New species and records of Plakolana Bruce (Crustacea: Isopoda: Cirolanidae) from Australia

13 Pages·1999·6.5 MB·English

by  S J Keable

NEW SPECIES AND RECORDS OF PLAKOLANA BRUCE (CRUSTACEA: ISOPODA:
CIROLAN1DAE) FROM AUSTRALIA
SJ. KEABLE
Keable, S.J. 19990630:NewspeciesandrecordsofPlakolana Bruce(Crustacea: Isopoda:
(irolanidae)fromAustralia.MemoirsojtheQueenslandMuseum43(2):763-775. Brisbane.
ISSN 0079-8835.
TwonewspeciesofPlakolanaaredescribed from thecontinental shelfofthe northernand
central eastcoastofAustralia. Arevised keytothespeciesofthegenusand new recordsof
G
the two otherAustralian species arealso provided. Isopoda, Cirolanidae, Plakolana,
Australia.
SJ. Keable, Crustacea Section, Australian Museum. 6 College Street, Sydney 2000,
Australia; 27February 1999.
Many species ofcirolanid isopods in various specimen was collected from offCoffs Harbour,
genera are known to feed as scavengers on the NSW, on the central east coast ofAustralia in a
flesh ofdead or dying vertebrates (for examples sampleofmuddysandtaken fromadepthof75m.
see Stepien & Brusca, 1985; Bruce, 1986; Wong This study documents 2 new species of
& Moore, 1996). These isopods may play an Plakolana, and new distribution records of P.
important role in ecosystems through the binyana and P. mandorah, apparent in
decomposition of carcasses and the associated collections made using baited traps in areas of
redistribution of available energy and nutrients NW, NE and SE Australia. To aid in the
(Keable, 1995). They may also be significant identificationofthesespeciesarevisedkeyforall
pests of&commercial fisheries (Sekiguchi, 1982; species ofPlakolana is also presented.
Stepien Brusca, 1985; Berrow, 1994; Mi/zan,
1995). METHODS
Cirolanid isopods in the genus Plakolana The specimens reported here were obtained
Bruce, 1993 are well documented scavengers
mostly using the trap design outlined by Keable
whicharereadilycollectedinbaitedtraps(Bruce, (1995), additional specimens of Plakolana
1993; Keable, 1997) but which have rarely been
binyana were also located in existing Australian
collected by other means. Prior to this study 4 Museum collections.
described species were placed in the genus.
Plakolana accola Bruce, 1993 and P. nagada The terminology and procedures used in
Bruce, 1993 are known only from trap samples description ofthe new species followthose sum-
collected on the outer reefslope and within the marised by Keable (1997). Particular attention
barrier reefofMadang Lagoon, northern Papua should be paid to the orientation used for the
New Guinea (Bruce, 1993). These species are anterior and posterior margins ofthe pereopods
found in depths of 300-450m and 16-22m, which follows that indicated by Bruce (1993).
respectively(Bruce, 1993).Plakolanamandorah Abbreviations: AM, Australian Museum,
Keable, 1997 has been recorded from trap Sydney; BMNH, The Natural History Museum,
samplescollected in DarwinHarbourand Torres London: QM, Queensland Museum, Brisbane;
Strait, northern Australia, in depths of 8-20m WAM, Western Museum, Perth; USNM,
(Keable, 1997). Plakolana binyana (Bruce, National Museum oory, Smithsonian Institution,
1991) has been documented previously only Washington, DC; n, number of specimens; x,
from a single specimen collected in a plankton times;CE,cephalon;Al,antennule;A2,antenna;
tow at a depth of221m over a bottom depth of CL, clypeal region; FL, frontal lamina; MD,
355-384m,offCrescentHead,NSW,onthecent- mandible; MP. maxilliped; MX1, maxillule;
ral east coast ofAustralia. Additionally, Bruce MX2, maxilla; PE, penes; PN, pleon; PI-7,
(1986) reported a single immature specimen of pereopods 1-7; U, uropod; PL1-5, pleopods 1-5;
Plakolana (as Cirolana sp.) that does not PT, pleotelson; Qld, Queensland; NSW, New
correspond to the morphology ofthe described South Wales; NT, Northern Territory; Tas.,
species in the genus (Bruce, 1993). This Tasmania: WA, Western Australia.
)
764 MEMOIRS OF THE QUEENSLAND MUSEUM
SYSTEMATICA 2.Pereopod7,merusanteriormarginwithoutrobustsetae . 3
Pereopod7,merusanteriormarginwithrobustsetae. . 4
Class Crustacea 3. Antenna, extending to pcreonite 4 or 5 when flattened
Order Isopoda alongbody;uropodendopod,robustsetaonmedial side
of apex approximately equal in length to robust seta
Family Cirolanidae proximaltoitonmedialmargin P.accola
Antenna, extending to pereonile 2 or 3 when flattened
Plakolana Bruce, 1993 alongbody;uropodendopod,robustsetaonmedial side
of apex approximately twice as long as robust seta
riakohmaBruce, 1993: 9; Brusca et al, 1995: 96. proximaltoitonmedialmargin P.nagada
TYPE SPECIES. Plakolana accola Bruce, 1993 by 4. Maxilliped palp, lateral marginwithplumosesetae
P. mandorah
original designation.
Maxillipedpalp,lateralmarginwithoutplumosesetae . 5
REMARKS. A comprehensive diagnosis of 5. Uropod exopod, some robust setae on medial margin
PlakolanahasbeenprovidedbyBruce(1993). In longerthan the exopod width lateral to their insertion:
tolhfoinstghdesiaibgmanpsolisesissoefittapeise.rsIetnaotptehodedtsghea4nt-et7rhieicsarnpetremoraviriokdrsemdaBrrwguiictneh Utaurhnroagopnlpoeotddohfeeexaenopdxppooorppodoox,ddi,amiwallitardteoetlbrhyuals4lta5at°sneedratatalmeaetpdooeinxatmhlee.imdria. ariPlgn.simeanracstruigftoiano;snrpmus.ihrnonogrpotoawednr
(1993) comments 'The flattened basis pereo- endopodlateralandmedialmarginsforminganangleof
paods [sic] 4-7 with a row ofsimple setae along approximately 60°atapex P.obtu.susp.now
theanteriormargin, istheonly characterthat can
be recognised as a potential unique apomorphy. Plakolana acuta sp. nov.
Nonetheless the combination of characters (Figs 1-3)
delimitsthegenus\ Itshouldbemadeclearthatat
least on pereopod 7 (and pereopods 4-7 in mat- ETYMOLOGY. Derived from the latin word acutiis.
erial examined here) the setae forming a row on meaning sharpened, pointed or acute, refering to the
theanterior(orientationdepictedbyBruce(1993 appearance ofthe uropodendopod, as comparedto some
fig. 2F,H) margin ofthe basis are plumose, not otherspeciesofPlakolana.
simple (see also descriptions of P. binyana, P. MATERIAL. HOLOTYPE: AMP546S1, M, 10mm, off
accola and P. mandorah in Bruce (1991, 1993) Flynn Reef, Qld, Australia, 16°41.32'S 146 18.26'E,
and Keable (1997)). A similar arrangement of baited trap, unknown substrate, 100m, J. Lowry, P.
plumose setae on the basis is known in species Freewater& W. Vader, 7-8June 1993, SEAS QLD-937.
placedinanumberofothercirolanidgenerasuch PARATYPES: QMW24682, M, F; AMP47679, 5 Fs;
as Aatokma Bruce, 1993, Bathynomus Milne BMNH1999.462, F; USNM288442, F; all samedataas
Edwards, 1879, Dolicholana Bruce, 1986, Nat- holotype. OTHER MATERIAL: AMP54682, 40
atolana Bruce, 1981 (see Bruce, 1986; Keable, specimens, east of Flynn Reef, Qld, 16°41.32'S
h1a9s96,als1o997b,ee1n99d8e)s.crTihbeedbaassisfolfatttheenepderienopboodtsh QL14Lo6wD°r-1y81.025&65'.E,Iv.baDietemdpstreayp,,un1k9-n2o0wnMasuyb,stra1t9e9,4,10S0mE,ASJ.
Dolicholana and Natatolana (Bruce, 1986).
Therefore,onphylogeneticgroundsthepereopod DIAGNOSIS. Dorsalinterocularfurrowdistinct,
characterdescribed by Bruce (1993) is relatively not extending across the cephalon. Medial
weak in definingPlakolana, probably represent- interocular furrow distinct, extending across the
ing a plesiomorphic state or homoplasy, rather cephalon. Pleotelson robust setae present, 4-6
than a 'unique apomorphy1. However, as Bruce altogether. Antenna ofmedium length, 0.34* as
( 1993)notesthesizeandshapeofthepleonite3 is long as body, when extended against the body
conspicuous, with a distinct posteroventral in- reaching to posterior ofpereonite 3. Maxilliped
cision and lateral rows ofsetae, and is unique to palp lateral margin plumose setae absent.
the species placed in Plakolana. Therefore, this Pereopod 7 merus anterior margin with robust
character can be recognised as an alternative setae. Uropod endopod robust setae long, 22%
putative synapomorphy which may be used to length oflateral margin; medial margin convex;
unambiguously define the genus. lateral and medial margins forming an angle of
approximately45° atapex;robustsetaon medial
KEY TO SPECIES OF PLAKOLANA sideofapexsubequaltorobustsetaproximaltoit
I. Udriostpaolldy endopod, medial margin stronglRyhs'imnyuuantue oEnxopmoeddimaeldimaalrgmianr;ginlatweirtahl smoamregirnobussttraisgehtta.e
Uropod endopod, medial margin straight or convex longer than the exopod width lateral to their
distally 2 insertion.
NEW SPECIES OF PLAKOLANA
765
FIG, 1. Plakolanaacuta sp. nov. Holotype. Scalebars = 0.2mm.
766 MEMOIRS OF THE QUEENSLAND MUSEUM
FIG. 2. Plakolanaacuta sp. nov. i[olotype. Scalcbars= 0.5mm.
DESCRIPTION (Holotype), Cephdlon. Ornamentation other than furrows or
Overall bodyfarm. Omm long: narrow, length ridges absent, surface smooth; rostrum bent
I
approximately 3.1> greatestwidth.Colourcream ventrally,anteriormarginrecessedindorsal view
in alcohol. Chromatophores absent. Cuticuiar (weakly recessed), rostrum not extending to
surfaces scale-like. frontal lamina, not dividing antennules; anterior
NEW SPECIES OF PLAKOLANA 767
margin not overriding antennules; cephalic Anfennule. Short, just reaching pereonite 1.
ridges absent, submarginal cephalic furrow well Peduncularbases touching(just); article 1 length
developed, runs entire length ofanterior margin subequal towidth, greaterthan article 2; article2
to eyes. Eyes present, well developed; visible in width subequal to length, anterodistal angle with
\entraJ view; moderate in size, round, length less 2 pappose setae, posterodistal angle with 1
than 2x height; colourcream inalcohol; partially slender seta; article 3 shorter than combined
overlapped by pereonite I; ommatidia arranged lengths of articles 1-2, longer than article I,
in rows, 8 ommatidia in horizontal diameter, 7 length greater than width. Flagellum longerthan
ommatidia in vertical diameter. Dorsal inter- peduncle; not formed into callynophore; articles
ocular furrow distinct, not extending across the notcompressed(lengthsofmostgreaterthanhalf
cephalon. Medial interocular furrow distinct, width); 13-arliculate; article short, length not
1
extending across the cephalon. Frontal lamina much greater than width; aesthetascs present,
linear, length approximately 3X basal width; iridescent (weakly).
Forming an angle of-45° with ventral surface of Antenna. Medium length, 0.34* as longas body,
cephalon; ventral surface flat, not produced; when extended against the body reaching to
lateral margins medially constricted; lateral posterior of pereonite 3. Peduncular article 2
margins concave; ventral surface not sculpted; shorterthanarticle3;article4slightlylongerthan
apexanteriorlyprojecting,visibleindorsalview, article 3, anterodistal angle with 2 slender setae,
expanded, in 1 plane (not 'stepped'), anterior posterolateral margin with penicillate seta.
margin rounded. Clypeus triangular: width posterodistal angle with4 slen1dersetae; article 5
greater than length; not sculpted. Labrum Hat; longer than article 4 and all other articles,
narrower than clypeus.
anterodistalanglewith4slenderand penicillate
1
Pereonites. 1 longest, 2 shortest, 3-7 subequal; setae, posterodistal angle with 1 slender and 1
without transverse carina; tubercles absent. penicillate setae. Flagellum 20-articulate; setal
Pleonites. 5 visible but pleonite 1 almost brush absent.
completely concealed along dorsal margin by Mandible. Molarwell developed; medial surface
pereonite 7; tubercles absent. Pleonite 1 post- covered with short Fine slender setae, cluster of
erolateral margins producedventrally. Pleonite 2 long slender setae proximally present, long
dorsal posterolateral margin clearly projecting slender setae submarginal to anterior margin
posteriortoventral posterolateral margin;ventral absent; robust setae present on anterior margin,
posterolateral margin acute, formed into short closeset. Setal rowwelldeveloped, with 7robust
process. Pleonite 3 posterolateral margins setae; intermediate slender setae absent; medial
extending posterior to posterodorsal margin of surface without setae. Incisor broad (wider than
pleonite 5, acute with ventral incision and two narrowest width of mandible), tridentate,
rows ofsetae. Pleonite 4 posterolateral margins posterior tooth larger than others. Palp article
1
less produced than those of pleonite 3; ventral longerthan article 3; article 2 ofmedium length,
margin enclosed by pleonite 3; posterodorsal approximately 2* the length of article 3, with
margin sinuate, convex proximal to meeting numerous slender and serrate setae.
ventral margin at apex, apex broadly rounded
Maxillule. Medial lobe with 3 large robust
dorsally, but meeting convex ventral margin at a
pappose setae, subequal in length; lateral margin
point, extending posterior to posterodorsal
with protuberance well developed. Lateral lobe
margin ofpleonite 5.
with 13 robust setae on distal surface.
Pleotelson.Length x basalwidth;dorsalsurface
with tubercles arid 1carinae absent; conspicuous Maxilla. Lateral lobe subequal and distinct from
Fine setae absent from dorsal surface; antero- middlelobe;slender,with 5 slendersetae. Medial
dorsal depression absent; anterodorsal uropodal lobe with 5 slenderand 1 1 plumose setae, with 2
sutures on anterolateral margins present (indist- medial plumose setae longest and bent. Middle
inct); anterolateral margins almost straight and lobe with 1 slender setae.
angling posteriorly toward the midline; postero- Maxilliped. Palp moderately setose; medial
lateral margins convex; apex not produced, margin slender setae along most ofthe length of
lateral margins meeting smoothly to a point; articles 2-5; lateral margin slender setae along
robust setae present, 6 altogether, 3 on each most ofthe length ofarticles 2-5, plumose setae
posterolateral margin; plumose setae present, absent; article 1 without transverse setal row;
restricted to posterolateral margins, moderately article3 lengthsubequal tobreadth,distalmargin
abundant, numerous proximal to robust setae. width greater than proximal margin ofarticle 4;
768 MEMOIRS OF THE QUEENSLAND MUSEUM
FIG. 3.Plakolanaacutasp. nov. Holotype. Scalebars=0.5mm.
article 4 length less than breadth, distal margin distinctlobe, extendingtodistomedial margin of
width greater than proximal margin ofarticle 5; palparticle2;rightenditewith2couplinghooks,
article5rounded,lengthlessthanbreadth,medial leftenditewith2 couplinghooks, and4plumose
margin serrate setae present. Endite forming a setae.
NEW SPECIES OF PLAKOLANA 769
Coxalplates. Shallow, not as high as long; fur- setae present; posterior margin with 4 robust
rows strongly developed, on all coxae. setae, non-robust setae absent; posterodistal
angle with 2 robust setae, slender setae absent.
Pereopods. Pereopods 1-7 dactylus secondary
Penes. Absent, vasa deferentia opening flush to
unguis slenderand lyingagainst primary unguis.
surface ofsternite 7.
Pereopods 1-3 merus posterior margin robust
setae strongly molariform on pereopod only. Pleopods. Exopod suture incomplete onpleopods
Pereopod 1 posteriormarginsetosefringea1bsent. 3-5; endopodplumose setae presentacross distal
Ischium anterodistal angle without robust setae; marginsofpleopods 1-4andabsentonpleopod5.
posterior margin without robust setae. Merus Pleopods 1-2 exopod broader than endopod;
exopod and endopod elongate (length more than
anterodistal anglewithoutrobust setae; posterior
margin with 9 robust setae. Carpus posterior 2x width). Pleopod 1 exopod medial margin
3marrogbiunstwistehta1eroobnusptalsmet,a.wPitrhopo1druosbursotbussett;awiotp-h eobnldioqpuoe,d plreonxgitmholsautbeerqaulalrotbousetxospeotda,ablasteenrta;l
margin concave. Pleopod 2 appendix masculina
posingdactylus. Dactylus long, 0.5-1* propodus
length. Pereopod 2 ischium anterodistal angle arising sub-basally; extending beyond tip of
endopod, 1.05* lengthofendopod from insertion
sweittahe.1 rMoebruustsseatnat;erpoodsitsetrailoramnagrlgeinwiwtihth22rroobbuusstt point; margins straight, approximately parallel
setae; posterior margin with 9 robust setae. along entire length; slender; apex not at angle to
margins, acute. Pleopods 3-4 endopod distinctly
rCoabrupsuts sweittaho3n rpoablums,t setraoeb.usPtrospeotdausoppwoitshing1 shorter than exopod. Pleopod 5 peduncle lateral
1 margin with broad, lamellar lobe; exopod distal
dactylus. Pereopod 3 ischium anterodistal angle margin rounded; endopod distal margin
with 1 robust seta; posteriormarginwith4robust narrowed to obscure point, proximomedial lobe
seiae. Merus anterodistal angle with 2 robust
strongly produced.
setae (and 1 set further back); posterior margin Uropods. Extending beyond pleotelson.
with 8 robust setae (and 1 set further back).
rCoabrupsuts sweittaho3n rpoablums,t setraoeb.usPtrospeotdausoppwoitshing1 Paenddun3cplleuvmeonsterolsaettaeer;allaatnegrlale mwiatrhgi1nrroobbuussttsseettaa,
dactylus. Pereopods 4-71 basis anterior margin present; distolateral angle rounded. Endopod
plumose setae present. Pereopod 7 basis of medialmarginconvex,with6robustsetae,robust
medium breadth, width 0.49* length; anterior setaelong,22% lengthoflateralmargin,plumose
margin setae plumose, present along entire setae present, along entire length, long; lateral
and medial margins forming an angle of
length, closely and regularly spaced along entire
length; medial carina setae slender, posterior approximately 45° at apex; apex entire, without
margin setae absent; posterodistal angle setae notch, with 2 robust setae, robust seta on medial
slender. Ischium anterior margin without robust side subequal to robust seta proximal to it on
medial margin, setal cluster present, formed by
setae, non-robust setae slender; anterodistal
plumose setae; lateral margin straight, with 2
angle with 12 robust setae (including 3 uniser-
robust setae,plumosesetaepresent, ondistalhalf
rate),slendersetaepresent;posteriormarginwith
(sparse), short. Exopod slightly shorter than
2 robust setae, slender setae present; postero-
endopod. 0.8* the lengthofthe endopod; medial
distal anglewith4 robust setae, non-robust setae
margin convex, with 3 robust setae, some robust
slender. Merus anterior margin with 6 robust
setae longerthantheexopodwidth lateraltotheir
setae, slender setae present; anterodistal angle
insertion, plumose setaepresent, not alongentire
with 9 robust setae, slender setae present;
length (on distal half), long; lateral and medial
posterior margin with 7 robust setae, slender margins forming an angle ofapproximately 35°
setae present; posterodistal angle with 8 robust
atapex;apex entirewithoutnotchandacute, with
setae, non-robust setae slender. Carpus anterior
2 robust setae, setal cluster present, formed by
margin without robust setae, non-robust setae
plumose setae; lateral margin convex, robust and
absent; anterodistal angle with 7 robust setae,
plumose setae continuous along margin, with 5
non-robust setae absent; posteriormargin with 3 robust setae, robust setae small, plumose setae
robust setae, non-robust setae absent; postero-
present, along entire length, long.
distal angle with 5 robust setae, non-robust setae
slender (1 present). Propodus anterior margin SEXUAL DIMORPHISM. Females differ from
without robust setae, non-robust setae absent; males only in the primary sexual characters and
anterodistal angle with 1 robust seta, slender do not have the pleopod 2 appendix masculina.
770 MEMOIRS OF THE QUEENSLAND MUSEUM
VARIATION. Pleotelson and uropod robust Overall bodyform. 9.5mm long; length approx-
setal counts from margins (N= 9, all paratypes): imately 2.79x greatest width.
Pleotelson 2:2 (11%), 2:3 (33%), 3:3 (56%). Cephalon. Eye colour pale orange in alcohol; 9
Endopod (medial) 5 (44%), 6 (56%); (lateral) 2 ommatidia in horizontal diameter, 8 ommatidia
(100%). Exopod (medial) 4 (100%); (lateral) 4 in vertical diameter. Frontal lamina lateral
(11%), 5 (89%). margins straight, parallel.
SIZE RANGE. Adults 10-15mm. Pereonites* 1 and 5-6 subequal in length and
longest, 4 and 7 subequal and longer than 2-3
REMARKS. See discussion section. which are subequal.
Pleotelson. Length 1.05x basal width; antero-
DISTRIBUTION. Australia, offCairns, Qld. In lateral margins convex; robust setae present, 6
depths of100m.
altogether.
Antennule. Pedunculararticle I length subequal
Plakolana obtusa sp. nov. to article 2; article2 longerthanwide. Flagellum
(Eigs 4-6) 12-articulate; article 1 elongate, length much
greater than width.
ETYMOLOGY. Derived from the latin word obtusits, Antenna. 0.35x as long as body. Peduncular
emnedaonpiondgibnlutnhti,ssapnedcireesfewrhsetnotchoemappapreeadratoncmeosotfothfethuerootphoedr article4muchlongerthanarticle3,posterolateral
speciesofPlakolana. marginwith 1 penicillateseta,posterodistalangle
with 4 slender setae, distal margin with
I
MATERIAL. HOLOTYPE: AM54683, M, 9.5mm, east penicillateand 1 slendersetae, anterodistal angle
of Fitzroy Reef, Great Barrier Reef, Qld, Australia, with 3 slender setae; article 5 anterodistal angle
23°32.53'S 152°16.441E, baited trap, unknown substrate, with 2 penicillate and 2 slender setae, postero-
100m, J. Lowry & K. Dempsey, 3-4 June 1994, SEAS distal anglewith2penicillateand2slendersetae.
OLD-1096. PARATYPES: QMW24683, M, F; AMP- Flagellum 25-articulate.
54684,8M's,23F's;BMNH1999.463-464,M,F;USNM-
288443, M, F, all same data as holotype. OTHER Mandible. Setal row with 9 robust setae. Palp
MATERIAL: AMP54685, 9 specimens, east of Flvnn article 1 subequal to article 3.
osR1uef9be9sCf4to,,rfaQfStlseEd.,AHa1S1r06b0°Qo4mLu1,rD3,J-.TN1SLS05oW51w,;4r6vA°3M01&P°81.4258K6..4'9E34,D'9eSb,maip13ts59ee3dvs°tp,2reaLcp19,i9JmuE-e,n2n0ksb,naMoiNatweEynd riMnoablxueisntttgutplhaetp.opMloeasdregieaselltaatleeo,rbaellawsriegtteahem;3eldlaiatraeglrealsaemntadars1gusibmneaqwluilatelhr
trap, unknownsubstrate, 100m,J. Lowry & K. Dempsey, protuberance absent.
9-10 Sept. 1994, SEASNSW-1006. Maxilla. Medial lobe with 6 slender and 8 plum-
ose setae. Middle lobe with slender setae.
DIAGNOSIS. Dorsal interocular furrow distinct. 1 1
Maxilliped.enditenotreachingdistomedial margin
not extending across the cephalon. Medial
ofpalparticle2;leftenditewith7plumosesetae.
interocular furrow distinct, extending across the
cephalon. Pleotelson robust setae present on Pereopods. Pereopod 1 merus posterior margin
margins, 6 altogether. Antenna 0.35x as long as with8robustsetae. Carpusposteriormarginwith
body, when extended against the body reaching 2robustsetae. Pereopod2ischiumposteriormar-
to posterior of pereonite 3. Maxilliped palp gin with 3 robust setae. Merus posterior margin
lateral margin plumose setae absent. Pereopod 7 with7robustsetae. Pereopod3 ischiumposterior
merus anteriormarginwithrobust setae. Uropod marginwith 3 robustsetae. Merusposteriormar-
endopod robust setae short, 11% length oflateral gin with 9 robust setae. Pereopod 7 basis broad,
margin; medial margin convex; lateral and width 0.56* length. Ischium anterodistal angle
medial margins forming an angle of with 9 robust setae; posterior margin without
approximately60° at apex; robust seta on medial robust setae; posterodistal angle with 2 robust
sideofapexshorterthanrobustsetaproximaltoit setae. Merus anterodistal angle with 8 robust
on medial margin; lateralmarginslightlyconvex. setae; posterior margin with 3 robust setae;
Exopod medial margin robust setae shorter than non-robust setae absent. Carpus anterior margin
the exopod width lateral to their insertion. non-robustsetaeslender;posteriormarginwith4
robust setae, non-robust setae slender; post-
DESCRIPTION (Holotype). Due tothe similarity erodistal angle with 7 robust setae. Propodus
ofthisspeciestoP. acutaonlyvariationsbetween anterior margin with non-robust setae slender.
the 2 species are included here. Pleopod 2 appendix masculina arising basally;
NEW SPECIES OF PLAKOLANA
111
FIG. 4. Plakolanaobtusa sp. nov. Holotype. Scalebars=0.5mm.
772 MEMOIRS OF THE QUEENSLAND MUSEUM
FIG. 5. Plakokmaahtu.su sp. nov. Iloloiype. Scalebars - 6.5mm.
extending subequal vvilh tip of endopod, 1* 0.79* the length of the endopod; with 4 robust
length ofendopod from insertion point. setae, robust setae shorter than the exopod vsidth
UropodSi peduncle ventrolateral angle with 2 lateral to their insertion; lateral and medial
robust setae. Endopod robust setae short. 11% margins forming an angle ofapproximately 50
length of lateral margin; lateral and medial at apex; lateral margin robust setae large.
margins forming an angle ofapproximately 60°
at apex; apex seta on medial side shorter than SEXUAL DIMORPHISM. Females differ from
robust seta proximal to it on medial margin; males only in the primary sexual characters and
lateral margin slightly convex. Exopod short. do not have the pleopod 2 appendix maseulina.