genus is represented in Southern waters by several species. One of the most characteristic of them lives in Dentalium, the tooth-shell. The outer surface of the right hand is formed to close the shell. All the ambulatory feet and the very small left hand fold beneath, leaving only the flat surface of one hand exposed to view. Another species lives in a shell covered with polyzoans.
Family CENOBITIDÆ
Genus Cenobita
C. diogenes. This large hermit-crab, found in Florida and in more southern waters, inhabits the beautiful pearly shell of Livona pica. It lives on land a part of the year, but spends the breeding season in the water. It can be distinguished by its land-roaming habits, its large left cheliped, very stout walking-legs, and compressed eye-stalks. This species climbs the hills, but is more frequently met with in low, shaded, marshy places. (Plate LIX.)
Family HIPPIDÆ
Genus Hippa
H. talpoida. This animal, commonly known as the "sand-bug," differs greatly in appearance from a crab. When the appendages are folded under the carapace it somewhat resembles an egg, the body being ovate, about half as broad as long, and the sides forming a nearly regular curve. The carapace is about one and a half inches long, convex, yellowish-white, and nearly smooth. The abdomen is long and pressed under the body, reaching nearly to the front. The eyes are minute and on the ends of long, slender stalks. The antennæ are plume-like and about as long as the carapace. Hippa lives on sandy beaches at or near low-water mark, exposed to the action of the waves. It burrows with great rapidity into the loose and shifting sands, using the short and stout second, third, and fourth thoracic legs and the appendages of the sixth abdominal segment [pg269] for pushing and digging. Crabs of this species are gregarious and may be seen in great numbers, though but few will be captured together by digging, as they rapidly disappear beneath the sand. Sometimes they are found swimming about in the tide-pools. They seem to live upon the organic particles contained in the sand, which they swallow, the mouth not being adapted for mastication. This species ranges from Cape Cod to Florida. (Plate LXI.)
H. analoga. Similar to H. talpoida, but broader and flatter. It is bluish above, yellowish-white below, and the fringing hairs are black. Found on the California coast.
Genus Albunæa
A. gibbesii. This animal is found with Hippa, and, like it, burrows rapidly in the sand. Its general outline is square. The surface of the carapace is marked off with denticulated lines, which make the back appear as if composed of plates. The front edge of the carapace has a row of teeth and a prominent spine at the anterior angles. The abdomen is doubled under itself (not fitting into a groove of the thorax, as in ordinary crabs), this animal being intermediate between the long- and the short-tailed forms. The eyes are on triangular, plate-like stalks. The antennules are very long and are fringed with hair. The chelipeds have claw-like joints, which close across the straight, broad end of the hand. The first two pairs of walking-feet have curious sickle-like terminal joints. The animal is about one and a quarter inches long. Albunæa does not extend as far north as Hippa, its range being from Georgia southward. (Plate LXI.)
Family PORCELLANIDÆ
The crabs of this family are little more than one quarter to one half of an inch across the back. The chelipeds are broad and flattened. The first three pairs of walking-legs are well developed, and the fifth pair are very small and are doubled over the base of the carapace. The sixth segment of the abdomen has a pair of biramous appendages, which, with the telson, form a swimming-fan.
Genus Porcellana
P. sayana. Carapace little longer than broad; breadth about one quarter of an inch; smooth; has three acute denticulations between the eyes, the middle one the largest and depressed in the center; two denticulations on each anterior side; chelæ fringed with hair on the edges; walking-legs somewhat hairy; fifth pair of legs folded over base of carapace; color reddish, with white spots. This species was once called occulata, because of the eye-like spots over its entire surface. The posterior part and abdomen have longitudinal bands of color. The claws are marked like the shell. Found from South Carolina southward, often in the shells inhabited by hermit-crabs. (Plate LXI.) [pg270]
Genus Petrolisthes
P. sexspinosus. Carapace longer than broad; breadth about one half of an inch; space between the eyes broad, but not divided into three teeth as in Porcellana sayana; second joint of the cheliped has five broad teeth on its front edge and five or six small spines on its outer edge; fifth pair of legs doubled over base of carapace; whole body traversed with broken red lines. Found from South Carolina southward. (Plate LXI.)
P. armatus. Carapace longer than broad; breadth about one quarter of an inch; prominent and wide between the eyes; a small sharp spine on each anterior side; chelipeds long; second joint of cheliped twice as long as broad, with three teeth on the front edge and four or five small spines on the outer edge. Found on the Florida coast. (Plate LXI.)
Family LITHODIDÆ
The species of this family have a broad, ovate, uneven body and a prominent rostrum. The fifth pair of legs are rudimentary and are folded under the carapace in the branchial chambers, so that the crabs appear to have but four legs on each side. This is the distinguishing feature of the family, and makes them easily recognized.
Genus Lithodes
L. maia. The carapace is cordate (heart-shaped), and longer than broad, exclusive of the rostrum. The margin is recurved all around, and is beset with numerous very long spines. Six spines on each anterior side margin are regular and longer than the others. The surface of the carapace is covered with tubercles and spines and elevated in places. The rostrum is spiny, a third as long as the carapace, and has two spines at the base, one above the other, a spine at each side, two lateral spines near the middle, and two terminal divergent spines. The chelipeds are unequal and are covered with spines, those on the inner margin being the longer. The color is yellowish-red, lighter underneath; the spines are darker. Found on the fishing-banks off the coast of Maine. (Plate LXI.)
| PLATE LXI. | |
|---|---|
| 1, Hippa talpoida. | 2, Albunæa gibbesii. |
| 3. 1, Porcellana sayana; 2, Petrolisthes armatus; 3, Petrolisthes sexspinosus. | |
| 4, Lithodes maia. | |
| PLATE LXII. | |
|---|---|
| Echidnocerus cibarius. | Cryptolithodes sitchensis. |
| Echidnocerus foriminatus. | Phyllolithodes papillosus. |
Genus Echidnocerus
E. cibarius. This curious crab has the carapace raised in front into a large cone-like elevation terminating in a long point. Three prominent but smaller cones extend across the center of the back, and two still smaller ones occur on the posterior sides and in the middle of the posterior margin. The whole surface of the carapace is covered with coarse granulations arranged in rosette-like groups. The chelipeds and legs are beset with large tubercles and fold together in such a manner that when retracted the crab is a close, compact, box-like mass, with a very rough, [pg271] spiny armature. The antennæ are broad at the base and covered with small spines on the sides and upper surface, and the eye-stalks are also spiny. This crab sometimes attains the size of ten inches across the carapace and a weight of seven pounds, being among the largest crabs known. It is found at the mouth of the Columbia River and along the northwest coast. (Plate LXII.)
E. foriminatus. This species resembles E. cibarius in the manner of closing the feet, forming a compact, box-like, spiny armature. The body is more depressed than that of the latter, and the cone-like elevations on the back are less prominent. The spines are hairy. The characteristic feature of this species is a semicircular cut in the second joints of the chelipeds, directly opposite to similar depressions in the first walking-legs, so that when the feet are folded a round hole is left, through which water flows freely to the gill-openings, which might, without these open holes, be obstructed by the close folding of the legs against the carapace. Found off the California coast near San Francisco. (Plate LXII.)
Genus Acantholithodes
A. hispidus. The whole body in this species, including the legs, is covered with hairy spines. The abdomen is broad, and covers about the whole under surface of the body, and is also beset with hairy spines, but they are less prominent than those on the upper side. The rostrum, terminating in spines, reaches to the tips of the eye-stalks, which are also spiny. The chelipeds are larger and longer than the walking-feet; the latter taper to a point, ending in a sharp nail. The shape of the body resembles somewhat that of a toad. This is a deep-water species, but it is sometimes brought ashore at Monterey, California, by fishermen who find it in the stomachs of fishes.
Genus Cryptolithodes
C. sitchensis. The most striking characteristic of this singular species is the great development of the carapace, which forms a broad, thin shield extending beyond the body and legs, and completely hiding the animal beneath it. The carapace is smooth and uneven, has a high ridge through the center of the anterior part, and the sides are broadly expanded and bluntly pointed at the extremity. The rostrum appears like a small rectangular piece cut out of the anterior side of the carapace. This species is found in the Strait of Fuca. A similar species, C. typicus, is found near low-water mark on the surf-washed rocks of the beach at Monterey, California. (Plate LXII.)
Genus Phyllolithodes
P. papillosus. The carapace is triangular, about two inches wide at the base, and narrowing to a long, pointed rostrum which terminates in a forked spine. The surface of the carapace is deeply depressed in parts, and forms a heart-shaped figure in the center. The lateral margins have four prominent spines on each side, the two at the posterior ends being [pg272] thicker than the other two. The abdomen is broad, covering the whole under side of the body, and is marked off with prominent raised ridges diverging from the center line. The legs are all beset with long, rough spines. Habitat, the northwest coast. Taken from the stomachs of fishes off Monterey, California. (Plate LXII.)
Suborder BRACHYURA THE CRABS
This group contains the true crabs, which are the highest of the Crustacea. In form they are quite the reverse of the first group. In the Macrura—except in the anomalous forms—the body is long and cylindrical and the abdomen extended, but in the Brachyura the body is flat and broad and the abdomen short and reflexed. Crabs of this suborder inhabit all seas of the globe, and are found from the shore to great depths. Some species live on land, some on the shore, some in deep water. Some forms burrow in the sand; others live under stones and boulders, or conceal themselves in crevices of rocks or in the cavities of sponges. They are divided into many families, and creep, climb, swim, or burrow, their structure being modified to their respective modes of life. There is also great variation in their shapes as well as in their color and markings. This diversity is so great and peculiar that it seems as though each one were more curious than the others.
In crabs the cephalothorax is depressed and often broader than long. The abdomen is relatively small and is folded under the thorax, lying in a groove which it fits so perfectly as to be quite hidden from above. The appendages of the abdomen are much reduced in number. The male has two pairs; the female has four pairs, which it uses for carrying its eggs. The first pair of walking-legs are comparatively large, and end in chelæ, or pinching-claws. The other eight legs terminate in simple points, except in the swimming varieties, when the fifth pair is flattened to form fins, or swimming-paddles. The eye-stalks are long and fit into sockets on the carapace. Both pairs of feelers are small. The antennules are frequently folded into small grooves. The external or third pair of maxillipeds are broad and flat, and cover the mouth-parts like a lid, or operculum. [pg273]
Crabs, like other crustaceans, are scavengers, living on dead animal matter; but the land species are also vegetarian in diet. They are great fighters, but are also wily, often averting danger by resorting to stratagem. They are an interesting and curious group, as they possess a good degree of intelligence and have amusing habits.
From the time they leave the egg until they attain the adult form they pass through several complete and singular metamorphoses. The most marked forms are called the Zoëa and the Megalops. So little do these resemble the adult that originally they were classed as distinct genera far removed from the one to which they really belong. After the larva has moulted several times it appears as in the illustration on page 248—the last zoëa stage. From this it changes directly to Megalops; the Zoëa, seeming to be attacked with violent convulsions, wriggles out of its skin a full Megalops (page 248). The animal then has enormous eyes, an extended abdomen, an elongated carapace, and swimming-legs. This stage is a short one, and at the first moulting changes to a form nearly approaching the adult. From this time they grow by shedding the shell at certain periods. This shedding is supposed to occur twice each summer until they have reached full growth, after which it is probable that they do not again moult; for often they are found with extraneous organisms, such as barnacles and sponges, upon them, of a size that must have required a considerable period of time for growth. The sexes of the same species sometimes differ so much that it is difficult to classify them. Even naturalists have been led into the error of assigning the male and female to separate species.
The front side margins of the carapace in many crabs are edged with a row of teeth or with spines, which vary in number and character in different species. In the spider-crabs the whole surface of the carapace is generally studded with tubercles, spines, and stiff hairs of a peculiar character. This armature is for protective purposes, and is often used to secure foreign bodies, such as algæ, hydroids, and polyzoans, which the crabs place upon their backs to disguise themselves. The burrowing crabs are usually smooth. When in motion the crab moves sideways, using the legs [pg274] of one side to pull with and those of the other side to push with. As all the legs do not move at the same time, a continuous and uniform motion is kept up. Some species move with great rapidity, notably the sand-crab, Ocypoda arenaria. Often when pursued they will run into the surf instead of to their holes. The common edible crab, Callinectes sapidus, of the Atlantic coast, the fiddler-crabs, and the spider-crabs are among the well-known representatives of Brachyura.
Family PORTUNIDÆ SWIMMING CRABS
Genus Carcinides