Alpheus naos, 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 : 12-17

publication ID	https://doi.org/ 10.5281/zenodo.179290
DOI	https://doi.org/10.5281/zenodo.6247387
persistent identifier	https://treatment.plazi.org/id/038E6046-FFF0-FF9F-37E3-FA2DFC6EAFE6
treatment provided by	Plazi
scientific name	Alpheus naos
status	sp. nov.

Treatment

Alpheus naos View in CoL n. sp.

Figs. 7–9 View FIGURE 7 View FIGURE 8 View FIGURE 9 , 11 View FIGURE 11 d, e

Material examined. 1 male (CL 6.8, TL 20.1), USNM 1100668, Panama, Pacific coast, Amador causeway near Panama City, Punta Culebra, rocky shore, under large mud-covered rocks on muddy sand, in burrow of Listriolobus sp. (host collected and preserved), extreme low tide, 2 Mar 2006, coll., A. Anker and C. Hurt [fcn 06-270].

Description. Carapace smooth, not setose, laterally not compressed. Rostrum short, subtriangular, distally subacute ( Fig. 7 View FIGURE 7 a), slightly descendant and situated below dorsal-most portion of orbital hoods ( Fig. 7 View FIGURE 7 b); mediorostral carina feebly marked, blunt, reaching beyond eye level, posteriorly flattening ( Fig. 7 View FIGURE 7 a); orbitorostral grooves very shallow; orbitorostral process not conspicuous. Orbital hoods moderately inflated, rounded, unarmed ( Fig. 7 View FIGURE 7 a). Pterygostomial angle rounded, not protruding ( Fig. 7 View FIGURE 7 b). Branchiostegial margin fringed with setae. Eyes completely concealed in dorsal, lateral and partly frontal view. Ocellar beak welldeveloped, protruding vertically towards rostrum. Epistomial sclerite without projecting tooth.

Antennular peduncles moderately stout, second segment slightly longer than dorsally visible portion of first segment, about 1.7–1.9 times as long as wide ( Fig. 7 View FIGURE 7 a); stylocerite short, distally blunt, almost reaching distal margin of first segment ( Fig. 7 View FIGURE 7 a); mesioventral carina of first segment with tooth as illustrated ( Fig. 7 View FIGURE 7 c); lateral flagellum without independent secondary ramus, groups of aesthetasc tufts present starting from about ninth segment ( Fig. 7 View FIGURE 7 a, b). Antenna with basicerite lacking ventrolateral tooth ( Fig. 7 View FIGURE 7 b); carpocerite robust, reaching slightly beyond distal margin of antennular peduncle and scaphocerite; scaphocerite exceeding distal margin of antennular peduncle, with deep cleft between distolateral tooth and blade, lateral margin almost straight ( Fig. 7 View FIGURE 7 a), distolateral tooth reaching well beyond anterior margin of blade ( Fig. 7 View FIGURE 7 a).

Mouthparts (mandible, maxillule, maxilla, first and second maxillipeds) typical for Alpheus . Third maxilliped moderately stout ( Fig. 9 View FIGURE 9 a); coxa with lateral plate ear-shaped, distally acute, furnished with some setae; antepenultimate segment flattened, with ventral margin somewhat rugose; ultimate segment very setose; exopod reaching penultimate segment; arthrobranch well-developed ( Fig. 9 View FIGURE 9 a).

Major cheliped ( Fig. 8 View FIGURE 8 a, 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 small blunt tooth ( Fig. View FIGURE 8

8a); 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. 8 View FIGURE 8 a, b), forming a broadly Ushaped groove in dorsal view; mesial face of palm smooth except for small depression near dorsal notch ( Fig. 8 View FIGURE 8 b); lateral face with small depression near dorsal notch and broad, very shallow depression extending from base of pollex to about mid-length of palm ( Fig. 8 View FIGURE 8 a); slightly more than 1/2 length of palm; dactylus with short, distally truncate plunger, latter with stamen-shaped sensillae ( Figs. 8 View FIGURE 8 a. b); adhesive discs small ( Fig. 8 View FIGURE 8 a).

Male minor cheliped ( Fig. 8 View FIGURE 8 c–e) with robust merus, more than twice as long as wide; dorsal margin distally unarmed; ventromesial margin straight, distally blunt ( Fig. 8 View FIGURE 8 c); carpus short, cup-shaped, with blunt distomesial lobe; chela with palm about 3/5 as long as fingers, without sculpture, ventral margin almost straight ( Fig. 8 View FIGURE 8 d, e), distomesial margin with promenent blunt tooth ( Fig. 8 View FIGURE 8 d); fingers long, slender, slightly gaping, laterally and mesially with rows of stiff setae along cutting edges, tips crossing when chela closed ( Fig. 8 View FIGURE 8 d, e). Female minor cheliped unknown.

Second pereiopod relatively slender; ischium slightly longer than merus; carpus with five articles, with ratios (from proximal to distal) of approximately 5: 3: 1: 1: 2 ( Fig. 9 View FIGURE 9 b); chela simple, with fingers subequal to palm; palm as long as distal carpal article. Third pereiopod ( Fig. 9 View FIGURE 9 c) with ischium bearing one ventrolateral spine; merus unarmed, at least five times as long as wide; carpus unarmed; propodus with four slender spines along ventral margin and a pair of distal spines ( Fig. 9 View FIGURE 9 c); dactylus simple, conical, not spatulate, gradually curved towards subacute tip, about 1/2 propodus length. Fourth pereiopod similar to third. Fifth pereiopod with different article proportions; ischium with ventrolateral spine; propodus with ventral spines and welldeveloped setal brush.

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 ( Fig. 7 View FIGURE 7 d) with appendix masculina longer than appendix interna, possibly partly fused to endopod, with slender spine-like setae distally and along endopod-facing margin ( Fig. 7 View FIGURE 7 d, e). Uropod ( Fig. 7 View FIGURE 7 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; lateral spine relatively strong, elongate; distal margins of exopod furnished with spinules ( Fig. 7 View FIGURE 7 f). Telson relatively narrow, tapering towards posterior margin ( Fig. 7 View FIGURE 7 g), 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. 7 View FIGURE 7 g); posterior margin broadly rounded, with one pair of small posterolateral spines at each angle, mesial spines being at least twice as long as lateral spines ( Fig. 7 View FIGURE 7 h); anal tubercles well-developed.

Gill/exopod formula as indicated for previous species.

Color. Background mostly white semitransparent, with numerous red chromatophores forming several bands, including a broad lateral band on abdominal pleurae, interconnecting with two broad transverse bands on second and fifth somites, and narrow, more irregular bands on first and fourth somites, sixth somite with narrow transverse band along posterior margin; telson and uropods red except for most proximal portions; dorsal portion of carapace with broad band of red chromatophores, descending to flanks; central dorsal portions of abdominal somites, especially third, fourth and sixth, as well as most of posterior and anterior carapace colorless; rostral region, anterolateral margins of carapace and antennular peduncles semitransparent speckled (more or less densely) with red chromatophores; antennal peduncle and walking legs mostly semitransparent white; cheliped merus and carpus hyaline white with red chromatophores; chelae pinkish red due to numerous red chromatophores, distally (proximal to fingers) with pale orange tinge; fingers of major and minor chelae mostly ivory white ( Fig. 11 View FIGURE 11 d, e).

Size. The CL of the holotype male specimen is 6.8 mm, TL 20.1 mm.

Etymology. The new species is named after Isla Naos , where the type locality (Punta Culebra) and the Naos Marine Laboratory of the STRI are situated.

Type locality. Punta Culebra, Isla Naos , Amador Causeway near Panama City, Pacific coast of Panama.

Distribution. Eastern Pacific: presently known only from the type locality on the Pacific coast of Panama.

Ecology. The holotype was collected by hand from a burrow of a large thalassematid echiuran (body length 150 mm, body diameter 10–15 mm, proboscis length 30 mm), Listriolobus sp. (see below). The burrow was dug horizontally into muddy sand under large mud-covered rocks, in the rocky intertidal, near the extreme low tide mark.

Taxonomic remarks on host. The original identification of the host as “ Listriolobus sp. aff. brevirostris Chen & Yeh, 1958 ” was tentative (G.-V. Murina, pers. comm.), partly because of the imperfect condition of the specimen from Punta Culebra (the animal died a few hours prior to preservation). Listriolobus brevirostris was originally described from China ( Chen & Yeh, 1958; Stephen & Edmonds, 1972) and is not known to occur in the eastern Pacific. On the other hand, specimens of its congener, Listriolobus cf. bahamensis Fisher, 1926 , were recently collected at Punta Culebra and other localities along the Pacific coast of Panama (Murina & Anker, in prep.). They are morphologically (at least externally) and ecologically very similar to the individual found with A. naos n. sp. As no other species of Listrilobus are known from the shallow waters of the tropical eastern Pacific ( Stephen & Edmonds, 1972), L. cf. bahamensis may well be the host of A. naos n. sp.

Remarks. Within the A. barbatus complex, A. naos n. sp. is morphologically closest to the eastern Pacific A. aequus and the western Atlantic A. christofferseni n. sp. (see above). It differs from A. aequus by the slightly narrower telson; the slightly longer second segment of the antennular peduncle; the broader blade of the scaphocerite; the lack of a slight sinus on the ventral margin of the palm of the minor chela; the less gaping fingers of the minor chela; a different palm/fingers ratio of the major chela; and the distinctly narrower merus of the third pereiopod. For differences between A. christofferseni n. sp. and A. naos n. sp. see remarks under the former species. Another possible difference between these two species may lie in the appendix masculina: its proximal half is apparently partly fused to the endopod in A. naos n. sp. ( Fig. 7 View FIGURE 7 e), whereas the entire appendix masculina is free-standing in A. christofferseni n. sp. ( Figs. 1 View FIGURE 1 i, 6e) All these features, however, need to be confirmed by observations in additional specimens.