Bioacoustics of Hartnollius quadratus

Description. Carapace transversely oval, wider anteriorly, strongly arched at level of branchial regions, anterolateral margin thin. Regions well-defined, delimited by shallow grooves. Branchial regions prominent. Fronto-orbital margin about half of maximum carapace width (Fig. 1B). Front about 1/4 length of carapace, deflexed, surface slightly concave; inferior margin lightly granulated, not raised from surface, straight, leaving visible basal segments of antennules; frontal lobes poorly defined ( Fig. 2E ). Orbits delimited by well defined, smooth, superior border. Infra-orbital margin granulated, interrupted by deep notch, continued as subrectangular or low subtriangular plate forming mesial lobe; area of contact between internal angle of front and mesial lobe of infraorbital margin of variable width ( Perger & Wall 2014 ), reaching superior border of epistome. Suborbital ridge softly marked, short, extending laterally from superior border of epistome, not reaching subhepatic suture. Third maxillipeds not closing completely, leaving rhomboidal gap; merus not reaching epistome, anterior border straight, occasionally with shallow emargination or discontinuity; ischium with scattered setae on mesial margin, subequal in width to merus, but longer than it ( Fig. 2E ). Palp short, hidden, articulated behind merus, directed laterally. Exognath hidden behind ischium, without flagellum, not reaching ischium-merus articulation. Chelipeds in both sexes subequal or similar, evident heterochely in largest males. Chelae with fingers longer than palm, with corneous tips, surface with longitudinal rows of pits and granules, more evident dorsally; cutting margins with distinct subacute tubercles along fingers length, dactyl slightly curved inwards, with 8-10 irregularly spaced small blunt teeth, largest tooth on proximal half; fixed finger with 11-12 irregularly spaced small blunt teeth, largest tooth on distal half; fingers gapping ( Fig. 2H ). Palm with internal surface smooth, swollen, without tuberculated longitudinal ridge, internal depression next to articulation with carpus. Carpus subtriangular, dorso-mesial margin smooth in large organisms or with spinules in small ones. Merus elongated, subtriangular, inner surface striated, used as stridulatory plectrum. Pereiopods long, slender with short setae; merus elongated, surface striated, dorsal ridge distally spinulated; carpus subtriangular, shorter than propodus, or almost of same length in fifth pair, distal half of dorsal ridge spinulated; propodus shorter than dactyl, dorsal, ventral and lateral ridges armed with short, thin spines; dactyli armed with 6 rows of spines ( Fig. 2G ), 5 rows in juveniles. Male and female abdomen as in species diagnosis. Male G1, as in genus diagnosis ( Fig. 3B, C ). Coloration. Dorsal surface of carapace dark purple, posterior and postero-lateral margins yellow or slightly orange, as well as the ambulatory appendages. Yellow or light orange patches above orbits, and on lower part of front. Chelipeds purple, carpus and merus darker (Fig. 1B). Measurements. Males: 35.8–54.3 mm CL; 44.9–71.7 mm CW. Females 33– 51.8 mm CL; 38.7–63.9 mm CW.

DIAGNOSIS Carapace Carapace smaller than that of Gecarcinus ruricola but larger than that of Hartnollius lateralis n. comb. , broader than long, relatively flat, with hepatic, subhepatic and branchial regions only slightly inflated; widest part of carapace being in line with antero-lateral angles of mesogastric region. Carapace front about as wide as distance between mesial ends of suborbital cristae. Dorsal surface with shallow grooves: cervical groove terminating anteriorly in a pit near orbital angle; median (or urogastric) groove and longitudinal mesogastric groove rising towards frontal margin. Fronto-orbital distance about half or a little less than one half of maximum carapace width in adults. Front short, broad, moderately produced and deflexed, widening very little below, its inferior margin being slightly arcuate. Numerous striae along lateral margins of the carapace, used as stridulatory pars stridens. Mesial lobe of infraorbital margin angular, just joining front edge and completely exposed. Antero-lateral margins entire, rounded, joining exorbital angle, with more or less marked junction, smooth in males; delineated by granular row in females. Cephalic structures Antennules very small, folded obliquely. Antennae very short, completely exposed. 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, reaching epistome, leaving between them a narrow rhomboid gap, in longitudinal position. Ischium and merus subequal, with their articulation only slightly obliquely directed; ischium barely smaller than merus, without longitudinal groove (only a small trace); merus slightly directed obliquely, anterior margin straight, without distinct emargination, at the very least barely concave, or showing only discontinuity or even having very small notch; meri of both sides practically joining medially; palp inserted below merus: palp with first article fused to merus internal surface and with only small portion of mobile distal article 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 largest males, not widely gaping; heterochely variable, usually slightly marked; occlusal margins of fingers with small, spaced teeth on both sides; in case of greatly heterochely, pronounced heterodonty. In adults, merus with only small granules and carpus smooth on inner lower margin. 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 six rows of small unequal spines, with 5 rows in juveniles. Sterno-pleonal cavity and pleon Sterno-pleonal cavity moderately setose, short, not close to sternal suture 2/3, with marked ridge around telson. Male pleon moderately long, bell-shaped; with all somites free plus telson; lateral margins only with fringe of setae; somite 6 with gently convex lateral margins, forming lateral shoulder; telson equilateral triangle-shaped, narrower than posterior margin of somite 6, lateral margins slightly concave. 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 slightly 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 margin at level of articulation of P1 and convex at junction of mxp3; 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 narrow median bridge at level of suture 7/8; 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 (see also Köhnk et al. 2017: 2112 ). 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 tip; laterally, a very long, narrow, horny, unfolded, curved tube, open over all along 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 Sex independent colour dimorphism: in males and females, purplish, red, white, with variously coloured spots, intense purple chelipeds and light yellow or orange legs ( Fig. 20 ). For more details, see Perger & Wall (2014: 101 , figs 4, 5D) and Toledano-Carrasco (2019: 24 , fig. 10B).