Cebudonus poppeorum, a new genus and new species of eumedonine crab (Crustacea: Decapoda: Brachyura: Pilumnidae) from the Philippines
Author
Ng, Peter K. L.
text
Zootaxa
2014
3815
1
94
102
journal article
45505
10.11646/zootaxa.3815.1.6
963ff3a4-4ab4-495b-95eb-a744279bc6a4
1175-5326
226599
51A13505-C327-49F7-8FCC-0C407927C76C
Cebudonus
n. gen.
Type
species
.
Cebudonus poppeorum
n. gen.
, n. sp.
, by present designation.
Diagnosis
. Carapace pentagonal; dorsal surface gently convex, covered with numerous small pits (
Figs. 1
,
2
); front with 2 long pseudorostral spines, subparallel, ca. 0.4 times total carapace length, separated by broad U-shaped cleft (
Figs. 1
,
2
,
3
C); anterolateral margin entire, with large, broadly triangular, sharp lateral tooth, projecting laterally, dorsal surface gently convex (
Figs. 1
,
2
,
3
A, 4A); antennae with subrectangular basal article, twice as long as wide (
Fig. 3
B); antennules folding at ca. 45° (
Fig. 3
B); epistome relatively broad with depressed median part (
Fig. 3
A–C); third maxilliped with ischium subrectangular, with deep submedian longitudinal sulcus (
Figs. 3
C, 4A), merus subquadrate, anteroexternal angle subauriculiform (
Figs. 3
C, 4A); ambulatory legs long, slender (
Figs. 1
,
2
,
4
E); ambulatory merus elongated, slender, surface with margins rounded, not cristate, not distinctly granular, dorsal distal tooth distinct but low (
Figs. 1
,
2
,
4
E); ambulatory propodus, dactylus with ventral margins lined with dense stiff setae, with distinct dactylo-propodal lock, not forming subchelate structure (
Figs. 1
,
2
,
4
D, E); cheliped merus rounded in cross-section; surface covered with numerous small pits (
Figs. 1
,
2
,
3
C); cheliped carpus surface with long, gently curved spine on distal inner angle (
Figs. 1
,
2
,
3
F); chela unarmed, margins not cristate (
Fig. 3
F); thoracic sternum relatively narrow transversely, surfaces pitted, sternites 3, 4 completely fused with median depression (
Figs. 3
C, 4B); male abdominal locking mechanism present as knob-like tubercle on distal one-third of thoracic sternite 5; male abdomen broadly triangular (
Figs. 3
D, 4C); G1 slender, sinuous, distal part elongated (
Fig. 4
F, G).
Etymology
. The new genus is named after Cebu City in the Visayas,
Philippines
; in arbitrary combination with the genus name
Eumedonus
. The gender of the genus is masculine.
Remarks
. The unusual combination of carapace, cheliped, ambulatory leg, thoracic sternal and abdominal characters in
Cebudonus poppeorum
n. gen.
, n. sp.
require the establishment of a new genus. While the carapace shape of
Cebudonus
n. gen.
superficially resembles species associated with echinoids like
Eumedonus intermedius
Chia & Ng, 2000
(
Madagascar
)
,
E. vicinus
Rathbun, 1918 (
Australia
)
, and
E. zebra
Alcock 1895
(Red Sea to East
China
Sea), especially with regard to the shape of the laterally directed spines; its front is completely different, with two long pseudorostral spines (
Figs. 1
,
2
) in contrast to
Eumedonus
, which has a lobiform pseudorostrum that is bifurcated distally to form two teeth (cf.
Chia & Ng 2000
: figs. 8, 9A, D, 10, 11, 12A, D, N, 13, 14, 15A, D, Q, R). The lateral carapace tooth and the dorsal surface adjacent to it is gently convex dorsally in
Cebudonus
n. gen.
(
Fig. 3
A) (the tooth is stout with the dorsal surface distinctly convex in
Eumedonus
; cf. Chia
et al.
1995: fig. 3A); the cheliped merus is relatively long and unarmed (
Figs. 1
,
2
,
3
C) (relatively short with numerous tubercles and granules in
Eumedonus
; cf.
Chia & Ng 2000
: figs. 8, 9B, 10, 11, 12B, L, 14, 15B, O); the meri of the ambulatory legs are long, subcylindrical and smooth, without any marginal cristae, and the dorsal distal tooth is relatively low (
Figs. 1
,
2
,
4
E) (short, laterally flattened with distinct marginal cristae and a strong dorsal distal tooth in
Eumedonus
; cf.
Chia & Ng 2000
: figs. 8, 9E, G, 10, 11, 12E, K, 13, 14, 15E, K); the anterior male thoracic sternum (sternites 1–4) are proportionately narrow transversely (
Figs. 3
C, 4B) (proportionately wider transversely in
Eumedonus
; cf.
Chia & Ng 2000
: figs. 9C, 11B, 12C, 14B, 15N); and the male abdomen is relatively wide (
Figs. 3
D, 4C) (proportionately narrower in
Eumedonus
; cf.
Chia & Ng 2000
: figs. 12J, 14J, 15N).
The unarmed and non-cristate ambulatory meri of
Cebudonus
n. gen.
resembles that of the echinoid symbiont
Gonatonotus
, but in the new taxon, it is proportionately much longer, more slender and almost smooth (
Figs. 1
,
2
,
4
E) (proportionately shorter and distinctly granular in
Gonatonotus
; cf.
Chia & Ng 2000
: figs. 17, 18E, G, 20, 21E, K, 22, 23E, K). The differences previously noted in the form of the front, anterolateral region, cheliped, thoracic sternum and abdomen between
Cebudonus
n. gen.
and
Eumedonus
also apply for
Gonatonotus
(cf.
Chia & Ng 2000
: figs. 17, 18A, D, 19A, 20, 21A, D, M, N, 22, 23A, D [front]; figs. 17, 18B, 20, 21B, 22, 23B [chelipeds]; figs. 17B, 19G, 20B, 21C, 22B, 23C [sternum]; figs. 19H, 21J, 22, 23J [abdomen]).
The form of the front, with the two long pseudorostral spines is similar to that of
Tiaramedon
and
Zebrida
, but these genera differ markedly from
Cebudonus
n. gen.
in several other characters.
Cebudonus
n. gen.
, can be separated from
Tiaramedon
by its smooth dorsal surface of the carapace (
Figs. 1
,
2
) (armed with additional gastric and branchial spines in
Tiaramedon
; cf
Chia & Ng 1998
: figs. 7A, 8A); the two pseudorostral spines joining medially without any trace of a median plate (
Figs. 1
,
2
) (with a small plate present between the pseudorostral spines in
Tiaramedon
; cf.
Chia & Ng 1998
: fig. 8A, B); the chela is unarmed (
Figs. 1
,
2
,
3
F) (with an additional spine on the dorsal distal margin in
Tiaramedon
; cf.
Chia & Ng 1998
: figs. 7A, B, 8K); the cheliped carpus has a single long inner spine (
Figs. 1
,
2
,
3
F) (2 large spines in
Tiaramedon
; cf.
Chia & Ng 1998
: fig. 7A); the ambulatory merus is long and slender with a short dorsal distal tooth (
Figs. 1
,
2
,
4
E) (short and stout with a long distal dorsal tooth in
Tiaramedon
; cf.
Chia & Ng 1998
: figs. 7, 8C); and the male anterior thoracic sternum is transversely narrow (
Figs. 3
C, 4B) (transversely broad in
Tiaramedon
; cf.
Chia & Ng 1998
: figs. 7B, 8D). The male abdomens of
Cebudonus
n. gen.
and
Tiaramedon
are nevertheless similar in shape (
Figs. 3
D, 4C; cf.
Chia & Ng 1998
: figs. 7B, 8F). The two genera are also different in terms of host specificity, with
Tiaramedon
always associated with crinoids (and with young crabs characteristically transversely striped like many other crinoid-associated eumedonines, see
Castro
et al.
1995
; Chia & Ng 1995, 1998) whereas
Cebudonus
n. gen.
with its longitudinal stripes is probably associated with echinoids.
Cebudonus
n. gen.
can be separated from the echinoid symbiont
Zebrida
by having two subcylindrical pseudorostral spines (
Figs. 1
,
2
) (distinctly lamelliform in
Zebrida
; cf. Ng &
Chia 2000
: figs. 2, 3A, B); the lateral carapace tooth and the dorsal surface adjacent to the tooth is dorsally convex (
Fig. 3
B) (the area is distinctly dorsally flattened in
Zebrida
; cf. Chia
et al.
1995: fig. 3B); the chela and merus are unarmed and the carpus has a long spine at the inner angle (
Figs. 1
,
2
,
3
F) (the chela has a large subdistal dorsal tooth, the carpus and merus each having three large lamelliform teeth in
Zebrida
; cf. Ng &
Chia 2000
: figs. 2, 3J); the ambulatory merus is long and slender with a short dorsal distal tooth (
Figs. 1
,
2
,
4
E) (short and stout with the margins cristate to dentate and with a large distal dorsal tooth in
Zebrida
; cf. Ng &
Chia 2000
: figs. 2, 3C, K, M); the ambulatory propodus and dactylus are normal (
Figs. 1
,
2
,
4
D, E) (forming a subchelate clasping structure in
Zebrida
; cf. Ng &
Chia 2000
: figs. 2, 3C, K, M); and the male anterior thoracic sternum is proportionately narrower transversely (
Figs. 3
C, 4B) (proportionately wider in
Zebrida
; cf. Ng &
Chia 2000
: figs. 2B, 3D). The male abdomens of
Cebudonus
n. gen.
and
Zebrida
are similar, with both relatively wide transversely (
Figs. 3
D, 4C; cf. Ng &
Chia 2000
: figs. 2B, 3F)
There are also similarities with
Zebridonus
but
Cebudonus
n. gen.
can be separated by its two long pseudorostral spines (
Figs. 1
,
2
) (with a distinctly dorsoventrally flattened lobiform pseudorostrum that is bifurcated distally to form two teeth in
Eumedonus
; cf. Chia
et al.
1995: figs. 1, 2A, K); the lateral carapace tooth and the dorsal surface adjacent to it is dorsally convex (
Fig. 3
B) (the area is distinctly dorsally flattened in
Zebridonus
; cf. Chia
et al.
1995: figs. 1, 2A, 3C); the chela and merus are unarmed, and the carpus has a long spine on the inner angle (
Figs. 1
,
2
,
3
F) (the chela has a distinct distal dorsal tooth, the carpus 2 large lamelliform teeth and the merus several distinct teeth in
Zebridonus
; cf. Chia
et al.
1995: figs. 1,
2
I); the ambulatory merus is long, subcylindrical and smooth, without any marginal cristae and the dorsal distal tooth is relatively low (
Figs. 1
,
2
,
4
E) (short, laterally flattened with distinct marginal cristae and a strong dorsal distal tooth in
Zebridonus
; cf. Chia
et al.
1995: figs. 1, 2B, C); the anterior male thoracic sternum (sternites 1–4) are proportionately narrower transversely (
Figs. 3
C, 4B) (proportionately wider transversely in
Zebridonus
; cf. Chia
et al.
1995: fig. 2D); and the male abdomen is proportionately wider (
Figs. 3
D, 4C) (proportionately narrower in
Zebridonus
; cf. Chia
et al.
1995: fig. 2F).