Plakarthrium australiense, a third species of Plakarthriidae (Crustacea:Isopoda)

10 Pages·2001·8.8 MB·English

by  G C B Poore

Memoirs of Museum Victoria 58(2): 373-382 (2001)
PLAKARTHRIUMAUSTRALIENSE, A THIRD SPECIES OF
PLAKARTHRIIDAE (CRUSTACEA: ISOPODA)
Gary C. B. Poore' and Angelika Brandt^
'Museum Victoria, GPO Box 666E, Melbourne, Vic. 3001, Australia
(gpoore(^museum.vic.gov.au)
^Zoological Institute and Museum, Martin-Lulher-King Platz 3, 20146 Hamburg, Germany
([email protected])
Abstract
Poore. G.C.B. and Brandt, A., 2001. P/akarthnum australiense^ a third species of Plak-
arthriidae (Crustacea: Isopoda). Memoirs of Museum Victoria 58(2): 373-382.
The Plakarlhriidae share with four genera of Sphacromatidae a flat habitus and a marginal
row of setae on antenna 1, coxae and uropods, modified to maintain contact with the substrate.
They do not possess areas of scales on pleopod 5, a probable sphacromatid synapomorphy. The
possibility exists that Plakarlhriidae arc a highly derived offshoot of a clade that also gave
rise to the flattened “cassidiniine” sphaeromatids. Plakarthriiim australiense sp. nov. is
described from the southern Australian marine shelf and compared with the only two other
species of the genus and family. The new species differs from P. typicum from New Zealand
and P. punctatissimum from subantarctic islands of the South Atlantic and Antarctic Peninsula
in having pleonite 1 fully indicated dorsally, only pleonite 2 indicated laterally and pleotelson
tapering to 80% of its anterior width posteriorly.
Introduction Hansen, 1905 (Iverson, 1982; Harrison and Ellis,
1991; Bruce, 1994). The monophyly of this and
The Plakarthriidae Hansen, 1905 are previously
other sphacromatid subfamilies remains doubtful
known from only two species, Plakarthrium
(N.L. Bruce, pers. comm.). The affinities of
typicum Chilton, 1883 and P. punctatissimum
Plakarthriidae were reviewed with a redescription
(Pfeffer, 1887). The family is confined to shallow
of P. typicum by Wilson et al. (1976) who con¬
marine shores in cool-tcmpcratc and cold
cluded “that the Plakarthriidae are unique with no
environments of the Southern Hemisphere.
close affinities with any other family.'’ Wagele
Plakarthrium typicum was described from New
(1989) placed the family within his suborder
Zealand and has been reported as far south as The
Sphaeromatidca, sister taxon to a clade including
Snares islands (48‘’S) (Hurley, 1961; Poore,
Serolidae, Balhynataliidae and Sphacromatidae.
1981) but not from Macquarie Island (GCBP col¬
Brusca and Wilson (1991) also assessed their
lections in Museum Victoria). It has also been
position, placing the family as sister taxon to
reported from southern Chile (Jaramillo. 1977)
Serolidae, and possibly Keuphyliidae and Bathy-
but this record is more likely to be the second
nataliidae. This paper, describing a new Aus¬
species, P. punctatissimum, if not an undescribed
tralian species, also addresses some newly recog¬
Chilean endemic. Plakarthrium punctatissimum
nised characters which may have a bearing on
is reported from subantarctic islands of the
plakarthriid relationships to Sphacromatidae in
South Atlantic and Antarctic Peninsula, namely
particular.
South Georgia (type locality). South Orkneys,
Pfeffer’s (1887) generic name Chelonidium is a
Petcmiann I., Booth-Wandel I. and Anvers I.
junior synonym of Plakarthrium Chilton, 1883, a
(Richardson, 1906, 1913; Tattersall, 1921; Pcsta,
fact realised by Richardson (1904: 6; 1906: 6)
1928; Wilson ct al., 1976). A third species from
who synonymised the two. Plakarthriidae
southern Australia is here reported.
(erected by Hansen (1905) as Plakarthriinac, a
The taxonomic affinities of Plakarthrium
subfamily of Sphacromatidae Latreille, 1825) is
Chilton, 1883 to other '‘flabellifcraiT* isopods has
the family name to have been used by most
remained enigmatic. Hansen (1916) erected the
authors and, under ICZN (1999) Article 40,
Plakarthriinac as a subfamily of Sphacromatidae
replaces Pfeffer’s (1887) family name, Cheloni-
and Menzies (1962) believed them to belong in
diidac. Both dales should be cited for the family.
the “platybranchiata” group of this family, a
Wilson et al. (1976) who incorrectly attributed
group more or less equivalent to Cassidininae
373
374 G. C. B. POORE AND A. BRANDT
the family name to Richardson (1904) reviewed Kussakin and Malyutina (1993). Bruce (1994: fig.
later accounts of plakarthriids by Richardson 50B) figured the membrana cingula for
(1906, 1913), Tattersall (1921), Pesta (1928), Platysphaera membranata Holdich and Harrison,
Nierstrasz (1931), Menzies (1962), Glynn (1970) 1981. Kwon (1990) figured a similar structure in
and Kussakin (1973). Leptosphaeroma gottschei Hilgendorf and we
Material is lodged in Museum Victoria, have observed the same in Museum Victoria
Melbourne (NMV) and the Zoological Institute material of Amphoroidella elliptica Baker. While
and Museum, Hamburg (ZMH). there is a strong similarity between the membrana
cingula in the four sphaeromatid genera, the
Plakarthriidac Hansen, 1905 (1887) equivalent structure in Plakarthriidac comprises
broad separate fringed overlapping setae and is
Chelonidiidac Pfeffer, 1887: 85.—Pesta. 1928.
complemented by a free skirt-like flange of
Plakarthriinae Hansen, 1905: 100.—Nierstrasz,
1931: 192. webbed setae underneath and parallel to the
Plakarthriidac.—Richardson, 1906: 6.—Richardson. margin of the body.
1913: 7.—Wilson el al., 1976: 334 (see above for other Within Flabcilifcra the pIcon fully fused to the
references). plcotclson is seen in at least one species of
Sphaeromatidae, Maricocens hrucei Poore, 1994.
Diagnosis. First coxa free and articulating.
This and similar genera, Juletta Bruce, 1993 and
Margin of the body being defined by peduncular
Margueritta Bruce, 1993 (both with free pleonitc
articles 1 and 2 of antenna 1, peduncular articles
1), are placed in the Dynamcninae and any
3 and 4 of antenna 2, all coxae, uropodal
similarity to Plakarthrium is coincidental.
rami. Plcotclson completely fused and without
The possibility exists that Plakarthriidac arc a
articulation.
highly derived early offshoot of a clade which
Composition. There is only one genus. also gave rise to fiattened “cassidiniinc'’ sphaero¬
matids. In this scenario some reversals may have
Remarks. The family was rediagnosed by Wilson
occurred (e.g. free coxa 1) as well as numerous
el al. (1976) and is recognised by the combination
synapomorphics in limbs and plcotclson.
of characters given in the diagnosis. Only the sec¬
ond character, the arrangement of the marginal
Plakarthrium Chilton, 1883
segmentation, is unique. Similar patterns involv¬
ing an expanded peduncle of antenna 1 and Plakarthrium Chilton, 1883: 74. - Hansen, 1905:
uropods are seen in some genera of "cassidiniinc" 115,—Menzies, 1962: 128.—Wilson ct al., 1976:
Sphacromatidac, in particular, Amphoroidella 334 -335. (type species: Plakarthrium typicum Chilton,
Baker, 1908, Leptosphaeroma Hilgendorf, 1885, 1883 by monotypy).
Chelonidium Pfeffer, 1887: 86 (type species Chcloni-
Paraieptosphaeroma Buss and Iverson, 1981. and
dium pxmetatissimum Pfeffer, 1887 by monotypy).
Platysphaera Holdich and Harrison, 1981. In all
four genera the body is flattened as in Plakarthri¬ Remarks. The genus has the characters of the
idac but antenna 2 docs not contribute to the body family. Only Chilton (1883) gave a diagnosis.
margin and the uropodal staicturc is typically
sphaeroniatid with peduncle and endopod fused. Plakarthrium australiense sp. nov.
Further, all possess the cuticular scale patches on
Figures 1-5
the end of the exopod of pleopod 5 which may be
a sphaeromatid synapomorphy absent in Material examined. Holotype. Australia, Tasmania,
Plakarthriidac (N.L. bruce, 1993, fig. IF; pers. Biclieno, granite reef 50 m offshore, N end of “The
comm.). The four genera arc unquestionably Gulch" (41°53'S, 147®18'E), 7 m. encrusting foliose
alga, SCUBA, G.C.B. Poore and 11.M. Lew Ton, 22
sphaeromatids and similarity to Plakarthriidac
Mar 1988 (stn TAS-87), NMV J47067 (1 ovigerous
seems on this evidence to be convergent. Another
female, 3.2 mm, with 3 slides).
similarity, an adaptation to maintaining a smooth
Paralypes. Collected with holotype: NMV J27472 (1
profile and minimum resistance to water move¬ male. 2.2 mm: 8 females, 1.9 2.8 mm. 1.9 3.2 mm);
ment, is what Buss and Iverson (1981) have NMV J47021 (I male, 2.4 mm); NMV J47068 (2
called the membrana cingula, a fringe around the females, 3.2, 2.3 mm): ZMH K-39833 (3 females).
edge of the body of webbed marginal setae. The Other material. Tasmania. Waterhouse Point. NMV
membrana cingula of Paraieptosphaeroma glynni J47066 (I juvenile, 1.9 mm). Western Bass Strait, 6 km
was illustrated in SEMs by Buss and Iverson W of Currie, King I., (39'=54.7*S. I43''43.4'E), 49 ni.
NMV J23890(8specimens. I.0-!.6mm). PegIcgCove,
(1981: fig. 4) and of the two other species of this
Deal I., between Pulpit Cove and Winter Cove
genus in line drawings by Muller (1990) and
(39°28'S, 147°22'E), 6 m, NMV J23891 (1 male. 1.7
NEW AUSTRALIAN ISOPOD OF THE GENUS PLAKARTHRIUM 375
Figure 1. Plakcirthrium australiense sp. nov. Holotype, NMV J47067: a, b, dorsal and lateral views, c, pereonite 7, pleo-
telson and uropods.
Plakarthrium typicwn Chilton. Male, NMV J683: d, pereonite 7, pleotcison and uropods.
376 G. C. B. POORE AND A. BRANDT
Figure 2. Plakarthrium australiense sp. nov. Holotype, NMV J47067: Al, A2, antennae 1, 2; MDI, MD r, left and right
mandibles; MXl, MX2, maxillae 1, 2; MP, maxilliped. Paratype male, NMV J4702I: Aim, A2m, antennae 1, 2.
NEW AUSTRALIAN ISOPOD OF THE GENUS PLAKARTHRIVM
Figure 3. Plakarthrium australiense sp. nov. Holotype, NMV J47067: P1-P7, pereopods 1-7.
378 G. C. B. POORE AND A. BRANDT
Figure 4. Plakarthnum ciu.s(raliefne sp. nov. Holotype, NMV J47067: PLI-PL5, plcopods 1-5; U, right uropod; X, ven¬
tral view of margins of IcA uropod and coxa 7.
mm). Hogan 1., Landing Beach (39°13'S, I46®59*E), 11 m, NMV J23896 (1 male, 2.1 mm; 1 female, 2.0 mm,
ZMH K-39834(l male, 2.0 mm). 2.0-2.1 mm). Cape Paterson, E side (38°4i’S.
Victoria, 75 m SW of Eagles Nest, Venus Bay 145°36'E), 6-3 m, NMV J23895 (1 male, 1 female, 4
(38°40*S, 145°40'E), 8 m. NMV J23893 (1 male. 3.0 immature). 50 m S of Twin Reefs, Venus Bay (38°4rS,
mm; 1 female, 2.0 mm, 2.0-3.0 mm). 1 km E of 145'^39'E), 9 m, NMV J23894 (1 male. 2.0 mm).
Harmers Haven, 500 m offshore (38°34'S, 145°40'E), Wilsons Promontory, Hobbs Head, NE shore (39°2'S,
NEW AUSTRALIAN ISOPOD OF THE GENUS PLAKARTHRIUM 379
Figure 5. Plakarthriwn australiense sp. nov. Paratypc male, NMV J47021: PI, P2, pereopods 1,2; PLl, PL2, pleopods 1,
2; P, penes; U, uropod.
146°28'E), NMV J47063 (1 female, 2.6 mm). Dutton Western Australia, Breaksea I., SW comer
Way, Portland (38°I8.4 S, I4P36.4'E), 3 m. NMV (35“3.90'S, 118^2.50'E). 15 m. NMV J23887 (2 man-
J47065 (1 ovigerous female, 3.0 mm). cas. 1 male, I.0-1.9mm): NMVJ23888(1 immature; 1
South Australia, Beachport, Snapper Point female, 2.1 mm; 4 males, 1.9-2.0, 1.6-2.1 mm). King
(37°29.3'S, I39°59.6'E). 6 ni. NMV J20434 (I female, George Sound. N of False I. (35°0.7()'S, 118°10.10'E),
2.4 mm). NE side of Topgallant 1., Investigator Group 27 m, NMV J23889 (4 males, 1.7-2.6 mm: 2 females,
(33‘’43.00'S, 134°36.60‘E), 12 m, NMV J23892 (1 1.9, 3.0 mm. 1.7-3.0 mm).
male, 1.8 mm).
380 G. C. B. POORE AND A. BRANDT
Other species. P. typicum. New Zealand. Auckland endite 4 times as long as wide, with 3 apical
region, Tawharanui Peninsula. 6 m, Carpaphvihim Jlex- robust setae and 6 slender setae; palp with short
uosum, R. Taylor. 3 Jun 1992, NMV J37I02 (14). article 1, longer article 2, substantially longer and
Opposite Edward Pcrcival Marine Station. Kaikoura broader article 3, convex and setose mesially,
(42°25'S. 173°42'E). 2 m. algae on boulders, G.C.B
article 4 0.6 times as wide as article 4, article 5 as
Poore et al.. 23 Mar 1997 (stn NZ97-022), NMV
long as and shorter than article 4, with 9 mesial
J39561-J39654 (25). The Snares Islands. D.S. Homing.
and distal setae.
NMV J682 (male, with 3 slides): NMV J683 (several).
P. punctatissimum. South Georgia. Royal Bight, Pereopod 1 elongate, longer than similar pereo-
Mollke Harbour (54^30.58'S. 36"0.45'\V). leaves of pod 2; pereopods 3 5 compact; pereopods 6-7
Macrocystis, Dr Karl von den Steinen. NMV J473II (3 more elongate. Pereopod I merus with anterodis¬
syntypes donated by Zoological Institute and Museum, tal row of complex setae; carpus half as long as
Hamburg). merus, with minute tubercles on posterior
Diagnosis. Pleotelson with pleonitc 1 fully indi¬ margin; propodus narrow; dactylus compact with
cated dorsally (not articulating), only pleonite 2 3-toothcd unguis. Pereopod 2 c. 85% length of
indicated laterally; pleotelson tapering to 80% of peroopod 1; meats with 2 distal robust setae;
anterior width posteriorly. Distal margins of compact dactylus with 3-toothcd unguis. Perco-
uropods aligned with margin of coxae. Coxae pod 3 less than half length of pereopod 1; ischium
with acute posterior comers. with posterodistal denticles; mems with
anterodistal row of complex setae; carpus almost
Description. Holotypc female. Body c. 1.35 times triangular, with posterodistal short robust seta;
as long as wide; ration of lengths of antenna I : propodus swollen; dactylus short, with simple
head : pereon : pleotelson : uropod in midline = curved unguis. Pereopods 4 and 5 similar to pere¬
13 : 18 : 33 : 27 : 9; widest at coxa 4 where each opod 3, 5 the most compact. Pereopod 6 about as
coxa comprises c. 27% of width. Head 1.9 times long as pereopod 2; merus with 1 very stout and 1
as wide as long, evenly rounded laterally, with shorter complex anterodistal setae; propodus with
excavated triangular front with triangular clypeus; row of 4 simple posterior setae distally; short
eyes with c. 10 ommatidia. Pereonite 1 narrower dactylus with 3-loothcd unguis. Pereopod 7
than head; pereonite 3 widest; perconites 6 and 7 longer but similar to pereopod 6.
shorter than others. Pleotelson with pleonite I Plcopod I peduncle twice as wide as long, with
fully indicated dorsally (not articulating), only 2 coupling hooks on mesiodistal comer; rami
pleonite 2 indicated laterally; pleotelson tapering attached on lateral half, not overlapping; endopod
to 80% of anterior width posteriorly; posterior and exopod with 13 and 11 mesial and distal
notch semicircular, about third width of posterior plumose setae respectively. Pleopod 2 peduncle
margin, bordered by fine setae. Marginal articles wider than long, with 2 coupling hooks; rami not
of antennae I and 2 and coxae of pereopods 1-7 overlapping; endopod and exopod with 10 and 12
each with small triangular lobe on anterodistal distal plumose setae respectively. Pleopod 3 with
and posterodistal comers; lower surface with peduncle wider than long, with 2 coupling hooks;
flattened marginal surface (c. fifth of coxal endopod triangular, without setae; exopod adja¬
length) defined proximally by a free skirt-like cent to endopod, with 7 distal plumose setae.
flange parallel to margin. Plcopods 4 and 5 similar to plcopod 3 but smaller
Antenna 1 peduncle with broad article 1, tri¬ and relatively wider; exopods with 8 and 9 distal
angular article 2 and smaller tapering article plumose setae respectively.
3 inserted in notch on lateral margin of article Uropod peduncle strongly tapering; endopod
2; fiagellum of 2 articles, first ring-like with attached mesially to peduncle, 2.5 times as long
2 pappose setae, second with 4 aesthctascs and as greatest width, triangular in lateral view, with
5 simple setae. Antenna 2 peduncle with small setose rounded margin anteriorly bordering
articles 1 and 2; article 3 short, broad; article 4 respiratory orifice strongly produced vertically,
4-sided; article 5 cylindrical, longer than wide, with 6 pappo.se setae near articulation with pedun¬
inserting on underside of margin of article 4; cle, mesial margin straight, posterior margin
flagellum of 12 cylindrical articles. curved and with c. 5 overlapping shingle-like
Mandible incisor with 2-3 obscure blunt teeth; scales; exopod c. 1.5 times as long as wide, with
spine row of 3 spines; without palp or molar. curved mesial margin against endopod, straight
Maxilla 1 with single lobe having 7 short apical lateral margin, convex distal margin with c. 11
robust setae. Maxilla 2 with single lobe with 8 overlapping shinglc-likc .scales.
short apical setae. Maxilliped without cpipod; Male. Differing slightly from female in some
NEW AUSTRALIAN ISOPOD OF THE GENUS PLAKARTHRIUM 381
proportions. Pleotelson more elongate. Antenna References
1 with article 2 of peduncle more rounded;
Baker, W.H., 1908. Notes on some species of the iso¬
flagellum with 6 acsthetascs. Antenna 2 with flag¬
pod family Sphaeromidae, from the South
ellum of 10 articles. Pereopods 1 and 2 slightly Australian coast. Transactions of the Royal Society
more robust. Pleopod 2 endopod with appendix of South Australia 32: 138-162, pis 3-10.
masculinis twice as long as endopod, attached Bruce, N.L., 1993. Two new genera of marine isopod
two-thirds way along. Uropod with narrower crustaceans (Flabcllifera: Sphaeromatidae) from
peduncle and rami than in female. Penes oval, southern Australia, with a reappraisal of the
fused basally, attached to posterior margin of Sphaeromatidae. Invertebrate Taxonomy 1:
151-171.
pereonite 7.
Bruce, N.L., 1994. The Cassidininae Hansen, 1905
Oistrihiition. Southern Australia, from central (Crustacea: Isopoda; Sphaeromatidae) of Aus¬
Victoria to southern Western Australia, including tralia. Journal of Natural Histoty 28: 1077-1173.
Tasmania; 6^9 m, on Amphibolis, Eckionia Brusca, R.C. and Wilson, G.D.F., 1991. A phylogenetic
analysis of the Isopoda with some classificatory
holdfasts, red algae. No records from New South
recommendations. Memoirs of the Queensland
Wales (P, Berents, Australian Museum, pers.
Museum 2>\: 143-204.
comm.).
Buss. L.W. and Iverson, E.W.. 1981. A new genus and
Remarks. The Australian species differs from the species of Sphaeromatidae (Crustacea; Isopoda)
with experiments and observation.s on its reproduc¬
other two species of Plakarthrium in having a
tive biology, interspecific interactions and color
clear demarcation dorsally of pleonite 1. In
polymorphisms. Postilla 184: 1-24.
P. typicum (see Fig. Id) and P. punciatissimum
Chilton, C., 1883. Further additions to our knowledge
pleonite I is indicated only laterally. Plakar- of the New Zealand Crustacea. Transactions of the
ihrium austvaliense differs from P. typicum, Royal Society of New Zealand 15: 69-86.
which it most resembles, in having the pleotelson Glynn, P.W., 1970. A systematic study of the Sphaero¬
tapering rather than more or less parallel-sided, matidae (Crustacea: Isopoda) of Isla Margarita,
and the distal margins of the uropods aligned with Venezuela, with descriptions of three new species.
the margin of the coxae. In P. typicum, the New Memorias de la Sociedad de Ciencias Naturales
‘Ea Salle" Ity. 1-48.
Zealand species, the uropodal exopods arc more
Hansen, H.J., 1905. On the propogation, structure
oval and protnide beyond the end of coxae of
and classification of the family Sphaeromidae.
pereopods 7 (Fig. Id). Plakarthrium typicum
Quarterly Journal of Microscopical Science 49:
lacks the acute comers of the coxae seen in the 69-135.
Australian species. Harrison, K. and Ellis, J.P.. 1991. The genera of
Plakarthrium australiense differs from P. pimc- the Sphaeromatidae (Crustacea: Isopoda): a key
tatissimum more markedly. The latter has and distribution list. Invertebrate Taxonomy 5:
pleonites 1-4 indicated laterally and uropods 915-952.
Hilgendorf, F., 1885. Eine neue Isopoden—Gattung.
produced more posteriorly.
Sitzungsherichte der Gesellschaft Naturfor-
The new species has a more pronounced lower
schender Freundc zu Berlin 1885: 185-187.
marginal contact surface on coxae, antennae and
Holdich, D.M. and Harrison, K., 1981. Platybranch
uropods than the other species. This surface seals
sphaeromatids (Crustacea: Isopoda) from the Aus¬
the underside of the animal and is made more tralian region with description of a new genus.
effective by the skirt-like fringe along its inner Records of the Australian Museum 33: 617-643.
edge. Hurley, D.E., 1961. A checklist and key to the Crus¬
tacea Isopoda of New Zealand and Subantarctic
Islands. Transactions of the Royal Society of New
Zealand (Zoology) 1: 259-292.
Acknowledgements
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the New Zealand and Australian species. We
Plakarthrium typicum Chilton, en bahia South
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382 G. C. B. POORE AND A. BRANDT
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