on the mode feeding of hermit crab pagurus euphenhardus

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On the Mode of Feeding of the Hermit-crab,Eupagurus Bernhardus, and some otherDecapoda

J. H. Orton

Journal of the Marine Biological Association of the United Kingdom / Volume 14 / Issue04 / May 1927, pp 909 - 921DOI: 10.1017/S0025315400051146, Published online: 11 May 2009

Link to this article: http://journals.cambridge.org/abstract_S0025315400051146

How to cite this article:J. H. Orton (1927). On the Mode of Feeding of the Hermit-crab, EupagurusBernhardus, and some other Decapoda. Journal of the Marine Biological

Association of the United Kingdom, 14, pp 909-921 doi:10.1017/S0025315400051146

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91 0 J . H. ORTON.with regard to bivalves and oysters. The hermit-crabs were placed inwell-aerated water and allowed several days to recover from the effects ofthe journey before a number of young oysters, 1\ to 2 inches long, wereadded to the dish in which the hermit-crabs were placed. Later freshbatches of hermit-crabs and some smaller oysters, with thin shells onlyabout 1 inch to 1J inches long, were obtained. At no time have the hermit-crabs been found to show any inimical interest in the oysters with whichthey were kept, and in view of what has been observed of their mode offeeding, it is highly probable that hermit-crabs are in no sense harmfulto healthy oysters, which have attained a size of about 1 inch or more,although like most crabs they would, no doubt, attack weak or dyingoysters. This hermit-crab is, however, BO clumsy, owing to the impedi-ment of the shell, which it carries, that it would probably be beaten byother crabs, especially Cardnus mamas, which is common on certainparts of the Fal Estuary beds, in a hunt for a weakly oyster.E. Bernhardus attempts to break barnacles and tubicolous worms(e.g. Pomatoceros) from stones and shells, and in this way will no doubtkill inadvertently a small proportion of very young oysters.It is possible that E. Bernhardus may also obtain oyster larvae, atthe time these settle, by scraping objects with its third maxillipedes;but various Amphipods, worms, and other animals are probably greaterenemies of the oyster at this stage of existence than is the hermit-crab.

OBSERVATIONS AND EXPERIMENTS ON THE MODE OF FEEDING OFE. BERNHARDUS.

Whilst observing the hermit-crabs, it was noticed that individualsscraped various objects in the dish with their third maxillipedes, and asPorcellana longicornis is known to use the similar appendages for catchingfood-particles (Gosse, see Potts, 1916), it was suspected that the hermit-crab obtained food in a similar way. To tes t this suspicion bunches ofAscidiella aspersa, which had accumulated much sediment and extraneousgrowth, were added to the dish, and the scraping operation was foundto be repeated. On confirmation of this fact it was decided to add sedi-ment to the dish to make it resemble the bottom on the oyster bed,which is mainly muddy or muddy gravel. A sediment usually rich inmicro-organisms was obtained from walings exposed at low water atthe Great Western Docks and made to form a layer on the bottom of thedish.As a result of this arrangement, an additional act of feeding could beseen. The hermit-crabs now scraped the bottom of the dishwith itscovering of sedimentwith its smaller claw, and passed on the productsof the scraping to the third maxillipedes, whose hairs were used like a brush


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MODE OF FEEDING OF HERMIT-CRAB. 9 1 1to transfer the collected particles towards the mouth. This movement iscarried out automatically for long periods, and if arrested can be startedby adding fresh material or the juices of fresh Pecten meat to the water.When the captured particles reach the smaller mouth parts they aresifted in some way, since a cloud of rejected material is borne forwardsand upwards in the stream of water emerging from the gill-chamber.From these actions it seemed clear that the hermit-crab was feeding onmaterial obtained by sifting and selecting from sedimentary deposits.In order to obtain more definite information a hermit-crab was isolatedfor a period without food in a clean bottle with circulating water, andto this water was added, after the period of isolation, brushings of thebrown incrustations found on stones and other objects on the foreshore.This brown material consists of a feltwork of small filamentous algas andchain and free diatoms, with Vorticellids, Acineterians, and other micro-organisms. After leaving the hermit-crab in the bottle with this materialovernight, the animal was anaesthetised and the contents of the gutexamined. The stomach and first part of the intestine were found tocontain quantities of the diatoms and algal threads and other materialsimilar in mass to th at added to the bottle, bu t already in a partly digestedstate.

To test whether the feeding action observed in the Laboratory occurredon the oyster beds, the stomachs and intestines of fourteen individuals,sent to the Laboratory in February, were examined.In the gut of these hermit-crabs was found a collection of detritic andfood material similar to that which may be found in the oyster or Crepi-dulae (Orton, 1912) with, in addition, microscopic bits of brown and greenalgse, in one case also algal ova, fragments of microscopic shells, crus-taceans, and polychsetes. The material in the gut which resembles thatfound in oysters and Crepidula consists of microscopic sand-grains, spongespicules, diatoms, foraminifera, algal threads, and polychsete and crus-tacean bristles, but the two latter kinds of material may have beenderived in the case of the hermit-crab from captured organisms.

The food found in the stomachs and intestines of hermit-crabs duringthe winter months is probably small in amount in comparison with whatmay be taken during the spring and summer, and observations will needto be continued throughout the year to obtain adequate information.It is clear, however, that the hermit-crab obtains its food largely byscooping up loose detritic material from the sea-bottom and objects onthe sea-bottom, and selecting therefrom the organic constituents. Inthis way are obtained small polychsetes, small crustaceans, small algse,foraminifera, diatoms, and other micro-organisms. The relative import-ance of this kind of food-material in comparison with that derived fromlarger food-organisms cannot be estimated without seasonal examination


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MODE OP FEEDING OF HERMIT-CRAB. 9 1 3section of the bottom fauna known as epifauna, it has unfortunatelybeen generally omitted from quantitative surveys carried out recentlyby naturalists with the Petersen grab, but Allen (1899) made an estimateof the relative frequency of species on and about the 30-fathom linenear Plymouth, and remarks that " th is hermit-crab is present on groundsof all kinds, though it is most abundant on the sand and on the graveland sand grounds where the fauna is generally rich." He records thespecies as most common on grounds II and III with respectively 95-8per cent fine sand with 1-9 per cent silt, and 82-7 per cent fine sand with1-1 per cent silt. On the estuarine grounds in the Pal Estuary the na tureof the bottom where this hermit-crab occurs in abundance varies frommuddy to a muddy gravel, in which the percentage of silt would every-where be very much higher th an on the grounds off P lym outh . Thesefacts indicate that the microfauna on a fine sandy ground may be, as isindicated by Hunt (1925), as great as on an estuarine muddy ground,but it is not impossible that other food-factors may govern the distri-bution of the hermit-crab. It may be remarked in passing th at as thishermit-crab is an important member of those animals which subsiston food-material derived from the sea-bottom, its omission frombottom-communities affords an example of the artificiality of theseso-called communities.

ON THE FUNCTION OF THE MOUTH PARTS, AND SOME UNUSUALFEATURES IN THE GUT, OF E. BERNHARDUS.

When it was found that the stomach and intestines of hermit-crabstaken from the oyster beds contained a large amount of food-materialpicked up from the sea-bed, the question arose to what extent the mouthparts might be modified for this purpose. Jackson (I.e.) shows themouth parts to be normal in form, but comparison with the similarappendages in Carcinus or Portunus shows that they are relatively feeble.The mouth parts in a hermit-crab are indeed not adapted in the sameway as those of the typical crabs mentioned for cutting up and ingestingsuch food as fish-meat. In order to obtain some expression of this differ-ence, E. Bernhardus, Carcinus mwnas, and Portunus jmber were fed withpieces of squid-meat of approximately the same size. The hermit-crabscould only nibble tiny pieces at a time from their food-masses, whilethe crabs cut up theirs rapidly. At the end of an hour and a quarter,the hermit-crabs had still one-fourth to one-third of their food left, whileboth Carcinus and Portunus had eaten and swallowed theirs in four toeleven minutes. Similar time-relations were found with regard to softerfoojd, such as the gills of Pecten or the visceral mass of Tapes. There can.be no doubt that these observations show that although E. Bernhardus


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91 4 J. H. ORTON.can eat portions of fish-meat, its mouth parts are not adapted to-a regular diet on this kind of food. I t is further significant th at allhermit-crabs (Anomura) differ from all crabs (Brachyura) in not havingthe third maxillipedes broadened out to form an operculum over theinner mouth parts (Caiman, 1909), and an important function of theopercular maxillipedes in crabs is to retain food-masses under pressurein contact with the cutting inner mouth parts, so that the food can bereadily and quickly sub-divided and ingested. I t is therefore a reasonableconclusion that the normal food of hermit-crabs and other Anomura islikely to differ from that of the tiue crabs.In view of the suggestions made later and the possibility of correlatingin detail the structure with the function of the third maxillipede, it isworth while to give here Caiman's review of the variations in form ofthis appendage in Decapoda. He states that " The third maxillipede may,in the N atantia, even exceed in length the next succeeding pair of append-ages. The exopodite and basipodite are almost always connected byan immovable articulation. In the Caridea the ischiopodite is quitecoalesced with the meropodite, and the dactylopodite is obsolete orcoalesced with the preceding segment. A serrate ridge or ' cresta dentata *is commonly present on the third segment, but no endites are developedfrom the first and second segments. Among the Brachyura the th irdmaxillipedes become greatly modified to form an operculum to thebuccal frame and entirely lose their pediform character. The icchiopoditeand meropodite become broad plates and the terminal three segmentsare often hidden behind the meropodite. The peduncle of the exopoditemay also be expanded and share in forming the operculum. It s terminalflagellum is either folded out of sight or may be entirely lost. The epipo-dite forms a long curved blade in most Brachyura."With regard to the ossicles in the stomach of E. Bernhardus, Jackson(l.c.) notes that " The cardiac ossicle is far more slender than is usual,and is bow-shaped ; the pterocardiac ossicles are also slender. . . . Thelateral teeth are unusually massive and are prolonged backwards intostrongly pectinated ridges. The summ it of the cardiopyloric valve alsobears a ridge of great b lunt setae like a comb." The slender nature ofsome of the ossicles gives a hint that the need for these organs for themanipulation of ingested food is not the same in this crustacean as insuch a form as Cancer, while the occurrence of pectinate lateral teeth andthe development of setae is in harmony with a mode of feeding on thesmaller organisms in sedimentary material. Po tts (1916) shows that anextreme reduction of the gastric ossicles occurs in the plaDkton-feedingcrabs, Hapalocarcinus and Cryptochirus.The form of the gut in E. Bernhardus is interesting in that Jackson hasfound (l.c.) the achitinousand absorptive- portion of the mid-gut to


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MODE OF FEEDING OF HERMIT-CKAB. 9 1 5be unusu ally long. This fact would lead one to infer t h a t th e food in-gested is either of a detritic or vegetable nature in conformity with thegeneral occurrence of a relatively long intestine in animals which feed onth e organic conten ts of detritus or on vegetable m att er. Bu t it wouldappear that this conclusion can hardly be permitted in the present stateof our knowledge of the natural food and physiology of digestion incrustaceans. The m id-g ut in E. Bernhardus gives off long-paired anteriorcaeca an d a long un pa ire d posterior caecum. The se facts a re ag ain sug-gestive of an effort to increase the absorptive area of the intestine incorrelation with the nature of the food, but the interpretation is not atpresent justifiable from the occurrence as noted by Jackson (I.e.) of avery short achitinous mid-gu t in E. longicarpus, an American he rmit-crab,which M. T. Thompson (1904) found to feed in the same way as E. Bern-hardus. Moreover, the lobster (Homarus) and the Norway lobster,Nephrops norvegicus, both have a long mid-gut, and both these animalsare believed to be carnivorous according to Herrick (1911) and Yonge(1923). Th e na tu ra l food of these forms is, how ever, very difficult todetermine, and it will be well worth while to review their feeding habitsin the light of the information which is accumulating with regard to theuse of th e th ird maxillipedes as a food-collecting org an. H erric k ex-amined stomachs of H. Americanus preserved during a period of sevenmonths (December to Jun e), an d ma kes th e following re m arks : " Aconsiderable num ber of these stomach s were e m p ty ; more tha n halfcontained remnants of recently devoured fish, a mass of scales and bones,mixed with fragmen ts of th e indigestible par ts of othe r organism s. I nmany cases it was quite evident that the bait of traps formed the onlyfood found in their s tomachs ." . . . " The s tomachs examined con-tained remnants of the following organisms placed in the order of theirrelative abundance: fish (procured independently of the traps) ; crus-tace a, embracing chiefly isopods and de ca po ds ; mollusca, consistinglargely of small univalves; algae; echinoderms and hydroids . . . . Inth e large lobster found at th e Vinal H av en Isla nds I h ave seen th e m udd ybottom scored in all directionsthe work of lobsters in their search forclams. . . . As a fisherman rem arked, if you pu t lobsters in a po undand do not feed them, they will soon turn over the bottom as effectually as itcould be done with a plough." * Pro m these observations the informationregarding the natural food of the American lobster must be regarded asunsatisfactory, and as our information regarding the English lobster(H. vulgaris) is similar to that of its American relative, there is reasonto believe that a special study of the food and mode of feeding of these. and allied forms, especially Palinurus, the crawfish, would be profitable.It would be easy to overlook the possibility of small organisms serving

* The italics have been inserted by the writer.


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91 6 J. H. ORTON.as food in the case of these large animals. In any event a physiologicalexplanation of the occurrence of a large achitinous mid-gut in someforms and a small one in others is required.

With regard to the histology of the gut and its appendages in E.Bernhardus, Jackson (I.e.) notes that " The histology of the digestivegland differs somewhat from that described by Pearson (1908) in Cancer.The so-called ' fat-cells ' are never scattered round the lumen, but bulgeou t (like a typhlosole) from one point only at a time. I t seems doubtfulwhether the division into ' fa t ' and ' fe rm ent' cells can be justified,and whether the fat-cells are not to be considered only as ferment-cells.The lining of the mid-gut is characteristic. The cells are columnar withlarge nuclei and considerable contents of fatty m atter ." From Jackson'sobservations there is an indication that the physiology of digestion intwo such-forms as Eupagurus and a truly carnivorous ally, such as Cancerprobably is, is different, and in conjunction with that in Porcellanalongicornis and Pinnotheres pisum , would afford an interesting com-parative study.ON THE MODE OP FEEDING AND FOOD OF SOME OTHER DECAPODA AND

THE FUNCTION OF THE THIRD MAXILLIPEDES.Now that it is established that E. Bernhardus obtains micro-organismsfor food by means mainly of its third maxillipedes, it is worth whilereviewing and, indeed, investigating the mode of feeding in all the formsclosely allied to Eupagurus. With regard to E. longicarpus, the Americanhermit-crab, M. T. Thompson (1904) remarks : " Like many otherDecapods, Eupagurus longicarpus is crepuscular, and during the daya majority of individuals remain buried in the sand or congregated inthe shade. They are omnivorous and must glean very closely, as theypick up bits of gravel or detritus from the bottom and brush them over

between the maxillipedes. They also toss sandusually with the smallerchelipeds onlyto the mouth parts, brush it between them, and let thegrains fall again in a continuous stream. Probably it is in this mannerthat they obtain the diatoms and foraminifera, which are found in thestomach and intestine. But although the food is thus very largelydiatomaceous, no sort of vegetable or animal matter is refused." I t isseen, therefore, that M. T. Thompson found that E. longicarpus feedsin the same way as E. Bernhardus. The experiment described on p. 910with regard to E. Bernhardus, if repeated on E. longicarpus, wouldapparently speedily prove that the latter does obtain its micro-organismsby the intermediary of the third maxillipede. I t has been noted tha t otherorganisms than diatoms are obtained by this mode of feeding, and someof these may have greater total food value than diatoms ; for instance,foraminifera and microscopic bivalves, polychsetes, and Crustacea.


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MODE OF FEEDING OF HEKMIT-CRAB. 9 1 7It is thus clear that two hermit-crabs obtain a large portion of theirfood from micro-organisms and others slightly larger, and there can beno doubt that allied species will be found similar in this respect. I t is

known that Porcellanaplatychelesalso uses its third maxillipede forobtaining food (Borradaile, 1921), and the writer has observed thatPorcellana longicornis uses the same organs, which when extended areas long or rather longer than the cephalothorax, like whips or lacrosserackets, throwing out the left and right one alternately, for catchingsuspended particles, which are removed from the basket-like organsby a scooping action of one of the inner mouth parts ; Hunt (1925) hasobserved that the stomach contents of this craband other Crustacea,which feed similarly, such as ckripedes and an amphipod" consist of anassortment of detritus and micro-organisms quite comparable to thatfound in the ciliary feeding suspension-feeders." Hapalocarcinus, likePorcellana, uses its third maxiUipedes for collecting plankton, whichprovides the sole form of food (Potts, 1916). I t is also well known thatthe females of the pea-crab, Pinnotheres pisumand no doubt otherpea-crabsfeed on the food caught in the mucus strings of its hosts,such as Mytilus, Cardium, and others (Orton, 1921) ; Pinnotheres thustakes the same kind of food second-hand, as Porcellana longicornis obtainsat first-hand. Hunt's valuable investigations on the food of the bottomfauna (1925) indicate, as might now be anticipated, that many decapodamay.be found to obtain their food by using the third maxiUipedes eitherfor collecting organisms in suspension, or in the sediments on the sea-bottom. For example, Hun t shows th at the burrowing forms, Callianassaand Gebia, had " nothing but a mixture of sand, mud and detritus withthe usual associated small organisms " in the stomachs of the specimensexamined, and other burrowing forms are probably largely similar intheir habits. In the stomach of Galathea nexa Hunt found small crus-taceans, small polychsetes and detr itus, with foraminifera, diatom s, cope-pod eggs, peridinians, a congeries of organisms very similar to thatoccurring in the gut of hermit-crabs from the oyster beds. This speciesof Galathea, and no doubt also its related species and genera, probablyfeeds with its third maxiUipedes in the sameor a similarmanner asPorcellana.In addition to these forms, the sluggish crabs, Hyas, Pisa, Dromia,Inachus, Macropodia, and possibly Maia, may be found to obtain amajor portion of their food by means of their third maxiUipedes afterthe manner described above for hermit-crabs and other Anom ura. I t willbe interesting to learn in what way the third maxillipede is modifiedthroughout the Decapoda to subserve different functions, but there cannow be no doubt that its form is directly correlated with its function,and that the difference in the form of this organ in crabs and other

NEW SERIES.VOL. XIV. NO. 4. MAY, 19 27 . 3 N


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91 8 J. H. ORTON.Decapoda, especially the old group, Anomura, denotes a fundamentaldifference in the mode of feeding. The modifications of this appendagein Hapalocarcinus, Macropodia, and Porcellana, figured by P otts(1916, Fig. 6), and the curious anomaly in the structure and dispositionof the same organs in Pinnotheres, described by the same writer, supportthe conclusion that the form of this organ is closely correlated with itsfunction. The degree to which these appendages and the related mouthparts are modifiable in response to change in function, even in a crab,is well brought out by Potts (I.e.), who shows that the mouth parts ofHapalocarcinus and Cryptochirus are modified to such a degree as toresemble those of a Branchiopod.

SOME RELATIONSHIPS OF THE HERMIT-CRAB WITHITS COMMENSALS.

The details of the mode of feeding of the hermit-crab, as described inthe preceding pages, enable the relationships of the commensals, Hydrac-tinia, Calliactis (Sagartia), and perhaps Nereis fucata, to be better under-stood.It has been noted that the hermit-crab is almost continuously, or atleast very frequently, scooping up portions of the sediment on the sea-bottom with such an inefficient scooper as the small claw, and sifting thesedimentary material in the outgoing respira tory current. As a resultof these actions a small cloud of the bottom sediment containing micro-organisms is frequently produced in the region surrounding the hermit-crab. If the hermit-crab is facing the tidal current, this cloud will becarried around the inhabited shell and the polyps of Hydractinia situatedthereon will receive a gratuitous supply of food-material and be therebyenabled to grow and multiply into large colonies on the shell. Whenthe hermit-crab is not facing the tidal current, or in situations wherethere is no current, the sedimentary material may frequently be carriedaway from the region of the shell, or a portion only be brouglit in contactwith the hydroids on the shell according to variable complex conditions,but there can be no doubt that Hydractinia obtains a greater supply offood-material as a result of the hermit-crab's habit of sifting bottomdeposits than it would if the food of the latter were entirely large organ-isms. Hydractinia will, however, obtain food also from the sedimentwhich is disturbed and lifted up in the water merely as a result of thehermit-crab dragging its shell over the bottom, and a greater amount offood would be obtained in this way on bottoms where the micro-fauna iseasily disturbed, as, for example, on muddy grounds and the softerdeposits. I t is interesting that Allen (I.e.) found Hydractinia onlysparingly associated with E. Bernhardus on fine sand, whereas the hydroid


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MODE OF FEED ING OF HERMIT-CRAB. 91 !>is commonly present on the muddy beds in the Fal Estuary, but otherconditions may also govern the distribution of this hydroid.The frequent scraping of the sea-bottom by the hermit-x;rab along:with the movement of the inhabited shell will certainly disturb organismssuch as polychsetes, small crabs and similar fo rms; and as the anemone,Calliactis (Sagartia) parasitica, which is frequently carried on the shell,has the habit of pressing its disc on to the surface of the bottom (Sine!,1906 ; and Orton, 1922), the anemone must in this way obtain its mainsupply of food. The anemone will also obtain additional food from thatspattered by the hermit-crab in its inefficient rending apart of largemasses of food-material, such as a weak or dying mollusc or small crab.Further, as the hermit-crab can only ingest food of the latter kind slowly,it must frequently happen that when the hermit-crab has accumulatedbetween the maxillipedes all the food it can carry, the remainder willbecome the share of the anemone or anemones. A hermit-crab with i tsfoot-jaws crammed with food will sometimes drag about the remainderof the unattacked food by means of its big claw. In these circumstancesa quick turn by the hermit-crab, such as no doubt frequently occursowing to other crabs smelling the food, and hunting for it, would oftenbring the spare food within reach of the anemone, which at once seizestenaciously morsels of this kind. The possibility that the herm it-crabmay definitely and willingly share a portion of its food, when it hasgorged its jaws with enough to eat for several hours, may now be con-sidered not unreasonable (Orton, 1922). In this connexion a little furtherlight is perhaps thrown on the observed act of Nereis fucata, the wormfrequently present in the shell inhabited by the hermit-crab, taking piecesof food out of the foot-jaws of its partner. If the hermit-crab has capturedeven a moderately large supply of food in mass, it will probably seldom beable to eat it all itself, owing to its slow rate of eating and the probabilityof other crabs soon finding and capturing the spare food which it cannotadequately defend. The loss of one portion of food, if others are available,would not therefore necessarily be a net loss, and the worm might obtaina portion of food without detriment to the hermit-crab. I t is unlikely,however, that the true relations of this worm to the hermit-crab will beproperly understood until a close study is made of their mutual behaviourduring feeding, and the gut contents of the worm, when freshly caught,have been determined. The only probable advantage to the hermit-crabfrom its association with the worm is th at of having the water in the shellrenewed by the rhythmical wave-like motion of the body of the worm,but it is also possible that the worm may assist the hermit-crab byremoving from the mouth parts of the latter undesirable food which mayinadvertently have been attacked.


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92 0 J. H. ORTON.

SUMMARY.The hermit-crab, Eupagurus Bernhardus, is common in the oyster beds

in the upper part of the Fal Estuary, and experiments indicate, whileobservations and experiments on the mode of feeding virtually prove,that these hermit-crabs do not harm healthy small oysters one inch ormore in length, and the larger oysters, but that spat less than one inchmay occasionally be damaged or eaten by hermit-crabs picking withtheir claws indiscriminately at growths on shells and stones.E. Bernhardus obtains food largely by its small claw and third maxilli-pedes, and may at certain periods of the year feed mainly on micro-organisms, and at others on macroscopic, but mainly tiny living organismswhich have been distuibed and captured in the deposits on the sea-botto m. Food can be obtained by the use of the third maxillipedes alone.The mouth parts of E. Bernhardus are not adapted for rapid ingestionof the meats of animals in bulk, and the gastric mill is less stronglydeveloped than in the carnivorous crabs ; these facts, along with certainfeatures of the gut, indicate morphological and anatomical modificationcorrelated with the food and mode of feeding.E. longicarpus feeds in the same way as E. Bernhardus, and alliedspecies may obtain food similarly.Some Decapoda are now known to obtain food mainly by use of thethird maxillipedes, as Porcellana, Hapalocarcinus, and some subsistentirely on planktonic food-material as Porcellana longicornis, Pinnotherespisum $, and it is probable that a large number of other Decapoda obtainsmall or microscopic organisms as food mainly by use of the th ird maxilli-pedes. The structure of the third maxillipede in all Decapoda is probablydefinitely correlated with its function in feeding actions.Some additional points in the relations of the hermit-crab with its com-mensals are better understood when the mode of feeding of the former isconsidered.

REFERENCES.ALLEN, E. J. 1899. On the Fauna and Bottom Deposits near the Thirty-fathom Line from the Eddystone Grounds to Start Point. Journ.Mar. Biol. Assoc, N.S., V, 1899.SINEL, J. 1906. An Outline of the Natural History of our Shores.THOMPSON, M. T. 1904. The Metamorphoses of the Hermit-Crab, No. 4.Proc. Boston Soc. Nat. Hist., XXXI, 1904.PEARSON, J. 1908. Cancer. L.M.B.C. Memoir, XVI, 1908, London.CAIMAN, W. T. 1909. A Treatise on Zoology. Edited by Sir E. RayLankester, Part VII, Appendiculata (Third Fascicle, Crustacea).


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MODE OP FEEDING OF HERMIT-CRAB. 9 2 1H E R R I C K , F . H . 1911. N atur al His tory of the Am erican Lobster.Bull. U.S. Bureau Fisheries, Washington, XXIX, Doc. No. 747.ORTON, J. H . 1912. The Mode of Feed ing of Crepidula, etc . Jo u rn .

Mar. Biol. Assoc, N.S., IX, p. 445.JACKSON, H . G. 1913. Eu pag urus . L.M.B.C. Memoir, X X I .POTTS, F . A. 1916. Ha palo carc inus , th e Gall-forming Crab, w ith som eNotes on the rela ted Genus, Cryp tothirus. Pu bn . No . 212, CarnegieInstitution of Washington (1915).BORRADAILE, L. A. 1921. Note on the Mouth Pa rts of certain Decapod.Crustaceans. Proc. Camb. Phil . S oc , X X .ORTON, J. H . 1921. Mode of Feeding and Sex-phenomena in th e Pea -

(Crab , Pinnotheres pisum. Nature, Vol. 106, p. 533.ORTON, J. H . 1922. The Eelationsh ip between th e common H erm it-Crab (Eupagurus Bernhardus) and the Anemone (Sagartia parasitica)-.Nature, Vol. 110, p. 735.Y O N G E , C. M. 1924. Studies on th e Com parative Physiology of Dig estio n..I I . The Mechanism of Feeding, Digestion, and Assimilation inx

Nephrops norvegicus. Brit. Journ. Exper. Biol. , Vol. I ,H U N T , 0 . D . 1925. The Food of the Bo ttom Fa un a of the Ply mo uthFishing Grounds. Jou rn. Mar. Biol. A sso c, N.S ., X II I . p. 560.

on the mode feeding of hermit crab pagurus euphenhardus

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