Alpheus mannarensis, Purushothaman & Abhilash & Kumar & Lal, 2021

Purushothaman, P., Abhilash, C. P., Kumar, T. T. Ajith & Lal, K. K., 2021, A new alpheid shrimp, Alpheus mannarensis sp. nov. (Crustacea; Decapoda; Alpheidae) from Gulf of Mannar, Southern India, Zootaxa 5026 (1), pp. 127-135 : 128-134

publication ID	https://doi.org/ 10.11646/zootaxa.5026.1.5
publication LSID	lsid:zoobank.org:pub:216B0A87-3F82-4F85-A40E-DFB841475521
persistent identifier	https://treatment.plazi.org/id/392F8795-6343-B137-FF14-A05EC658E89A
treatment provided by	Plazi
scientific name	Alpheus mannarensis
status	sp. nov.

Treatment

Species Alpheus mannarensis sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined: Holotype: male, CL 12.0 mm, Accession No: NBFGR /ALPAMAN–00, ID No NBFGR: TNG– 14, Rocky shore, Thoothukudi coast, Tamil Nadu, India, Gulf of Mannar region, Indian Ocean (08°42ʹ N, 078°24ʹ E), 15 m, hand net, December 2020 GoogleMaps . Paratypes: male, CL 12.0 mm, Accession No: NBFGR /ALPAMAN–01, ID No NBFGR: TNG–13, Rocky shore, Thoothukudi coast, Tamil Nadu, India, Gulf of Mannar region, Indian Ocean, 15 m, hand net, December 2020 .

Description. Males: medium-sized species (CL 12 mm). Carapace ( Figs. 1A–C View FIGURE 1 , & 2A, B View FIGURE 2 ) glabrous with scattered pubescent on dorsal region, without median tooth or tubercle. Rostrum short, slender, directed downwards distally, not reaching to distal margin of first antennular peduncle; postrostral carina prominent, extending to posterior base of orbital hoods. Orbital hoods swollen, glabrous, projecting anteriorly, without marginal tooth; barely concave in between anterior margin of rostrum and orbital hoods; shallow depression present at the margin of antennal region; pterygostomial region broadly rounded.

Abdominal segments ( Fig. 2C View FIGURE 2 ) subcylindrical, not compressed laterally; first to fourth pleura commonly rounded; second pleuron sub-triangular shaped; fifth pleuron with extended leaf-like process posteroventrally; sixth pleuron without posteroventral spine, posterolateral process barely truncate.

Telson ( Fig. 2D, E View FIGURE 2 ) broad, barely tapering lateral margins, about 1.5 times as long as proximal width, 2.1 times as long as posterior width; dorsal surface with two pairs of movable spines, proximal pair situated about 0.45 of telson length, second pair appeared at 0.72 of telson length; posterior margin broadly convex, bearing a pair of small posterolateral spines, inner margin furnished with 29–32 long plumose setae and 27–28 spiniform setae. Uropod broad, slightly extended to distal margin of telson; outer uropod with a movable and fixed spine at posterolaterally, the posterodorsal region with transverse groove, posterior and inner margins furnished with long plumose setae; inner uropod simple, broad, furnished with long plumose setae on marginally.

Eyes ( Fig. 1C View FIGURE 1 ) small, hidden completely by orbital hoods; anterodorsal region slightly produced or swollen; cornea globular shaped with dark coloured.

Antennular peduncle ( Fig. 2B View FIGURE 2 ) reaching near to distal margin of antennal scaphocerite; first segment short, with triangular lamina, ventromesial carina with a hook-like structure; stylocerite broad, flatted, terminating a spine, reaching to distal margin of the first segment. Second segment long, about 2.7 times as long as maximum width, few setae on dorsally. Third segment short, about 0.5 lengths of second with few setae on dorsally; outer flagellum shorter than inner with numerous thin aesthetascs present on about 13–15 segments, secondary ramus thin and rudimentary.

Antennal segments ( Fig. 2A View FIGURE 2 ) with well-developed basicerite, bearing a sharp ventrolateral spine. Carpocerite relatively long, subequal to antennal segments with a row of long setae on ventral margin. Scaphocerite ( Fig. 2B View FIGURE 2 ) long, overreaching to distal margin of third antennular peduncle, about 4 times as long as carapace, 2.5 times as long as maximum width, lateral margin slightly concave with a small distolateral spine, not over exceeding to distal margin of lamella; a transverse crest starting from base of distolateral spine to posterior deep; distal margin of lamella and inner margin fringed with long setae.

Mouthparts left side dissected. Mandible ( Fig. 2F View FIGURE 2 ) robust with two-segmented palp laterally fringed with numerous setae; molar process strong, terminating with blunt tips, broad triangular tip with truncated in medially; incisor process broad, well developed, curved with 9 truncate tips at distally. First maxilla ( Fig. 2G View FIGURE 2 ) well-developed, bilobed palp, distal margin with 15 tuft spines; outer lobe moderately broad with long setae on lateral and distal margins; inner lobe curved slightly with a large distal seta. Second maxilla ( Fig. 2H View FIGURE 2 ) simple, palp somewhat bilobed tip; scaphognathite broad, inflated, lateral and distal margin with long plumose setae; basal endite with few long setae on marginally.

First maxilliped ( Fig. 2I View FIGURE 2 ) with two-segmented endopod; caridean lobe well-developed, exopodite flagellum long, fringed with few setae on distal margin; epipod broad and bilobed; basial endite bigger than caridean lobe with tuft numerous spiniform; coxal endite somewhat mixed with basial endite.

Second maxilliped ( Fig. 2J View FIGURE 2 ) with epipod broad and inflated; endopod five segmented, inner margin of carpal segment with spiniform, propodus distal part with a triangular margin and stiff setae, dactylus about 4.3 times as long as width, fringed with dense of spiniform setae along the distal margin; exopod slender, elongated with few setae on distal margin.

Third maxilliped ( Fig. 2K View FIGURE 2 ) slender with three-segmented, slightly exceeding to distal margin of antennal scaphocerite; antepenultimate segment broad, inferior distal margin rounded with long setae, about 4.5 times as long as broad; penultimate segment short, inner margin broad, produced blunt process with tuft long setae, extended distal margin of the ultimate segment; ultimate segment about 3.5 times as long as penultimate, tapering lateral margins gradually with long plumose setae along the lateral margin, distal margin bluntly rounded with numerous long setae.

First pereiopods are asymmetrical in shape and size. Right side pereiopod or major cheliped ( Figs. 3A–C View FIGURE 3 ) overreaching to distal margin of antennal scaphocerite by entire length of chela. Ischium short, about 1.6 times as long as maximum width; dorsal margin with 4–5 small setae; inferior margin with few long setae. Merus broad, trigonal, about 3.4 times as long as greater width; dorsal margin with numerous small setae without any tooth or projection; inferior outer margin minutely serrated; inferior inner margin barely serrated, base with two small spines, middle to distal regions with long setae, distal margin produced acute triangular process. Carpus short, triangular cup-shaped, dorsal margin with subtriangular projection distally with few long setae; inferior margin very short with few long setae. Chela broad, compressed laterally, about 2.7 times as long as maximum broad, with a fixed finger holding distal 0.25 length. Palm somewhat sub-rectangular shaped, about 1.8 times as long as greater width, mesial surface smooth and partially faint granulated, superior margin fringed with numerous long setae with a faint transverse groove proximal to dactylar articulation; proximal to base of dactylus with deep curve and arranged setae; ventral margin of palm with long plumose setae. Pollex or fixed finger strongly curved, terminating acute tip, inner margin without any tooth, dorsal surface with few number of patches of long setae, lateral margin covered with long setae. Dactylus thick, compressed laterally, dorsal margin regularly rounded with blunt tip, slightly longer than pollex; dorsal surface and lateral margin with patches of short and long setae; inner distal margin regularly rounded, plunger reduced form, found at proximal to mid of inner margin, oblique broad notch present at below the plunger.

Left side first pereiopod or minor cheliped ( Fig. 3D, E View FIGURE 3 ) comparatively slender than major cheliped, laterally compressed, covered with dense of long setae on laterally, balaeniceps in both male individuals. Ischium and merus similar to major cheliped, ischium about 1.6 times as long as broad; merus about 3.1 times as long as maximum width, inferior inner margin of base with three small spines, distal margin with long setae. Carpus triangular, cupshaped, more or less sub-triangular tooth-like process on upper distal margin with few long setae; ventral margin normal with few small setae on distally. Chela sub-rectangular, about 3.5 times as long as maximum broad, without any depressions, grooves, and patches; palm about 1.7 times as long as width, dorsal surface with small granulated partially, superior margin fringed with dense of long setae, a small gradual slope present at proximal to dactylar articulation; both the fingers equals, slender, slightly longer than palm, about 1.2 times as long as palm, curving blunt tip, with a different group of setae, dorsal sides of each with balaeniceps ridges, inner margin of both fingers with a thin corneous blade from proximal to near the distal margin ( Fig. 3E & F View FIGURE 3 ).

Second pereiopod ( Fig. 3G View FIGURE 3 ) slender, extending beyond distal margin of antennal scaphocerite by proximal second segment of carpus. Ischium about 5.5 times as long as broad, 0.96 times as long as merus; both segments with few small setae on dorsally. Carpus subdivided into five-segment, proximal second segment longest one; the ratio of five segments is 3.5:4.5:1:1:1.6. Chela short, small, about 3.1 times as long as width; palm sub-cylindrical, without any setae; fingers about 1.3 times as long as palm, lateral and dorsal surface with numerous long and small setae, inner margin of fingers with a row of small setae, distal margin terminated with blunt acute tip and few long setae.

Third pereiopod ( Fig. 3H & I View FIGURE 3 ) moderately slender, overreaching to distal margin of antennal scaphocerite by distal ¼ of carpus; ischium armed with a small spine on ventrobasally, about 1.7 times as long as distal width; merus inflated, trigonal, unarmed, few small setae on dorsally, about 4.5 times as long as maximum wide, 3.4 times to ischium; carpus unarmed, with few long setae on dorsally, inferior distal margins barely projected; propodus subequal to carpus, with numerous long setae on dorsally, inferior margin with 6–7 spines, 1 pair of distal spines, about 1.9 times as long as dactylus; dactylus subspatulate shaped, 5–6 patches of small setae on dorsally, about 5.9 times as long as basal width.

Fourth pereiopod ( Fig. 3J View FIGURE 3 ) more or less similar to third pereiopod, extended to antennal scaphocerite by distal 1/2 of propodus; ischium armed with a ventrobasal spine, about 1.7 times as long as distal width; merus about 5.6 times as long as maximum width, 2.4 times as long as ischium with few small setae on dorsal and ventral surface; propodus about 1.3 times as long as carpus, 2.1 times as long as dactylus, inferior margin armed with 8 spines and a pair of distal spines, numerous long setae on dorsal and ventrally; dactylus about 6.2 times as long as basal width.

Fifth pereiopod ( Fig. 3K View FIGURE 3 ) comparatively slender than third and fourth pereiopods, just overreaching to antennal scaphocerite; basis unarmed, about 0.6 times as long as ischium with stiff long seta on distally; ischium with a ventrobasal spine, about 3.1 times as long as distal width; merus unarmed, about 2.4 times as long as ischium, 1.2 times as long as carpus, with few small setae on distal and ventral margin; propodus subequal length to carpus, inferior margin armed with 7 spines and a pair of distal spines with few long setae, cleaning brush like dense of tuft short setae present on ventral third of distal region; dactylus slender, slightly curved, about 0.4 times of propodus, with few patches of setae.

The first pleopod of endopod reduced, subspatulate shaped with small setae on distally; exopod leaf-like structure, fringed with dense of long setae. Second pleopod: endopod similar to exopod with appendix interna and masculina; appendix interna subequal to masculina with long setae on lateral and distal margin; exopod simple and covered with long setae.

Colouration in Life. Body commonly translucent with red chromatophores,irregular red patches and longitudinal lines ( Fig. 1A–C View FIGURE 1 ). Carapace with reddish irregular longitudinal lines on dorsally, lateral surface translucent with irregular red patches.Antennal and antennules segments are covered with translucent red patches; all flagellum with translucent dark pinkish, setae are whitish. First pereiopod covered with irregular patches on dorsally, pinkish-red patches in ventrally, finger with terminal margin pale whitish. The second to fifth pereiopods are covered with dark pinkish and red patches, dactylus terminal margin with pale whitish. All pleopods are covered with pale whitish. Abdomen segments with numerous red longitudinal lines on dorsally, which are arranged by small red patches; three irregulars, broad longitudinal lines found by the accumulation of small red patches. Telson and uropods covered with translucent irregular red patches, distal long setae with pale whitish. Eyes are translucent with the small red patch, cornea with pale darkish.

Habitat and Distribution. Alpheus mannarensis sp. nov. is known only from shallow regions with a small rocky area of Thoothukudi coast, Gulf of Mannar at the depth of 15 m. The species has occurred with other fishes such as Grouper, Anthias and Three spot damsels.

Etymology: The species is named after the type location, Gulf of Mannar.

Remarks: Alpheus mannarensis sp. nov. have glabrous body with light pubescent on the carapace, short rostrum, orbital hoods without a spine in the anterior margin, major chela compressed with transverse groove proximal to dactular articulation and palm with slightly subrectangular shaped in cross-section, the ischium of third to fifth pereiopods with a strong ventrobasal spine, and subspatulate shaped dactylus for third to fourth pereiopods. These morphological characteristics assured to place Alpheus mannarensis sp. nov. within the species group of Alpheus brevirostris ( Olivier, 1811) .

The important special features of Alpheus mannarensis sp. nov. have carapace with light pubescent, short postrostral carina and compressed major chela. Similarly, pubescent carapace with short rostral carina was also present in A. pubescens de Man, 1908 , A. williamsi Bruce, 1994 , A. savuensis de Man, 1908 , A. djeddensis Coutière, 1897 and A. djiboutensis de Man, 1909 . However, the present new species have the most similar morphological characters with A. djeddensis , which occurred throughout the Red Sea and A. djiboutensis known from the Red sea to the Society Islands through Indo-Pacific and Yellow sea ( Banner & Banner 1981, 1982; Sha et al. 2019).

However, Banner & Banner (1982) has given elaborate morphological details on the name of A. djiboutensis from the Australian waters which were placed in the synonymy of A. djeddensis . Consequently, Bruce (1994) has given the illustrative characters only for A. djeddensis along with the brevirostris group from the Indo-Pacific regions. Accordingly, Anker and De Grave (2016) are reported that A. djeddensis and A. djiboutensis are problematic and species complex in the A. brevirostris group. They were also noted that many of earlier records and colour photographs from the Indo-Pacific waters were reported on the name of A. djeddensis and A. djiboutensis . Also, Anker has reexamined the Singapore specimen (male; ZRC 1979.3.30.11) and placed it into the species complex of A. djeddensis – A. djiboutensis ( Anker & De Grave 2016) and specified the morphological features were closely agreed with A. djiboutensis sensu lato in Banner & Banner (1982). Therefore, as per our re-examination of the illustrative figure of the yellow water materials of A. djiboutensis , it should be considered the synonymy of A. djeddensis .

We have established the following differences between A. djeddensis – A. djiboutensis complex and A. mannarensis sp. nov from the Gulf of Mannar region, India. This new species is compared with A. djiboutensis sensu lato in Banner & Banner (1981 & 1982), type materials of A. djeddensis and A. djiboutensis .

Antennal scaphocerite is 2.5 times as long as maximum width, the lateral margin of scaphocerite is slightly concave bearing a small distolateral spine, and it is not over exceeding the distal margin of lamella for A. mannarensis sp. nov. ( Fig. 2B View FIGURE 2 ). On the other hand, the material of A. djiboutensis in De Man (1909 ; See fig. 17, 19) clearly shows that scaphocerite is 3.0 times as long as the maximum width, lateral margin concave, and distolateral spine strong, overreaching to distal margin of the lamella (See Banner & Banner, 1891).

The ultimate segment of the third maxilliped about 6.1 times as long as broad for A. mannarensis sp. nov. ( Fig. 2f View FIGURE 2 ) which is higher than A. djiboutensis (4.0 to 4.2 times long as the broad: Banner & Banner 1982; Sha et al. 2019).

Chela of major pereiopod is about 2.7 times as long as maximum width, palm without any crest in internal side and merus is 3.4 times as long as maximum width with two small spines in the inferior inner margin for A. mannarensis sp. nov. Wherein, A. djiboutensis , chela and merus of major pereiopod are 2.5 times as long as maximum width with several meral spines and palm with distinct crest, runs from the constriction to the carpal joint ( De Man 1909; Banner & Banner 1981).

De Man (1909) type material showed that the first segment of the carpus is the longest one and the ratio of five segments is 3.3:2.4:1.04:1: 1.4 in A. djiboutensis . In contrast, the second segment of the carpus is longer than the first segment and the ratio is 3.5:4.5:1:1:1.6 for A. mannarensis sp. nov.

The fifth pereiopod is similar to the third and fourth pereiopods, without ischium spine for individuals of A. djiboutensis found in the Yellow sea ( Sha et al. 2019). While the fifth pereiopod is more slender than other pereiopods with an ischium spine and the dactylus is slightly curved for A. mannarensis sp. nov.

Antennal scaphocerite is 2.6 times as long as carapace, with distolateral spine, not exceeding the distal margin of lamella of A. mannarensis sp. nov. ( Fig. 2B View FIGURE 2 ). Where the type material of A. djeddensis in Coutière (1897) clearly shows that scaphocerite is 3.1 times as long as carapace, with distolateral spine slightly overreaching to distal margin of the lamella ( De Man 1909; See illustrative fig. 25, 26).

The colour pattern of A. djeddensis – A. djiboutensis complex had muddy white or yellowish and dark green to brownish transverse stripes on the carapace. Abdomens have dark bands present on the antennal segments and first to fifth pereiopods have dark blue with yellow bands that was noticed from the Singapore materials of Alpheus djeddensis Coutière, 1897 sensu lato ( Anker & De Grave 2016). The present new species, A. mannarensis sp. nov. differentiated from the A. djeddensis – A. djiboutensis complex by the presence of reddish irregular longitudinal lines on the dorsal and lateral side of carapace and abdomens, those longitudinal lines formed by the accumulation of small red patches. All pereiopods are covered with dark pinkish and red patches, telson had translucent irregular red patches on dorsally ( Fig. 1A & B View FIGURE 1 ).

Alpheus savuensis is not reported from the Indian waters which were distributed in Taiwan, Fiji Islands, and Indonesia. This species was distinguished from the A. mannarensis sp. nov. with the presence of postrostral carina extended near mid of the carapace, third pereiopod with simple dactylus and conical shaped ( Bruce 1994). Where in A. mannarensis sp. nov., the postrostral carina not reached the middle of the carapace and third pereiopod with subspatulate dactylus.

Alpheus pubescens and A. williamsi are readily differed from the present new species by (i) presence of the pubescent carapace (vs glabrous carapace with light pubescent on dorsally), (ii) postrostral carina extended middle of the carapace (vs carina extended up to the level of the base of the orbital hood), (iii) distolateral tooth of the scaphocerite is robust and distinctly extended the margin of lamella (vs distolateral tooth not exceeded the margin of lamella), (iv) merus of major pereiopod is 2.7–3.0 times as long as maximum broad with 4–7 small inner marginal spines (vs 3.4 times as long as broad, 2 small spines in inner margin), (v) proximal segment of the carpus in the second pereiopod is equal or longer than the second segment (vs proximal segment of carpus shorter than the second segment), (vi) third pereiopod merus is greater than 5.0 times as long as maximum broad (vs 4.4 times as long as maximum broad) ( Banner & Banner 1982; Bruce 1994).