The talitrid amphipods of Tonga (Crustacea, Amphipoda, Talitridae)
Author
Lowry, J. K.
Author
Bopiah, Arundathi
text
Zootaxa
2013
3681
4
347
370
journal article
10.11646/zootaxa.3681.4.2
6a348ac2-6af7-42fa-a33d-dfc8d19a9567
1175-5326
249123
28B58895-38AF-4694-8014-B038B2186028
Platorchestia ano
sp. nov.
(
Figs 1–4
)
Platorchestia platensis
.—
Myers, 1985
: 134
, figs 108, 109.
Type
material.
Holotype
male,
9 mm
, AM P.87313, from white sand beach with thick cover of fine
Zostera
and other plant debris (about
5–6 cm
deep) at top of intertidal,
Ano
Beach,
Pangaimotu
Island
, Vava’u,
Tonga
(
18°42’08.60”S
173°59’19.62”W
), talitrids very abundant, J.K. Lowry & G.C.B. Poore,
11 October 2011
;
paratypes
:
1 female
, AM P.87314,
29 males
,
149 females
and juveniles (many juveniles, only 2 ovigerous females) AM P.87325, same locality as
holotype
.
Additional material examined.
Five males (only 1 mature),
95 females
and juveniles (many juveniles) AM P.87326, coarse coral rubble on top of fine white sand beach near the commercial harbour, Nuku’alofa, Tongatapu,
Tonga
(
21°08.443’S
175°10.426’W
), talitrids under dried algae on sand under coarse rubble, J.K. Lowry & G.C.B. Poore,
13 October 2011
;
1 specimen
, AM P.80738,
Ano
Beach,
Pangaimotu
Island
, Vava’u,
Tonga
(
18°42’S
173°59’W
), Greg Towner,
19 September 2009
.
Type
locality.
Ano
Beach,
Pangaimotu
Island
, Vava’u,
Tonga
(
18°41.211’S
174°01.139’W
).
Etymology.
Named for the
type
locality,
Ano
Beach,
Tonga
.
Colour.
Body evenly light tan, antenna 2 darker orange.
Habitat
. Beach-hoppers occurs on sandy shores under supralittoral wrack or terrestrial plant material.
Description.
Based on
holotype
male,
9 mm
, AM P.87313.
Head
.
Eye
medium (1/5–1/3 head length).
Antenna 1
short, not longer than article 4 of antenna 2 peduncle.
Antenna 2
up to half body length; peduncular articles incrassate; article 5 longer than article 4; peduncular articles with many small robust setae.
Mandible
left lacinia mobilis 5-dentate.
Maxilla 1
palp vestigial, 1-articulate.
Maxilliped
palp article 2 distomedial lobe well developed, article 4 reduced, button-shaped.
Pereon
.
Gnathopod 1
sexually dimorphic; subchelate; coxa smaller than coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus 2 × as long as propodus, 3.25 × as long as broad; propodus 'subtriangular' with well developed posterodistal lobe, anterior margin with 3 groups of robust setae, lateral surface with 4 cuspidate setae, posterolateral surface with 6 serrate setae, medial surface with 4 cuspidate setae, posteromedial surface with 5 serrate setae; palm slightly obtuse, with 7 serrate setae; dactylus subequal in length to palm.
Gnathopod 2
sexually dimorphic; subchelate; gill lobate; basis slightly expanded; ischium with rounded lobe on mid-anterior margin, without posterodistal lobe on medial surface; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent; propodus subrhomboidal, 1.5 × as long as wide; palm slightly acute, reaching about 25% along posterior margin, lined with robust setae, evenly rounded, with weak palmar sinus or notch, without palmar protuberances, posteromedial surface of propodus with groove, with cuticular patch at corner of palm; dactylus slightly longer than palm, spatulate distally; gill bilobate, not incised.
Pereopods 2–4
coxae as wide as deep.
Pereopods 3–7
cuspidactylate; dactyli with distal patch of many rows of tiny denticles on the anterior margin.
Pereopod 4
significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3; dactylus thickened proximally with a notch midway along posterior margin.
Pereopod 5
propodus distinctly longer than carpus.
Pereopods 6–7
short (1/3 length of body).
Pereopod 6
not sexually dimorphic; slightly shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin perpendicular to ventral margin, posterior lobe without ridge; gill convoluted, coxa not incised.
Pereopod 7
not sexually dimorphic; basis lateral sulcus present, slightly pronounced, basis posterior margin with distinct minute serrations, each with a small seta, slight posterodistal lobe present, shallow, broadly rounded; merus and carpus slender; merus posterior margin straight.
FIGURE 1.
Platorchestia ano
sp. nov.
, holotype, male, 9 mm, AM P. 87313,
Ano
Beach,
Pangaimotu
Island, Vava’u, Tonga. Scale lines for H represents 200 µm; rMD, MP, MX1 represent 100 µm; and lMD, UL, LL, MX2 represent 20 µm.
FIGURE 2.
Platorchestia ano
sp. nov.
, holotype, male, 9 mm, AM P. 87313, female, AM P.87314,
Ano
Beach,
Pangaimotu
Island, Vava’u, Tonga. Scale lines for male and female G1 & G2 represent 100 µm.
FIGURE 3.
Platorchestia ano
sp. nov.
, holotype, male, 9 mm, AM P. 87313,
Ano
Beach,
Pangaimotu
Island, Vava’u, Tonga. Scale lines for P3, P4, P5 represent 100 µm; P6, P7 represent 200 µm.
FIGURE 4.
Platorchestia ano
sp. nov.
, holotype, male, 9 mm, AM P. 87313,
Ano
Beach,
Pangaimotu
Island, Vava’u, Tonga. Scale lines for U3 represents 20 µm; EP, Ur, T, U1, U2 represent 100 µm.
Pleon
.
Pleopods 1–3
well developed; biramous; outer ramus subequal in length to peduncle.
Pleopods 1–2
peduncles with sparse marginal robust setae.
Pleopod 3
peduncle without marginal setae.
Epimeron 2
subequal in length to epimeron 3.
Epimeron 3
posterior margin minutely serrate, with minute setae, posteroventral corner with small subacute tooth, ventral margin without robust setae.
Uropod 1
not sexually dimorphic, peduncle with 8 robust setae, distolateral robust seta present, small (less than 1/4 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, with 3 marginal robust setae; outer ramus without marginal robust setae.
Uropod 2
not sexually dimorphic; peduncle with 7–8 robust setae; inner ramus subequal in length to outer ramus, with 4 marginal robust setae; outer ramus with 2 marginal robust setae.
Uropod 3
peduncle with 3 robust setae; ramus subequal in length to peduncle, linear (narrowing), with 2 marginal robust setae, with 4–5 apical setae.
Telson
as broad as long, apically incised, dorsal midline at least halfway, with 7 marginal and apical robust setae per lobe.
Female
(sexually dimorphic characters). Based on
paratype
female, AM P.87314.
Antenna 2
peduncular articles slender, with sparse, small robust setae.
Gnathopod 1
parachelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; carpus as long as propodus, 3.25 × as long as broad; propodus subrectangular, medial surface with 1 cuspidate seta; palm transverse, without serrate setae; dactylus longer than palm.
Gnathopod 2
mitten-shaped; basis expanded anteroproximally; ischium without rounded lobe on mid-anterior margin, posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; palm obtuse, smooth, lined with serrate setae, without protuberance or shelf near dactylar hinge; without cuticular patch at corner of palm; dactylus subequal in length to palm, not modified distally.
Remarks.
The populations of
Platorchestia ano
from
Tonga
and from
Fiji
(
Myers 1985
) are very similar. Both have similar palms and similar apical tips on male gnathopod 2. The Fijian population is much larger (
15 mm
) than the Tongan populations (
9 mm
), the length to width ratio of the male gnathopod 1 carpus is different (
2.2 in
the Fijian populations versus
3.2 in
the Tongan one) and the
telson
is about as long as broad in the
Tonga
population (broader than long in the
Fiji
population). A molecular analysis of these populations would be informative.
This is the first (group 2) species of
Platorchestia
from the western Pacific islands. It appears to be most similar to
P. jo i
Stock & Biernbaum, 1994 from the north-western Pacific coasts of
Japan
,
Korea
and
Russia
.
Platorchestia ano
differs from
P. j o i
, mainly in the shape of the palm of male gnathopod 2 which is smooth along the margin with a small proximal sinus (
P. j oi
has a distinct midmedial sinus).
Distribution
. Vava’u,
Tonga
(current study); Nasese, Suva,
Fiji
(
Myers 1985
).