Alpheus christofferseni, Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2007

Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2007, Three transisthmian snapping shrimps (Crustacea: Decapoda: Alpheidae: Alpheus) associated with innkeeper worms (Echiura: Thalassematidae) in Panama, Zootaxa 1626, pp. 1-23 : 3-12

publication ID	https://doi.org/ 10.5281/zenodo.179290
DOI	https://doi.org/10.5281/zenodo.6247385
persistent identifier	https://treatment.plazi.org/id/038E6046-FFF9-FF84-37E3-F8B3FA5AAE46
treatment provided by	Plazi
scientific name	Alpheus christofferseni
status	sp. nov.

Treatment

Alpheus christofferseni View in CoL n. sp.

Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 , 11 View FIGURE 11 a–c, 12b, c

Material examined. Holotype: male (CL 6.8, TL 20.1), MNRJ 17905, Brazil, Atol das Rocas, Ilha do Cemitério, coll. F. B. Pitombo and R. Barroso, 24 Dec 2000. Paratypes: 1 female (CL 7.0, TL 22.9), MNRJ 20048, same collection data as holotype; 2 females (CL 6.2, TL 17.5 and CL 6.2, TL 16.9, latter dissected), MNRJ 17926, Brazil, Atol das Rocas, in front of Ilha do Cemitério, near algal crest, with suction pump, coll. F. B Pitombo and R. Barroso, 31 Dec 2000.

Additional material examined. 1 male (CL 6.7, TL 19.7), USNM 1100667, Panama, Caribbean coast, Bocas del Toro, Isla Carenero, near Bucaneer resort, 15 m from shore, depth 0.5 m, fine sand flat with seagrass, with suction pump, from burrow of Ochetostoma cf. edax (host collected and preserved), coll. A. Anker, 17 Oct 2005 [fcn 05-019].

Description. Carapace smooth, not setose, laterally not compressed. Rostrum short, triangular to subtriangular, distally subacute ( Fig. 1 View FIGURE 1 a, h), situated somewhat below dorsal-most portion of orbital hoods ( Fig. 1 View FIGURE 1 b); mediorostral carina feebly marked, blunt and short, not reaching beyond eye level, posteriorly flattening ( Fig. 1 View FIGURE 1 a); orbitorostral grooves very shallow; orbitorostral process not conspicuous. Orbital hoods moderately inflated, rounded, unarmed ( Fig. 1 View FIGURE 1 a). Pterygostomial angle rounded, not protruding ( Fig. 1 View FIGURE 1 b). Branchiostegial margin furnished with scarce setae. Cardiac notch relatively small. Eyes completely concealed in dorsal, lateral and partly frontal view. Ocellar beak well-developed, protruding vertically towards rostrum, visible in lateral view ( Fig. 1 View FIGURE 1 b). Epistomial sclerite without acute projecting tooth.

Antennular peduncles moderately stout, second segment slightly longer than dorsally visible portion of first segment, about 1.5 times as long as wide ( Fig. 1 View FIGURE 1 a); stylocerite short, distally blunt to subacute ( Fig. 1 View FIGURE 1 a, b), not reaching distal margin of first segment; mesioventral carina of first segment with tooth as illustrated ( Fig. 1 View FIGURE 1 c); lateral flagellum without independent secondary ramus, groups of aesthetasc tufts present starting from fifth segment ( Fig. 1 View FIGURE 1 a, b). Antenna with basicerite lacking ventrolateral tooth ( Fig. 1 View FIGURE 1 a, b); carpocerite robust, reaching distinctly beyond distal margin of antennular peduncle and scaphocerite; scaphocerite exceeding distal margin of antennular peduncle, with deep cleft between distolateral tooth and blade ( Fig. 1 View FIGURE 1 a, d), lateral margin slightly concave ( Fig. 1 View FIGURE 1 d), distolateral tooth reaching beyond anterior margin of blade ( Fig. 1 View FIGURE 1 a, d).

Mouthparts (mandible, maxillule, maxilla, first and second maxillipeds) typical for Alpheus . Third maxilliped relatively stout ( Fig. 1 View FIGURE 1 e); coxa with lateral plate ear-shaped, distally acute, furnished with long setae; antepenultimate segment flattened, with ventral margin somewhat rugose, dorsal margin with short, blunt distal projection; ultimate segment very setose; exopod not reaching penultimate segment; arthrobranch welldeveloped ( Fig. 1 View FIGURE 1 e).

Major cheliped ( Figs. 2 View FIGURE 2 a–c; 5a, b) with short, robust ischium; merus stout, about twice as long as wide, dorsal margin distally blunt, not projecting, ventromesial margin finely toothed, distally with subacute tooth ( Fig. 2 View FIGURE 2 a, b); carpus cup-shaped, without distinct distal lobes; chela ovate, laterally compressed, subrectangular in cross-section; dorsal margin of palm with deep transverse notch subdistally ( Fig. 2 View FIGURE 2 a, b), forming a broadly U-shaped groove in dorsal view; mesial face of palm smooth except for small depression near dorsal notch ( Fig. 2 View FIGURE 2 a); lateral face with narrow, longitudinal dorsal depression extending from dorsal notch to linea impressa, and broad, very shallow ventral depression extending from base of pollex to about mid-length of palm ( Fig. 2 View FIGURE 2 b); fingers about 3/5 length of palm; dactylus with short, distally truncate plunger, latter with stamen-shaped sensillae ( Figs. 2 View FIGURE 2 b, 5c); adhesive discs rather small ( Fig. 2 View FIGURE 2 b).

Female minor cheliped ( Fig. 2 View FIGURE 2 d, e) with robust merus, about 2.5 times as long as wide; dorsal margin distally unarmed; ventromesial margin finely toothed, distally with small subacute tooth ( Fig. 2 View FIGURE 2 d, e); carpus short, cup-shaped, with dorsomesial distal lobe; chela with palm about 3/5 as long as fingers, without sculpture, ventral margin slightly concave, distomesial margin with prominent tooth ( Fig. 2 View FIGURE 2 d, e); fingers relatively long, slender, gaping, laterally and mesially with rows of stiff setae along cutting edges, tips crossing. Male minor cheliped similar to female minor cheliped, but with fingers slightly longer and more robust ( Figs. 2 View FIGURE 2 f, 5d, e).

Second pereiopod relatively slender; ischium slightly longer than merus; carpus with five articles, with ratios (from proximal to distal) of approximately 5: 3: 1.5: 1.5: 2 ( Fig. 3 View FIGURE 3 a, h); chela simple, with fingers subequal to palm; palm as long as distal carpal article. Third and fourth pereiopods similar in shape, length and armature ( Fig. 3 View FIGURE 3 b, d); ischium armed with small ventrolateral spine; merus unarmed, about four (P3) to five (P4) times as long as wide; carpus unarmed; propodus with five spines along ventral margin and a pair of distal spines ( Fig. 3 View FIGURE 3 b–e, i); dactylus simple, conical, not spatulate, gradually curved towards subacute tip, about 0.3 (P4) to 0.4 (P3) propodus length ( Fig. 3 View FIGURE 3 c, e). Fifth pereiopod much more slender than third and fourth pereiopods; ischium with small ventrolateral spine ( Fig. 3 View FIGURE 3 f); merus about six times as long as wide; propodus with four spines on ventral margin ( Fig. 3 View FIGURE 3 g), ventrolateral margin with five or six rows of grooming setae ( Fig. 3 View FIGURE 3 f, g); dactylus simple, conical, about 0.45 propodus length, with some subdistal setae.

Abdominal somites with broadly rounded posteroventral margins; fifth somite with rounded-angular posteroventral margin; sixth segment without articulated flap, posterior margin straight, dorsolateral projections rounded; preanal plate rounded. Male second pleopod with appendix interna subequal to appendix masculina, latter with slender spine-like setae distally and along margin opposed to endopod ( Fig. 1 View FIGURE 1 i). Uropod ( Fig. 1 View FIGURE 1 f) with protopod bearing distally two strong acute teeth; exopod with diaeresis bearing one subtriangular lateral lobe proximal to distolateral spine and two well-marked rounded lobes at mid-length and mesially ( Fig. 1 View FIGURE 1 g); lateral spine relatively strong, elongate; distal margins of exopod furnished with spinules ( Fig. 1 View FIGURE 1 g). Telson relatively narrow, tapering towards posterior margin, with two pairs of short dorsal spines inserted at some distance from lateral margins, first pair at about mid-length, second pair at 3/4 of telson length ( Fig. 1 View FIGURE 1 f); posterior margin broadly rounded, with one pair of small posterolateral spines at each angle, mesial spines being twice as long as lateral spines; anal tubercles well developed.

Gill/exopod formula typical for genus: 5 pleurobranchs (P1-5); 1 arthrobranch (Mxp3); 0 podobranch (Mxp2); 2 lobed epipods (Mxp1-2), 5 strap-like epipods = mastigobranchs (Mxp3, P1-4), 5 sets of setobranchs (P1-5); 3 exopods (Mxp1-3).

Color. No color notes were made for the four specimens from the Atol das Rocas type series. However, the specimen from Bocas del Toro was photographed alive (11a-c, 12b, c) and may be described as following: background mostly semitransparent, with numerous reddish chromatophores forming several diffuse bands, including a broad band running laterally on abdominal pleurae, and interconnecting with broad transverse bands on first, second, fourth, fifth and sixth somites; dorsal portion of carapace speckled with red chromatophores, latter arranged in a transverse band running along posterior margin of carapace and connecting to most-anterior transverse band on abdomen; central dorsal portions of abdominal somites colorless; tail fan, rostral region, antennular and antennal peduncles, and walking legs semitransparent, speckled (more or less densely) with red chromatophores; chelipeds hyaline-grey with red chromatophores arranged in patches and longitudinal bands in some areas, leaving other areas colorless; palm of major chela distally pale orange; fingers of both chelipeds ivory-pinkish ( Fig. 11 View FIGURE 11 b, c).

Size. The CL of males ranges from 6.7 to 6.8 mm, TL 19.7 to 20.1 mm, respectively; the CL of females ranges from 6.1 to 7.1 mm, TL 17.2 to 22.1 mm, respectively.

Etymology. The new species is named after Dr. Martin L. Christoffersen (Universidade Federal de Paraíba, João Pessoa), for his significant contributions to the knowledge of the Brazilian alpheid and other caridean shrimps (see Christoffersen, 1998 and references therein).

Type locality. Atol das Rocas, Brazil.

Distribution. Western Atlantic: presently known only from the type locality, Atol das Rocas, off northeastern Brazil, and Bocas del Toro, Caribbean coast of Panama.

Ecology. The Atol das Rocas specimens were collected with the aid of a bait suction pump from burrows on an intertidal sand flat. The Bocas del Toro specimen was collected on a shallow (0.5–1.0 m) seagrass sand flat, about 15 m from a sand beach with a few mangrove trees, backed by a peat swamp ( Fig. 12 View FIGURE 12 a). It was extracted with a bait suction pump from the possibly U-shaped burrow of a relatively large (body length 95 mm, body diameter 15 mm, proboscis length 10 mm) thalassematid echiuran, Ochetostoma cf. edax ( Fisher, 1946) ( Fig. 12 View FIGURE 12 b, c).

Taxonomic remarks on host. Ochetostoma edax Fisher, 1946 (identification by G.-V. Murina) was originally described from Baja California in the eastern Pacific ( Fisher, 1946) and was previously not known from the Atlantic Ocean ( Stephen & Edmonds, 1972). The individual from Bocas del Toro – host of A. christofferseni n. sp. ( Fig. 12 View FIGURE 12 b, c) – was extracted with a suction pump from a vertical shaft-like burrow on a seagrass sandflat, whereas all eastern Pacific individuals of O. edax were found in horizontal burrows in muddy sand under rocks (see below). As noted by Anker et al. (2005) for Ochetostoma erythrogrammon Leuckart & Rüppel, 1828 , the paucity of morphological, anatomical and color-based characters in species-level taxonomy of the Echiura makes detection of cryptic taxa nearly impossible. Therefore, taxa with pantropical or transisthmian distributions, such as O. erythrogrammon , or O. edax , respectively, should also be examined genetically. For the time being, the Bocas del Toro specimen of Ochetostoma , which appears to be ecologically different from O. edax , is referred to as O. cf. edax , awaiting further taxonomic studies.

Variation. The new species appears to be variable in the shape of the rostrum: it may be extremely short and blunt, as in the specimen from Bocas del Toro ( Fig. 4 View FIGURE 4 a), broad and triangular, as in the first paratype ( Fig. 1 View FIGURE 1 h), or more slenderly triangular, as in the second paratype ( Fig. 1 View FIGURE 1 a). The Bocas del Toro specimen also has a much broader telson compared to the Atol das Rocas type specimens (cf. Figs. 1 View FIGURE 1 f, 4e). A slight variation also exists in the ratio of carpal segments in the second pereiopods (cf. Figs. 3 View FIGURE 3 a, h, 6a).

Remarks. Within the A. barbatus complex, A. christofferseni n. sp. is morphologically most similar to the eastern Pacific A. aequus and to the below described A. naos n. sp. It differs from A. aequus by the presence of a large, acute tooth on the ventromesial margin of the merus of the major chelipeds. Kim & Abele (1988) mentioned in the description of A. aequus that it has “no spine at distal end” on the “inferior inner” (ventromesial) margin of the merus of the major cheliped. This margin may be at most bluntly projecting, as in the two specimens of A. aequus from Coibita ( Fig. 10 View FIGURE 10 b). The homologous tooth on the minor cheliped also separates these two species: it is present, although small, in A. christofferseni n. sp., and absent in A. aequus ( Kim & Abele, 1988) . Furthermore, A. christofferseni n. sp. differs from A. aequus by the somewhat longer and more slender major chela (cf. Figs. 2 View FIGURE 2 a, b, 5a, b, 10b, c). The main differences between A. christofferseni n. sp. and A. naos n. sp. are the length of the stylocerite: not reaching distal margin of first antennular segment in A. christofferseni n. sp. vs. reaching or almost reaching this margin in A. naos n. sp.; and the shape of the rostral carina: very narrow in A. christofferseni n. sp., broader in A. naos n. sp. (cf. Figs. 1 View FIGURE 1 a, 4a, 7a). Alpheus christofferseni n. sp. may be separated from the eastern Atlantic A. ribeiroae by the shape of the scaphocerite, with distolateral spine distinctly exceeding the anterior margin of the blade (not exceeding in A. ribeiroae ); fingers of the minor chela bearing dense rows of setae (absent in A. ribeiroae ); and a stouter major cheliped, which differs in the palm/finger ratio (cf. Anker & Dworschak, 2004). Finally, the western Atlantic species, as well as both eastern Pacific species (see below) differ from the Indo-West Pacific A. barbatus in several characters, e.g., by the proportions of the major chela, the less dense setal brushes on the fingers of the minor chela, and the much more elongate and narrower scaphocerite (cf. Banner & Banner, 1982).

The color pattern of A. christofferseni n. sp. appears to be nearly identical to that of A. aequus (cf. Fig. 11 View FIGURE 11 ), and (although less intense) is also similar to the color pattern of A. naos n. sp. (see below). The only noticeable differences between A. christofferseni n. sp. and A. naos n. sp. is that the posterior dorsal half of the carapace of A. christofferseni n. sp. is covered with small reddish chromatophores ( Fig. 11 View FIGURE 11 b), which are absent in A. naos n. sp. ( Fig. 11 View FIGURE 11 d). However, in both A. christofferseni n. sp. and A. naos n. sp., the red bands may increase in intensity or fade away (almost disappearing completely, cf. Figs. 11 View FIGURE 11 a, b) depending on the shrimp’s condition, which may be affected by stress, exposure to light, etc. Nomura (2000) attributed a similar color variation in A. barbatus to “the brightness of the day and night”. However, the color variation in A. barbatus is more pronounced, especially on the major chela (cf. Nomura, 2000, fig. 1B, F). Both color and morphological variation in A. barbatus suggest presence of at least two cryptic species in the Indo-West Pacific (A. Anker, pers. obs.).