Parasesarma otiense, Shahdadi & Hosie & Hara & Chan, 2025

Shahdadi, Adnan, Hosie, Andrew M., Hara, Ana & Chan, Benny K. K., 2025, A new species of Parasesarma (Brachyura, Sesarmidae) from Western Australia, with a key to the species from Australia, ZooKeys 1255, pp. 275-290 : 275-290

Parasesarma otiense sp. nov.

Figs 2 , 3 , 4

Material examined.

Holotype. Australia • WAM C 74523 , male (14.0 × 11.0); Western Australia, Exmouth Gulf, Bay of Rest mangroves ( 22°18'54"S, 114°7'33"E); 21 June 2019; Bush Blitz Cape Range; coll. Hosie, A. M. & Hara, A. Paratypes. • WAM C 74411 , male (12.1 × 9.8); Western Australia, Exmouth Gulf, Bay of Rest mangroves ( 22°18'44"S, 114°7'38"E); 4 June 2016; NCB Exmouth Muirons; coll. Hosie, A. M. & Hara, A. • WAM C 74686 male (6.5 × 5.4); Western Australia, Exmouth Gulf, Bay of Rest mangroves ( 22°18'54"S, 114°7'33"E) ; • WAM C 86047 , Female (9.4 × 7.6); Western Australia, Exmouth Gulf, Bay of Rest mangroves ( 22°18'44"S, 114°7'38"E); 4 June 2016; NCB Exmouth Muirons; coll. Hosie, A. M. & Hara, A. • ASIZCR 000470 male (8.6 × 6.8), Western Australia, Exmouth Gulf, Bay of Rest mangroves ( 22°18'44"S, 114°7'38"E); 4 June 2016; NCB Exmouth Muirons; coll. Hosie, A. M. & Hara, A.

Diagnosis.

Ambulatory legs relatively long, P 4 longest, ~ 1.7 × cw. Carapace rectangular, broader than long, dorsal surface smooth, front moderately deflexed, shallowly sinuous in dorsal view, median postfrontal lobes as wide as lateral ones. Eyestalk longer than wide, cornea wider than eyestalk. Chelipeds without subdistal spine on dorsal border of merus; male chela with 2 transverse pectinated crests on the upper surface of palm, dactylus with 8 asymmetric tubercles with proximal slope shorter than distal slope, tubercles with transverse keel and wrinkles. Male pleon triangular, somite 2 medially longer than lateral edges. G 1 stout, straight, apical corneous process relatively long, bent at an angle of ~ 45 ° to vertical axis, aperture subterminal.

Description

(morphometrics based on the holotype but with variation and ranges in parentheses). Carapace (Figs 3 A, C , 4 A , 5 A ) rectangular, broader than long, greatest width between exorbital angles, cw / cl = 1.27 (1.20–1.27); dorsal surface smooth and shiny (Fig. 3 A, C ); front in holotype ~ 0.55 × cw (0.55–0.58), moderately deflexed, shallowly sinuous in dorsal view; postfrontal lobes distinct, median lobes as broad as lateral lobes, separated by well-pronounced furrow (Fig. 3 A, C ); dorsal regions well indicated, gastric region demarcated, cardiac region not well separated from intestinal region; lateral branchial ridges prominent; anterolateral margin with sharp exorbital angle directed anteriorly; lateral margins straight with no indication of epibranchial tooth, edged with row of short setae. Eyestalk longer than wide, cornea wider than eyestalk (Fig. 3 C ).

Chelipeds similar (Figs 3 A, B , 4 A ); chelae (Figs 3 E, F, G , 4 B, C ) large, palm length 0.76 × cw, robust, palm length 1.77 × palm width. Merus with finely granulate dorsal border, but no subdistal spine; ventral border granulate; anterior border granulate, with large subdistal spine; inner face smooth with a longitudinal row of setae. Upper surface of palm with 2 transverse pectinated crests and 2 or 3 crests consisting of granules (Figs 3 F , 4 C ), distal (primary) crest composed of 14 or 15 tall teeth (varying on opposite claws of holotype), secondary crest well developed, with 13 teeth; both crests ending on inner side in short swollen, tubercular ridge and several small granules at outer side; upper margin of palm distal to pectinated crests with some setae (Fig. 3 F ); outer surface of palm with fine granules, with granules forming a line on fixed finger (Figs 3 E , 4 B ); inner surface of palm with granules but no vertical ridge; ventral border of chela sinuous with granules; length of cutting margin of fixed finger of holotype ~ 0.4 × length of entire propodus. Dactylus (Figs 3 E, F, G , 4 B, C ) straight in outer view but slightly curved inward, ~ 0.6 × propodus length in holotype; dorsal surface bearing 8 rounded asymmetric tubercles with proximal slope shorter than distal slope, distinct to tip, tubercles with transverse keel and wrinkles, creating step-like shape for each tubercle, proximal tubercles positioned at inner part of upper dactylar face, row of small rounded tubercles on proximal half of inner edge of dorsal surface; fingers with chitinous tips, cutting edge of both fingers with a series of variably sized teeth.

Ambulatory legs (Figs 3 A , 4 A , 5 A ) relatively long; P 4 longest, length (ischium – dactylus) 1.66 × cw (1.62–1.78), merus with anterior margin crenulated, ~ 2.3 × as long as wide, propodus ~ 3.2 × as long as wide, dactylus length ~ 0.8 × length of propodus. Male pleon (Fig. 3 D ) triangular; telson slightly shorter than basal width, slightly longer than somite 6; somite 6 longer than others; somite 5 and 4 trapezoidal, somite 3 widest, laterally convex, somite 2 medially longer than lateral edges. G 1 (Fig. 3 D – G ) stout, straight, stem triangular with blunt angles in cross-section; apical corneous process relatively long, bent at an angle of ~ 45 ° to vertical axis, tip rounded, aperture subterminal.

Females (Fig. 5 ) with proportionally smaller chelipeds than males, palm length 0.50 × cw; pectinated crest absent on palm, replaced by rows of granules; dactylus with 8 small but distinct, round tubercles. Pleon (Fig. 5 B ) broad, rounded, broadest at somites 3 and 4, fringed with long setae, touching coxae of ambulatory legs. Vulva (Fig. 5 C ) in depression on anterior edge of sternite 6, operculum oval, parallel and touching line of sternite 5, oval operculum in anterior part of vulva.

Etymology.

The species name is derived from the Latin noun otium, meaning rest, and the gender-neutral suffix, - ense, in reference to the type locality, the Bay of Rest in Exmouth Gulf, Western Australia.

Habitat.

Intertidal fringing mangrove and associated mud flat.

Figures

Figure 2. Bayesian Inference phylogram constructed in BEAST 2.7. 7 for 16 S sequences of Parasesarma. The numbers behind the nodes refer to the support values (posterior probability) (posterior probabilities under 0.90 are not shown). Sequences belonging to Sesarmoides longipes, Fasciarma fasciatum, and Perisesarma dussumieri were used as outgroups. The numbers in front of species names are GenBank accession numbers. Sequences obtained in the present study are shown in red and the newly described species are in bold font (the numbers left to species names are Western Australian Museum numbers).

Figure 3. Parasesarma otiense sp. nov., holotype, WAM C 74523, male (14.0 × 11.0), Western Australia, Exmouth Gulf, Bay of Rest mangrove. A. Dorsal habitus; B. Frontal view; C. Carapace, dorsal view; D. Pleon and mouth; E. Right chela, outer view; F. Left chela, dorsal view; G. Dactylus of right chela, dorsal view.

Figure 4. Parasesarma otiense sp. nov., paratype, WAM C 74411, male (12.1 × 9.8), Western Australia, Exmouth Gulf, Bay of Rest mangrove. A. Dorsal habitus; B. Left chela, outer view; C. Left chela, dorsal view; D – G. Left G 1; D. Full dorsal view; E. Distal tip, dorsal view; F. Distal tip, ventral view; G. Distal tip, dorsal view, denuded.

Figure 5. Parasesarma otiense sp. nov., paratype, WAM C 86047, Female (9.4 × 7.6), Western Australia, Exmouth Gulf, Bay of Rest mangrove. A. Dorsal habitus; B. Ventral habitus; C. Vulvae (Op = operculum).