Salmoneus venustus, Anker, 2019

Anker, Arthur, 2019, On three symbiotic species of the alpheid shrimp genus Salmoneus Holthuis, 1955 from the Indo-West Pacific, including one new to science (Malacostraca: Decapoda: Caridea), Zootaxa 4651 (1), pp. 51-63 : 52-58

Salmoneus venustus sp. nov.

Figs. 1–4

Type material. Holotype: non-ovigerous specimen (cl 6.4 mm, dissected), MNHN-IU-2014-20290, Vietnam, Nha Trang Bay , north side of Che Island, depth: 6–8 m, in burrow of Glypturus sp., suction pump, leg. I.N. Marin, 24.10.2012.

Additional material. 1non-ovigerous specimen (cl 5.5 mm), OUMNH. ZC.2015-08-0031, Oman, northern coast east of Muscat, shallow bay between Yiti and Sifah, shallow bay with sand-mud, fringed by mangroves, near shore and mangroves, depth at low tide: 0.7 m, in burrow in muddy sand, suction pump, leg. A. Anker, 23.08.2010.

Description. Small-sized (cl 5.5–6.4 mm) alpheid shrimp with stout, non-compressed body. Carapace mostly glabrous, with very few setae (holotype) or more densely setose dorsally (paratype). Rostrum moderately developed, broadly subtriangular, about as long as wide at base, acute distally, reaching distal margin of first article of antennular peduncle, lateral margins feebly concave; rostral or mid-dorsal carina absent ( Fig. 1a, b, h ). Orbital teeth relatively small, sharp distally, pointing slightly mesially in dorsal view, anteriorly in lateral view ( Fig. 1a, b, h ). Pterygostomial region broadly rounded; anterolateral suture present ( Fig. 1b ); cardiac notch well developed. Epistomial sclerite with short acute process.

Pleon with first to fourth pleura broadly rounded to slightly angular; fifth pleuron with posteroventral margin forming subacute angle; sixth pleonite with short suture but without articulated flap, posterior margin produced into long sharp tooth flanking telson ( Fig. 1c ); preanal plate rounded. Telson fairly slender, subrectangular, slightly tapering distally, almost three times as long as maximal (proximal) width; dorsal surface with two pairs of small cuspidate setae both inserted at some distance from lateral margin, first pair slightly posterior to telson mid-length, second pair between 0.7 and 0.8 of telson length; posterior margin with shallow notch; posterolateral angles each with one pair of spiniform setae, mesial stouter and about 1.3–1.4 times as long as lateral ( Fig. 1d, e ).

Eyes completely concealed in dorsal view, partly exposed in lateral view; cornea reduced, restricted to dorsolateral surface of eyestalk; anteromesial margin of eyestalk with dorsally produced tubercle ( Fig. 1a, b, h ).

Antennular peduncle stout; stylocerite moderately long, slender, with sharp tip reaching or almost reaching midlength of second article; ventromesial carina with small, anteriorly directed tooth; second article about 1.3 times as long as wide; lateral antennular flagellum with very short fused portion, consisting of at most three discernable subdivisions, and well-developed secondary ramus, latter with five or so groups of aesthetascs; mesial antennular flagellum much stouter than lateral ( Fig. 1a, b ). Antenna with stout basicerite, its distoventral margin bearing robust subacute tooth; scaphocerite ovoid in general shape, not reaching end of antennular peduncle, with straight lateral margin and very broad blade, latter highly convex anteriorly and significantly overreaching small sharp distolateral tooth; carpocerite short, cylindrical, reaching mid-length of scaphocerite ( Fig. 1a, b ).

Mouthparts not dissected, typical for genus in external observation. Third maxilliped slender, pediform; coxa with somewhat elongated, oval-shaped lateral plate; antepenultimate article slightly flattened ventrolaterally; penultimate article about four times as long as wide; ultimate article with numerous rows of short serrulate setae and longer simple setae, tip with blunt corneous point, apparently without spiniform setae; arthrobranch well developed ( Fig. 2a, b ).

Chelipeds very asymmetrical in shape and dissimilar in size, carried flexed when not in use. Major cheliped relatively slender; ischium unarmed, flattened ventrolaterally; merus slender, more than six times as long as proximal width, widening distally, smooth, distodorsal and distomesial margins with rounded lobes, ventrolateral surface depressed distally; carpus short, cup-shaped, with strong subacute distoventral process; chela subcylindrical, more or less rounded in cross-section, with palm about as long as fingers, smooth, except for some small bumps on ventrolateral surface; fingers not gaping when closed, subequal, strongly crossing distally, not noticeably twisted, with evenly serrated cutting edges; cutting edge of both dactylus and pollex with about 14–15 teeth gradually increasing in size from most proximal tooth to mid-length teeth, then decreasing again towards most-distal tooth ( Fig. 3 a–d). Minor cheliped significantly smaller than major cheliped, slender; ischium unarmed on ventrolateral surface; merus longer than ischium, not swollen or widening distally, smooth, unarmed, slightly depressed ventrally; carpus about 1.1 times length of merus, cylindrical, slightly widening distally; chela 0.6 times length of carpus, simple, with palm subequal to fingers in length, smooth; fingers noticeably gaping when closed, subequal in length, crossing distally, cutting edges armed with four or five minute teeth ( Fig. 3e, f ).

Second pereiopod slender; ischium unarmed on ventrolateral surface; merus noticeably longer than ischium; carpus with five subdivisions, first surpassing four others combined, with ratio approximately equal to 5.0/1.0/0.8/0.8/1.2; chela longer than distal-most carpal subdivision, simple ( Fig. 2c ). Third pereiopod slender; ischium with three cuspidate setae on ventrolateral surface; merus about seven times as long as wide, unarmed; carpus almost 0.7 times length of merus, noticeably more slender, with small spiniform seta distoventrally; propodus not noticeably longer than carpus, with two widely spaced spiniform setae on ventral margin, in addition to three longer spiniform setae near dactylar base; dactylus about half-length of propodus, slender, conical, simple, smoothly curving distally ( Fig. 2d, e ). Fourth pereiopod more slender than third pereiopod; ischium unarmed on ventrolateral surface; merus almost eight times as long as wide; carpus 0.7 times length of merus, more slender than merus, unarmed distoventrally; propodus distinctly longer than carpus, without spiniform setae on ventral surface, distoventral margin adjacent to dactylus with one long spiniform seta; dactylus about half-length of propodus, similar to that of third pereiopod ( Fig. 2f ). Fifth pereiopod as slender as fourth pereiopod; ischium unarmed; merus almost eight times as long as wide, unarmed; carpus noticeably more slender than merus, as long as merus, unarmed distoventrally; propodus very long, slender, 1.5 times as long as carpus, with numerous rows of progressively longer serrulate setae forming dense cleaning brush on distal ventrolateral surface, ventral and ventromesial margin without spiniform setae; dactylus about 0.4 times length of propodus, similar to that of third and fourth pereiopods ( Fig. 2g ).

Second pleopod with appendix masculina as long as appendix interna, furnished with numerous short stiff setae, as illustrated ( Fig. 1f ). Uropod with lateral lobe of protopod ending in subacute tooth; exopod broadly ovoid, with small distolateral tooth and moderately developed distolateral spiniform seta; diaeresis sinuous, with broad subtriangular lobe mesial to spiniform seta; endopod as long as exopod, ovoid, without specific features ( Fig. 1g ).

Gill formula typical for genus.

Colouration. Semitransparent-whitish, with red chromatophores forming diffuse transverse bands on pleon, some red chromatophores scattered over selected areas of carapace; antennules, antennae and tail fan also with patches of red chromatophores; major chela hyaline-white; walking legs, antennular and antennal flagella colourless and semi-translucent; yellowish and brown-orange inner organs (including ovaries) visible through partly translucent carapace ( Fig. 4 ).

Type locality. Nha Trang Bay , Vietnam .

Distribution. Indo-West Pacific: currently only known from Nha Trang Bay in southern Vietnam, and west of Muscat in northern Oman.

Ecology. Shallow mud-sand flats, from about 0.7 down to 8 m; associated with burrows, presumably made by large ghost shrimps, such as Glypturus sp. (see below).

Etymology. The new species’ name is the Latin adjective venustus , for graceful or attractive, alluding to the pretty reddish colouration of the new species (contrasting to many bland, rather whitish or pale-yellowish species in the genus Salmoneus ).

Remarks. Salmoneus venustus sp. nov. is still distinguishable from all other species of Salmoneus by a combination of morphological characters and colouration. In the general shape of the frontal and dorsal areas of the carapace, including the very broad, laterally convex rostrum, the absence of a strong mid-dorsal carina, the absence of a dorsal depression, and the eyes being concealed in dorsal view, as well as in the general shape, degree of asymmetry and armature of the major and minor chelipeds, S. venustus sp. nov. appears to be most similar to S. serratidigitus ( Coutière, 1897) , S. sibogae ( De Man, 1910) , S. latirostris ( Coutière, 1897) , S. nhatrangensis Anker & Marin, 2006 , S. mauiensis ( Edmondson, 1930) , S. arubae ( Schmitt, 1936) , S. setosus Manning & Chace, 1990 , S. rocas Anker, 2007 , S. teres Manning & Chace, 1990 , and S. kekovae Grippa, 2004 .

Salmoneus venustus sp. nov. may be separated from S. serratidigitus , S. sibogae S. latirostris , S. mauiensis , S. nhatrangensis , S. arubae , S. setosus , S. rocas , S. teres , and S. kekovae by the longer second article of the antennular peduncle, being 1.3 times as long as wide (vs. as long as wide or wider than long in the other species); from S. serratidigitus , S. sibogae , S. latirostris , S. mauiensis , S. rocas , and S. kekovae by the much shallower median incision on the posterior margin of the telson; from S. serratidigitus , S. sibogae , S. latirostris , S. nhatrangensis , S. mauiensis , S. arubae , S. setosus , S. rocas , S. teres and S. kekovae by the distinctly shorter stylocerite, reaching to the mid-length of the second article of the antennular peduncle (vs. at least to the distal margin of the second and often to the midlength of the third article in the other species); from S. serratidigitus , S. sibogae , S. mauiensis , S. setosus , S. rocas and S. kekovae by the shape of the rostrum and size and direction of the extra-corneal teeth; from S. nhatrangensis by the much shallower rostro-orbital notches; from S. arubae by the much longer minor cheliped carpus and third pereiopod dactylus; from S. setosus by the absence of numerous thickened setae on the carapace and pleon; from S. teres in the absence of a spiniform seta on the ischium of the second pereiopod; and from S. kekovae by the much less swollen major chela (cf. Coutière 1897, 1899: fig. 21; De Man 1911: fig. 10; Schmitt 1936: fig. 2; Banner 1953: fig. 2; Banner & Banner 1981: fig. 8; Manning & Chace 1990: figs. 9, 10; Grippa 2004: figs. 1, 2; Anker & Marin 2006: fig. 2; Anker 2007: fig. 4). In addition, the presence of a strong distoventral process on the major cheliped carpus, the absence of spiniform setae on the fourth pereiopod, and the eyestalks with reduced cornea and pointed anteromesial tubercle, combined with several other characters, separate S. venustus sp. nov. from most of the species mentioned above.

The characteristic colour pattern of S. venustus sp. nov., which basically consists of diffuse red bands on the pleon ( Fig. 4 ), allows an easy separation of living individuals of the new species from those of S. serratidigitus , S. mauiensis (both uniformly bright yellow-orange), S. sibogae , S. nhatrangensis (both whitish or pale yellowish), S. setosus (bright yellow) and S. kekovae (pink-orange) (cf. Coutière 1899; Edmondson 1930; Banner & Banner 1981; Grippa 2004; Anker & Marin 2006; Anker et al. 2016). The only other known brightly transversely red-banded species of Salmoneus are S. latirostris and S. cristatus ( Coutière, 1897) , although some other species of the genus have darker brown-purple transverse bands (see below) or display red chromatophores on the carapace only ( Anker et al. 2014) or on the carapace and the first two pleonites (Anker et al. 2015).

Salmoneus latirostris was described by Coutière (1897, 1899) as “incolore, corps régulièrement annelé de rouge vif” (= colourless, with regular intense transverse red banding), and by L.B. Holthuis in Banner & Banner (1981) as red banded on the pleon, with one red band at the middle or the end of the tail fan and three transverse rows of red chromatophores or red lines on the carapace, and with the antennular and antennal peduncles red or with red spots (with one specimen having a distinct red spot on the scaphocerite). According to the brief notes in Coutière (1897, 1899), S. cristatus is also red-banded, similar to S. latirostris (“coloration comme chez S. latirostris ”). L.B. Holthuis in Banner & Banner (1981) supplied more detailed colour notes for S. cristatus , which can be summarised as following: body transparent, whitish; carapace with short median red line extending from the rostral tip to slightly behind the rostral base; posterior portion of the carapace with transverse red line, its lateral ends curving slightly forward; third paired red lines extending ventrally from near the eyes; second to sixth pleonites each with distinct red line running from bases of pleura along posterior margin of tergum; uropodal endopod with one red spot basally; antennular peduncle with some red spots; eggs orange red. Based on the above colour descriptions, both S. latirostris and S. cristatus have red lines or bands on the carapace, which are absent in S. venustus sp. nov. In addition, in S. venustus sp. nov. the red bands on the pleon appear to be narrower and somewhat diffuse ( Fig. 4 ), rather than sharply marked, as in S. latirostris and S. cristatus (A. Anker, pers. obs.). These differences in the colouration add to several morphological differences between these three species, especially between the new species and S. cristatus , which possesses a well-developed rostral and mid-dorsal carina not seen in S. venustus sp. nov. ( Coutière 1899; Banner & Banner 1981; Ďuriš & Horká 2016).

The two species presently known from incomplete specimens, S. hilarulus ( De Man, 1910) and S. tafaongae Banner & Banner, 1966 (holotype lost in the fire of the Hawaii Marine Laboratory) differ from S. venustus sp. nov. in several important features, such as the much stouter dactylus of the third pereiopod in the former species (cf. De Man 1911: fig. 10g), and the much longer rostrum and up-turned orbital teeth in the latter species ( Banner & Banner 1966).

Salmoneus venustus sp. nov. appears to be an obligate burrow symbiont, as indicated by the significantly reduced, poorly pigmented corneas ( Fig. 4 ) and the microhabitat / collection data. Brief field notes accompanying the Vietnamese specimen (holotype) suggest that its host may have been a large ghost shrimp from the genus Glypturus sp. ( Callianassidae ). Spacious galleries of Glypturus spp. are known to harbour a number of other alpheid “commensals” (e.g. Anker et al. 2006; Dworschak et al. 2006; Anker & Dworschak 2007; Anker & Marin 2009).

Figures

FIGURE 1. Salmoneus venustus sp. nov.: holotype, non-ovigerous specimen (cl 6.4 mm) from Nha Trang Bay, Vietnam, MNHN-IU-2014-20290 [a–g]; non-ovigerous specimen (cl 5.5 mm) from northern Oman, OUMNH.ZC. 2015-08-0031 [h]; a—frontal region, dorsal view; b—same, lateral view; c—posterior pleonites, lateral view; d—telson, dorsal view; e—same, posterior margin, dorsal view; f—second pleopod, appendix interna and appendix masculina, lateral view; g—uropod, dorsal view; h—rostro-orbital area of carapace and eyes, lateral view.

FIGURE 2. Salmoneus venustus sp. nov.: holotype, non-ovigerous specimen (cl 6.4 mm) from Nha Trang Bay, Vietnam, MNHN-IU-2014-20290; a—third maxilliped, lateral view; b—same, tip of ultimate article, lateral view; c—second pereiopod, lateral view; d—third pereiopod, lateral view; e—same, propodus and dactylus, mesial view; f—fourth pereiopod, lateral view; g—fifth pereiopod, lateral view.

FIGURE 3. Salmoneus venustus sp. nov.: holotype, non-ovigerous specimen (cl 6.4 mm) from Nha Trang Bay, Vietnam, MNHN-IU-2014-20290; a—major cheliped, lateral view; b—same, mesial view; c—same, carpus and chela, ventrolateral view; d—same, chela fingers opened, ventrolateral view; e—minor cheliped, lateral view; f—same, carpus and chela, mesial view.

FIGURE 4. Salmoneus venustus sp. nov.: non-ovigerous specimen (cl 5.5 mm) from northern Oman, OUMNH. 2015-08-0031 [a, b]; holotype, non-ovigerous specimen (cl 6.4 mm) from Nha Trang Bay, Vietnam, MNHN-IU-2014-20290 [c]; a—living individual, dorsal view; b—same, lateral view (both photographs by the author); c—fresh specimen post-mortem, lateral view (photograph courtesy of Dr. Ivan N. Marin).