TasNat 1909 Vol2 No1 Pp5-9 Smith TasmanianCrustacea

7/30/2019 TasNat 1909 Vol2 No1 Pp5-9 Smith TasmanianCrustacea

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THE TASMANIAN NATURALIST 5The leaves arise from a broad base, entirely sheathing the stem andtaper to a point; they do not leave scars on the stem.

Rkhed. The flowers are in clusters in the axils of leaf-like bracts.Corolla has only very minute lobes and is thrown otT like a hood bysplitting round near the base. I n one of our rare forms, R. milligani,the corolla generally splits On one side and shrivels on the bush. Theleaves are as in Sprengelia, but leave ringlike scars.Dracnphylltltll ditTers from Richea practically only in the corollasbeing bell-shaped and persistent. One of our two species is dwarf andforms dense cushions indistinguishable from Abrotanella and Donatia.

In this species the flower is solitary and terminal; the other is very likeour Giant Grasstree, but does not attain such large proportions, andinstead of the insignificant flowers of that plant it bears a terminal looseflower cluster of most beautiful little pendant, pinkish, white bells.

notes on Casmanian Crustacea.By G. W. SMITH, M.A., OXFORD.

'=li'''HE class Crustacea includes a very great number of animals, mostl \ of which live in the sea, but a very large number of them inhabitfresh-water lakes, ponds and streams, and it is of these that I intendchiefly to speak.

Probably the Crustacea that are best known to most of us are thosewhich are seen in shop windows and sometimes find their way on to thedinner table; such are the prawns and shrimps, and the large red crayfish (Panulirus), which is also prized as a delicacy on the Mediterraneancoasts, and is eaten there under the name of Langouste.

The fresh-water lobster of Tasmania is also very good to eat (Astacopsis Franklinii), and grows to a very large size in the rivers of northernand western Tasmania; but in the rivers and creeks round Hobart thelobster appears always to remain smail and insignificant, whether for lackof food or because it is a distinct smaller species, is not known forcertain.Fresh water lobsters are found pretty well all over the temperateregions of the world, but they are not found at all in the tropics. The

Tasmanian lobster is closely related to those found in Australia, NewZealand, South America, and Madagascar-/:e., in the temperatesouthern hemisphere; and it is quite distinct from those which occurall round the north kmperate zone in North America, Europe, anJChina.This is a remarkable fact, because the land regions in the southern

hemisphere are at the present time separated by very wid.e and deepoceans, across which the fresh water lobsters could not possibly ever


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THE TASMANIAN' NATlJRAI.ISThave crossed; that the present distriblltion of these lobsters informsus pretty certainly that at some rather remote period there mllst havebeen a continent somewhere in the antarctic "icas cOllnecting thesouthern most parts of SoUtil Amcrica, New Zealand, J\lIstralia, andMadagascar together, and in this region the ancestors of all thesesouthern lobsters inust have lived.

The socalled landcrab of Tasmania which lives in deep burrowsupon marshy plains in the mountains, especially near the west coast, isreally a lobster, too, closely related to the Astacopsis; its scientificname is Engaeus. fOS50r. Curiously enough, some of the KorthAmerican lobsters of the genus Cambarus have also taken to makingburrows in the. earth,and have quite forsaken their natural element ofwater.

The Crustacea we have hitherto mentioned, namely, shrimps,lobsters, crayfish, and crabs, although they differ from one another inmany points, are really all built upon the same plan, and are made up ofthe same number of segments. I f you look at a lobster or shrimp youwill see that its hinder end or tail is composed of a nu'mber of rings orsegments, to each of which is attached a pair of jointed limbs. Thefront part of the body or cephalothorax (i.e., head-chest) does notshow clearly this structure of ringing or segmentation, but the limbsattached to this part of the body indicate the number of segments outof which it is constructed.

Now in all the above-mentioned Crustacea there are 20 segments with their limbs, i.e., two pairs of feelers or atcnn:c; three pairsof jaws, which are used for biting the food, hilt arc really Illodiliedlimbs; three pairs of auxiliary jaws or maxillipeds, which are half jawsand half legs; five pairs of walking legs, some of which end in pincers;and then follows the seven tail segments or rings, which carry seven pairsof swimming legs.As before stated, the first thirteen segments of the body are allfused together to form a carapace or shell, so that there is no outward'sign of segmentation except the limbs, and the front, ones of these are somuch drawn into the mouth to act as jaws that one can hardly believethat they correspond to limbs attached to regular segments as in the tailregion.

Now it is the unique distinction of Tasmania (or was until the otherday when a similar discovery was made in Victoria), to possess a verypeculiar shrimplike animal in which the body is segmented or ringed allthe way down, and in which the limhs preserve their simple character ofdoublepronged oars right up into the region of the mouth.

It is clear that this animal (Anaspides Tasmani:c, Thomson)preserves the simple primitive plan-th" diagrammatic forlll as it wereupon which the higher Crustacea are huilt, and everything we can learnabout its structure and habits is of great interest. I t a ppears to liveonly in mountain streams and clear tarns at a. great elevation, the l o ~ a l i -


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ties for its, o/:currence b ~ i n g the tol) of Mount Wellington, the Hart!.Mountains, and Mount Field. A figure of the ~ n i n l a \ ' i ; appearance isgiven, here.

FIg-. -ANASPIDES TASMANlfE.

The two pronged orbiramous character of thelimbs is especially to benoted, as this is characteristic of the young stagesin growth of almost allCrustacea, and its beingretained here in the adultis another l } l ~ i m i t i \ " e orancestral featme. . nothercharacter of llle 1l10tllltainshrimp is that instead ofthe, female carrving ahouther.eggs with It;,r as in allother Crustacea, she hidesthem under stones and inthe roots 0'[ water plants.

We have so far only spoken of the higher Crustacea in which thebody is always composed of twenty segments. These are calledMalacosttaca. There, are besides a host of small Crustacea in which thebody is not composed 'oLany constant number of segments but may bcless or more than twenty according to the species under consideration.These Crustacea are classed together as Entomostraca.

Probably the most familiar of these are the Barnacles, the littlesharp shells attached to rocks at tide marks. Ead, of these little hoxesreally contains a live Crustacean, which, when he is covered with water,pokes out his legs and sweeps particles of food into his mouth.

Besides the Barnacles or Cirripeds there is a great number of smallCrustacea which .swarm on the surface of the sea, and afford a veryimportant article of food to the shoals of fIshes' and. even to wl1ales.1'hese little Crustacea,'each single olle of which is not bigger than apip.'s head, are often present in such enormous quantities t'hat the seaDlay be coloured red with them and have the consistency of chocolate.Some of these marine forms are highly phosphoresth in the lake,. ~ , \ , , ~ t b , ~ e qeature.s qmnot bear the direct rays of the sun upon them.


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8 THE TASMANIAN NATURALIST-------------But besides the large lakes in Tasmania the smallest ponds andpuddles will b ~ found to contain Entol1lostraca.These are all varieties of the three types figured below; they neverrun to any great size but are always visible to the naked eye.

A-Cyclops.Fill

B-Daphnia.

B

C-Ostracode.You may wonder how it is that these acquatic animals can surviveand multiply in small pools which must frequently dry up in the heat ofsummer. The method by which this is effected in the Cladocera wasdiscovered some years ago by the great German biologist and student ofheredity, P r ~ ~ e s s o r Weisman. He found out that whilst favourable conditions prevai.\ these animals were all female, which produced veryrapidly eggs, that did not require fertilisation in order to develop. Butwhen unfavourable conditiolls arrived, such as extreme heat or cold, thefemales began to lay a different kind of egg, which had to be fertilized

by the male, and which was afterwards encased in a little air-tight boxmade by the female out of her own shell.The fertilized egg, so shut up, is now capable of being frozen ordried up, or blown about by the wind, indeed almost anything exceptburnt, and still when it falls into a favourable pond or puddle, after aninterval of even several years, it will hatch out and give rise to anothergeneration of water fleas.Weisman also believed that the production of these' resting' eggswas not directly called forth by the approach of danger, but that each

different kind of water flea produced them at regular intervals mechanic-


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TH E TASMANIAN NATURALIST 9ally, according to the kind of pond or lake it lived in-those kinds thatinhahit small ponds, frequently liable to dry up, producing' resting' eggsat more frequent intervals than those inhabiting large lakes. But to gofuller into that question would lead us into very deep waters, so deepthat no Crustacea would be found in them but only abstract ideas andmetaphysical speculations.

Mr. Smith has since sent us an account of his work in Tasmaniawhich appeared in the proceedings of the Royal Society, from whichFigs. , and 3 are taken; and also the following concerning Paranaspideslacustris : This type of a new genus of the Anaspididre was found byme in the Great Lake, onthe central plateau of Tasmania, at an elevation of3,700 feet. I t inhabits thelittoral zone of the lake,living among the rocks andwater weeds, rather afterthe manner of a prawn.It is totally different inexternal appearance to An-aspides, being of a green FI&". 3-PARANASPIDES LACUSTRIS.transparent colour sparcelypowdered with black dots, and the body exhibits a marked dorsal flexurevery much as in Mysis, to which it bears an extraordinary superficialresemblance. The largest specimen obtained was about an inch inlength. It pursues a swimming habit, with which is correlated theflexure of the body, the elongation of the abdomen, the enlarged tail fan,and the enlarged scales on the second antennre The extremely abundant developement of this Crustacean fauna in the littoral zone of theGreat Lake was very striking, and it seems probable that it furnishes animportant part of the food for the imported English brown trout, whichin this lake may attain to the enormous weight of 25 Ibs. A dissectionof the stomachs of several trout revealed the fact that they had beenfeeding upon these creatures. The Anaspidacea and Phrcatoicidre ofSouthern Australia and Tasmania really stand in much the same relationto other Crustacea as the Monotremata do to normal mammals. and it isof interest to enquire whence these peculiar Crustacea have been derived,and how it comes about" that they are now restricted to this isolatedcorner of the Antipodes. The most striking thing about their distribution at the present time is the fact that not only are they absolutelyconfined to the temperate parts of the Australasian region, but also tothe coldest parts of the temporate zone, the majority of the Anaspidaceaand Phreatoicidre being found at considerable elevations on mountainranges which are covered with snow for at any rate a great part of the!\vinter. They are absolutely unknown from Australia north of the : Dividing Range.

TasNat 1909 Vol2 No1 Pp5-9 Smith TasmanianCrustacea

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