Pacific Science (1975), Vol. 29, No.3, p. 259-266Printed in Great Britain

A New Hawaiian Hermit Crab of the Genus Trizopagurus (Crustacea,Decapoda, Diogenidae), with Notes on its Behavior I

PATSY A. McLAUGHLIN2 AND JULIE H. BAILEy-BROCK3

ABSTRACT: A new deep-water Hawaiian hermit crab, Trizopagurus hawaiiensisn. sp., is described and illustrated. Observations on its behavior, feeding habits,and growth rates have been obtained from a specimen kept in the laboratory formore than a year.

17-2

Trizopagurus hawaiiensis new species

Figures 1-3

cited, without description, a second new species,Trizopagurus krempji, which he described sub­sequently in a more complete review of thegenus (Forest 1952b). An eighth species,Trizopagurus shebae Lewinsohn, recently hasbeen described from the Red Sea (Lewinsohn1969).

Heretofore, in the Hawaiian fauna, Trizo­pagurus has been known only from T. strigatus(ef. Edmondson 1925, 1946, 1952, as Aniculusstrigatus). From the collections of the Bernice P.Bishop Museum and the National MarineFisheries Service (NMFS) research vesselTownsend Cromwell (TC), a second, and new,species has been discovered. A living specimen,collected during one of the NMFS cruises,was given to one of the authors (JHB) whowas able to maintain it in the laboratory for21 months, during which time observations onfeeding habits and molting frequencies weremade.

The holotype and female paratype have beendeposited in the collections of the NationalMuseum of Natural History, SmithsonianInstitution (USNM). Additional paratypes havebeen deposited in the collections of the BerniceP. Bishop Museum (BPBM), Honolulu, Hawaii,and the Allan Hancock Foundation (AHF),University of Southern California.

Holorype

Male (SL = 4.8 mm), NMFS station TC61-119, 21 °01.8' N, 156°06.5' W, 2 November1972, 172-230 m, USNM.

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THE SUPERFICIAL SIMILARITIES in the generaAniculus Dana, Dardanus Paulson, and Clibana­rius Dana have been the source of manycarcinological problems. During a study ofpagurids from the Belgian OceanographicExpedition to the south Atlantic, Forest(1952a) encountered a specimen which he couldnot adequately assign to any of the knownpagurid genera. In many ways this specimenresembled both Aniculus and Clibanarius, butdiffered from both in several significantcharacters. Comparative studies of speciesassigned to these genera showed that severalspecies, variously assigned to Aniculus, Clibana­rius, and Dardanus (as Pagurus sensu Dana, cf.Rathbun 1903, Hemming 1957) by earliercarcinologists, agreed better in all diagnosticcharacters with his new taxon than with thegenera to which they had been assigned. Con­sequently, Forest (1952a) erected the new genus,Trizopagurus Forest, for these species. Inaddition to his new species, Trizopaguruscaparti Forest, he included Clibanarius strigi­manus (White), C. magniftcus Bouvier, C. melitaiChevreux & Bouvier, Aniculusstrigatus(Herbst),and A. tenebrarum Alcock. At that time he also

I Scientific contribution 1832 from the RosenstielSchool of Marine and Atmospheric Science. Researchwas supported, in part, by research grant GB 40062from the National Science Foundation and by a Univer­sity of Hawaii biomedical support grant 1970/1971,Manuscript received 25 September 1974.

Z University of Miami, Rosenstiel School of Marineand Atmospheric Science, 10 Rickenbacker Causeway,Miami, Florida 33149. Present address: Florida Inter­national University, Department of Biological Sciences,Tamiami Trail, Miami, Florida 33174.

3 University of Hawaii, Department of Zoology, 2538The Mall, Honolulu, Hawaii 96822.

260 PACIFIC SCIENCE, Volume 29, July 1975

FIGURE 1. Trizopagurus hal/laiiensis n. sp., male (SL = 4.6 mm). a, shield and cephalic appendages; b, 3rd rightpereiopod (lateral view); c, 4th left pereiopod (lateral view).

Scales equal 3 mm (a, b) and 1 mm (c).

A New Hawaiian Hermit Crab-McLAUGHLIN AND BAILEy-BROCK 261

FIGURE 2. Trizopagttrtls hawaiiensis n. sp., male (SL = 4.6 mm). Left cheliped: a, dorsal view; b, lateral view; f,mesial view.

Scale equals 3 mm.

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l

a

t

PACIFIC SCIENCE, Volume 29, July 1975

9

FIGURE 3. Trizopagurus halJ'aiiensis n. sp. a-e, mouthparts (left, internal view): a, maxillule; b, maxilla; c, mxp,;d, mxpz; e, mXP3' i, sternite of 3rd pereiopods. g, 6th abdominal segment and telson.

Scale equals 1 mm.

Paratypes

1 male (SL = 5.6 mm), 1 female (SL = 4.7mm), NMFS station TC 61-119, 21°01.8' N,156°06.5' W, 2 November 1972, 172-230 m,AHF, USNM; 1 male (SL = 4.6 mm), off Oahu, 23September 1971, 382 m, BPBM; 1 male (SL =4.9 mm), off Haleiwa, Oahu, Hawaii, 20 June1970, T. Clarke collector, 382 m, BPBM S-8400.

Type Locality

Hawaii, 21 °01.8' N, 156°06.5' W.

Diagnosis

Chelae and carpi of both chelipeds withtransverse rows of small spines dorsally andlaterally. Meri of second ambulatory legs eachwith row of small spines on ventral margin.

A New Hawaiian Hermit Crab-McLAUGHLIN AND BAILEy-BROCK 263

Description

Shield usually slightly longer than broad;anterolateral margins sloping, anterior marginbetween rostrum and lateral projections straightor somewhat concave; posterior margintruncate or roundly truncate; dorsal surfacewith incomplete subovate demarcation pos­teriorly (Figure 1a) and with few scattered tuftsof setae; degree of dorsoventral flattening con­tingent upon habitat (see remarks). Rostrumshort, not exceeding lateral projections; ter­minating acutely or subacutely and with smallspine or spinule. Lateral projections obtuselytriangular, each with small submarginal spine.

Ocular peduncles long, exceeding length ofshield, cylindrical, slightly inflated basally andvery slightly dilated in corneal region; dorsaland dorsomesial faces usually with few tufts orlongitudinal row of fine short setae. Ocularacicles narrowly triangular, mesial marginsusually straight, lateral margins sloping;terminating acutely and with small marginal orsubmarginal spine; separated basally by one­half to two-thirds basal width of one acicle.

Antennular peduncles moderately long,usually reaching to base of corneae; ultimateand penultimate segments each usually withfew scattered setae; basal segment with smallspine at ventrodistal margin, laterodistal marginwith one-five strong acute spines, lateral facedorsally occasionally with small spinule.

Antennal peduncles moderately short, one­third to two-thirds length of ocular peduncles;with supernumerary segmentation (cf. Mc­Laughlin 1974). Fifth segment with fewscattered tufts of short setae. Fourth segmentwith small spine at dorsodistal margin. Thirdsegment with strong acute spine at ventrodistalmargin and few tufts of moderately long setae.Second segment with dorsolateral distal angleproduced, terminating in moderately strong,simple or bifid spine, lateral margin with one­three small spines and few moderately longsetae, mesial margin unarmed or with one ortwo small spines; dorsomesial distal ;tngleusually with very small spinule or with one ortwo adjacent small spines, mesial margin withtufts of setae and occasionally with one or twoadjacent small spines. First segment with smallspine on lateral face distally; ventral margin

produced, with row of small spines or spinuleslaterally. Antennal acicle short, reaching proxi­mal third of ultimate peduncular segment;terminating in acute, simple or bifid spine;dorsomesial face with two-seven small spinules,lateral margin with one-four moderately strongspines. Antennal flagella long, considerablyoverreaching chelipeds; usually each articlewith one or two minute bristles.

Mandible without distinguishing characters.Maxillule (Figure 3a) with three or four stiffbristles on moderately well-developed internallobe, external lobe extremely well developed,recurved; proximal endite subquadrate, supero­distal angle slightly produced. Maxilla (Figure3b) with broad, tapering endopodite slightlyexceeding scaphognathite in distal extension.First maxilliped (Figure 3c) with basal segmentof exopodite moderately slender. Secondmaxilliped (Figure 3d) with basis-ischiumfusion incomplete. Third maxilliped (Figure3e) with basis-ischium fusion incomplete;basis unarmed; ischium with crista dentata welldeveloped, without accessory tooth; merus andcarpus unarmed.

Chelipeds (Figure 2a-c) equal or slightly sub­equal, short; similar in armature and ornamen­tation. Dactyls moderately short, slightlyshorter than or equal to length of palms;cutting edge each with one or two prominentcalcareous teeth proximally, few corneous teethmedianly, and terminating in very strong,elongate corneous claw;, dorsomesial marginsnot markedly delimited, dorsal and mesialfaces each with one-four irregular, shallow,transverse furrows and irregular rows of low,often corneous-tipped, tuberculate spines prox­imally, scattered, corneous-tipped small spinesdistally partially obscured by tufts of long stiffsetae; ventral surface with few tufts of stiffsetae or bristles. Palms moderately long,usually exceeding length of carpus; dorso­lateral margins not delimited, dorsal, lateral,and mesial faces each marked by shallow trans­verse furrows; dorsally and laterally, eachfurrow usually bounded proximally by row ofmoderately strong, often corneous-tippedspines or spinulose tubercles interspersed withvery short fine setae; fixed finger distally withscattered spines partially obscured by tufts oflong stiff setae; furrows of mesial face bounded

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proximally by transverse rows of corneous­tipped rods forming stridulating apparatus;ventral surfaces each with few transverse fur­rows mesially and laterally, and scattered tuftsof long setae. Carpi moderately short, one-halfto two-thirds length of meri; subtriangular;dorsal, lateral, and mesial faces each withseveral shallow transverse furrows, dorsally andlaterally each usually bounded proximally byrow of small spines or spinules interspersedwith fine short setae; distal margin dorsallyand laterally with row of moderately strong,occasionally corneous-tipped spines and rowof short fine setae. Meri subtriangular ; dorsalmargins, lateral and to lesser extent mesial faceseach with shallow transverse furrows, boundedproximally by rows of short fine setae andoccasionally by a row of small spines orspinules; dorsal margin also usually with fewspines most prominent distally; ventral surfaceoften· with prominent large tubercle, ventro­mesial and ventrolateral margins usually withshort row of spines distally. Ischia each withrow of short setae and occasionally one or twosmall spines on ventromesial margin. Coxaeeach with tuft of long setae at ventromesialdistal angle and row of setae on ventromesialmargin.

Ambulatory legs moderately long, usuallyoverreaching chelipeds by full length of dactylsof P 2; generally similar in armament andornamentation. Dactyls moderately long, equal­ling or slightly exceeding length of propodi; inlateral view, straight or slightly curved ven­trally; in dorsal view, straight; dorsal surfaceseach with irregular rows of tufts of long stiffsetae, often arising from low protuberances;lateral and mesial faces each with irregular rowsof shallow depressions and tufts of long setae;ventral surfaces each with row of moderatelystrong corneous spines, increasing in sizedistally and partially obscured by tufts of longsetae. Propodi moderately long, one-fourth toone-third longer than carpi; each with series ofprominent ridges (Figure 1b) and rows of shortfine setae circumscribing segment, moreirregular and somewhat interrupted onP3 ;

dorsal surfaces also with additional tufts oElongsetae. Carpi moderately short, one-third to two­thirds length of meri; dorsal and lateral, andless fr-equently, mesial surfaces each with series

PACIFIC SCIENCE, Volume 29, July 1975

of short transverse ridges and rows of shortfine setae, dorsally also armed with few smallspines or spinules (P2) or unarmed (P3),dorsodistal margins each with strong spine.Meri moderately long, laterally compressed;dorsal surfaces each with row of low transverseridges and short setae, extending laterally andmesially in distal half; ventral margins eachwith single or double row of small spines (P 2)or unarmed (P3) and with row of tufts of shortsetae. Ischia each with row of setae on ventralmargin. Coxae each with rows of tufts of setaeon ventromesial and ventrolateral margins.Sternite ofthird pereiopods roundly rectangular,anterior margin with long, moderately finesetae (Figure 31).

Fourth pereiopods (Figure 1c) subchelate;dactyls apparently 'Yithout preungual process;propodal rasp very\iTell developed, encompass­ing approximately one-half to two-thirds oflateral face; carpi each with small spine atdorsodistal margin.

Fifth pereiopods chelate.Males with four biramous unpaired pleopods,

with external rami moderately well developed,internal rami reduced. Females with fourbiramous unpaired pleopods, with both ramimultisegmented and well developed.

Uropods generally symmetrical. Postero~

lateral angles of sixth abdominal segment eachwith one-five small spines (Figure 3g). Telsonwith posterior lobes broadly subtriangular,symmetrical or slightly asymmetrical, withmoderately shallow median cleft; posterolateralangles acutely or broadly rounded, terminalmargins with long setae.

COLOR IN PRESERVATIVE (ethanol): Shieldgenerally light orange with darker mottling ofreddish orange laterally; rostral point dark red­orange. Ocular peduncles and acicles dark tolight reddish orange. Antennular and antennalpeduncles colorless, except for antennal aciclesand second peduncular segments, which appearmottled orange. Chelipeds with furrowed areascream-colored, remaining surfaces reddishorange to orange, flecked with white or cream.Ambulatory legs generally mottled orange andcream; dactyls more uniformly dark reddishorange with cream-colored depressions andtips; propodi white or cream distally. All color

A New Hawaiian Hermit Crab-McLAUGHLIN AND BAILEy-BROCK 265

fading in time to white or straw-color. Inspecimens lacking color, the shallow furrows ofthe chelipeds are often difficult to discern.

COLOR IN LIFE: An overall red-orange color,of brighter tones than the preserved specimen.The shallow furrows of the chelipeds and theapical tips of the antennules are bright yellow.

Distribution

At present known only from the HawaiianIslands; 172-382 meters.

Affinities

Trizopagurus hawaiiensis appears most closelyallied to T. tenebrarum from the Indian Oceanand the Gulf of Aden. However, the prominentshallow furrows and stronger spination of thechelipeds and the armature of the carpi andmeri of the second pereiopods of T. hawaiiensisimmediately distinguish this species from theformer. The presence of spines on the cheli­peds also distinguishes T. hawaiiensis fromT. strigatus, the only other representative ofthe genus known from Hawaiian waters. Asuperficial similarity also exists between T.hawaiiensis and the Hawaiian Aniculus maximusEdmondson and the Indo-Pacific Aniculusaniculus Fabricius; however, the generic charac­ters which distinguish Trizopagurus fromAniculus clearly confirm the distinction ofTrizopagurus halvaiien:ris.

Remarks

Forest (1952b), in his characterization ofTrizopagurus, did not mention the rather unusualmultisegmented condition of the female pleo­pods. This segmentation is very pronounced inT. hawaiiensis. In the three other species ofTrizopagurus available to the authors, varyingdegrees of segmentation were observed. Inboth T. strigatus and T. magniftcus, segmentationof the rami was incomplete; in T. tenebrarum,segmentation was distinct.

As previously indicated, a male specimen of

T. hawaiiensis was maintained in the laboratoryfor a period of 21 months. At the time of itscapture, this specimen occupied a shell ofTerebra gouldii Deshayes. Shortly after thedemise of a hermit crab, which occupied a shellof Xenophora tenuis Fulton and which shared theaquarium with Trizopagurus hawaiiensis, thelatter took up residence in the Xenophora tenuisshell. As is common with hermit crabs, this"house swapping" occurred more than once.T. hawaiiensis eventually took up permanentresidence in the lighter and less cumbersomeTerebra gouldii shell. Examination of this speci­men after its preservation revealed no dorso­ventral flattening of the carapace. In contrast,specimens of this species collected and pre­served in their shells of Xenophora tenuis didexhibit varying degrees of dorsoventral com­pression. These observations lend support toForest's (1952a) proposition that the markeddegree of carapace compression seen in somespecies of Trizopagurus is more a function ofhabitat than a genetic trait.

Although the specimen of T. hawaiiensis wasmaintained on a diet of fish chunks, during itsfirst few days in the aquarium it eagerly ate theserpulid worms encrusting the shells ofXenophora tenuis and Terebra gouldii. Whileinhabiting the Xenophora tenuis shell, the crabsimply picked the worms from the tubesattached to the shell of Terebra gouldii. However,after returning to the more elongate T. gouldiishell, Trizoj)agurus hawaiiensis would balanceagainst the Xenophora tenuis shell, using theambulatory legs and the apex of its shell as atripod, and pick the worms from their tubeswith its chelae.

During the 21 months in the aquarium, thespecimen molted four times, the first moltoccurring 4.5 weeks after capture (late October).Although growth measurements were not takenwith successive molts, the specimen increasedfrom a shield length of 3.1 mm at the time ofthe first molt to a shield length of 4.6 mm at thetime of its preservation, or an average ofslightly less than 0.4 mm increase in shieldlength per molt.

The specific name of this species is derivedfrom the type locality, Hawaii.

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ACKNOWLEDGMENTS

The authors are indebted to Drs. Paul J.Struhsaker, National Marine Fisheries Service,Honolulu, Hawaii, and Dennis M. Devaney,Bernice P. Bishop Museum, for providing thespecimens of T. hawaiiensis. Thanks are also dueMiss Janet Haig, Allan Hancock Foundation,and Dr. Anthony J. Provenzano, Jr., OldDominion University, Norfolk, Virginia, forthe use of comparative materials from theircollections.

LITERATURE CITED

EDMONDSON, C. H. 1925. Crustacea. Pages3-69 in C. H. Edmondson, W. K. Fisher,H. L. Clark, A. L. Treadwell, and J. A.Cushman. Marine zoology of tropical centralPacific. Bull. Bernice P. Bishop Mus. 27.148 pp.

---.1946. Reef and shore fauna of Hawaii.Spec. Publ. Bernice P. Bishop Mus. 22.iii+381 pp.

___. 1952. Additional central Pacific crus-taceans. Occ. Pap. Bernice P. Bishop Mus.21(6): 67-86.

PACIFIC SCIENCE, Volume 29, July 1975

FOREST, J. 1952a. Sur Trizopagurus caparti gen.et sp. nov., paguride de la cote occidentaled'Afrique. Bull. Inst. R. Sci. Nat. Belg. 28:1-8.

___. 1952b. Contributions a la revision descrustaces Paguridae. 1. Le genre Trizopagurus.Mem. Mus. Nat. Hist. Nat., ser. A, Zool. 5:1-40.

HEMMING, F., ed. 1957. Opinion 472. Additionto the official list of generic names in zoologyof the generic name Pagurus Fabricius, 1775,with Cancer bernhardus Linnaeus, 1758, as typespecies (class Crustacea, order Decapoda).Opinions and Declarations of the Inter­national Commission for Zoological Nomen­clature 16: 213-276.

LEWINSOHN, C. 1969. Die Anomuren des RotenMeeres (Crustacea Decapoda: Paguridea,Galatheidea, Hippidea). Zool. Verh. Rijks­mus. Nat. Hist. Leiden 104. 213 pp.

McLAUGHLIN, P. A. 1974. The hermit crabs(Crustacea Decapoda, Paguridea) of north­western North America. Zool. Verh. Rijks­mus. Nat. Hist. Leiden 130. 396 pp.

RATHBUN, M. J. 1903. Japanese stalk-eyedcrustaceans. Proc. U.S. Nat. Mus. 26: 23-55.