Alpheus lentiginosus, Anker, Arthur & Nizinski, Martha, 2011

Anker, Arthur & Nizinski, Martha, 2011, Description of a new deep-water species of Alpheus Fabricius, 1798 from the Gulf of Mexico (Crustacea, Decapoda, Alpheidae), Zootaxa 2925, pp. 49-56 : 50-55

Alpheus lentiginosus n. sp.

( Figs. 1–3 )

Type material. Holotype: male (CL 7.9 mm), USNM 1145505, North Atlantic Ocean, Gulf of Mexico, 188.8 km south of Louisiana, expedition USGS DISCOVRE GOM, cruise JSLII-09- GOM, vessel Seward Johnson – DSR/V Johnson Sea Link II, Sta. JSL 3726, 28°11’41”N 89°47’59”W (28.1947250, -89.7999167), Lease Block MC751, Bucket 1, depth 434–438 m, patch reef on soft bottom, base of Lophelia pertusa, S.W. Ross et al. , 19 September 2009. Paratype: female (CL 10.1 mm), USNM 1145818, North Atlantic Ocean, Gulf of Mexico, 261.82 km south of Louisiana, expedition USGS-GOM-Lophelia I, cruise USGS-GOM, vessel Seward Johnson – DSR/V Johnson Sea Link I, Sta. JSL 4745, 29°05’53”N 88°23’06”W (29.0979533, -88.3849800), Lease Block VK906/862, Bucket 11, depth 336 m, K. Sulak et al., 30 July 2004.

Description. Body moderately slender, laterally not compressed. Carapace glabrous, without marked sculpture; frontal margin with well-developed rostrum and orbital teeth; rostrum subtriangular, distally acute, longer than as wide, without setae; tip not reaching half-length of first article of antennular peduncle; rostral carina not distinct; orbital teeth in marginal position, narrow, slightly directed mesially, distally acute, shorter than rostrum; margin between orbital teeth and rostrum almost straight, transversely oblique; orbital hoods moderately swollen, complete, enclosing eyes from all sides ( Fig. 1 a, b); orbito-rostral process simple. Pterygostomial angle rounded, not protruding anteriorly ( Fig. 1 b); cardiac notch deep.

Abdominal somites with posteroventral margins broadly rounded to somewhat angular; sixth somite without articulated flap, distodorsal margin bluntly projecting on each side of telson. Telson subrectangular, tapering posteriorly, more than twice as long as wide at base; lateral margins slightly and broadly convex; dorsal surface with two pairs of strong spiniform setae inserted far from lateral margin, first pair anterior to half-length of telson, second pair between 2/3 and 3/4 length of telson; posterior margin broadly convex, with two pairs of slender posterolateral spines, mesial twice as long as lateral, margin between spines without spiniform setae ( Fig. 1 k); anal tubercles well developed.

Eyes with well-developed, normally pigmented corneas; anteromesial margin protruding as large bump ( Fig. 1 l). Ocellar beak acute, rather small, not visible in lateral view. Epistomial sclerites without acute projections.

Antennular peduncle slender; stylocerite well developed, with acute tip, falling short of distal margin of first article; ventromesial carina with subtriangular tooth as illustrated ( Fig. 1 c); second article much longer than dorsally visible portion of first article, about three times as long as wide; third article shortest, about one third length of second ( Fig. 1 a); lateral flagellum with groups of aesthetascs starting from 10th article, aesthetascs longer and more dense distally, secondary ramus composed of at least two articles. Antenna with basicerite terminating in stout sharp distoventral tooth; carpocerite slender, exceeding both scaphocerite and antennular peduncle; scaphocerite with shallowly concave lateral margin; distolateral tooth stout, reaching far beyond distal margin of blade, and also reaching slightly beyond distal margin of antennular peduncle ( Fig. 1 a, b, m).

Mouthparts not dissected, appearing genus-typical in external observation; mandible with biarticulated palp, incisor process with distal margin furnished with seven subtriangular teeth, most-anterodistal margin without teeth. Third maxilliped fairly slender; coxa with lateral plate bluntly produced dorsally, distal margin with row of setae; exopod long, overreaching distal margin of antepenultimate article; antepenultimate article somewhat flattened, subtriangular in cross-section, ventral margin setose; distodorsal margin with one particularly long thick seta; penultimate article subcylindrical, about four times as long as wide, distally widening, dorsal margin with stiff setae; ultimate article slender, unarmed distally, with long setae ( Fig. 1 d).

Male minor cheliped with short ischium, its ventral margin furnished with small stout spiniform setae; merus broad, subtriangular in cross-section; ventrolateral margin smooth, unarmed; ventromesial margin straight, furnished with small spiniform setae, and ending in sharp distomesial tooth; dorsal margin ending bluntly distally; carpus rounded, cup-shaped; chela strongly compressed, with sculpture on distal portion of palm typical of A. macrocheles group: lateral face of palm with low crest starting at about 3/5 length of chela and ending in a sharp distolateral tooth; ventral margin with deep notch continuing as shallow depression on lateral side but barely noticeable on mesial surface; dorsal margin with short subcylindrical elevation distally with adhesive disk; mesial margin with crest ending in stout sharp tooth; linea impressa poorly marked; fingers slightly longer than palm; pollex with excavated cutting edge; dactylus flattened, lamellar, twisted laterally, strongly convex dorsally ( Fig. 2 a, b). Female minor cheliped generally similar to male minor cheliped.

Male major cheliped with ischium short, furnished with small stout spiniform setae on ventromesial surface; merus stout, subtriangular in cross-section; ventrolateral margin smooth, unarmed; ventromesial margin straight, furnished with numerous small spiniform setae, and ending in stout, sharp distomesial tooth; dorsal margin ending bluntly distally; carpus very short, cup-shaped; chela compressed, with sculpture typical of A. macrocheles group; lateral face of palm with low crest starting at about 3/5 length of chela and ending in sharp distolateral tooth; ventral margin with deep notch continuing as shallow depression on lateral side and as shallow groove on mesial side; dorsal margin with subcylindrical elevation bearing adhesive disk distally; mesial margin with transversally interrupted crest ending in sharp tooth, latter overhanging propodo-dactylar articulation; linea impressa poorly marked; ventral surface with blunt setiferous tubercles; pollex short, somewhat twisted laterally, cutting edge with minute tooth followed by small notch; dactylus flattened, strongly turned laterally, convex dorsally; plunger reduced ( Fig. 2 c–e). Female major cheliped slightly smaller than male major cheliped, but generally similar in shape and proportions.

Second pereiopod elongate, slender; ischium subequal to or slightly longer than merus; carpus with five articles with ratio approximately equal to 5–6: 3: 1.5: 1.5: 2; chela simple, fingers with tufts of setae ( Fig. 1 e, n). Third pereiopod slender, with ischium bearing small ventrolateral spine; merus long, 11–12 times as long as wide, compressed, ventral margin unarmed; carpus more slender than merus, about half as long as merus, compressed, ventral margin unarmed; propodus much longer than carpus, ventral margin with a row of several slender spiniform setae, most distal ones in pairs, in addition to a pair of distoventral spiniform setae; dactylus about 1/4 length of propodus, subconical, curved ventrally, with acute tip and with minute dent subdistally ( Fig. 1 f, g). Fourth pereiopod generally similar to third; fifth pereiopod with setal brush on propodus.

First pleopod with small endopod furnished with setae. Male second pleopod with appendix masculina exceeding appendix interna, but not reaching distal margin of endopod, with numerous setae as illustrated ( Fig. 1 h).

Female second pleopod with appendix interna only. Uropod with protopod bearing large acute lateral tooth; sinuous diaeresis with blunt tooth adjacent to stout distolateral spiniform seta, and row of small spiniform setae on endopod ( Fig. 1 i, j).

Gill formula typical for Alpheus , including five pleurobranchs (above P1 –5), one arthrobranch (Mxp3), two epipods (Mxp1–2), five masigobranchs (Mxp3, P1–4), and five setobranchs (P1–5).

Colour pattern. Body reddish-orange due to groups of reddish chromatophores on pale yellow background; chelipeds more yellow-orange; antennular and antennal flagella yellowish; walking legs yellowish with some red chromatophores ( Fig. 3 ).

Variation. The female paratype is very similar to the male holotype, except for the slightly shorter orbital teeth (cf. Fig. 1 a, l) and a somewhat different ratio of carpal articles in the second pereiopod, with the first article being about 1.5 times as long as the second in the male holotype, and almost twice as long in the female paratype (cf. Fig. 1 e, n). The major and minor chelipeds of the male and female are fairly similar, except for some minor discrepancies in the proportions.

Etymology. The name ( lentiginosus = freckled in Latin) refers to the reddish spots formed by groups of chromatophores.

Ecology. The holotype of A. lentiginosus n. sp. was found in a sediment sample taken at the base of a colony of Lophelia pertusa (Linnaeus, 1758) ( Scleractinia , Caryophylliidae ) attached to carbonate rock at 434– 438 m. The general habitat was videotaped and can be described as soft sediments overlying carbonate rock with patch reefs comprised of L. pertusa , various octocorals, some with associated ophiuroids, and sea anemones; squat lobsters and various demersal fishes were also observed at this site. The paratype was collected near a tilefish burrow located in a low relief mud bank. The bottom adjacent to and above the burrow was carbonate rock, covered with mud and cobble; pencil urchins ( Cidaridae ) and anemones were common throughout the area.

Remarks. The new species clearly belongs to the Alpheus macrocheles (Hailstone, 1835) group defined mainly by the shape of the major chela, usually with two sharply ending crests on the palm and a flattened, somewhat twisted dactylus; in addition, most species also have well-developed, acute orbital teeth (see Banner & Banner 1982; Kim & Abele 1988). This group is represented by 11 species in the Atlantic Ocean, seven of them in the western Atlantic and four in the eastern and central Atlantic. At least six Atlantic species have been collected at depths below 100 m ( Crosnier & Forest 1966; Chace 1972; Christoffersen 1979).

Alpheus pouang Christoffersen, 1979 , a deep-water species from southern Brazil and Uruguay, differs from A. lentiginosus n. sp. by the much deeper subtriangular indentations on the anterior margin of the carapace, between the rostrum and the orbital hoods; the more pronounced longitudinal groove on the lateral palmar surface of the minor chela; and the shorter, less twisted dactylus of the major chela (see Christoffersen 1979: fig. 15).

Alpheus puapeba Christoffersen, 1979 , another deep-water species distributed from southern Brazil to Argentina, shares with A. lentiginosus n. sp. a similar rostro-orbital region, but the former species can be easily distinguished from the new species by the dorsally non-expanded finger of the minor cheliped and the more pronounced and overhanging shoulder on the ventral palmar margin of the major chela (see Christoffersen 1979: fig. 16).

Alpheus amblyonyx Chace, 1972 , a western Atlantic shallow-water species, differs from A. lentiginosus n. sp. by the stouter third to fifth pereiopods; stouter antennular peduncles; and the shorter and dorsally non-expanded dactylus of the minor chela (see Chace 1972: fig. 16). Williams’ (1988) material from Veatch Canyon (off Rhode Island) and off eastern Florida tentatively assigned to A. cf. amblyonyx needs re-examination. Several morphological differences and a different habitat suggest that this material does not represent A. amblyonyx sensu Chace (1972) . Interestingly, some of Williams’ (1988) specimens were collected from burrows of the blue-line (= grey) tilefish Caulolatilus microps Goode & Bean, 1878 (Malacanthidae) [remark: the paratype of A. lentiginosus n. sp. was found close to a tilefish burrow]. Gore (1981) briefly mentioned deep-water material from Florida assigned to A. amblyonyx , however, from depths significantly exceeding the normal depth range of this species in the Caribbean ( Chace 1972; Anker, pers. obs.); this material also needs to be re-examined.

Alpheus platydactylus Coutière, 1897 , a deep-water species from the northeastern Atlantic, differs from A. lentiginosus n. sp. by the dorsally non-expanded dactylus of the minor chela; the deeper subtriangular indentations on the anterior margin of the carapace, between the rostrum and the orbital hoods; and the more slender antennular peduncles (second article with length–width ratio> 4 in A. platydactylus (see Crosnier & Forest 1966: fig. 2e) vs. 4<in A. lentiginosus n. sp., see Fig. 1 a).

The eastern and central Atlantic Alpheus macrocheles (Hailstone, 1835) is closely related to A. lentiginosus n. sp., but is distinguishable by the shorter, stouter major chela (see Crosnier & Forest 1966: fig. 2b), and stouter antennular peduncles (second article with length–width ratio 2.3–2.5 in A. macrocheles (see Crosnier & Forest 1966: fig. 2a) vs. 3.4-3.6 in A. lentiginosus n. sp., see Fig. 1 a). Alpheus macrocheles is normally found from the lower intertidal down to about 50 m ( Crosnier & Forest 1966), but was also reported from a considerable depth of 1182 m ( Garcia Raso 1996), which raises questions about the accuracy of the latter identification.

All the other Atlantic species of the Alpheus macrocheles group are only distantly related to the new species. For instance, the western Atlantic A. hortensis Wicksten & McClure, 2003 and the eastern/central Atlantic A. cf. crockeri (Armstrong, 1941) , two closely related species associated with shallow to moderately deep hard bottoms, differ from A. lentiginosus n. sp. by the smooth dorsal and ventral margins of the palm of the major chela and slen- der, dorsally non-expanded dactylus of the minor chela (see Crosnier & Forest 1966: fig. 5; Wicksten & McClure 2003: fig. 2). The eastern Atlantic A. dentipes Guérin-Méneville, 1832 and the western Atlantic A. peasei (Armstrong, 1940) , both mostly subtidal, can be easily separated from the new species by the shape of the frontal region and the presence of a stout distoventral tooth on the merus of third and fourth pereiopods (see Crosnier & Forest 1966: fig. 3; McClure 2005: fig. 20). Alpheus vanderbilti Boone, 1930 , an amphi-Atlantic shallow-water species, differs from A. lentiginosus n. sp. in many features, the most obvious ones being the reduced orbital teeth and rostrum, the cylindrical major chela, without much sculpture, and the slender, gradually curving fingers of the minor chela (see Anker et al. 2008: fig. 2). Finally, the poorly known A. candei Guérin-Méneville, 1855 differs from A. lentiginosus n. sp. by the pronounced rostral carina and a markedly biunguiculate dactylus on the third to fifth pereiopods (see Coutière 1910: fig. 1), which only bears a minute dent on the ventral margin in A. lentiginosus n. sp. (see Fig. 1 g).

The eastern Pacific is home to seven species of the Alpheus macrocheles group: A. bellimanus Lockington, 1877 ; A. rectus Kim & Abele, 1988 ; A. hoonsooi Kim & Abele, 1988 ; A. clamator Lockington, 1877 ; A. inca Wicksten & Méndez, 1981 ; A. grahami Abele, 1975 ; and A. cylindricus Kingsley, 1878 . Two of them, A. clamator and A. cylindricus , can be distinguished from A. lentiginosus n. sp. by the same criteria as A. dentipes and A. vanderbilti , respectively (see above), and are not closely related to A. lentiginosus n. sp. (see Kim & Abele 1988: figs. 9, 19). Alpheus bellimanus can be separated from A. lentiginosus n. sp. by the relatively more slender minor chela and the presence of stout spiniform setae on the male second pleopod (see Kim & Abele 1988: fig. 5). Alpheus rectus can be separated from the new species by the shorter, moderately compressed dactylus of the major chela, which also has a distinct plunger (see Kim & Abele 1988: fig. 6). Alpheus hoonsooi is characterised by a slight convexity on the frontal margin between the rostrum and orbital hoods, which is absent in A. lentiginosus n. sp. In addition, this species bears a small distoventral tooth on the merus of the third pereiopod, which is lacking in the new species, and also has a more pronounced ventral shoulder on the palm of the minor chela (see Kim & Abele 1988: fig. 7). Alpheus inca , a coldwater species from Chile and Peru, differs from A. lentiginosus n. sp. by the shorter orbital teeth, much stouter walking legs (P3–5), as well as several important features on the major and minor chelipeds (see Kim & Abele 1988: fig. 9). Finally, A. grahami can be distinguished from the new species by the shape of the frontal margin of the carapace and frontal appendages, proportions of articles in the carpus of the second pereiopod, and most importantly, by the very differently shaped major and minor chelae (see Kim & Abele 1988: fig. 10).

Alpheus exilis Kim & Abele, 1988 was described based on two incomplete specimens from Baja California and Galapagos, both missing their major and minor chelipeds ( Kim & Abele 1988). No other specimens matching A. exilis have been collected so far and it remains unknown to which species group of Alpheus it actually belongs. Perhaps the best diagnostic character of A. exilis is the presence of very dense setae on the coxal lateral plate of the third maxilliped (see Kim & Abele 1988: fig. 45d). These setae are also present in A. lentiginosus n. sp. ( Fig. 1 d), although in the new species they are not as dense as in A. exilis . Another feature that may link A. exilis to A. lentiginosus n. sp. is the presence of a minute dent on the dactylus of the third pereiopod ( Fig. 1 g; see also Kim & Abele 1988: fig. 45g). In addition, A. exilis is also a deep-water species, with the depth range of 64– 146 m. The main difference between A. exilis and A. lentiginosus n. sp. lies in the shape of the frontal margin of the carapace: the margin between the rostrum and orbital hoods is slightly more deeply indented in A. exilis , whereas the rostrum is somewhat broader in A. lentiginosus n. sp. (compare Fig. 1 a and Kim & Abele 1988: fig. 45a). The above observations suggest that A. exilis may be a deep-water member of the A. macrocheles group, and perhaps closely related to A. lentiginosus n. sp.

Wicksten (1994) suggested that A. exilis may be a junior synonym of Alpheus tenuimanus Lockington, 1878 , a poorly described alpheid of unknown generic assignment from the Gulf of California. However, Wicksten’s tentatively proposed synonymy is not supported by Lockington’s (1878) description and Kim & Abele’s (1988) description and figures. In A. tenuimanus , the rostrum was described as being much longer than orbital teeth, the stylocerite as overreaching the distal margin of the first article of the antennular peduncle; and the third to fifth pereiopods as unarmed (“posterior pairs of without spines or spinules on any of the joints”). In contrast, in A. exilis , the rostrum is only slightly longer than the orbital teeth, the stylocerite does not reach the first article of the antennular pedunce, and the propodus is furnished with small spiniform setae ( Kim & Abele 1988). Therefore, the synonymy of A. exilis with A. tenuimanus must be rejected.

Burukovsky (1990) described A. romensky Burukovsky, 1990 on a single heavily damaged specimen dredged from 540–560 m on the Salas y Gómez Ridge, eastern-most point of the Polynesian triangle. This species shows some similarities to A. lentiginosus n. sp., especially in the frontal margin of the carapace, but can be separated from the new species by the more slender major and minor chelipeds (see Burukovsky 1990: fig. 3A).

In the Indo-West Pacific, at least three deep-water species from the taxonomically problematic A. hailstonei Coutière, 1905 species complex, including A. brachymerus ( Banner, 1953) , resemble A. lentiginosus n. sp. in the general shape of the major cheliped, but differ in the shape of the minor chela and numerous minor details (see Coutière 1905; Banner 1953; Banner & Banner 1982).

With regard to bathymetry, A. lentiginosus n. sp. becomes the deepest alpheid shrimp known in the Gulf of Mexico, extending by almost 200 m the previous depth record of 250 m ( Felder et al. 2009). The new species also appears to hold the deepest record of the Alpheidae in the entire western Atlantic, with no other alpheid exceeding the depth of 300 m in this area (see Chace 1972; Christoffersen 1979; Felder et al. 2009).

Figures

FIGURE 1. Alpheus lentiginosus n. sp., holotype male (a – k), paratype female (l – n), from northern Gulf of Mexico: a, anterior region, dorsal; b, same, lateral; c, tooth on ventromesial carina of first article of antennular peduncle; d, third maxilliped, lateral; e, second pereiopod, lateral; f, third pereiopod, lateral; g, same, propodus and dactylus, lateral; h, second pleopod, mesial, detail of appendix masculina and appendix interna; i, uropod, dorsal (setae omitted); j, same, detail of spiniform setae on distal margin of endopod, dorsal; k, telson, dorsal; l, frontal margin of carapace, dorsal; m, antennal scaphocerite, dorsal (setae omitted); n, second pereiopod, lateral.

FIGURE 2. Alpheus lentiginosus n. sp., holotype male from northern Gulf of Mexico: a, minor cheliped, mesial; b, same, lateral; c, major cheliped, lateral; d, same, proximal portion (ischium to carpus), mesial; e, same, chela, mesial.

FIGURE 3. Alpheus lentiginosus n. sp., holotype male (a), paratype female (b), from northern Gulf of Mexico, habitus and colour pattern. Scale in b in cm / mm. Photographs by Cheryl Morrison (USGS).