■J EVOLVT IO R- PEARL c O; X: £| _i = CD- S "1 = r^ = o si-o i »^ : o I a □ m o B300QSQOQOSSOSSE3E Marine Biological Laboratory Library Woods Hole, Mass. Presented by From the estate of Louis W, Hutchins May, 1964 N D D 3 3EaBQbdbdBQfc^bdbdQQQQB3E A NATURAL HISTORY OF THE SEAS By the Same Author THE AQUARIUM BOOK With 1 6 pages half-tone illustrations and 39 line illustrations in the text by L. R. Brightwell. "Contains a host of entertaining stories. ... Will make a strong appeal to all lovers of nature, whilst for those who are thinking of starting a small aquarium of their own it will be found almost indispensable."—!^ Sphere oo u J3 ■i-j 'J U-i n 3 c a o u pq PQ H < Z <4. ■a A NATURAL HISTORY OF THE SEAS By E. G. BOULENGER Director, Zoological Society's Aquarium o y r D APPLETON-CENTURY COMPANY INCORPORATED NEW YORK 1936 Printed and made in Great Britain CONTENTS CHAPTER PAGE Introduction ------- 9 I. The Simplest Animals - - - - - 13 II. Polyps ---------19 III. Crustaceans -------33 IV. ECHINODERMS -------59 V. Worms and Polyzoa ----- 73 VI. Molluscs --------84 VII. TUNICATES OR ASCIDIANS AND LANCELETS - 114 VIII. Fishes --------- 120 IX. Reptiles --------171 X. Mammals - - - - - - - -183 XI. Sea Monsters - - - - - - -198 Index --------- 209 83079 LIST OF ILLUSTRATIONS PAGE FORAMINIFERA --------- ja Portuguese Man-of-War (Pbysalia) - - - - 22 Giant Jellyfish sheltering young Horse Mackerel --------25 (a) Sea Fan (Gorgonia). (b) Polyps magnified - 27 Plumose Anemones 31 Larva of Crawfish ------- 24 Goose Barnacles -------- ^-j Flat Lobsters -------- 42 Hermit Crab with Anemone attached - - 45 Spider Crab (Pisa) dressing itself with Seaweed - 49 Sectional drawing illustrating Masked Crab (Corystes) breathing through Antennae whilst buried in the sand - - - - 52 King Crabs --------- 56 Sea Gherkin {Cucumarid) - - - - - - 61 Rosy Feather Star (Antedon) ----- 63 Starfish (Asterias) -------65 Sea Urchin (Echinus) climbing rock - - - 69 Feathery Sea Worm (Sabelld) ----- 78 Whelk (Buccinium) and its eggs 90 Sea PI are (Aplysia) -------93 Cuttlefish {Sepia)- - - - - - - -109 Common Octopus (Polypus) - - - - - -in Tube Sea-Squirt (Ciona). Above : Larval stage (enlarged) - - - - - - - -116 Lancelet (Amphioxus)- - - - - - -118 General Topography of Sea Bream - - 121 Mud Skippers (Periophthalmtis) - - - - 122 Flying Fish --------- 123 Dragon Fish- - - - - - - - -126 Lesser Weever : and details of poison spine on gill cover -------- 129 Shark -suckers or Remoras - - - - - 130 Sting-Rays ---------133 7 8 LIST OF ILLUSTRATIONS PAGE Globe Fish 134 Cow Fish - - - - - - - - -135 Lampreys- - - - - - - - - -137 Whale Shark - - - - - - - -141 Saw Fish -------- _ 143 Sword Fish ---------145 John Dory ------- -_ 148 The " Swallower " (Chiasmodon) - - - -151 Deep Sea Fishes - - - - - - - -153 Development of Eel - - - - - - -158 Butter Fish and Eggs in Oyster Shell - - - 166 Lump-suckers - - - - - - - - -167 Common Sea Horse ------- 168 Deep Sea Angler Fish with parasitic males - 170 Green Turtles - - - - - - - -175 Sea Iguana - - - - - - - - -179 Sea Snake (Hydrophis) - - - - - - -181 DUGONGS - - - - - - - - -185 Killer Whale - - - - - - - -195 Ribbon Fish --------- 201 LIST OF PLATES FACING PAGE Crawfish {Astacus) -------42 Langouste (Palinurus vulgaris) ----- 42 Scorpion Fish - - - - - - - -128 Ray (showing underside of body) - - - - 132 Spotted Puffer Fish- - - - - - -136 John Dory --------- 146 Deep-Sea Angler-Fishes - - - - - -152 Californian Sea-Lions - - - - - -182 Manatee (coming to surface to breathe) - - 184 INTRODUCTION IN this book an endeavour has been made to survey systematically the ocean's teeming populace in a manner acceptable to the general reader. I have attempted to summarise all the principal groups of maritime life, pointing out the more interesting members and in particular showing how each group contains individuals attuned to almost every conceivable environment provided by the open waters or the coastal areas constituting their boundaries. How vast is the ocean and how pregnant it is with as yet unexplored possibilities, we are only to-day beginning to fully realise. In the days of early Greece the ocean was regarded as a river flowing round the then known world. Nowadays the ocean is mapped with some accuracy, its waters and the countless waterways which serve to feed it covering more than two-thirds of the earth's surface. The portion immediately washing the great land masses rests upon what is known as the Con- tinental Shelf and is comparatively shallow. This, however, quickly descends to considerable depths and the deeps proper — many of which doubtless yet remain to be discovered — plunge vertically into Stygian blackness for from two to more than four miles. The vastness of this body of water reduced to figures is scarcely less intimidating than the statistics inseparable from the study 9 IO A NATURAL HISTORY OF THE SEAS of astronomy. Even the annual evaporation is so vast that the mind can scarcely grasp it, yet in the immense clock of geologic time such matters seem as moments of an hour, and are not the less impressive when it is borne in mind that they were established features of the natural order millions of years before the human race had come into existence. Heavily populated as are many portions of the earth's crust — notably the great forest and jungle areas — the terrestrial population is as nothing compared with the waters which are congested with uncountable entities invisible to the naked eye. It was less than ioo years ago that biologists came to the conclusion that both plants and animals ceased to exist in the sea beyond a depth of a few hundred fathoms, but more recent researches have established that even the greatest depths are not without a fauna of their own — a fauna which apparently varies but little in abyssal areas no matter in what portion of the sea they may be situated. Life itself is believed to have had its first inception in the great waters, though the precise nature of such life is at present still conjectural. Though a tolerable census of the coastal forms of life has been generally appreciated from early times, anything approaching a systematic survey is of comparatively recent date. The British Marine Biological Association — the oldest institution of its kind — dates back as recently as 1884, but since that period almost every civilised nation has followed suit, and by organising research stations, oceanographic expeditions, and a constant interchange and pooling of the knowledge so obtained, a tolerably comprehensive idea of the sea's potentialities is fast being INTRODUCTION 1 1 arrived at. The work has been materially forwarded by the vast strides in mechanism of every kind which the last few decades has seen. Drift bottles and other appar- atus serve to track the rate and direction of ocean currents, deep-sea thermometers now give accurate temperature readings, whilst a bewildering diversity of nets allow little that is plant or animal to escape scientific notice. The vast floating populace of microscopic organisms known as plankton is now measured by a device not unlike a large camera film. A gauze ribbon is steadily unwound, whilst being towed behind the survey ship, all creatures adhering to the gauze being automatically preserved as the exposed ribbon winds itself upon a drum. By this means the precise nature and quantity of the plankton over a wide area is accurately ascertained. The survey ship may use a score of nets attached at intervals to a tow-rope which descends perhaps to a depth of several miles. Yet another device — the " grab " — extracts samples of the sea-floor from any depth required. The contents of fish stomachs are also now largely relied upon to give an idea of the forms of life existing in many situations beyond the reach of either grab or deep-sea trawl net. Finally the last few years have produced that astonishing device the bathysphere — a huge steel observation chamber which can be let down from a specially equipped ship to a depth of half a mile and from which the scientist armed with a search-light looks out upon the world undreamed of by the early naturalist. To the layman much of the work that exercises our marine biologists may seem of purely scientific interest 12 A NATURAL HISTORY OF THE SEAS and having little bearing upon practical matters, far less world economy. With each succeeding year, however, the complex interdependence of all animate nature is being more fully appreciated and it may well be that the plankton taken by some scientist to-day may bear indirectly but not the less forcibly upon human welfare several decades hence. It is generally recognized, for example, that all marine life is ultimately dependent for its being on the myriad microscopic plants that throng the waves in the spring and early autumn. They constitute the first link in what is nowadays generally termed the " food chain." As an example it may be pointed out that such plants form the basis of food which nourishes the minute creatures that go to feed the first stages of the herring and many other food fishes. The larger herring itself eats its smaller brethren, whilst sea birds, large fish, seals, whale and man depend largely upon the herring for their sustenance. It will be appreciated, therefore, that plankton and all the factors which control its rise and fall are matters of primary importance and much more than a mere academic study for the laboratory worker. In the following pages the marine fauna of the world will be dealt with in scientific order, though only those creatures of more striking interest or more obvious im- portance to human welfare can be touched upon in any detail. CHAPTER I THE SIMPLEST ANIMALS THE Protozoa, or simplest animals, constitute the most vital portion of the sea's population. They consist essentially of a single-cell and are not built up of millions of cells as are the vast majority of other animals. Most of these minute creatures are in varying degree mobile. Some are highly so and row themselves hither and thither at a great pace by means of minute hairlike organs or " whips." Some are naked, others are endowed with shells, and a few are of such indeter- minate structure feeding in the manner of plants that there is still much doubt as to whether they fall in the animal or vegetable kingdom. The shelled species (Foraminijera and Radiolarid) show a bewildering diversity in the structure of their minute homes — often of exquisite design, and were until 1835 regarded as minute molluscs akin to the whelk and oyster. It was Du Jardine who in that year startled the scientific world by establishing that the animals within were of the simplest construction — mere blobs of protoplasm which crept along by extending hairlike filaments through minute orifices in the shell's walls. Large areas of the ocean bed are covered many yards deep with their deposits and the dead shells of these animals may eventually become 13 14 A NATURAL HISTORY OF THE SEAS by compression solid ground. When raised above sea level, they form the well-known limestone cliffs. Whilst the vast majority of Protozoa must be thought of as creatures of from one-hundredth to three-hundredth of an inch in diameter, a few are just visible to the naked eye. Large examples are the beautiful marine Noctiluca — " night-light " creatures which when they congregate in millions light up wide areas of the sea with a vivid phos- phorescent glow. Foraminifera A sponge is fairly typified in the minds of most persons by the common bathsponge which is so extensively farmed in warm seas for toilet purposes. The form that is sold in shops is but the horny skeleton of a large colony, each individual being bound one to the other to form a single solid mass. All are interdependent for the general welfare on the other members of the community. To appreciate the true nature of a sponge one should obtain a portion of one of the many species common round our shores, or failing this, a branch of the vivid green fresh-water sponge so common upon lock gates and canal buttresses. A fresh specimen placed in water to which THE SIMPLEST ANIMALS 1 5 has been added a little carmine soon reveals the fact that it is not, as at first appears, a vegetable growth, incapable of independent action, since the coloured water can be seen to be flowing in a rhythmic pulsating manner. The holes or pores of the sponge lead to a complex series of canals off which branch small chambers lined with hairlike whips which ceaselessly lash the water, and by so doing set up currents that carry food to the sponge's interior. The non-assimilated matter is ejected by outflowing currents which escape by special openings. The body substance as seen in the bathsponge is composed of minute pieces of a material chemically allied to silk, and these in life are bound together by a slimey pulpy tegument often of vivid coloration. Sponges are reproduced by means of egg-cells. The larvse hatched from these lead free-swimming lives for a few days, later settling down and forming the basis of a sponge colony which by cellular division may eventually increase to giant proportion. Sponges are classified according to the presence or absence of a skeleton and its nature. The pretty little Flask Sponges (Sycon), which build their skeletons of car- bonate of lime, are abundant amongst tufts of seaweed. They vary from a half to seven inches in length, and if placed in water will demonstrate the circulatory system common to the entire order. The graceful Fig Sponge (Ficulina) seems to be especially associated with a hermit crab. Other sponges of this order become attached to the shells of crabs or encrust the mollusc homes affected by hermit crabs, on which they may grow to a large size. When this occurs the sponge may almost completely cover the shell, leaving the 1 6 A NATURAL HISTORY OF THE SEAS crustacean with merely a small opening to obtain its food. The Glass Sponges, which belong to the group of siliceous sponges, come from deep water, usually in tropic seas, and include some of the most beautiful species known. The skeletons are built up of large six-rayed spicules, which combine to form intricate and exquisite designs. The Glass-rope Sponges from Japan are remarkable for a species of root-tufts of immensely long spicules which form a tassel of what appears to be finely spun and very flexible glass threads, the whole somewhat suggestive of a flat-tailed fly whisk. The Glass-rope, as it is aptly called, serves in life as an anchor holding the upper portion or sponge proper securely to a muddy sea floor. The first specimens acquired in this country were supplied by Japanese dealers, who by way of adding to the specimens' interest fixed the glass rope into pieces of coral — a piece of trade deception which mystified scientists until living specimens were finally obtained by the dredge. Some smaller but similar sponges are found off Portugal, and both there and in Japan are commonly brought to the surface attached to the hooks of fishermen. The common or fleshy sponges are abundant in all seas and comprise a great variety of forms. The Boring Sponge (Cliona) is too abundant to please those responsible for oyster farms or the maintenance of sea walls. It tunnels both oyster shell and hard lime-stone boulder until the solid matter is reduced to so much honeycomb and disintegrates from erosion. A peculiar boring sponge excavates long galleries in the oyster's shell, covering the outside of the shell with a slimey film of white or creamy THE SIMPLEST ANIMALS 1 7 tint. At some oyster stations it is common to grow the oysters on wire frames which can be raised at intervals and exposed to a shower of rain. The fresh water kills the sponge, but the oyster by closely shutting its shell remains unscathed. To this group belong the vivid green fresh-water sponges. The Bathsponges with their skeletons of horny yellowish substance, and the highly-organised industry to which they have given rise, deserve special mention. Three main species are fished in the Mediterranean ; the most important fisheries have long been established in Florida, the Aegean Sea and North Africa. These sponges, so attractive in their commercial form, are black and slimey during life and are securely anchored to shells, rocks or other solid objects. Up-to-date diving apparatus is often used to gather them, but much of the work is still done by naked native divers, whose methods of operation vary with the locality. The native divers of the Aegean are world-famous for their skill and endurance. The diver has a life-line attached to his right arm and thus equipped leaps overside with a 30 lb. block of marble, which bears him to the sea-bed 12 to 40 fathoms below. Here he stays for about two minutes, filling a basket with sponges at lightning speed, when he is hauled to the surface, his marble " sinker " attached to another line being recovered separately. The sponges are stamped upon and beaten and then hung overside for twenty-four hours in order to remove the last of the slimey substance. There follows more beating, many washings, and finally a period of drying in the hot sun, the sponges being hung on lines. In some areas bathsponges are propagated by 1 8 A NATURAL HISTORY OF THE SEAS cutting. A small portion is cut off, care being taken that some of the outer skin is retained or the operation comes to nothing, and under favourable conditions a cubic inch of sponge will reach marketable size in about seven years. Unknown to the bather myriads of embryo sponges may surround him in the sea-water and many species which from time to time appear in the Zoo Aquarium brought in with fresh consignments of Atlantic sea-water are unsuspected until they attain to discernible proportions. CHAPTER II POLYPS UNDER the convenient name of Polyps (Coele titer ata) are massed together a vast number of creatures which though sufficiently diverse of form have many features in common. The group in question in- cludes such apparently dissimilar animals as the Sea Anemones, reef-building Corals, and Jellyfishes. A typical Polyp is an individual creature of simple design, having a cylindrical hollow body, one end of which is fixed by an adhesive disc to some stable object. The other end is ringed with arms or tentacles, which gather food from the water and thrust it into the body cavity into which the mouth opens direct. A typical Polyp expands when desiring food and when at rest, as during the processes of digestion, contracts sometimes to a more or less shapeless mass of jelly. Though apparently soft and defenceless it is usually well armed with stinging cells — to be described later — and being of an elastic nature can often overpower and engulf a victim larger than itself. The group is broadly divided into : (i) Hydroids — Sea-firs and small Jellyfishes ; (2) Siphonophores — Portuguese Man-of-war, etc. ; (3) the Scyphozoa — the true Jellyfish ; (4) Ctenophores — or Sea Gooseberries, etc. ; (5) Corals and Sea Anemones. 19 20 A NATURAL HISTORY OF THE SFAS To the casual observer many of the Hydroids will not be recognisable as animals at all since the bulk suggest tangled tufts of weed. The lens, however, will reveal them all as branching tubular growths. The animals — flowerlike in form, are built much on the plan of a Sea Anemone, and, like the Sea Anemone, feed on living organisms which they capture with their petals or tentacles. Each separate animal is known as a Polyp and each is connected to its fellow by living tissues. These colonies of Polyps increase by the mode of reproduction known as " an alternation of generations, by budding off, or by laying eggs." In the first method certain of the Polyps give rise to a colony of buds which presently develop into a series of minute jellyfish piled like saucers one upon another. These in due season break away and swimming off on their own account lay eggs which eventually give rise to other branching colonies of fixed Polyps. Thus a fixed generation gives rise to a swimming one, and the swimming one to a fixed one. A large number of these quaintly-formed, exquisitely- coloured Hydroids are found throughout the summer in home waters. A common species is sometimes found on whelk shells tenanted by the common hermit crab and owing to the spiny nature of the colony's horny skeleton is known as the Hedgehog Hydroid (Hydractinid). In this form the expanding Polyps are about half an inch long and may be observed twisting from side to side and snatch- ing at scraps of food in the liveliest manner. In some tropic seas Hydroids reach a huge size. In the British Museum may be seen a Japanese species dredged from deep water which consists of a single solitary Polyp POLYPS 21 anchored in the mud. The single Polyp may be 4 ft. long with a 2-ft. spread of tentacles and is the subject of a weird legend current among the native fishermen, namely that it guards the bower of a beautiful sea-maiden. Next in order to the Hydroids are the Siphonophores. Though commonly called Jellyfish, these are more complex creatures than the true Jellyfishes found stranded on our shore or the minute Jellyfishes of the Hydroids just described. The Siphonophores appear to be individuals, but are in fact colonies of many individuals. Some are concerned only with the capture and digestion of food ; others concentrate upon reproduction ; whilst others again have formidable batteries of stinging cells which kill or sting the prey and keep foes at a distance. Most of these creatures carry a floating bladder filled with gas which acts as a support in the water. The commonest of our home species is a small transparent bell-shaped form having no other name than Muggiaea atlantica. More startling are the forms popularly known as the Sallee-rover and the Portuguese Man-of-war semi-tropical forms which occasionally appear off Devon and Cornwall in vast numbers. Each colony is supported by a gas-filled bladder an inch or two across and of a vivid indigo blue. Fleets of these creatures may form long lines or platforms visible far out at sea and drift helplessly before the wind. As they reach colder waters they soon die and disintegrate, detached floats or bladders sometimes surviving as far eastwards as the Sussex coast. The float of a Portuguese Man-of-war carries a crest which projects above the surface of the water and acts as a sail. It may reach a foot in length, and is a most con- 22 A NATURAL HISTORY OF THE SEAS Portuguese Man-of-War (Pbysalia) POLYPS 23 spicuous object, being of a vivid azure blue topped with pink. Long bright blue tassels of stinging cells depend from the disc for several yards beneath the float and upon coming into contact with a living object at once contract and draw the prey, paralysed and unresisting, up to the many " mouths." As with a large number of other members of this and allied orders, the Man-of-war provides for a number of " gate-crashers." Chief of these are certain small fishes which live amongst the deadly stinging cells apparently enjoying their protection. The stinging powers of the Man-of-War are more severe than those of any other known Jellyfish, and in tropic seas native pearl and sponge divers dread them even more than they do the shark. It may be not inappropriate here to offer a word of explanation regarding the stinging properties common to all creatures under consideration in this chapter. The small Sea Anemone or Jellyfish may cause no more than a tingling sensation to the human hand, but the same creatures can spell death to small animals. This paralysing influence is exerted by myriads of minute mechanisms, each one a miniature replica of the old-time harpoon with its attached rope. When highly magnified, a stinging cell is seen to consist of a double-barbed dart attached to a neatly-coiled thread, the whole enclosed in a compact ovoid capsule. At the small end of the capsule is a spring trigger arrangement and this being touched by some foreign body automatically releases barb and thread with con- siderable force. The Sgpho^oa or true Jellyfishes when adult swim freely in the open sea. The common Moon Jelly (Aurelia), 24 A NATURAL HISTORY OF THE SEAS often distressingly abundant in warm weather off our coasts, may be taken as a typical example. In its early stages it becomes attached to a rock at low tide and may then be mistaken for a very small Sea Anemone. As it increases in size, however, an extraordinary transformation takes place. The creature develops a long series of con- strictions throughout its length and it is later apparent that the animal is not one but many individuals all circular in shape with tentacles arranged round the circumference, the whole piled one upon the other like a stack of dinner plates. When fully developed these detach themselves one after the other, each embarking on a career of its own and progressing by means of those umbrella-like expansions and contractions which every seaside visitor has observed. The commonest stinging form which is justly dreaded by bathers is Chrysaora. The largest species found in our seas is Rhi^pstoma, which may have a diameter of 2 ft. The fry of the horse mackerel habitually shelter beneath its large flattened umbrella, which protects them from the searching eyes of sea birds, whilst the abundant stinging cells ward off predacious species of their own order. The giant of the race is Cyanea — the Sea Blubber, which reaches its maximum diameter of 8 ft. with tentacles 120 ft. long in the waters north of Cape Cod. It is likewise a noxious jellyfish. Such a monster is, like the rest of its clan, composed largely of sea-water, the actual organic tissue in its composition comprising not more than five per cent, of the entire bulk. The Ctenophores, or Sea-gooseberries, carry swimming plates — combes of partly fused hair-like organs — that by POLYPS 25 continually lashing the water propel the creatures onwards. A familiar form in home waters is the little Sea Gooseberry. Giant Jellyfish sheltering young Horse Mackerel From its globular form depend two long threads. These threads can be drawn up into pockets and when extended 26 A NATURAL HISTORY OF THE SEAS may attach themselves to small animals. Though no larger than the fruit from which it takes its popular name, the Sea Gooseberry does considerable damage to shoals of fish fry, besides killing large numbers of larval crabs and lobsters. Certain Ctenophores inhabiting foreign waters are of a weird and beautiful design. To these belongs the ribbon- shaped Venus's Girdle (Cestui), which grows to several feet in length. In this animal the constant movement of the prismatic swimming plates causes an unbroken succession of dazzling colours to play over its entire length. Coral is a term given to a group of polyps which manu- facture a skeleton of lime. Some are solitary, but the majority form colonies in which the various individuals are connected by a system of tubes so that the food of one is shared by all, whilst the entire assemblage is embedded in and supported by spicules of carbonate of lime. The skeletons may form solid stony masses as in the Precious and Reef-building Corals. When the spicules are scarce and scattered the result is a " Flexible Coral," of which home waters supply several beautiful examples. The commonest perhaps is the form known by the gruesome name of Dead Men's Fingers (AJcyonium), often seen in its contracted form attached to oyster and scallop shells. In water the little Polyps slowly expand suffusing the dead creamy coloured finger-shaped mass with a rosy pink flush. More striking still is the lovely Sea Fan (Gorgom'a), whose spreading pinkish-orange fronds are dredged just beyond low- water mark. This coral has a tough horny internal skeleton, which when found washed POLYPS 27 (a) Sea Fan (Gorgonia). (b) Polyps magnified 28 A NATURAL HISTORY OF THE SEAS ashore and denuded of its limey Polyp shells is often mistaken for a shrub torn from the cliff or foreshore. Polyps which invest themselves with stony tenements abound in most tropic seas but are by no means confined to them. Several species come from deep water in northern latitudes and one is tolerably common off our south- western shores. The latter is known as the Devonshire Cup Coral (Caryophyllia). Its white stony house stands about half an inch high and the brilliant flower-like Polyp when expanded towers above it, retreating with lightning speed, however, at the slightest disturbance. Since the publication of Darwin's famous work much literature has been devoted to the study of corals and coral reefs, whilst the coral iself has been devoted to innumerable uses from the earliest times. The famous Precious Coral comes chiefly from the Mediterranean and from earliest antiquity has been prized as an ornament, and an antidote to poisons, as well as a general panacea. This coral reproduces by eggs or buds, the male and female polyps being segregated in separate colonies. The gathering of the Precious Coral is effected by a crude drag made of thick nets attached to two heavy beams joined in the form of a cross. The coral being brought ashore is stripped of its outer bark and subjected to an elaborate process of polishing. Reef-building Coral forms the stable building material in all the countries where it occurs. Reef Corals are the result of the union of Polyps, each divided Polyp raising around itself a wall of hard limey material. Since the colonies grow from the bottom upwards, the pressure exerted by later generations consolidates the vacated homes POLYPS 29 of defunct members into one massive block, which otters considerable resistance to wind and waves. It likewise serves as a haven for the enormous numbers of molluscs, worms, sponges, etc., that habitually tunnel into it for shelter. Reef Corals can only form in comparatively shallow water, light and air being essential to their makers' well-being. Two such reefs are world-famous — the Great Barrier Reef of Australia, extending for 1,315 miles from New Guinea southwards along the entire coast of Queens- land, and the notorious Cocos Atoll, never for long out of the news as a home of treasure trove. Coral reefs are divided into three well-defined groups. (1) Fringing reefs, which occur round continents or islands ; (2) Barrier reefs, that form much farther out from land masses, with a deeper channel between them and the land than is permitted by the former type ; and (3) Atolls, which are roughly circular in formation, often situated far from land, with much of their boundaries raised above sea level. Within the atoll reef is a still lagoon never exceeding 50 fathoms in depth. The shelter afforded transpires to make these reefs the retreat of innumerable sea animals of every kind and constitute a wealth of life that would appear to be literally unlimited despite its wholesale exploitation and despoliation at the hands of man. Sea Anemones are practically world-wide in distribution, and their variety of size and coloration is so great that it can here be only touched upon. Most Anemones remain fixed to some stable object throughout life, though many can slowly glide from one spot to another by means of the flattened lower portions of the body. The crown 30 A NATURAL HISTORY OF THE SEAS of retractile tentacles varies in number from a few score to many thousands according to species and they are constantly employed to seize and convey food to the stomach cavity which constitutes the bulk of the cylindrical body. Multiplication is effected by means of eggs, budding off, or even as the result of mutilation. Some species if cut in fragments give rise to as many new individuals. A large number of species are found in our own waters, and their ways of life are infinite. The majority anchor themselves to rocks, whilst a few, like the Dahlia Anemone {Telia crassicornis) and the Sand Anemones, attach them- selves to shell fragments buried some distance in sand or gravel, the crown of tentacles showing just at the surface when the animal is searching for prey. The Opelet Anemone {Ammonia sulcata), one of our commonest native species, often chooses such unstable anchorage as the fronds of seaweeds. Anemones are of little direct economic value to man, though the Dahlia is sometimes eaten on the Continent, and on our own northern coasts is in demand as bait for long lines. A highly interesting feature of the group is the extent to which many species are found in peaceable association with widely different creatures. Our own shores provide two notable examples. The common Parasitic Anemone {Sagartia parasitica) is a large species invariably found attached to shells tenanted by the common hermit crab. There is little doubt that the crab derives direct benefit from its cumbersome messmates — for three or more anemones sometimes attach themselves to a single shell. POLYPS 3 1 Not only are the anemone tentacles a deterrent to hostile fishes, but the polyp when irritated throws out from its columns immense numbers of long white threads which Plumose Anemones not only entangle the aggressor but have marked stinging properties. The benefits afforded to the anemone are very obvious, for when the crab is feeding the polyp 32 A NATURAL HISTORY OF THE SEAS bends over towards the centre of operation and take its full share of the feast. Recent observations have shown that sometimes the crab's lodgers become so large and numerous as to con- stitute an embarrassment and force him to seek another home. The Velvet Cloak Anemone (Adamsia palliatd) is likewise parasitic, living on a small hermit crab. The polyp in time dissolves the shell and the crab is thus comfortably ensconced in an elastic tenement permitting his ample expansion and no longer necessitating as he grows in size that constant search for more spacious accommoda- tion which occupies so much of the average hermit crab's career. The Velvet Cloak Anemone is found only in association with the smooth-clawed hermit crab, and invariably tucks itself just underneath the shell so that its eager tentacles are always within easy reach of the crab's mouth and any food the latter may be negociating. Still more remarkable is the partnership between a small Indo-Pacific crab and certain anemones. The crab de- taches the anemones from the rocks and carries them in its claw, employing them as knuckle-dusters to ward off foes. A giant anemone of the Barrier Reef may reach 2 ft. in diameter, and is the chosen host of certain brilliant little Coral Fishes of a kind often exhibited in the Zoo Aquarium. These fishes and also a species of prawn closely approximate to the anemone's colouring and habitu- ally shelter in the polyp's gastric cavity, always hurrying to this strange shelter on the slightest hint of danger. CHAPTER III CRUSTACEANS NO branch of the animal kingdom is more abundantly- represented on land or in the waters — fresh, brackish and salt, than is that of the jointed animals or Arthropoda. The group includes the Crustaceans, Trilobites, Spiders, Centipedes and Insects, all of which have representatives within the maritime zone, the Crustaceans being, however, predominant in that region. The Crustaceans are known to the general public by such common forms as the Wood Louse, Sandhoppers, Barnacles, Shrimps, Crabs and Lobsters, animals sufficiently diverse in appearance and economy yet all presenting certain points in common. The bodies of all these creatures are divided into segments, each segment bearing a pair of appendages. These organs are modified in a variety of ways, some serving as tactile organs, others being employed for seeing, chewing food, or various means of progression. The animals are encased in more or less unyielding suits of armour which must be periodically cast off to permit of expansion, a new shell being formed beneath the old one. Reproduction is almost invariably effected by means of eggs, the young sometimes resembling the parents, but in many cases passing through a series of complex trans- formations before reaching the adult form. 33 c 34 A NATURAL HISTORY OF THE SEAS The Copepods, though small, are of enormous impor- tance in the balance of life, for they form the staple of the plankton and not only do much useful work as scavengers, but feed much larger creatures, some forming the bulk Larva of Crawfish of the " whale food " consumed by the cetaceans. A vast number of these minute but restlessly swimming creatures abound in the sea throughout the summer months, whilst our inland ponds and ditches supply such a common form as the Cyclops. CRUSTACEANS 3 5 In the sea the Copepods both as regards species and individuals are indeed legion. One abundant form, Calanus, deserves to be as well known as the crab or lobster since it is infinitely more abundant, and without it the herring harvest would fail to reach maturity. This minute crustacean may so abound at times as to cover some square miles of the sea surface with a reddish scum and a single tow of a few minutes' duration has choked a muslin net with two and a half million specimens — sufficient to fill ten pint tumblers solid. Some Copepods are of exquisite form and colour, whilst many display many fantastic spines and fancy appendages, which serve to maintain their balance. The group known as Cirripedia includes a large number of strangely divergent forms spoken of collectively as Barnacles. The majority commence life as active free- swimming creatures, but after casting their shells several times they attach themselves by the head to some solid object — rock, stone, crag, or ship's keel, and there undergo a startling transformation. The shell or carapace which encloses the larval body changes into a tower-like structure made of several neatly welded plates, the upper or open end being closed by two pairs of folding doors, which can be pushed aside to admit the free passage of the legs. The latter organs no longer of service in rowing the animal through the water serve merely, as Professor Thomas Huxley aptly put it — to kick the food into the stomach. By far the best known example is the little Acorn Barnacle (Balamis balanoides), which covers every rock and harbour pile, its sharp-edged shells being justiy disliked 36 A NATURAL HISTORY OF THE SEAS by the bather. On a very still day one may hear a gently hissing sound which is caused by countless millions of these creatures oscillating the jointed lids of their residences in impatient anticipation of the returning tide. In the far north these barnacles reach a large size, one species having a shell fully four inches in height. Another abundant form is the Goose Barnacle (Lepas anatifera), which may be recognised by its flattened shell and the long tough sinuous stem which anchors it to floating timber and which represents the last remnants of the creature's head. In mediaeval times this crustacean was in some way confused with the barnacle goose, the bird having been seen in the vicinity of the tree branches which at low tide revealed themselves as being covered with barnacles. It thus happens that many quaint old woodcuts testify to the once general belief that the barnacles grew on trees and actually developed into birds. Some assert that the belief, which dates from the twelfth century, had its origin in a priestly desire to give the goose a vege- table origin and so extend the Lenten bill of fare. On our southern coasts and much more abundantly in the Mediterranean there abounds a form, allied to the common Goose Barnacle, but having less solidly formed shells, which is sold for food. One species of sessile barnacle, Tubicinella, actually burrows into the skin of whales. A very remarkable group of barnacles has carried de- generation yet a stage farther. The seaside visitor may often find a crab with a tough fleshy knob firmly attached to its abdomen. This is the Sack Barnacle, Sacculina. It hatches from an egg into a free-swimming larva almost CRUSTACEANS 37 identical with that of the Acorn Barnacle, but it later Goose Barnacles loses every vestige of shell and becomes a mere stomach 38 A NATURAL HISTORY OF THE SFA.S attached to a crab, deriving nourishment by sending an endlessly ramifying series of roots into every portion of the more active crustacean's interior. A crab so visited is usually doomed, but before succumbing to its repulsive parasite undergoes various modifications, the male crabs taking on certain female characteristics. The Isopods — claw-footed crustaceans — are typified in the common Wood Louse, and in the maritime zone present a galaxy of varied forms. They have no carapace and the eyes are set flat and not raised on stalks. The Gribble Limnoria, though of minute proportions, does immense damage to all wooden structures exposed to salt water, eating away the wood until it is of the con- sistency of a sponge. Many ships, piers, and harbour structures have thus been completely undermined much as terrestrial woodwork often succumbs to the death-watch beetle. The Isopods also include the common Sea-Slater (Ligia) — a useful scavenger — and many large and handsome fish parasites, including the strange degenerate creature Bopjrus. In the latter crustacean the female takes up residence in the gill chamber of the common prawn, causing a blister-like protrusion of the carapace and earning for its host the fishermen's somewhat ribald appellation of " Face-ache " Prawn. The Amphipods are well known to all by the Common Fresh- water Shrimp and the still more abundant Sandhopper or " Beach Flea." The latter literally swarms on most shores, and unlike the Fresh-water Shrimp always keeps CRUSTACEANS 39 just above water-mark, where it devours refuse of every description, 20,000 having been counted on a single small sea-urchin. Many carry the eggs beneath them in the manner of crabs and lobsters, and a number of species construct nests. A few take up their residence within jellyfish, apparently being immune to the Coelenterate's stinging cells. Most striking of all the Amphipods perhaps are the grotesque " Skeleton " Shrimps, which abound amongst corallines clambering about the tangled growths in the manner of looper caterpillars. To the Amphipods also belong the large Whale Lice that attach themselves to cetaceans by means of their strongly-hooked legs. The Stomatopoda or Mouth-footed Crustaceans are represented by the remarkable Mantis Shrimps (Squilla) found on our southern shores and attaining a large size in all tropical seas. They are long flattened creatures with a pair of huge scythe-like forelimbs which in general structure and the sharp spines fringing their inner surface recall the well-known Praying Mantis, one of the tigers of the insect world. These crustaceans lay several thousands of eggs which are rolled into a ball and carried in the mouth of the female for a period of two or three months. Mantis Shrimps though abundant are seldom seen since they dig deep burrows just beyond low-water mark, leaving these retreats only after dark. Being of excellent flavour they are much prized for food, and in many lands, especially in Italy, where they are known under the name of " Scampi," it is customary to lure them into traps by means of lantern lights. 40 A NATURAL HISTORY OF THE SEAS The Decapod Crustaceans, as the name implies, have ten walking limbs, two of which are usually developed into large and well-formed pincers characteristic of the Crabs, Lobsters and their allies. The group's distribution is world-wide, its representatives abounding both in the shallows and the abyss, and are not only of great com- mercial value but have played an important part in the beliefs and folk-lore of various nations. The Ancient Greeks and Romans promoted the crab to be an important constellation — Cancer being the fourth Zodiac or sign of the heavens. Olaus Magnus, Archbishop of Upsala, and a great disseminator of" unnatural history" in the sixteenth century, placed on record that the seas around the Hebrides harboured a lobster capable of capturing a man and similar stories may be found amongst the legends and beliefs of many primitive people to this day. The group is divided into the Long-tailed, Short-tailed, and Anomura, which by some is regarded as an aberrant offshoot of the first-named. The long-tailed crustaceans are exemplified by the graceful prawns abundant on all rocky shores and represented both in coastal waters and the uttermost depths. Deep water species are usually of a vivid red tint and are often poised on abnormally long legs, a provision for walking upon shifting and unstable ooze, much as some Fenland shepherds tend their flocks on stilts. A large number of species of shrimps and prawn are found around our coast, the prawns usually being caught in baited pots whilst the shrimps are dredged. A common edible prawn {Pandulus montagui) is taken in the trawl, and being of delicate structure is cooked on board. CRUSTACEANS 41 Examination will reveal that its pincers are minute and placed at the end of long whiplike limbs, a modification believed to be brought about by constantly probing the long and tortuous tubes of certain sandworms which appear to be its principal food. Of late years several very large prawns from both sub- Arctic and Mediterranean waters have become a regular feature of our markets. Prawns, like all the long-tailed crustaceans, are of very active habit and by suddenly " snapping " the tail fin can project themselves through the water backwards at high velocity and with considerable precision. The prawns like all the members of the three groups carry their eggs attached to the " swimmerets " of their undersurface, the emergent young passing, as a rule, through a series of transformations before attaining maturity. Often these larvae bear grotesque horns and other balancing appendages and it is of interest to note — as indicating a common ancestry — that widely dissimilar adult forms of different species often show a remarkable uniformity in their larval stages. Several species of prawn bear light organs, whilst one abysmal species covers retreat in a smoke-screen of highly phosphorescent fluid, which it ejects from a special sac much as the cuttlefish of shallow water discharges its ink cloud. The lobsters include the largest members of the group. Our Common Lobster {Homarus vulgaris) and its common American relative (Homarus amerkanus) have a northern range, the New World species being of stouter build, its great crushing claw alone sometimes weighing 10 lbs. 42 A NATURAL HISTORY OF THE SEAS The crushing claw may be either right- or left-handed, speci- mens occasionally having both claws of the crushing or cutting type. Lobsters show great variety of colour, deep water specimens tending to be of a darker blue than the shallow-water forms, whilst such colour freaks as pale blue, mauve, red and even albino lobsters are not unknown. These crustaceans are omnivorous and are highly pug- nacious. The entire group has the power to reproduce lost limbs, a useful provision since injuries necessitating the discarding of the limb at a special joint are of frequent occurrence. The smaller and more elongate Norway Lobster or Dublin Bay Prawn (Nephrops norvegius) occurs in deep water off our western coasts. Allied to the lobsters are the handsome Crawfish and Flat Lobsters, which lack the large pincered claw of the true lobsters. The Common Crawfish, or Langouste of the French (Palinurus vulgaris), is the largest of all the long- tailed crustaceans, the body and tail often measuring 2 ft. in length, whilst the long and inflexible antennas considerably exceed this measurement. By rubbing the bases of its antennas against the central beak or rostrum it can produce a loud grunting noise. In the related Flat Lobster {Arctus ursus) the antennas form large broad flattened plates, which serve to shovel up silt and conceal food. Recent researches have shown that the long-tailed Crustacea, though like the other groups without any true hearing apparatus, can " tune in " or at least pick up vibrations in the surrounding water by means of certain " auditory hairs " fringing their legs. These convey the 1 .9 w H D O o z