Potamonautes baziya Daniels & Barnes & Marais & Gouws 2021, sp. nov.

Potamonautes baziya sp. nov.

urn:lsid:zoobank.org:act: 32688368-D8DB-4B60-B801-99B43291E34A

Figs. 1,7–10; Table 1

Diagnosis

CARAPACE. Ovoid, highly flat (CH /CL = 0.45) (Table 1); postfrontal crest well-defined, complete, lateral ends meeting anterolateral margins; epigastric crests faint, median sulcus between crests short, not forked posteriorly; exorbital, epibranchial teeth reduced to granules; anterolateral carapace margin smooth (Fig. 7A).

THIRD MAXILLIPED. Ischium with distinct vertical sulcus (Fig. 7B–C); s3/s4 complete, V-shaped, deep, midpoint almost meeting anterior margin of sterno-pleonal cavity; margins of s4 low, not raised (Fig. 7B).

CHELIPED. Dactylus (moveable finger) slim, highly arched, enclosing oval interspace, with three larger teeth interspersed by smaller teeth along length; propodus (fixed finger) with four larger teeth interspersed by smaller teeth along length (Fig. 8A); carpus inner margin distal tooth large, pointed, proximal tooth reduced to granules (Fig. 8B); medial inferior margin of merus lined with series of small granules terminating distally at small, low distal meral tooth, lateral inferior margin smooth.

G1 TERMINAL ARTICLE. 1/3 length of subterminal segment; first third straight in line with longitudinal axis of subterminal, middle part directed outward at 45°, widened by raised rounded ventral lobe, tip curving sharply upward (Fig. 9A–B).

Etymology

Named after the Baziya forest station. The specific epithet is used as a Latin noun in apposition.

Material examined

Holotype SOUTH AFRICA – Eastern Cape Province • ♂; Baziya Forest station, Afrotemperate forest streams; 31º33.917, S, 28º25.176′ E; 999 m a.s.l.; 19 May 2021; S.R. Daniels and A. Barnes; SAM A-094474.

Paratype SOUTH AFRICA – Eastern Cape Province • 1 ♂; same collection data as for holotype; SAM A-094475.

Other material

SOUTH AFRICA – Eastern Cape Province • 8 ♀♀, 8 ♂♂, 4 juvs; same collection data as for holotype; SAM A-094476.

Description

Based on male holotype (CWW = 40.30 mm, Table 1).

CARAPACE. Lacking dentition on the anteriolateral margins; widest anteriorly, narrowest posteriorly (CWP/CL = 0.47); flattened (CH /CL = 0.45) (Fig. 7A); front broad, one-third of CWW (FW/CWW = 0.35); urogastric, cardiac grooves distinct, other grooves faint or missing; postfrontal crest complete, anterolateral margin posterior to epibranchial tooth smooth, meeting epibranchial teeth; epigastric crests faint, median sulcus between crests short, forked posteriorly; anterolateral margin between exorbital, epibranchial teeth faintly granulated, curving slightly outward, lacking intermediate tooth (Fig. 7B–C); branchiostegal wall vertical sulcus faint, meeting longitudinal sulcus, dividing branchiostegal wall into 3 parts, suborbital, dorsal pterygostomial regions granulated, hepatic region smooth; suborbital margin faintly granulated.

THIRD MAXILLIPED. Filling entire buccal frame, except for respiratory openings; exopod with long flagellum, ischium with faint vertical groove (Fig. 9D). Epistomial tooth large, triangular, margins lined by large granules.

MANDIBLE. Palp two-segmented; terminal simple; tuft of setae at junction between segments.

STERNUM. s1, s2 fused; s2/s3 deep, completely crossing sternum; s3/s4 complete, V-shaped, deep, midpoint almost meeting anterior margin of sterno-pleonal cavity; margins of s4 low, not raised.

CHELIPED. Dactylus (moveable finger) slim, arched, enclosing oval interspace, with three larger teeth interspersed by smaller teeth along length; propodus (fixed finger) with four larger teeth interspersed by smaller teeth along length (Fig. 8A–B); carpus distal tooth large, pointed, proximal tooth small but distinct, followed by granule; both inferior margins of merus lined by series of small granules, distal meral tooth small, pointed.

PEREOPODS. Walking legs slender, pereopod 3 longest, 5 shortest; dorsal margins with fine sharp bristles, dactyli of walking legs ending in sharp point, with rows of spine-like bristles along segment.

PLEON. Outline broadly triangular with straight margins.

G1 TERMINAL ARTICLE. Short (1/3 length of subterminal segment), curving away from midline, first third straight in line with longitudinal axis of subterminal, middle part directed outward at 45°, widened by low raised rounded ventral lobe, tip curving gently upward. G1 subterminal broad at base, tapering to slim junction with terminal article distally where these two parts have same width, ventral side of segment with heavily setose margins; with setae-fringed flap covering lateral half of segment; dorsal side smooth, no flap, with broad membrane on dorsal side of suture marking junction between terminal, subterminal parts (Fig. 9A–B).

G2. Terminal article long, flagellum-like, 0.5 times length of subterminal article (Fig. 9C).

Size

A medium-bodied species (CL= 29.28 mm for holotype) and wide (CWW = 40.30 mm).

Colour in life

Dark brown carapace when alive (Fig. 10A).

Distribution

To date, the species has only been collected from Baziya forest station. It is likely to also occur at other localities along the Great Drakensberg Escarpment in the Eastern Cape.

Ecology

The species occurs under large boulders in small mountain streams. The sides of the streams are covered by Afrotemperate forests at Baziya forest station outside of Mthatha, Eastern Cape province, South Africa (Fig. 10B).

Remarks

Potamonautes baziya sp. nov. is sister to P. depressus from the central Drakensberg Mountains, while P. clarus is sister to the latter clade (Fig. 1). The former pair of sister species can be differentiated based on colour when alive; P. baziya sp. nov. has a chocolate brown-coloured carapace, while P. depressus from the central Drakensberg Mountains has a dark brown to yellow brown carapace (Gouws et al. 2000). In addition, P. baziya sp. nov., has a narrower carapace dorsally (CL/ CH = 2.17–2.08), while P. depressus has a more dorsally flattened carapace (CL/ CH = 2.3–2.6) which is smooth (Peer et al. 2017). Potamonautes clarus is confined to the northern Drakensberg Mountains of KwaZulu-Natal (Gouws et al. 2000). Potamonautes clarus has a bright orange ovoid carapace when alive and viewed dorsally, while the species is cream coloured ventrally. The carapace is more vaulted (CH /CL = 0.49) and the species is small-bodied (CWW = 42.7 mm) (Gouws et al. 2000). The dactylus of the right cheliped is highly arched in all three species, a pattern typical of mountain-dwelling species. The terminal segment of gonopod 1 in P. clarus is slightly longer and more slender in comparison to P. depressus. Krauss (1843) only drew the dorsal aspect of P. depressus and did not illustrate gonopods one or two. From his original drawings, it is evident that the holotype has a highly arched right cheliped. The right cheliped of P. baziya sp. nov. is also arched, albeit less so than in the P. depressus holotype; this character is likely to vary with the age of the specimen. Bott (1955) illustrated the first gonopod of P. depressus, which differs from that of P. baziya sp. nov. in being slightly more tapered towards the tip. Cumberlidge & Tavares (2006) reported that P. depressus is also possibly in Eastern Cape province. An examination of P. depressus specimens deposited in the South African Museum of Natural History, Cape Town, revealed two localities from the southern Drakensberg that are in Eastern Cape Province and, notably, also includes specimens from Hogsback. The latter locality represents the as yet undescribed species.

Four described mountain-living freshwater crab species occur in the Cape Fold Mountains. Potamonautes baziya sp. nov., can easily be distinguished from P. parvispina which has a yellowish, green-coloured carapace when alive, with an cephalothorax that is ovoid, a carapace that is flat (CH /CL = 0.50) and which is small-bodied (CWW = 38.4 mm). The species lives in first order streams in the Cederberg where is present in the upper reaches of the Olifants and Berg River systems in Western Cape Province (Stewart 1997b). Since P. parvispina has a small spine on the anterolateral carapace margins, it can easily be distinguished from the three other described species (Stewart 1997b). These three remaining species lack dentition on the anterolateral carapace margins, have an ovoid cephalothorax and are generally flat (CH /CL <0.50), with P. parvicorpus being a small-bodied species (CWW = 25.31mm) confined to the Cape Peninsula and the adjacent mountainous interior (Stewart 1997a; Daniels et al. 2001). Potamonautes brincki is also small-bodied (CWW = 32.9 mm) and known from the Hottentots Holland Mountains, while P. tuerkayi is also small-bodied (CWW = 30 mm) and known from the Overberg in Western Cape province, South Africa (Stewart 1997b; Daniels et al. 2001; Wood & Daniels 2016). Ecologically, the three latter species occur under stones in first order, fast-flowing mountains streams, and occur sympatrically with P. perlatus in the lower reaches. The undescribed species from Hogback is also present at Katberg and Fort Fordyce Nature Reserve in the Eastern Cape, South Africa (Daniels unpubl.). The undescribed Hogsback species occurs along steep cliffs under stones in high altitude (> 800 m a.s.l.) Afrotemperate forested areas where there is frequently very limited water flow, and it is sympatric with P. danielsi.