Rhopalophthalmus mumbayensis, Panampunnayil & Biju, 2006

Panampunnayil, S. U. & Biju, A., 2006, Four new species of the genus Rhopalophthalmus (Mysidacea: Crustacea) from the northwest coast of India, Journal of Natural History 40 (23 - 24), pp. 1389-1406 : 1391-1396

Rhopalophthalmus mumbayensis sp. nov.

( Figures 1–27 )

Material

Holotype: adult male (IOBC-0503-10-50-1999). Allotype: adult female (IOBC-0503 A- 10-50-1999). Paratypes: five adult males and five adult females (IOBC-0503 B-10-50- 1999).

Dharamtar: (18 ° 42.00 9 N, 73 ° 01.80 9 E); October to November 1984, 34 adult males, 46 adult females, 12 immature males, 24 immature females, and eight juveniles. Thane: (19 ° 11.20 9 N, 72 ° 59.20 9 E); March 1990, four adult males, one adult female, and two immature females. Bassein: (19 ° 18.80 9 –19 ° 19.20 9 N, 72 ° 44.70 9 –72 ° 51.20 9 E); April 1989, January 1990. Large number of males and females of all stages. Daman: (20 ° 24.70 9 N, 72 ° 50.11 9 E); February 1990, 32 adult males, seven immature males, 46 adult females, and four immature females.

Description

Body robust and strongly built. Carapace with dorso-median nodules; anterior margin lacking rostrum, postorbital spines prominent, keels prominent, cheeks sinuous. Eyes stout, extending to distal end of first segment of antennule, cornea occupying little more than half of eye and wider than stalk ( Figures 1, 2 ).

Antennule more robust in male, first segment longer than rest of peduncle, outer distal angle drawn out and armed with few stout plumose setae, outer margin armed with row of 10 long curved plumose setae, inner margin with five to six short slender plumose setae; second segment short and armed with two long and three short hooked setae on inner distal angle, four setae on outer distal angle and three setae on dorsal margin; third segment broader and armed with one spinous seta on outer margin, and four hooked setae and group of seven long plumose setae on inner distal margin; mid-dorsal lobe between flagella present, base of outer flagellum swollen and thickly hirsute ( Figure 3 ). In female antennular peduncle longer, first segment with row of 13 long curved plumose setae along outer margin; second segment with setae on outer and inner distal angles and on mid-dorsal margin; third segment with group of long plumose setae extending from inner distal angle to inner middle margin, hooked setae absent ( Figure 4 ). Antennal scale slightly overreaching antennular peduncle, nearly five times as long as broad, outer margin straight and terminating in strong spine extending beyond rounded apex; antennal peduncle short, less than half of scale; inner distal angle of sympod armed with two long and two short spines, second spine longest ( Figure 5 ). In young and immature specimens one or two secondary spinules present on second longest spine.

Labrum wider than long with transverse anterior margin and without any process in front ( Figure 6 ). Mandibular palp slender, second segment four times as long as third and with row of barbed setae; third segment armed with group of modified setae on distal border ( Figures 7, 8 ). Inner lobe of maxillule with five plumose setae and three stout barbed spines, outer lobe with nine strong spines on distal border ( Figure 9 ). Maxilla with large basal lobe and deeply cleft distal lobe; exopod relatively small ( Figure 10 ).

Basis of first thoracic endopod with prominent lobe, claw present ( Figure 11 ) second; thoracic endopod stout, dactylus armed with strong peculiarly barbed spiniform setae ( Figure 12 ). Endopods of third to seventh thoracic limbs slender, becoming longer in posterior pairs; third and fourth endopods with three to four, fifth endopod with four to five, and sixth and seventh endopods with five to six propodal segments ( Figures 13–16 ). All endopods profusely setose, setae on seventh endopod spinulose ( Figure 17 ); outer distal corner of basal plate of exopod rounded, flagelliform part 11–14-segmented. Endopod of eighth limb three-segmented, second segment short with five long plumose setae on inner margin, third segment long and bent, shorter than basal segment of exopod lacking setae ( Figure 18 ). In female, endopod unsegmented, tapering, shorter than basal plate of exopod and armed with short simple seta on inner margin ( Figure 19 ).

In male first abdominal segment with semicircular pleural plates. Pleopods biramous; first pleopod with 11-segmented exopod, and unsegmented endopod ( Figure 20 ); second pleopod with 11-segmented endopod and 15-segmented exopod, first 10 segments with usual pair of plumose setae, distal five segments without setae, terminal segment longest and armed with three long barbed setae ( Figure 21 ). Third and fourth pleopods with 11- segmented and fifth with 10-segmented rami ( Figure 22 ).

In female, pleopods simple, rod-like, becoming longer towards posterior and with row of plumose setae ( Figures 23, 24 ).

Telson broad, 1.3 times longer than last abdominal segment, 2.3 times as long as basal width, abruptly constricted near base to form waist, slightly broadening towards middle and gradually narrowing towards broadly rounded apex; lateral margins armed along distal half with 11–12 stout spines in male, gradually increasing in length towards posterior, apex with two pairs of long stout spines, outer pair slightly longer than inner pair and nearly onequarter length of telson, each spine with row of bilaterally arranged subsidiary teeth progressively more flattened towards tip of spine ( Figures 26, 27 ). In female, lateral margin of telson armed with 12–14 pairs of spines.

Uropods longer than telson, two-segmented and setose all round; endopod with stout spine near middle on inner margin; exopod longer than endopod ( Figure 25 ).

Length: adult male 8.3–11 mm, adult female 9–12 mm.

Etymology

This species was collected from areas around Mumbai and hence the species name mumbayensis .

Remarks

Rhopalophthalmus mumbayensis sp. nov. is related to R. kempi O. Tattersall, 1951 , R. orientalis O. Tattersall, 1957 , R. tattersallae Pillai, 1961 , R. macropsis Pillai, 1964 , and R. longipes Ii, 1964 in having two long and two short spines on the antennal sympod, but they differ from the new species in the following points. In R. kempi , there are only three carpopropodal segments in the third to seventh thoracic endopods, and the vestigial endopod of the eighth thoracic limb of both sexes is longer than the basal plate of the exopod. In R. tattersallae , one of the long spines on the antennal sympod is barbed; thoracic endopods three to seven have only four carpopropodal segments and the inner pair of apical spines of the telson are longer than the outer pair. In R. macropsis and R. longipes , the carpopropodus is four-segmented and the telson is long and narrow. In R. orientalis there are four carpopropodal segments, and the telson has 15–16 lateral spines and the apical pairs of the telson spines are equal in length. The combination of characters afforded by the spines on the antennal sympod, the carpopropodal segments of the thoracic endopods, and the armature of the telson will serve to identify this species.

Ecological note

At Bassein, this species occurred in large numbers during April. Ninety-five per cent of the samples were constituted by adult males and females, and 80% of the females were carrying 6– 20 eggs or larvae in the brood pouch. It occurred at 5–10 m depth, where the bottom sediment was sandy or silty clay. The temperature and salinity recorded ranged from 21 to 33 ° C and from 29.4 to 38.0 psu, respectively. Its occurrence at 5–10 m depth proves it is a littoral species, and the large number of specimens in the samples indicate that this species is a gregarious form.

Figures

Figures 1–10. Rhopalophthalmus mumbayensis sp. nov. (male, unless indicated). (1) Anterior part of body. (2) Carapace, lateral view. (3) Antennule. (4) Antennule of female. (5) Antenna. (6) Labrum. (7, 8) Mandible. (9) Maxillule. (10) Maxilla.

Figures 11–19. Rhopalophthalmus mumbayensis sp. nov. (male, unless indicated). (11) First thoracic endopod. (12) Second thoracic endopod. (13) Third thoracic endopod. (14) Same, tip of endopod. (15) Fifth thoracic endopod. (16) Seventh thoracic endopod. (17) Same, one propodal segment. (18) Eighth thoracic limb. (19) Eighth thoracic limb of female.

Figures 20–27. Rhopalophthalmus mumbayensis sp. nov. (male, unless indicated). (20) First pleopod. (21) Second pleopod. (22) Third pleopod. (23) First pleopod of female. (24) Fifth pleopod of female. (25) Posterior part of body. (26) Telson. (27) Apical spines of telson.