Parasesarma hartogi, Davie & Pabriks, 2010

Davie, P. J. F. & Pabriks, L., 2010, A new species of Parasesarma (Crustacea: Brachyura: Sesarmidae) from the mangroves of Western Australia, Zootaxa 2564 (1), pp. 62-68 : 63-67

Parasesarma hartogi sp. nov.

( Figs 1 , 2 )

Sesarma (Parasesarma) sp. 1: Davie, 1982: 207 (in list).

Material examined. Holotype: WAM-C118-76, ♂ (35.5× 28.8 mm), Shark Bay , WA, 25°47’59"S, 113°1’11"E, mangroves. 4.10.1975, R. G.W. George.

Paratypes: WAM-C118-76, 3 ♂ (37.7×31.1, 31.1×24.4, 35.6× 27.8 mm), Shark Bay , WA, 25°47’59"S, 113°41’11"E, mangroves, 4.10.1975, R. G.W. George. WAM-C1-62, ♂ (22.3× 17.7 mm), ovig. ♀ (20.0× 15.5 mm), Herald Bluff, Shark Bay , WA, 25°38’59"S, 113°35’11"E, mangroves, 2.01.1962., D.G. Bathgate. WAM- C158-63, 2 ♂ (31.5×26.3, 34.1× 26.9 mm), Faure Island , Shark Bay , W.H. Butler, 13.05.1959. WAM-C40375, ♂ (34.3× 27.1 mm), Faure I., Shark Bay , WA, no date, B. R. Wilson. WAM-C40374, ♂ (29.4× 23.5 mm), Faure I., Shark Bay , WA, no date, B. R. Wilson. WAM-C40376, 2 ♂ (30.6×23.3; 30.0× 23.3 mm), ♀ (24.2× 18.3 mm), west side of Hooley Creek mouth, Onslow, WA, 14.11.2008, B. R. Wilson. WAM-C40371, ♀ (13.4× 10.2 mm), bank of Four Mile Ck, west of Onslow , WA, 14.11.2008, B. R. Wilson. WAM-C40372, ♀ (13.4× 10.2 mm), bank of Four Mile Ck, west of Onslow , WA, 14.11.2008, B. R. Wilson. QM-W28879, 3 ♂ (27.6×20.8; 28.7×21.9; 19.0× 13.4 mm), Four Mile Ck, west of Onslow , WA, 21°27' S, 119°23' E, estuarine, 14.02.2009, B. R. Wilson. WAM-C40377, 3 ♂ (20.0×15.2; 21.3×16.4; 23.0× 17.7 mm), entrance to main channel, south side, c. 1 km from mouth of Ashburton River , WA, 14.02.2009, B. R. Wilson. WAM-C40377, ♂ (16.1× 12.4 mm), entrance to Ashburton River, WA, 14.02.2009, B. R. Wilson. WAM-C40373, ♂ (15.5× 12.1 mm), south side of main channel, Ashburton River, WA, 14.02.2009, B. R. Wilson. WAM-C161-63, ♂ (27.7× 21.1 mm), ♀ (24.2× 18.5 mm), Old Landing, Mundabulleagapa, northern WA, approx. 20°20' S, 118°32' E, mangroves, 3.11.1960, M. Tyndale-Biscoe .

Diagnosis. Carapace rectangular, greatest width between prominent epibranchial angles; lateral margins slightly convergent posteriorly. Carapace surface relatively smooth; setae very short, sparsely scattered. Chelipeds with upper surface of palm bearing 2 transverse, pectinate crests; primary (distalmost) crest composed of 9–13 tall, broad teeth; secondary crest with 9–11 slightly shorter teeth. Cutting edge of fixed finger 0.47 to 0.48 times length of chela. Dorsal surface of dactyl with 8 or 9 symmetrical, rounded, calcareous tubercles, indistinct proximally, becoming higher distally. Wide gape between cutting margins of large adult males. Male abdomen moderately broad, somite 6 with convex margins, about twice as wide as long; telson slightly longer than wide (1.1 times), about same length as somite 6, evenly rounded. Male G1 moderately stout, straight, apical process corneous, strongly produced, lying about 45° to stem.

Description. Carapace rectangular, greatest width between epibranchial angles; males 1.2–1.28 times broader than long, females typically slightly broader (1.26–1.31); deep, dorsal surface evenly convex; regions moderately well defined. Lateral margins slightly convergent posteriorly behind prominent epibranchial angles. Front 0.55 times fronto-orbital width; sinuous; lateral angles weakly produced, pointed anteriorly. Post-frontal lobes distinct; median lobes slightly broader than laterals. Epi-branchial and branchial ridges prominent. Carapace surface relatively smooth; setae very short, sparsely scattered over entire surface. Antennal flagellum small, entering orbit. Basal antennular segment not swollen. Inter-antennular septum moderately wide, 0.27 times width of front.

Chelipeds subequal, large, robust; merus trihedral with posterior border carinate, minutely granulate; broad, triangular, subdistal spine before wide, smooth sulcus; anterior inner border with row of large granules leading to acute, broad, anteriorly directed spine at about two-thirds distal length; outer margin coarsely granular; carpus with inner angle not produced, inner margin granular; dorsal surface of outer margin striated. Upper surface of palm with 2 transverse, pectinate crests; primary (distalmost) crest composed of 9–13 tall, broad teeth; secondary crest similarly strongly developed, with 9–11 slightly shorter teeth. Outer surface of palm evenly granular; without median longitudinal row; granules becoming striated ventrally; without setae. Inner surface of palm with moderately raised coarsely granular vertical crest curving towards fixed finger. Fixed finger rounded on outer surface distally; with low flattened depression basally; obvious granular ventral ridge extending onto palm below articulation; length cutting edge 0.47 to 0.48 times length propodus. Ventral border of chela relatively straight, slightly concave at base of fixed finger. Dorsal surface of dactyl with 8 to 9 symmetrical, rounded, calcareous tubercles, indistinct proximally, becoming higher distally. Fingers curved inwards; wide gape between cutting margins of large adult males; dentition relatively even, without conspicuous, larger, prominent teeth; tips chitinous, apically cleft.

Walking legs medium length, relatively slender, laterally flattened; third pair the longest, 1.7 times maximum carapace width. Merus of third leg 2.4 times longer than wide; propodus 2.4 times longer than wide; dactylus subequal in length to propodus, stout, slightly recurved; terminating in acute chitinous tip. Merus anterior margin with acute sub-distal spine; unarmed terminally; upper surface with relatively long transverse striations anteriorly. Carpus with 2 accessory longitudinal carinae on upper surface. Propodus with inferior longitudinal accessory carina along entire length. Legs fringed with stiff bristles except on meri; denser “fur” of setae on anterior surfaces of propodi and distal half of carpi, densest on legs 1–3.

Male abdomen moderately broad, lateral materal margins of somites 3–6 relatively evenly converging; somite 6 with convex margins, approximately twice as wide as long; telson slightly longer than wide (1.1 times), about same length as somite 6, evenly rounded.

Male G1 moderately stout, straight, apical process corneous, strongly produced, lying about 45° to stem. Gonopore sub-terminal, tip cut away ventrally. Long setae mainly restricted to outer margin of distal quarter and around tip.

Habitat. Favours burrowing around high water mark amongst mangroves. Collector’s notes included: “burrows above high water mark among sticks and salt bush; brackish water”; “among mangroves in burrows on banks of channel”, and “mud bank, grass and Avicennia mangrove fringe”.

Etymology. Named for Dirk Hartog, the Dutch ship commander, who landed at the type locality in Shark Bay in 1616, thus becoming the first European to land on the western coast of Australia.

Distribution. Known from Western Australia, from Shark Bay north to Mundabulleagapa, south of Port Hedland. May possibly extend further south as far as the Houtman Abrolhos Islands which are classified by Duke (2006) as having the same type of “Ephemeral Arid Embayments” mangrove habitat.

Remarks. Parasesarma hartogi sp. nov. belongs to the Parasesarma plicatum species-group (sensu Rahayu & Ng 2010), and thus its closest congeners are P. plicatum ( Latreille, 1803) , P. affine (De Haan, 1837) , P. ungulatum (H. Milne Edwards, 1853) , and P.dumacense ( Rathbun, 1914) . The review by Rahayu & Ng (2010), has clarified the taxonomic and nomenclatural confusion in this species group, and has made the task of comparing the new species much simpler.

Parasesarma hartogi sp. nov. differs from all other similar Parasesarma species by its carapace shape, which is significantly broader between the epibranchial angles, whereas other species appear to be widest across the exorbital angles (or at least equally wide at this point). In addition, the epibranchial angles of P. hartogi sp. nov. are unusual by almost forming a tooth in some individuals, though always remaining obtuse despite being acutely prominent. In this character P. hartogi sp. nov. certainly begins to approach species in its sister-genus Perisesarma . Mature males of the new species also seem to develop a significantly larger gape between the fingers than do the other species of the Parasesarma plicatum species-group (c.f. figures in Rahayu & Ng 2010).

The true Parasesarma plicatum from the eastern Indian Ocean is easily separated as it has a greater number of more prominent dactylar tubercles (11–14), although as with P. hartogi , the proximal ones are smaller, and the distal ones become very low.

Parasesarma affine , so far known from Japan, China, Taiwan and Hong Kong, is similar to P. hartogi sp. nov. in having 8 or 9 dactylar tubercles, but in P. affine these tubercles are also proportionately larger, more prominent, and have a narrow, transversely subovate median flattened ridge marking the highest point. Furthermore, the G1 apex of P. affine (see Rahaju & Ng 2010, fig. 7A–D) is somewhat different, with the shaft more evenly tapering distally, and the tip, while bent at a similar angle, has its outer distal edge straight from the base such that it lacks the more clearly defined and narrower snout of P. hartogi sp. nov. ( Fig. 3C, D ) Life colours are also quite different (compare Fig. 4 with Rahaju & Ng 2010, fig. 8).

Parasesarma ungulatum is the most widely distributed of the members of this species-complex, occurring from western Thailand, through the central Indo-Malaysian region and north to Hong Kong. It can be easily separated from P. hartogi sp. nov. by the greater number of dorsal dactylar tubercles (10–12). Like P. hartogi sp. nov., these are small proximally, becoming larger distally, but all tubercles are distinct, subcircular, marked with fine transverse lines, and carry a transverse ridge on the tip. The G1 tip is also markedly different, being only slightly bent distally and the corneous apical portion is very broad and stout ( Fig. 3C, D ; cf. Rahaju & Ng 2010: Fig. 10A–D).

Parasesarma dumacense , currently only known from the Philippines, has the same number of dactylar tubercles as P. hartogi sp. nov., but they are relatively more prominent, and the apex of each tubercle is marked by a narrower, flattened ridge. In addition, the greatest carapace width is between the exorbital angles in P. dumacense (further back between the epibranchial angles in P. hartogi sp. nov.); the male G1 is less bent and the corneous distal portion is broader; and the live colours differ, with the claw of P. dumacense being predominantly bright orange yellow, and the carapace patterned with blotches (compare Fig. 4 with Rahaju & Ng 2010, fig. 12).

Figures

FIGURE 1. A–E, Parasesarma hartogi sp. nov., holotype ♂, 35.5×28.8 mm (WAM-C118-76). A, Dorsal view of carapace and legs; B, enlargement of carapace in more vertical view; C, frontal view of carapace, orbits and pterygostome.

FIGURE 2. Parasesarma hartogi sp. nov., holotype ♂, 35.5×28.8 mm (WAM-C118-76). A, frontal view of left chela and carpus; B, dorsal view of chela showing pectinate crests, dactylar tuberculation, and crested inner face of chela; C, male abdomen; D, female abdomen.

FIGURE 3. Parasesarma hartogi sp. nov. A, outer face of chela; B, male abdomen; C, enlargement of tip of G1 (denuded); D, G1 in lateral view; E, female abdomen. A, C, D = holotype ♂ (WAM-C118-76); B = paratype ♂ (WAM- C158-63); E = paratype ♀(WAM-C161-63). Scale A, B, E = 5 mm; C = 2 mm; D = 0.5 mm.

FIGURE 4. Parasesarma hartogi sp. nov., variations in colour (specimens were all unpreserved and recently dead): A, B, moderate size male, showing typical pale fawn to orange colour with darker orange claws; C, slightly larger male, and somewhat darker; D, E, large male showing dark red-brown carapace, and dark maroon chelipeds with distinctive bright orange patches around base of gape, on base of dactyl, and around inner margin of carpus; the presence of these contrasting colours in large specimens appears characteristic of the species, but the pattern and extent of coverage is variable amongst individuals. All photographs relate to specimens examined, but were not cross-referenced to individuals in the field.