Bioacoustics of Mursia bicristimana

Remarks. The genus suffered from taxonomic confusion due to the relative rarity and superficial resemblances of its species. Twenty-eight species are known, of which thirteen have been described in the past two decades. Mursia bicristimana was described and illustrated from a single pre-adult female (CL 21 mm ) from the Gulf of Manaar (Alcock & Anderson 1894a: 179; 1896, pl. 24, fig. 5) ( Fig. 5 ). A larger male specimen (CL 47 mm ) subsequently collected off Colombo, Sri Lanka , was listed by Alcock (1896: 150; 1899: 23, pl. 3, figs 3, 3a, b) and Alcock & Anderson (1896, pl. 24, fig. 5). These specimens, deposited in the collections of the Zoological Survey of India , Calcutta, were unavailable for examination. Therefore Galil (1993: 356, figs. 1f, 3j–k, 5c–d) based her description and illustrations of M. bicristimana (1993: 356, figs. 1f, 3j–k, 5c–d) on a pre-adult male specimen (CL 19.1 mm , NHM 1898.8.26.3) labeled “ Syntype ? Alcock det., 11˚14’30"N 74˚57’15"E, 68–140 fathoms, coll. Indian Museum”. Spiridonov & Apel (2007: 2861) pointed out that the presumed syntype specimen was most probably “collected at a different locality and four years after the description of M. bicristimana was published” and consequently could not have been a syntype . Spiridonov & Apel (2007) assigned the specimen from Lakshadweep (= Laccadive Is) to a new species, M. minuta Spiridonov & Apel, 2007 , and noted that the lateral spines “in adult specimens from the Andaman Sea and the Nicobars reach about 0.15–0.18 times CW, while the Gulf of Aden specimens have somewhat shorter spines reaching only about 0.10 times CW in adult specimens”, but opted not to take “further taxonomic and nomenclatural actions” pending comparison with the type material of Alcock (Spiridonov & Apel 2007: 2866). Owing to the erroneous labeling of the NHM material and resulting misidentification, a large male specimen (CL 42.2 mm ) collected in the Andaman Sea (ZRC 1999.0086) was misidentified, first as M. africana (Ng et al . 2002), and then as a new species (Lai & Galil 2006). Although the types of M. bicristimana could not be examined, careful scrutiny of the descriptions and illustrations (Alcock & Anderson 1894a: 179; 1896, pl. 24, fig. 5; Alcock 1896: 150; 1899: 23, pl. 3, figs. 3, 3a, b, fig. 5) allows assigning the Kerala material, as well as to the specimens collected in the Andaman Sea (USNM 309672), to M. bicristimana . The general form and carapace proportions, and the characteristic palmar crest, (“sharp crest, the edge of which is unevenly trilobed, the proximal lobe being short acute and spiniform, the middle lobe being broad and obtuse, and the distal lobe being narrow and obtuse”; Alcock & Anderson 1894a: 179) are similar, as is the straight postero-lateral margin (“the postero-lateral margins are without the angular bend inward”; Alcock, 1896: 150). The specimens collected in the Gulf of Aden, having noticeably shorter lateral spines, undulating postero-lateral margin, and differing in the shape of palmar crest, dactylar stridulating ridge and female genital opening cap, are here referred to as a new species of Mursia .

Description. Carapace transversely subovate, convex, regions poorly marked, 1.35 wide as long (excluding lateral spines). Dorsal surface covered with closely­spaced perliform granules increasing in size laterally. Granular protuberances, diminishing in size posteriorly, disposed in 7 radial rows on dorsal surface of carapace. Mesogastric region highest part of carapace. Gastric, cardiac, intestinal regions separated from branchial regions by shallow, sinuous longitudinal grooves. Anterolateral margin arcuate, crenulate, denticulate and beaded. Lateral spine slim, acuminate, slightly curved upwards and forwards, about one sixth (0.17) carapace width, proximally granulate on upper surface. Posterolateral margins beaded, oblique, sharply convergent. Posterior margin intermittently beaded, lateral teeth triangular, dorsoventrally flattened, median lobe nearly obsolescent. Front as wide as orbit. Frontal margin projecting beyond orbits, trilobate, median lobe broadly triangular, at lower plane than lateral lobes; lateral lobes rounded, separated from supraorbital margin by shallow concavity. Antennules obliquely folded. Supraorbital margin with a single slight fissure, minutely granulate, bearing long plumose setae. Inner orbital tooth separated from outer orbital margin by deep U­shaped cleft, and from front by orbital hiatus. Antennae small, slender, basal segment article subrectangular, lodged in orbital hiatus. Eyes retractable, eyestalk short, granulate, setose. Buccal frame rhomboidal, narrowing anteriorly. Thick fringe of plumose setae running the length of third maxilliped endopod, merus and ischium granulate, bearing short setae. Subhepatic region tomentose. Sternum granulose. Male abdomen with segments 3–5 fused; prominent trilobate carina on second segment, prominent subquadrate lateral lobes separated by narrow clefts from lower subquadrate median lobe (see fig 1A); sixth abdominal segment subquadrate, lateral margins sinuous; telson triangular, slightly shorter than sixth segment. Chelipeds massive, granulate, nearly equal. Merus bispinose dorsodistally, distal spine longer, stouter than subdistal spine. Antero­distal margin of carpi ending in triangular denticle. External surface of manus convex, upper margin crested, setose. Larger chela bearing dorsal crest with seven denticles, teeth 1–3 successively larger, teeth 4–7 progressively more laciniate (numbered from proximal to distal). External surface prominently granulate, with 3 small granular tubercles near base of crest, several nearly effaced, granulate tubercles mid chela, and prominent, sinuous ridge, proximally unidentate, with closely granular margin, above lower margin. Internal surface with tomentose band near lower margin. Lower margin granulate, serrate, serrations successively smaller proximally. Upper margin of dactylus crested, setose, proximally granulate; with curved rounded tooth proximally fitting into depression in molariform tooth in pollex; inner surface of dactylus bearing stridulating ridge consisting of about 30 striae larger medially. Smaller chela lacks the large dactylar tooth. Pereopods 2–5 slender, laterally compressed, upper and lower margins minutely granulate; upper margin of carpi distally spinose; dactyli slender, longer than propodi, styliform. First male pleopod tapering evenly, curved, distally spinulose. Second male pleopod long, slender; cornute, distal portion crook­shaped, tip twisted inwards, upcurved ( Fig. 2 A)