Bioacoustics of Hartnollius lateralis

Diagnosis. Male abdomen triangular; telson campanulate, narrower than sixth abdominal somite, lateral margins slightly marked, tip rounded. Sixth somite with convex lateral margins, forming lateral shoulder ( Fig. 2B ). Female abdomen subcircular, completely or almost completely covering thoracic sterna; telson triangular, as wide as posterior margin of sixth somite, lateral margins straight, smooth ( Fig. 3D ). Antero-lateral margins of sternite 3 slightly convex, those of sternite 4 straight, with slight concavity ( Figs. 2B , 3D ). Shallow endostomial ridges delimiting efferent branchial channel, poorly defining this region. Third maxilliped with merus generally concealing epistome. Adult male chelae different in size and robustness; inner surface of palm of major chela with longitudinal tuberculated ridge, used as stridulatory plectrum.

Description. Based on adult male with G1 well developed ( 54.3 mm CL, 71.7 mm CW). Carapace transversely oval, wider anteriorly, strongly arched at level of branchial regions, anterolateral margin incipient, posterior portion of external orbital angle slightly marked, armed with minuscule granules. Regions well defined, delimited by shallow grooves. Branchial regions prominent. Fronto-orbital margin about 1/2 of maximum carapace width (Fig. 1A). Front about 1/4 length of carapace, deflexed, surface slightly concave, occasionally straight, inferior margin granulated, raised from surface, straight, generally concealing basal segments of antennules; frontal lobes poorly defined ( Fig. 2A ). Orbits delimited by well defined, smooth superior border. Infra-orbital margin granulated, interrupted by deep notch, continued as triangular plate forming mesial lobe. Suborbital ridge well marked (stridulating crest of Guinot et al . 2018 ), extending from superior border of epistome to subhepatic suture. Surface of anterolateral wall of carapace reticulated (pars strident). Third maxillipeds not closing completely, leaving rhomboidal gap; merus covering epistome anteriorly, anterior border with medial notch, occasionally straight; ischium longer than merus, subequal in width. Palp short, hidden and articulated behind merus, directed laterally ( Fig. 2A ). Short exognath hidden behind ischium. Strong heterochely in males, subequal chelipeds in females; fingers longer than palm, with corneous tips; longitudinal rows of granules throughout surface; cutting margins bearing 6–8 irregularly spaced blunt teeth; dactyl slightly curved inwards; fingers gapping ( Fig. 2D ). Internal surface of palm swollen, with distinct longitudinal ridge along midsection, used as stridulatory plectrum, internal depression next to articulation with carpus. Carpus subtriangular, dorso-mesial margin smooth in large organisms, spinulous in small ones. Merus elongated, subtriangular, internal border granulated. Pereiopods (2–4) long, slender, with short setae; merus elongated, surface striated; carpus subtriangular, shorter than propodus, or almost of same length in fifth pair, dorsal margin toothed; propodus shorter than dactyl, dorsal and ventral margins formed by short, slender spines; dactyli armed with 4–6 rows of spines, those on lateral carina poorly developed to absent ( Fig. 2C ). Male and female abdomen as in species diagnosis. Male G1, as in genus diagnosis ( Fig. 3A ). Female ( 39 mm CL, 33–50 mm CW), with gonopore on sixth plate of thoracic sternum, protruding. Ring around operculum oval, with sharp edges; operculum a large, oval, protruding lobe. Coloration . Dorsal surface of carapace dark, lateral margins orange, posteriorly light cream. Chelipeds and lower portion of front orange (Fig. 1A) Measurements. Males: 28.6–49.1 mm CL; 33.9–64.5 mm CW. Females 27.3–39 mm CL, 33–50 mm CW.

DIAGNOSIS Carapace Carapace of smaller size than Gecarcinus ruricola , broader than long but proportionally less broad than G . ruricola , relatively flat, with hepatic, subhepatic and branchial regions not markedly inflated; widest part of carapace being in line with antero-lateral angles of mesogastric region. Fronto-orbital distance about half or a little less than half of maximum carapace width in adults. Dorsal surface with shallow grooves: cervical groove ending anteriorly in a pit near orbital angle; median (or urogastric) groove and longitudinal mesogastric groove rising towards frontal margin. Numerous striae along lateral margins of the carapace, used as stridulatory pars stridens. Front short, broad, moderately produced and deflexed, widening very little below, its inferior margin being slightly arcuate. Mesial lobe of infraorbital margin angular, just joining front edge and completely exposed. Antero-lateral margins entire, not markedly rounded, joining exorbital angle, with more or less marked junction; marked by granular row in females. Cephalic structures Antennules very small, folded obliquely. Antennae very short, completely exposed. Orbits small, with marked angle at anterolateral margin. Eyestalks relatively short, curved. Proepistome, epistome and pterygostome Proepistome covered by subfrontal plate. Epistome developed, with one median crest and a lateral crest on each side, setose. Buccal cavity rhomboid. Subhepatic and pterygostomial region glabrous, with many striae. Mxp3 Mxp3 rather small, not reaching epistome, leaving between them a narrow rhomboid gap, in longitudinal position. Ischium and merus subequal, with their articulation only slightly oblique; ischium barely smaller than merus, without longitudinal groove (only a small trace); merus only slightly directed obliquely, not narrowing anteriorly; anterior margin with slight but distinct emargination, sometimes only concave and with barely marked notch; meri of both sides not joining medially; palp inserted below merus: palp with first article fused to merus internal surface and with mobile distal article barely exposed. Exopod of mxp3 as narrow plate, completely concealed by fringe of thick setae, apex not reaching ischium-merus articulation; without flagellum. Chelipeds Male chelipeds massive but not extraordinarily enlarged, very unequal especially in old males, widely gaping; heterochely variable, usually slightly marked; occlusal margins of fingers with small, spaced teeth on both sides; in the rare cases of greatly uneven chelipeds (heterochely), a more pronounced gap and pronounced heterodonty. Merus and carpus of adults without row of granules, entirely smooth or may be with two spiniform granules; young adults with two rows of teeth on merus and spiniform granules on inner margin of carpus. Inner surface of palm of chelae used as stridulatory plectrum by rubbing on pterygostomial striae (pars stridens). Female chelipeds subequal or nearly so, moderately gaping, therefore sexual dimorphism moderate. Ambulatory legs P3 moderately spiny. Propodus with unequally developed lateral carinae bearing four rows of weakly developed spines. Dactylus with four rows of small equal spines. Sterno-pleonal cavity and pleon Sterno-pleonal cavity completely glabrous, short, ending far from sternal suture 2/3, with marked ridge around telson. Male pleon moderately long, bell-shaped; with all somites free plus telson; lateral margins with fringe of setae; somite 6 with convex lateral margins, forming lateral shoulder; telson campanulate, narrower than somite 6, with lateral margins slightly marked, tip rounded, relatively narrow. Female pleon subcircular; telson forming isosceles triangle, as wide as or slightly narrower than posterior margin of somite 6, lateral margins straight, smooth. Thoracic sternum, locking pleonal structures and setal tufts Thoracic sternum wide, narrowing at level of somite 5, thus restricted at level of P1; sternite 1 as small triangular tooth, not separated by suture from sternite 2, not recessed; sternite 2 semi-ovate, with strongly convex margins; suture 2/3 present, practically straight or barely concave and only forming an obtuse angle; suture 3/4 absent, without lateral trace; sternites 3 +4 completely fused, with concave, obliquely directed margins; sutures 4/5 to 7/8 interrupted; sternites 5-7 similarly shaped, sutures well defined; suture 7/8 rather short; sternite 8 not developed medially, totally hidden when pleon is folded; posterior emargination reaching sternite 7; at level of suture 7/8 only some traces of bridges; deep median line only along sternite 7. Locking pleonal structure as prominence covered by setae, rather close to suture 4/5; corresponding pleonal sockets not delineated, so pleonal locking no longer functional ( Guinot & Bouchard 1998: 660 , 685; Köhnk et al. 2017: 2212 ). Setal tufts of more or less dense hydrophilic setae located along first pleonal somites, margins of pleon and at its junction with carapace. Male gonopore and penis Male gonopore and penis at level of suture 7/8 emerging rather far from P5 coxo-sternal condyle. G1 and G2 G1 slightly tapering at its extremity, apex short, with unequal setae at its end; laterally, a very long, narrow, horny, unfolded and curved tube, open over a long length and exceeding G1 tip; several horny setae at its base. G2 very small, without flagellum. Vulvae Protruding, oriented nearly horizontally, normally occluded by rigid calcified immobile operculum. COLOUR Based on Gecarcinus lateralis from Bermuda described by Verrill (1908: 308) , Rathbun (1918: 356) wrote: “Commonly the carapace is mostly of a deep reddish brown or plum color; often this color is replaced posteriorly by a wide transverse band of lighter color spotted with yellow; this band extends forward, along each side, becoming narrower and darker, disappearing near the eye-sockets; a pair of small white spots close behind the eye-sockets and another pair in the cardiac region; legs light grayish brown; chelipeds darker and more red; last joint bright orange, underside white.” See also Chace & Hobbs (1969: 198 , figs 5A-C, 6A-C, 7, 8, as G. lateralis ); Parasram et al. (2021 : fig. 8, as G. lateralis ) ( Fig. 19 ). According to Perger & Wall (2014: 105 , table 2), the colour of the Pacific Gecarcinus lateralis they examined showed little variation (see their figs 5A, 7E-F, 8G, H) and did not approach the range of variability found in G. lateralis from the Atlantic coast of Central America, characterised by morphs with transitional forms (see their figs 5B, C, 7A-D, 8A-F). For a detailed study of the colour variation in G. lateralis from Bimini , Bahamas , and from the Bermudas , see Martinez & Bliss (1989 : figs 1-12, pls 1-3, as G. lateralis ). VERNACULAR NAMES ‘Black land-crab’, ‘common land-crab’ ( Rathbun 1918 ); ‘black-backed land crab‘ in Saint Martin ( Yokoyama 2013 ). Also called ‘Tourloulou’ or ‘Touloulou’, like other species of Gecarcinidae , including Gecarcinus ruricola .