Albertine Rift Valley endemics: three new species of freshwater crabs (Brachyura: Potamoidea: Potamonautidae) from Uganda, the Democratic Republic of the Congo, and Rwanda
Author
Cumberlidge, Neil
Author
Clark, Paul F.
text
Journal of Natural History
2018
2018-07-05
52
25 - 26
1637
1656
http://dx.doi.org/10.1080/00222933.2018.1480812
journal article
10.1080/00222933.2018.1480812
1464-5262
5174988
FC681BD6-6FB2-4A14-B068-89FC3EB26605
Potamonautes rwenzori
sp. nov.
(
Figures 3a,b
,
4c
,
5c,f
,
6c,f
,
7c
,
8c
)
Material examined
Type material.
Democratic Republic of the Congo
.
Holotype
(here designated): adult
♂
,
CW 24.3
,
CL 16.7
,
CH 8.9
,
FW
7.3 mm
, from
River Talya
,
Maya Moto
, near
Mutsora
(a station in the
Virunga National Park
, formerly the
Albert National Park
), western foothills of the
Rwenzori Mountains
,
0.316728°N
,
29.750125°E
1100
–
1200 m
asl
, date and coll
.
unknown (
NHMUK
reg. 2018. 6, pres. the
Royal Belgian Institute of Natural Sciences
,
Brussels
,
Belgium
)
.
Paratypes
:
2 adult
♂♂
,
CW 21.4
,
CL 15.3
;
CW 23.2
,
CL 16.1
,
2 adult
♀♀
,
CW 24
,
CL 17.5
;
CW 21.3
,
CL
15.9 mm
, same details as
holotype
(
NHMUK
reg. 2018. 7
–
8),
0.316728°N
,
29.750125° E
.
Other material.
Uganda
.
Adult
♂
,
CW 25.8
,
CL
17.5 mm
;
three subadult
♂♂
,
CW 19.2
,
CL 14.3
;
CW 18.8
,
CL 13.8
;
CW 17.8
,
CL 12.7
;
three adult
♀♀
,
CW 24.3
,
CL 17.1
;
CW 21.4
,
CL 16.1
;
CW 20.5
,
CL 15.2
,
Rwenzori Mountains
,
0.239081°N
,
29.942965°E
, coll
.
unknown,
1 November 1952
(
NHMUK
reg. 2018. 9
–
15)
.
Diagnosis
Carapace: medium height (
CH
/FW 1.2); exorbital, epibranchial teeth each reduced to granule, postfrontal crest complete, faint medially, lateral ends well defined, meeting epibranchial teeth; anterolateral margin posterior to epibranchial tooth finely serrate, almost smooth (
Figure 3a
); vertical sulcus on carapace branchiostegal wall faint, meeting longitudinal sulcus, dividing carapace wall into three parts not meeting anterolateral margin (
Figure 4c
). Third maxilliped: ischium with vertical sulcus; s3/s4 complete, deep. Cheliped: inferior margins of merus with series of small granules, distal meral tooth small; propodus (fixed finger) of major cheliped with large teeth along cutting edge, largest molars proximal; dactylus (movable finger) with series of small teeth along cutting edge interspersed by two medium-sized teeth in middle, not arched, enclosing long narrow interspace when closed (
Figure 5c
); carpus distal tooth large, pointed, proximal tooth small, pointed (
Figure 5f
). G1: terminal article straight, entire terminal article directed outwards at 45° to longitudinal axis of subterminal segment, median part widened slightly by low slim ventral lobe (
Figure 6f
), tip slightly upturned (
Figure 6c,f
).
Description
Carapace: medium height (
CH
/FW 1.2); front broad, measuring one-third CW (FW/CW 0.3); semi-circular, urogastric, cardiac, posterior, cervical carapace grooves all faint; postfrontal crest complete, faint, lateral ends well defined meeting epibranchial teeth; epigastric crests distinct, median sulcus between crests short, forked posteriorly; exorbital, epibranchial teeth each reduced to granule; anterolateral margin between exorbital, epibranchial teeth smooth, curving slightly outward, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth smooth (
Figure 3a
); vertical sulcus on carapace branchiostegal wall distinct, incomplete, beginning at longitudinal sulcus not meeting anterolateral margin, dividing carapace branchiostegal wall into three parts; suborbital margin smooth. Third maxilliped: exopod with long flagellum, ischium with distinct vertical sulcus. Epistomial tooth: large, triangular, margins lined by faint granules (
Figure 3b
). Mandible: palp two-segmented, terminal segment simple. Sternum: s2/s3, s3/s4 deep, wide, both completely crossing sternum; s4/e4, s5/e5, s6/e6, s7/e7 all faint (
Figure 3b
). Cheliped: propodus (fixed finger) of adult male with series of small, medium sized teeth along cutting edge interspersed by two large pointed teeth in middle; dactylus (movable finger) with series of small teeth along cutting edge interspersed by two medium sized teeth in middle, not arched, enclosing long narrow interspace when closed (
Figure 5c
); inferior margins of merus with series of small rounded teeth, distal tooth small, low; distal tooth on inner margin of carpus large, pointed, proximal tooth very small, granular (
Figure 5f
), superior surface of merus granulated. Pleon: outline broadly triangular with straight margins. G1: terminal article straight, entire terminal article directed outwards at 45° to longitudinal axis of subterminal segment, median part widened slightly by low slim ventral lobe, tip slightly upturned (
Figure 6c, f
). G2: terminal article long, flagellum-like (
Figure 7c
). Small-sized species, adult size range between CW
20.5
–
25.8 mm
.
Distribution
This species is found in the Rwenzori Mountains from two localities, one in the western foothills of the Rwenzori Mountains in the
DRC
, and one in the central and eastern parts of the Rwenzori Mountains in
Uganda
(
Figure 8c
).
Type
locality
DRC
,
River Talya
,
Maya Moto
, near
Mutsora
, a station in the
Virunga National Park
, formerly the
Albert National Park
, western foothills of the
Rwenzori Mountains
(
0.3166667°N
,
29.75°E
),
1100
–
1200 m
asl
, in the intermediate/transitional forest zone
.
The Rwenzori Mountains
lie on the border between
Uganda
and the DRC and reach
5109 m
asl
, which is high enough to support permanent snowcaps and glaciers despite its close proximity to the equator (
Plumptre et al. 2007
)
.
This mountain range
is one of the sources of the
Nile River
and includes two national parks: the
Rwenzori Mountains National Park
and the
Virunga National Park
.
Ecology
The Rwenzori Mountains lie in the
DRC
and
Uganda
in the southern part of
Upper Nile
Ecoregion 522 (
Thieme et al. 2005
;
Abell et al. 2008
) which includes
Lake
Albert and the River Semuliki in the Western Rift Valley. Most of this ecoregion lies to the north of these mountains in the drainage basin of the River Nile in
South Sudan
,
Sudan
and
Ethiopia
, and includes the vast Sudd swamplands. Both of the known localities where
P. rwenzori
sp. nov.
occurs (in the western foothills and in the central and eastern side of the Albertine Rift Valley) are in protected areas (the Rwenzori Mountains National Park and the Virunga National Park). The Rwenzori Mountains National Park is in
Kabarole
,
Kasese
and
Bundibugyo
Districts in Western
Uganda
and is a UNESCO World Heritage Site that borders the Virunga National Park in the
DRC
. Despite the apparent protection offered by these two national parks there are potential threats from agricultural encroachment and collection of wood in the parks, with the result that the Rwenzori Mountains National Park is also on the List of World Heritage in Danger (
Plumptre et al. 2007
).
Conservation status
An IUCN conservation assessment of
P. rwenzori
sp. nov.
has not yet been carried out, but given the fact that this species is known from only a few specimens from two localities it will
probably be eventually regarded as Data Deficient. Each of the localities where this species is known to occur is in a protected area.
Etymology
The new species is named for the Rwenzori Mountains where this species was first collected. The specific epithet
rwenzori
is used as a Latin noun in apposition. The vernacular name is the Rwenzori crab.
Remarks
Potamonautes rwenzori
sp. nov.
differs from
P. bwindi
sp. nov.
and
P. kivu
sp. nov.
in that the major cheliped propodus has large teeth along the cutting edges in the proximal region (
Figure 5c
) (vs a cheliped propodus that has medium and small teeth along the cutting edges in
P. bwindi
sp. nov.
and
P. kivu
sp. nov.
;
Figure 5a,b
); and the tip of the G1 terminal article is straight or only slightly upturned (
Figure 6c,f
) (vs a sharply upturned terminal article tip in
P. bwindi
sp. nov.
and
P. kivu
sp. nov.
;
Figure 6a,b,d,e
).
Potamonautes rwenzori
sp. nov.
differs from other, similar small-bodied species of freshwater crabs from
Uganda
in that s3/s4 is a long, deep sulcus that completely crosses the sternum (
Figure 3b
) (vs two short shallow sulci at the margins and otherwise smooth in
P. elgonensis
and
P. kanstyore
) (
Cumberlidge and Clark 2010a
,
2017
); the third maxilliped ischium has a deep vertical sulcus (
Figure 4c
) (vs a smooth ischium lacking a sulcus in
P. amalerensis
,
P. busungwe
,
P. elgonensis
,
P. entebbe
,
P. imatongensis
,
P. kantsyore
and
P. morotoensis
; cf.
Cumberlidge and Clark 2010a
,
2016
,
2017
); the cheliped carpus distal tooth is large and pointed (
Figure 5f
) (vs a small and low cheliped carpus tooth in
P. amalerensis
,
P. elgonensis
,
P. loveni
,
P. morotoensis
and
P. williams
; cf.
Cumberlidge and Clark 2010a
,
2010b
,
2016
); and the cheliped dactylus is broad, not highly arched, and encloses a long rectangular interspace (
Figure 5c
) (vs a highly arched dactylus enclosing a broad oval interspace in
P. amalerensis
,
P. busungwe
,
P. elgonensis
,
P. entebbe
,
P. imatongensis
,
P. loveni
,
P. morotoensis
,
P. mutandensis
and
P. williamsi
; cf.
Cumberlidge and Clark 2010a
,
2010b
,
2016
,
2017
;
Cumberlidge and Meyer 2011
).
Potamonautes rwenzori
sp. nov.
is also found in the same region of
Uganda
as
P. aloysiisabaudiae
and the two species share a number of carapace characters such as an extremely low exorbital tooth, an epibranchial tooth that is reduced to a small granule, and a smooth anterolateral margin immediately behind the epibranchial tooth. The two species can be distinguished in that
P. rwenzori
sp. nov.
is a small species that is adult at CW
24 mm
(vs
P. aloysiisabaudiae
which is adult at CW
45 mm
), and the margin of the merus of the cheliped of
P. rwenzori
sp. nov.
is granulated with a small but distinct distal meral tooth (
Figure 5f
) (vs
P. aloysiisabaudiae
which has a cheliped merus margin that is smooth with a distal meral tooth reduced to a granule); and the distal tooth of the cheliped carpus is large and pointed (
Figure 5f
) (vs a low blunt cheliped carpus tooth in
P. aloysiisabaudiae
); and the ischium of the third maxilliped is smooth (
Figure 4c
) (vs an ischium with a distinct vertical groove in
P. aloysiisabaudiae
).
General remarks
Potamonautes bwindi
sp. nov.
,
P. kivu
sp. nov.
and
P. rwenzori
sp. nov.
share a number of characters with each other and several additional species in this genus from East Africa. For example, the three new species described here all share an extremely low exorbital tooth and an epibranchial tooth that is reduced to a small granule; all have a smooth anterolateral margin immediately behind the epibranchial tooth (
Figures 1a
,
2a
,
3a
); and all are adult at a small carapace size (CW 19.8
–
24.0 mm). Ugandan crabs that share this suite of characters include
P. amalerensis
,
P. busungwe
,
P. elgonensis
,
P. entebbe
,
P. imatongensis
,
P. kantsyore
,
P. loveni
,
P. morotoensis
,
P. mutandensis
,
P. rukwanzi
and
P. williamsi
(cf.
Corace et al. 2001
;
Cumberlidge and Clark 2010a
,
2010b
,
2016
,
2017
;
Cumberlidge and Meyer 2011
).
Until the present study, only three species of freshwater crabs were known from the Albertine Rift Valley: two large and abundant species of river crabs (
P. aloysiisabaudiae
and
P. niloticus
), and one small lake-living species (
P. mutandensis
) (
Cumberlidge and Meyer 2011
).
Potamonautes aloysiisabaudiae
is widespread throughout western
Uganda
and its range includes the Virunga and Rwenzori Mountains and the associated rivers and lakes that flow north into the Nile River basin (
Bott 1955
; Cumberlidge unpubl. data).
Potamonautes niloticus
is one of the most widespread species in Africa and is found throughout the Nile River basin from
Rwanda
to
Egypt
(
Cumberlidge 2009
), while
P. mutandensis
occurs in lakes from southern
Uganda
to Lake Kivu in
Rwanda
(
Cumberlidge and Meyer 2011
).