Macrobrachium irwini, Kunjulakshmi & Santos & Prakash, 2022

Kunjulakshmi, K., Santos, Maclean Antony & Prakash, S., 2022, Macrobrachium irwini sp. nov., a new species of freshwater shrimp from Western Ghats, India (Caridea: Palaemonidae), Zootaxa 5194 (3), pp. 416-425 : 418-424

Macrobrachium irwini sp. nov.

( Figure 3 & 4 )

Type material. Holotype. 1 male (ZSI/SRC/C-354) CL (carapace length) 22 mm, TL (total length) 41 mm, collected from Nandhini River at Kateel, Karnataka, India (13°0′44″N; 77°32′10″E), Jan 2022. Coll. Maclean Antony Santos.

Paratypes. Male (ZSI/SRC/C-355), CL 19 mm, TL 30 mm; Female (ZSI/SRC/C-356), CL 22 mm, TL 49 mm, same data as holotype.

Diagnosis. Rostral formula 13/2 with 6 postorbital teeth, distal end of rostrum slightly curved upwards; carapace scabrous with minute spines, branchial margins with setae; second chelate legs unequal; propodus of second major pereiopod is 2.07 times as long as dactyl and 5.78 times longer than width. Cutting edges of immovable fingers armed with 11–16 tubercles and 10–12 along the movable fingers. The setae on the palm and basal regions of the fingers are matted together to form a velvety covering. Propodus of minor second pereiopod is 1.92 times longer than dactyl and 5.69 times as long as width. Second minor pereiopod with 4–5 tubercles on the immovable fingers and 4 tubercles on the movable fingers at the proximal cutting edges. Orange colouration at the extreme tips of claw. Appendix interna is 1.4 times longer than appendix masculina with numerous stiff setae on distal border, and extended up to 2/3 of endopod.

Description. Rostrum ( Figure 3 A, B ) straight, slightly curved upwards distally, reaching distal margin of third antennular peduncle. Dorsal margin bearded with 13 teeth, 6 teeth appeared behind orbital margin and first three proximal teeth equally spaced. Distal end of the rostrum extends only as far as the terminal segment of antennular peduncle. Ventral margin slightly curved upwards, with two teeth, long setae closely arranged in between them.

Carapace ( Figure 3 A ) scabrous with minute spines; antennal spine well developed, situated below the orbit. Gastro-frontal carina turning anterodorsally upon itself at posterior end. Adrostral sulcus and carina falling distinctly short. Long cervical grooves, extending almost to dorsal midline of carapace. Hepatic spine shorter appeared lower than antennal spine. Hepatic carina and sulcus well marked. Eyes well developed; cornea longer and broader than stalk.

Abdomen segments ( Figure 3 C ) smooth, glabrous, first to third pleura broadly rounded; fourth subtriangular, fifth subrectangular and sixth pleuron with a distal sharp edge at the posterodistal margin.

Antennular peduncle ( Figure 3 D ) three segmented. Middle segment is the shortest. Basal segment of antennular peduncle broad, 1.73 times as longer than middle and 1.44 times as long as the terminal segment. Two branches of outer flagellum of antennule fused basally for 6 segments. Antennal scale ( Figure 3 E ) large, rectangular, 3.2 times as long as width, lateral margin straight, sharply pointed in disto‐lateral end.

Telson ( Figure 3 F ) conical and slender with two pair of dorsal spines. First and second pair of dorsal spines are located at 2.47 mm and 3.828 mm from the anterior region of telson. Posterior end with two pairs of spines, outer pair smaller than inner pair, a tuft of long plumose setae present in between the inner pair of spines. Telson terminated with a conical spine at the apices. Uropodal diaeresis with an accessory spine longer than the major one bordering long setae.

First pleopod ( Figure 3 G ) The exopods from the first pair of pleopods was approximately twice the length of the endopods. The endopods had no appendix interna and no cincinulli.

Second pleopods ( Figure 3 H ) with well-developed appendix masculine, almost reaching middle of endopod, bearing numerous spines on distal margin. Appendix interna is 1.4 times longer than appendix masculina with numerous stiff setae on distal border, and extended up to 2/3 of endopod.

First pereiopod ( Figure 4 A, B ) slender; ischium slightly inflated, shorter than merus; carpus 2.45 times longer than propodus, 4.64 times than dactyl and 1.3 times than merus. Palm cylindrical, equal length to fingers; fingers slender, equal sized with tufts of setae on outer margins.

Second pereiopods ( Figure 4 C, D ) unequal, dorsal surfaces of dactyl, propodus, carpus, merus and ischium covered with minute spines and long setae. The major second pereiopod sub-equals to size of total body length. Ischium 0.4 times as long as merus; merus subequal to (1.02 times) carpus; carpus short, conical shaped, with proximal part narrow, about 0.4 times as long as propodus; propodus 2.08 times as long as dactyl and 5.78 times longer than width. Fingers nearly straight with pointed tips and dark reddish setae in claw tips, 13–16 blunt teeth along both cutting edges, reduce gradually in size towards the distal end. The setae on the palm and basal regions of the fingers are matted together to form a velvety covering. Minor second pereiopod ( Figure 4 E, F ) short and slender, with minute spines and setae as on major second pereiopod, about 0.69 times of body length; ischium 0.68 times as long as merus; merus 1.01 times as long as carpus; carpus 0.57 times longer than propodus; propodus 1.92 times longer than dactyl and 5.69 times as long as width. Fingers with blunt teeth on both the proximal cutting edges.

Third to firth pereiopods ( Figure 4 G–L ) nearly equal sized, slender and smooth with long setae scattered on the lateral margins. Dactylus slender, sharply pointed and hooked with tuft of setae. The propodus of pereiopods have 8 prominent spines on the dorso‐ventral margin.

Live colour patterns. Male: In wild, the carapace is dark brown. A yellow transverse band runs along the dorsal surface from the rostral tip up to the last abdominal segment. Lateral sides of the abdomen are black with sparsely scattered yellow dots. First and third to fifth pereiopods are encircled with alternative black and yellow bands. Second pereiopods brownish yellow with black claws; extreme tips are orange. Telson black with yellow uropods. ( Figure 5 A, B )

Female: In wild, the carapace is dark blue.A discontinuous yellow transverse band runs along the dorsal surface from the rostral tip to the last abdominal segment. A prominent yellow and black band around the third abdominal segment. Lateral sides of the abdomen are bluish-black with sparsely scattered yellow dots. First and third to fifth pereiopods are encircled with alternative blue and yellow bands. Second pereiopods blue with extreme tips of the claw in orange. Telson black with blue uropods. ( Figure 5 C )

In aquarium, the colour fades over time until the body appears translucent. Initially, the first third to fifth pereiopods are encircled with alternative light blue and pale‐yellow bands. Second pereiopods appears yellow with black patches on the margins and dorsal surface. Blue spots towards the distal ends on uropods.

Habitat. Specimens of Macrobrachium irwini sp. nov. were collected from a river running through a secondary forest with heavily vegetated banks. The river is fast flowing with deep waters during monsoon to almost dry with few patches of water during the summer season. The topography of the river is rocky bed with rubbles and abundant in aquatic plants, leaf litters and driftwoods that make this place an excellent habitat for freshwater shrimps for feeding and hiding. ( Figure 2 )

Etymology. The new species Macrobrachium irwini sp. nov., has been honoured in the name of Stephen Robert Irwin (also Steve Irwin), nicknamed ‘The Crocodile Hunter’. The ‘ irwini ’ has also been dedicated to his entire family members Terri Irwin (Wife), Robert Irwin (Son), Bindi Irwin (Daughter), Candler Powell (Son in law) and Gracy Warrior (Grand Daughter) for being an inspiration for nature enthusiasts through multitasking role as zookeeper, conservationist, television personality and wildlife photographer. Overall, we would like to dedicate the new species to Irwin’s family efforts in continuing Steve Irwin’s mission of “Conservation Through Exciting Education” in Australia Zoo, Queensland.

Distribution. Known only from Nandini River, Kateel, Dakshina Kannada District, Western ghats (Karnataka), India.

Remarks. The new species is morphologically different to M. snpurii and M. scabriculum . It can be clearly distinguished from the other species in the genus based on set of characters such as rostrum, tubercles of second pereiopods and color pattern ( Table 1 ).

First, the distal end of the rostrum reaching up to the tip of antennular peduncle in M. irwini sp. nov., compared to not exceeding the tip of 3 rd antennular segment in M. snpurii . Whereas in M. scabriculum , it generally reach as far as the tip of the antennular peduncle, but in some cases may fall short or extends slightly beyond ( Henderson & Matthai, 1910). Distal end of the rostrum is slightly curved upwards in M. irwini sp. nov., whereas straight in M. scabriculum and upwards in M. snpurii ( Pillai & Unnikrishnan, 2013) . The dorsal rostral dentition is 13–14 in M. irwini sp. nov., 12–14 in M. snpurii and 12–15 in M. scabriculum . Dorsal margin with 6 post‐orbital teeth in M. irwini sp. nov., 2 in M. snpurii and 4–5 in M. scabriculum . The ventral rostral dentition is 2 in M. irwini sp. nov., compared to 4 in M. snpurii and 2–3 in M. scabriculum .

The distance between the ventral rostral teeth clearly varies between M. irwini sp. nov., and M. snpurii . In M. irwini sp. nov., the first three proximal rostral teeth on dorsal region are widely spaced, where in M. snpurii only the first two proximal rostral teeth is widely spaced. Uniform distance is maintained between the remaining series of teeth in M. irwini sp. nov., compared to the even distribution of second to tenth and uneven distribution of tenth to twelfth rostral teeth in M. snpurii . The carapace is rugged and scabrous in M. irwini sp. nov. and M. scabriculum ( Jalihal et al. 1988) , compared to the smooth and glabrous carapace in M. snpurii .

First pereopod: Carpus of M. irwini sp. nov. is 2.5 times longer than propodus compared to is 2.42 times in M. snpurii and 2.0 to 2.3 times in M. scabriculum . Palm is cylindrical in M. irwini sp. nov., and M. snpurii compared to inflated palm in M. scabriculum .

Second pereiopods of M. irwini sp. nov., and M. scabriculum is unequal in size for males and subequal for females, however it’s equally sized in M. snpurii . Large second pereiopod of M. irwini sp. nov. have 11–16 tubercles along the cutting edges of immovable finger, whereas 22–29 in M. scabriculum ( Jalihal et al. 1988) and 2 in M. snpurii . Similarly, 10–12 tubercles along the cutting edges of movable fingers of M. irwini sp. nov., compared to 18–28 in M. scabriculum and 2 in M. snpurii . The surface of second pereiopod from dactyl to merus is rugged with minute close‐set spinules in M. irwini sp. nov., however, in M. scabriculum only the chelipeds and lower surface of carpus are furnished with minute spinules. In males, the setae of large second pereiopod is matted together to form a velvety covering on the chela of M. irwini sp. nov., and M. scabriculum which is absent in M. snpurii . In M. scabriculum and M. snpurii a wide gaping exist when fingers are closed as the opposed margins do not meet, compared to a narrow gap in M. irwini sp. nov..

In second major pereiopod, propodus is 2 times longer than dactyl in M. snpurii and 1.6 to 2.1 times for M. scabriculum . However, in M. irwini sp. nov., the propodus is 2.08 times longer than dactyl of major pereiopod. Carpus is 1.06 times longer than propodus in M. snpurii whereas it’s 0.4 to 0.6 times as long as propodus in M. scabriculum and 0.4 times as long as propodus in M. irwini sp. nov.. Size of merus is nearly equal to carpus in M. scabriculum compared to 1.02 times as long as carpus in M. irwini sp. nov., and 0.52 times as long as carpus in M. snpurii ( Pillai & Unnikrishnan, 2013) . Ischium and merus are of equal length in M. snpurii compared to ischium longer than merus by 0.4 times in M. irwini sp. nov., and 0.5 to 0.8 times in M. scabriculum .

Lastly, M. irwini sp. nov., can also be easily distinguished from closely related species based on colour pattern. A pale band runs along the dorsal surface from the tip of the telson to the rostrum in M. scabriculum compared to a yellow transverse band that runs along the dorsal surface from the rostral tip up to the last abdominal segment in M. irwini sp. nov. In M. scabriculum , the fingers of shorter cheliped are dark blue except its extreme tips whereas in M. irwini sp. nov., fingers are black with extreme tips in orange colouration ( Figure 5 ). In M. scabriculum the uropods are violet with white borders compared to the pale‐blue patches on the uropods of M. irwini sp. nov., and have tuft of long plumose setae on telson, whereas M. scabriculum possess 15–20 pair of setae and M. snpurii has a single pair of plumose setae.

Discussion. M. irwini sp. nov., is known only from the type‐locality. It has considerable potential for commercial exploitation in the aquarium trade, because of its striking colour patterns. The species is threatened by over‐harvesting and deterioration of the freshwater habitats due to non‐judicious anthropogenic interventions. In order to guarantee supply for the ornamental trade, and to protect the species from over‐exploitation, protocols for sustainable harvesting and culturing of this shrimp have to be established to promote livelihood sustainability. Further, more exploration needs to be done in Western ghats region, which is a hotspot for biological diversity to document more endemic species.

Figures

FIGURE 2. (A–D) Diffferent sampling sites of Macrobrachium irwini sp. nov. near Kateel, Karnataka, Western ghats, India

FIGURE 3. Macrobrachium irwini sp. nov., holotype male (ZSI/SRC/C-354), TL 41 mm, CL 22 mm. A—Lateral view of rostrum and carapace; B—Dorsal view of rostrum; C—Lateral view of abdomen; D—Dorsal view of antennal peduncle; E— Dorsal view of scapocerite; F—Telson; G—Dorsal view of 1st pleopod; H—Dorsal view of 2nd pleopod. (Scale bar: A, B, D, E, F, G, H = 1.0 mm; C = 2.0 mm)

FIGURE 4. Macrobrachium irwini sp. nov., holotype male (ZSI/SRC/C-354), TL 41 mm, CL 22 mm. A—Lateral view of 1st pereiopod; B—Lateral view of chela of 1st pereiopod; C—Lateral view of major 2nd pereiopod; D—Lateral view of chela of major 2nd pereiopod; E—Lateral view of minor 2nd pereiopod; F—Lateral view of chela of minor 2nd pereiopod; G,I,K—Lateral view of 3rd,4th,5th pereiopod; H,J,L—Lateral view of dactylus of 3rd, 4th, 5th pereiopod. (Scale bar: A, B, D, F–L= 1 mm; C, E= 2 mm)

FIGURE 5. Live colouration of Macrobrachium irwini sp. nov. (A) Lateral view; (B) Dorsal view (male); (C) Dorsal view (female). Image courtesy: Mr. Thejas.

Tables

TABLE 1. A comparison of Macrobrachium irwini sp. nov. with other closely related species. Characters Macrobrachium snpurii Macrobrachium scabriculum Macrobrachium irwini sp. nov.

Characters	Macrobrachium snpurii	Macrobrachium scabriculum	Macrobrachium irwini
			sp. nov.
Rostrum	Rostrum not exceeding the	Rostrum generally reach as	Distal end of the rostrum
	tip of 3 rd antennular segment;	far as the tip of the anten-	reaching up to the tip of an-
	directed upwards	nular peduncle, but in some	tennular peduncle; is slightly
		cases may fall short or	curved upwards
		extends slightly beyond;
		directed straight
Number of dorsal rostral	12–14	12–15	13–14
teeth
Number of post-orbital	2	4–5	6
teeth
Number of ventral rostral	4	2–3	2
teeth
Nature of carapace	Smooth and glabrous	Scabrous	Rugged and scabrous
First pereiopod	Carpus 2.42 times longer	Carpus 2.0 to 2.3 times	Carpus 2.5 times longer than
	than propodus; cylindrical	longer than propodus; in-	propodus; cylindrical palm
	palm	flated palm
Second pereiopod	Equal. Large second pereio-	Unequal in size for males;	Unequal in size for males
	pod have 2 tubercles along	right or left can be the	and subequal for females.
	the cutting edges of immov-	major pereiopod. Subequal	Large second pereiopod have
	able finger. 2 tubercles along	for females. Large second	11–16 tubercles along the
	the cutting edges of movable	pereiopod have 22–29 tuber-	cutting edges of immovable
	fingers.	cles along the cutting edges	finger. 10–12 tubercles along
		of immovable finger. 18–28	the cutting edges of movable
	Propodus is 2 times longer	tubercles along the cutting	fingers.
	than dactyl; carpus is 1.06	edges of movable fingers.
	times longer than propodus;		Propodus 2.08 times longer
	merus is 0.52 times as long	Propodus 1.6 to 2.1 times	than dactyl; carpus 0.4 times
	as carpus; ischium equal to	longer than dactyl; carpus	as long as propodus; merus
	merus.	0.4 to 0.6 times as long as	1.02 times as long as carpus;
		propodus; merus is nearly	ischium longer than merus
		equal to carpus; ischium	by 0.4 times.
		longer than merus by 0.5 to
		0.8 times.
Number of plumose setae	A pair	15–20 pair	A tuft of plumose setae
on telson