Redescription Of Iais elongata Sivertsen and-Holthuis, 1980, From The South atlantic Ocean (Crustacea, Isopoda, Asellota)

9 Pages·1994·2.5 MB·English

by  B Kensley

PROC. BIOL. SOC. WASH.
107(2), 1994, pp. 274-282
REDESCRIPTION OF lAISELONGATA
SIVERTSEN & HOLTHUIS, FROM THE
1980,
SOUTH ATLANTIC OCEAN
(CRUSTACEA: ISOPODA: ASELLOTA)
Brian Kensley
Abstract.—Iais elongata is redescribed from a freshwater stream on Inac-
cessible Island, Tristan da Cunha archipelago. The presence ofseveral males,
each in amplexus with a stage 1 manca, demonstrates that precopula or mate
guarding, which also provides some measure ofoffspring protection in a swift-
flowing stream, occurs in this species.
About 130 specimens of a tiny asellote above beach. North Point, Inaccessible Is-
isopod were collected from a freshwater land.—Stream flowing to Blenden Hall
stream on Inaccessible Island (37°02'S, beach. Inaccessible Island, 37°02'S,
12°12'W) in the Tristan da Cunha archi- 12°12'W: Sample TDC 2A, 2 ovig. 2, 21 $,
pelago ofthe South Atlantic, by Mrs. Helen 16 <5 (6 3 with manca), 13 Oct 1989.-Sam-
James of the Albany Museum, Grahams- ple TDC 1 II, 4 ovig. 5, 20 2, 10 5(13 with
town, SouthAfrica.Thecollectionwasmade manca), 23 Oct 1989.-Sample TDC II, 5
in the course ofa survey ofthe invertebrate ovig. 2, 26 2, 30 $ (3 with manca), 23/24
NMNH
fauna of the island, and submitted to the Oct 1989 (3 ovig. 2, 10 2, 10 3 in
Smithsonian Institution for identification. collection).
The bulk ofthe collection is housed in the Description.—Body (Fig. lA) about 3.5-
Albany Museum; a representative sample 3.8 times as longas wide. Integument bear-
hasbeendepositedintheNationalMuseum ing short scattered setae, some stouter than
of Natural History, Smithsonian Institu- others. Cephalonaboutone-thirdwiderthan
tion. midlength, slightly narrowerthan pereonite
Althoughthe isopodsweredeterminedto 1; anterior margin with broadly rounded
be a recently described species, it was de- rostrumreachingtoabout midlengthoffirst
cided to provide a fuller redescription with antennular article. Eyes well pigmented, of
illustrations, especially as some interesting 2 ommatidia each. Coxae visible in dorsal
details ofthe biology were revealed. view on all pereonites. Pereonite I slightly
shorter than pereonite 2; pereonites 2-4
Family Janiridae subequal in length and width, each with se-
lais elongata Sivertsen & Holthuis, 1980 toseanterolateral rounded lobe; pereonite 5
Figs. 1-5 shortest and narrowest; pereonites 6 and 7
& withsetoseposterolateraltergallobes. Pleon
lais elongata Sivertsen Holthuis, 1980:
consisting of single short anterior segment
104, Fig. 34. [Described from 2 $ and 1 plus pleotelson; latter subequal in length to
2]. pereonites 6 and 7, lateral margins weakly
Material examined.—Trondheim Uni- convex with about 15 short setae, posterior
versity Museum, Holotype, 5 TL 1.2 mm, margin weakly convex between uropodal
paratypes 1 5, 1 9, (3 slide preparations), sta insertions.
m
136, pool of brackish water in cave 2 Antennule (Fig. IC) of6 articles, almost
VOLUME NUMBER
107, 2 275
D-H, J-L
Fig. 1. laiselongata: A, Adultin dorsal view, scale = 0.2 mm; B, Antenna; C, Antennule; D, Upperlip; E,
Lower lip; F, Distal part ofleft mandible; G, Mandibular palp; H, Right mandible; I, Ventral view oflast
pereoniteand pleon ofmale; J, maxilla 1; K, Maxilla 2; L, Maxilliped.
276 PROCEEDINGSOFTHE BIOLOGICALSOCIETY OFWASHINGTON
reachingdistal margin ofantennal article 5, shorterthanpereopod2, withbiunguiculate
article 1 widest and longest, twice length of dactylus; pereopods 2-3 and 5-7 in male
article 2; terminal article bearing single and pereopods 2-7 in female essentially
aesthetasc. Antenna(Fig. IB)equalin length similar, becoming more elongate posteri-
to cephalon plus pereonites 1-5 and halfof orly, with basis moderately broad, bearing
pereonite 6; peduncle articles 1-4 shorter strong seta on anteroproximal margin, is-
thanwide; article 3 with minutedistolateral chium with 2 or 3 setae on anteriormargin,
scale bearing 2 short setae; articles 5 and 6 merus with group of 3 anterodistal setae,
longer than wide, article 5 about three- carpus subequal in length to merus and is-
fourthslengthofarticle6; flagellumofabout chium together, with short posterodistal
19 setosearticles in male, 16 in female. Up- spine, propodus about halfwidth and sub-
per lip (Fig. ID) about 1.8 times broader equal length ofcarpus, with short postero-
basally than midlength, distally broadly distal spine, dactylus with 3 hooked claws.
rounded, setose. Mandibularpalp (Fig. 1G) Pereopod 4 in maleabouttwo-thirdslength
of3 articles, article 1 abouttwo-thirdslength of pereopod 3 or 5, propodus with stout
of article 2, with single strong distolateral posterodistal spine, dactylus bearing ter-
seta; article 2 bearing 2 strong bilaterally minal hooked claw, and reflexed subter-
pectinate setaelaterallyindistalhalf; article minal claw.
3 withmesialmarginconvex, lateralmargin Female pleopod 2 forming broad oper-
straight with 5 spines increasing in length culum (Fig. 4A), midlength subequal to
distally; mandibular molar cylindrical, greatestwidth,distallybroadlyroundedwith
grinding surface sclerotized, truncate; inci- 2 submesial setae. Male with short conical
sor of 4 sclerotized cusps; spine row of 3 penes (Fig. 4B) on posterior sternal margin
short and 2 elongate spines (left, Fig. IF), ofpereonite 7,justreachingbaseofpleopod
4-toothed lacinia mobilis, 2 short and 2 1. Male pleopods 1 and 2 together forming
elongate spines (right. Fig. IH). Lower lip operculum; pleopod 1 elongate (Fig. 4B),
(Fig. IE)deeplycleft, lobeslaterallybroadly rami with fused portion 3.5 times longer
convex, mesiodistally strongly setose. Max- than free, distal rami rounded and bearing
illa 1 (Fig. IJ) with mesial lobe bearing 1 about 7 simple setae, distolateral projection
distomesialand6distal simplesetae; lateral short, narrowly rounded. Pleopod 2 (Fig.
lobe bearing 1 1 stout toothed spines distal- 4C) peduncle roughly triangular, lateral
ly. Maxilla 2 (Fig. 1K), mesial lobe bearing margin convex; exopod with 2 articles sub-
about 13 mostly simple setae mesiodistally; equal, article 2 distally rounded; endopod
2 lateral lobes each with 4 elongate unilat- with article 1 about halflength ofarticle 2,
erally pectinate setae. latter slender, curved, tapering to narrow
Maxillipedal palp (Fig. 1L) of 5 articles, apex reaching distal end ofpeduncle, with
article 1 broader than long, article 2 twice narrow open furrow. Pleopod 3 (Fig. 4D)
length and slightly wider than article 1, ar- withexopodof2articlessubequalinlength,
ticle 3 three-fourths length and two-thirds article 1 wider than 2, lateral margin con-
width ofarticle 2, articles 4 and 5 slender, vex, setose; article 2 taperingdistally lateral
article 4 2.7 times length ofarticle 5; endite and mesial margins setose, with single sim-
reachingto midlength ofpalparticle4, with ple setae apically, endopod roughly ovate,
2 coupling hooks on mesial margin, distal with irregular margin, reaching distal half
marginwithsubmarginalrowof6 stoutpec- ofexopod article 2. Pleopod 4 (Fig. 4E) ex-
tinate spines, marginal row of7 slender se- opod ofsingle slender article bearing single
tae; epipod ovate, distally broadly rounded, elongatedistalseta;endopodbroad,roughly
reaching palp article 3. Pereopods (Figs. 2, ovate, with irregularmargin. Pleopod 5 (Fig.
3) all ambulatory, pereopod 1 only slightly 4F) ofsingle irregular roughly ovate ramus.
VOLUME 107, NUMBER 2 277
0.1
Fig. 2. laiselongata, female, pereopods 1-7.
Uropod (Fig. 4G) about halflength ofpleo- growing closely along the banks. The spec-
telson, peduncle with single strong dis- imenswerefoundunderstonesinthestream,
tomesial seta; endopod 2.8 times length of usually several animals per stone.
exopod, with several terminal simple setae; Gutcontents.—Y>eXermmedfrom2cleared
exopod with 3 terminal setae. specimens: several kinds ofdiatoms, spore-
Habitat.—The. specimens were collected like structures, and fine filamentous algal-
from a narrow, fairly swiftly flowing stream like structures in addition to unidentifiable
(about 60 cm wide, 50 cm deep), arising fragments. The female paratype, clearedand
from a spring and running less than one mounted on a microscope slide, has the en-
kilometer before dropping to a boulder tire gut packed with diatoms.
beach. The stream waterwasclear, pH neu- ^/z^-.-Males total length (tl) 1.08-1.30
tral; the grass Spartina arundinacea was mm, possibly in 2 size-groups; males with
278 PROCEEDINGSOFTHE BIOLOGICALSOCIETYOFWASHINGTON
Fig. 3. laiselongata, male pereopods 1-7.
mancatl 1.13-1.30 mm, mancatl0.43 mm; lected were each found to be carryinga sin-
femalestl0.75-1.45 mm, possiblyin 2 size- gle large manca, tucked between the pereo-
groups; ovigerousfemalestl 1.20-1.48 mm. pod bases (Fig. 5). All the mancas (manca
mm
Ovigerous females (average for 1 1 spec- I stage, 0.43 total length) were female;
imens tl 1.32 mm) somewhat larger than all were oriented in the same way, i.e., dor-
mature males (average for 9 specimens tl sum ofmanca pressed to ventrum ofmale,
1.22 mm). headdirectedposteriorlywith respecttothe
Broodsize.—ConXenis ofbrood pouch in male.Thisisclearlyacaseofmateguarding,
ovigerous females: 1 egg— 1, 2 eggs—2, 3 with thejuvenile partner held in precopula.
eggs—2, 2 manca—4, 3 manca—1. The fourth pereopods of the male, which
Mateguarding.—Tenofthe 56 malescol- hold the manca in position, are two-thirds
VOLUME 107, NUMBER 2 279
Fig. 4. lais elongata: A, Female pleopod 2 operculum; B, Male pleopod 1 and penes; C, Male pleopod 2;
D, Pleopod 3; E, Pleopod4; F, Pleopod 5; G, Uropod.
the length of the third or fifth pereopods, Copulation in isopods takes place during
and have one ofthe dactylarclaws reflexed. the biphasic molt to the adult brooding
This precopulatory mate guarding strat- phase. The posterior half molts first, fol-
egy(seeDunham&Hurshman 1991,Franke lowed by insemination, then the anterior
1993) has been observed in a number of halfmolts, along with deployment ofoos-
crustaceans (Ridley 1983) including iso- tegites. Eggs are released into the brood-
pods. Precopula ensures that the male is pouch once molting is complete (Veuille
present when a female is receptive during 1978). Most isopods have internal insemi-
thebriefbiphasic molt, eitherbybeing pas- nation (Ridley 1983). Several asellote gen-
sively attached to the female, orbyactively erahavebeennotedtoresorttomateguard-
carrying her around. ing; species of Jaera and Munna carry
280 PROCEEDINGSOFTHE BIOLOGICALSOCIETY OFWASHINGTON
during precopulation and copulation
(Veuille 1980). The same leg is used in am-
plexusin the primitive asellotes Caecidotea
(Lewis & Bowman 1981) andAsellus (Gru-
ner 1965).
At a maximum total length of 1.48 mm,
thisspecies iswithin meiofaunal size-range.
Many meiofaunal organismsexhibitregres-
siveevolutionofbodysize(Swedmark 1964)
accompaniedbyreductioninnumberofeggs
and offspring per brood. In this case, four
eggs was the maximum number observed
within a brood-pouch while two manca per
brood pouch was the commonest number
{n = 4) ofmanca observed. Given this very
low number ofoffspring per brood, contin-
ued care ofoffspring after release from the
brood-pouch would greatly improve the
survival rate, especiallygiven the habitat of
a fairly swiftly flowing stream. This post-
marsupial care is afforded bythe male'suse
of precopulatory mate guarding of the fe-
male manca. The male is already adapted
for amplexus, and this adaptation becomes
a form ofoffspring care. This double use of
an adaptation is more parsimonious than if
the female, which lacks any clasping mod-
ifications, were to provide some form of
post-marsupial care. The use ofthe fourth
pereopod ofthe male for hanging onto the
female is probably a primitive character
within the Asellota, beingfound in theasel-
lids, while the loss ofone ofthe three dac-
tylar ungui, and the flexing of one of the
remaining ungui along with marked short-
ening ofthe leg seen in the janirids, repre-
sent a more advanced state than that seen
in the asellids.
Remarks. —The genus lais Bovallius,
1886, at present contains five species (see
Nierstrasz 1941:53; Menzies & Barnard
Fig. 5. lais elongata, composite SEM photograph 1951:138; Coineau 1977:436). Menzies &
ofadult male holding female manca.
Barnard, 1951, expressed the opinion that
true species oflais are always found in as-
around potential mates (Veuille 1980, Hes- sociation with sphaeromatid isopods, and
sler & Stromberg 1989, Franke 1993). As that the free-living species may well belong
in the present species, in Jaera the fourth to a different genus. There are at least three
pereopodofthemale isshortenedandbears records of free-living lais: I. pubescens of
specialized spines for clasping the female Barnard, 1965 fromGough Island, /. aquilei
.
VOLUME 107, NUMBER 2 281
Coineau, 1977 from St. Helena Island, and rica, for making the material of/. elongata
/. elongataSivertsen&Holthuis, 1980from available for study. The expedition to In-
Inaccessible Island in the Tristan archipel- accessible Island that yielded this material
ago. All three ofthese South Atlantic island was organized by the Percy Fitzpatrick In-
records are from freshwater habitats at stitute for African Ornithology at the Uni-
varying(butnevergreat) distancesfrom the versityofCapeTown. IthankMrs. Michelle
sea. Possibly we are dealingwith a complex van der Merwe of the South African Mu-
ofisland species ofa genus other than lais. seum, Cape Town, and Dr. Tor Stromgren
MaterialfromTristandaCunha, takenfrom of the Trondheim University Museum,
the fully marine sphaeromatid Isocladus Norway, for the loan of comparative ma-
tristanensisandidentifiedas/.pubescensby terial. Dr. George Wilson ofthe Australian
Barnard (South African Museum, A2286, Museum generously shared his thoughts on
A2452) appears to be closely similar to /. asellote evolution, in correspondence over
pubescens, widespreadthroughthesouthern this paper.
ocean. Examination ofcommensal material
from Auckland, New Zealand, taken from
Literature Cited
Exosphaeroma gigas, from southern Peru
taken from Sphaeroma peruvianwn, along Barnard, K. H. 1965. Isopoda and Amphipod col-
with the abovementioned Tristan material lectedbytheGough IslandScientificSurvey.—
reveals considerable variation in body and AnnalsoftheSouthAfricanMuseum48(9):195-
appendage proportions, suggesting a com- 210.
Bovallius,C. 1886. NotesontheFamilyAsellidae.—
plex ofspecies rather than a single circum- Bihangtill Kongliga Svenska Vetenskaps-Aka-
polarspecies, masqueradingunderthename demiens Handlingar, Stockholm 11(15):3-54.
/. pubescens. Coineau,N. 1977. LafauneterrestredeI'iledeSainte-
lais elongata is very similar to /. aquilei Helene. 4. Isopodes aquatiques.—Annales du
from St. Helena Island, even in the total Musee Royal de I'Afrique Centrale, Tervuren,
Belgique,ser.8°,SciencesZoologiques,220:427-
length of adult males and females. Coi-
443.
neau's thorough description and figures Dunham,P.J.,&A.M.Hurshman. 1991. Precopula-
(1977), however, do reveal some subtle dif- torymateguardinginaquaticCrustacea: Gam-
ferences: the basal article ofthe antennule mamslawrencianusasamodelsystem. Pp. 50-
is relatively broader in /. aquilei; the third 66, in R. T. Bauer &J. W. Martin, eds.. Crus-
tacean Sexual Biology. Columbia University
article ofthe mandibular palp has 3 distal Press, New York.
spines (5 in /. elongata); the maxillipedal Franke, H.-D. 1993. Matingsystemofthecommen-
enditehas 8 distalbroadspines(6 in/. elon- salmarineisopodJaerahopeana(Crustacea).—
gata); maxillipedal palp article 4 is rela- Marine Biology 115:65-73.
Gruner, H.-E. 1965. Krebstiere oder Crustacea V.
tively longer in /. elongata; there are fewer Isopoda.—Die Tierwelt Deutschlands und der
distal setae on pleopod 1 <5 in /. elongata; angrenzenden Meeresteile, nach ihre Merkma-
the endopod of pleopod 3 is relatively len und nach ihrer Lebensweise 51:1-149.
smaller compared with the exopod in /. Hessler, R. R., &J.-O. Stromberg. 1989. Behaviour
elongata; the exopod ofpleopod 4 and es- ofJaniroidean isopods (Asellota), with special
reference to deep-sea genera.—Sarsia 74:145-
pecially the single distal seta are relatively
159.
larger compared with the endopod in /. Lewis,J.J.,&T.E.Bowman. 1981. Thesubterranean
elongata; the uropodal exopod is relatively asellids(Caecidotea)ofIllinois(Crustacea:Isop-
more elongate compared to the endopod in oda:Asellidae).—SmithsonianContributionsto
/. aquilei. Zoology 335:1-66.
Menzies, R. J.,&J. L. Barnard. 1951. Theisopodan
Acknowledgments genuslais(Crustacea).—BulletinoftheSouthern
I am grateful to Mrs. Helen James ofthe NierstraCsazl,ifoHr.niFa.Ac1a9d4e1.myDoifeScIisenocpeosde5n0(3d)e:r13S6i-b1o5ga1-
Albany Museum, Grahamstown. South Af- Expedition. IV. Isopoda Genuina III. Gnathi-
282 PROCEEDINGSOFTHE BIOLOGICALSOCIETYOFWASHINGTON
idea, Anthuridea, Valvifera, Asellota, Phreato- ganesreproducteursfemelles.—CahiersdeBiol-
coidea.—Siboga-Expeditie monographic 32d: ogic Marine 19:385-395.
235-306. -. 1980. Sexualbehaviourandevolutionofsex-
Ridley, M. 1983. The explanation oforganic diver- ualdimorphism in body size inJaera(Isopoda
sity: the comparative method and adaptations Asellota).—Biological Journal of the Linnean
formating. Clarendon Press, Oxford, 272 pp. Society 13:89-100.
Sivertsen, E., & L. B. Holthuis. 1980. The marine
isopod Crustacea ofthe Tristan da Cunha Ar- DepartmentofInvertebrateZoology,Na-
chipelago.—Gunneria 35:1-128. tional Museum ofNatural History, Smith-
Swedmark, B. 1964. Theinterstitialfaunaofmarine
sand.—Biological Reviews 39:1-42. sonianInstitution,Washington, D.C. 20560,
Veuille, M. 1978. Biologic de la reproduction chez U.S.A.
Jaera (Isopode Asellote). 2. Evolution des or-