A new species of the alpheid shrimp genus Triacanthoneus Anker, 2010 (Crustacea: Alpheidae) from Belize

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Zootaxa 3768 (1): 088–094

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http://dx.doi.org/10.11646/zootaxa.3768.1.6

http://zoobank.org/urn:lsid:zoobank.org:pub:C081C8BF-B536-41F3-9A6B-9A34443009CE

A new species of the alpheid shrimp genus Triacanthoneus Anker, 2010

(Crustacea: Alpheidae) from Belize

FERNANDO ALVAREZ1,3, THOMAS M. ILIFFE2 & JOSÉ LUIS VILLALOBOS1

1Colección Nacional de Crustáceos, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-153, Méx-

ico 04510, D.F., México. E-mail: [email protected], [email protected] of Marine Biology, Texas A&M University at Galveston, Galveston, Texas 77553-1675, U.S.A. E-mail: [email protected] author

Abstract

A new species of the alpheid shrimp genus Triacanthoneus Anker, 2010, is described based on material collected in a ma-

rine cave off Caye Chapel, Belize. Triacanthoneus chapelianus sp. nov. is the fifth species in the genus and can be distin-

guished from the other four species by the position of the dorsolateral teeth on the carapace, which in the new species have

an anterior (= submarginal) position, and by the configuration of the posterior margin of the telson, with a notch in the

middle portion and two pairs of spines and one pair of plumose setae. A key to the five species of Triacanthoneus is pro-

vided.

Key words: Caridea, Alpheidae, Triacanthoneus, Belize, cave shrimp, new species

Introduction

The genus Triacanthoneus Anker, 2010 is composed by four species of small alpheid shrimps distributed in the coastal waters of the Pacific coast of Colombia and Panama, and in the western Atlantic from the Caribbean coast of Panama to the southern Gulf of Mexico (Anker, 2010; Alvarez et al., 2012). Triacanthoneus is a rarely collected genus, with currently only 11 individuals known, representing four species, T. toro Anker, 2010, T. pacificus Anker, 2010, T. alacranes Anker, 2010, and T. akumalensis Alvarez, Iliffe, Gonzalez & Villalobos, 2012, one of them (T.

alacranes) was described based on a single individual. Anker (2010) in the diagnosis of Triacanthoneus stated that the genus was characterized by three teeth on the

carapace, one in a mediodorsal position on the posterior half of the carapace and two in post-hepatic position, a pattern that is seen in the four known species so far. Here we describe a new species from Caye Chapel, Belize, in which a different pattern is observed: the mediodorsal tooth is on the anterior half of the carapace and the pair of lateral teeth are in a submarginal position behind the orbits. In addition to the unique position of the teeth on the carapace, the single specimen from Caye Chapel has a distinct posterior margin of the telson with a notch similar to that of T. akumalensis Alvarez, Iliffe, Gonzalez & Villalobos, 2012, but with an additional pair of setae. The holotype of the new species is deposited in the Colección Nacional de Crustáceos, Instituto de Biología, Universidad Nacional Autónoma de México, Ciudad de México, Mexico (CNCR). Abbreviations used in the text are: cl, carapace length; tl, total length.

Taxonomy

Family Alpheidae Rafinesque, 1815

Genus Triacanthoneus Anker, 2010

88 Accepted by J. Goy: 17 Jan. 2014; published: 24 Feb. 2014

Triacanthoneus chapelianus sp. nov.

(Figs. 1–4)

Type material. Holotype: ovigerous female, cl 4.3 mm, tl 17.3 mm; Belize, marine cave off Caye Chapel (17º42'46" N, 88º02'05" W), depth 8–10 m, 18 February 1989, coll. T.M. Iliffe and S.M. Sârbu, CNCR 28284.

Description. Small-sized shrimp (tl less than 18 mm), carapace length approximately one fourth of total length. Carapace with one pair of acute teeth immediately posterior to extra-corneal angle and sharp tooth along medio-dorsal line, on anterior half of carapace (Figs. 1A, B, 2A, B). Rostrum reaching distal half of second antennular article, pointing forwards, dorsal margin smooth, ventral margin with one tooth (Fig. 2B). Cardiac notch reduced to small incision (Fig. 2B).

Eyes not completely covered by carapace, visible in dorsal and lateral views (Figs. 2A, B). Cornea not faceted, with dark granules of pigment.

Ventral margins of pleura of first three abdominal somites rounded, posterolateral angle of fourth somite subacute, and that of fifth somite acute. Third and sixth somites subequal in length (Fig. 1A).

Telson 1.5 times as long as sixth abdominal somite, 2.2 times as long as its anterior width. Dorsal surface with two pairs of spines, anterior pair on proximal half, posterior pair on distal third. Posterior half with shallow median groove, becoming more evident posteriorly, ending in U-shaped notch on posterior margin. Posterior margin with two pairs of strong spines, subequal in length; one medial pair of plumose setae, shorter than adjacent spines, on lateral margins of median notch (Figs. 2D, E). Uropods with exopod and endopod subequal in length, slightly longer than telson (Fig. 2D).

Antennule with well developed stylocerite, tip acute, reaching middle portion of second article of antennular peduncle (Fig. 2A). First article of antennular peduncle longer than second and third. Lateral flagellum divided after third article, accessory branch with five articles and series of long aesthetascs (Figs. 3A–C). Antenna with strong carpocerite bearing large tooth on lateroventral angle; scaphocerite ovate, as long as antennular peduncle, distal margin rounded, reaching beyond distolateral tooth (Fig. 2A).

Mouthparts not dissected, of typical appearance for the genus in external observation. Third maxilliped pediform, last article with transversal rows of short setae, exopod reaching distal margin of merus (Fig. 4A). First pair of pereiopods strongly asymmetrical in shape and size. Major cheliped about half as long as total body length; ischium with three lateral spines, 0.5 times length of merus; merus cylindrical, 1.5 times length of carpus; carpus becoming wider distally; propodus longest article, 1.4 times length of merus; dactylus 0.6 times length of propodus; palm somewhat inflated, thicker than fingers, fingers closing completely except for distal fifth, cutting edges with minute teeth alternating when fingers completely closed, finger tips strongly crossing (Fig. 3D). Minor cheliped less than half length of major cheliped; ischium 0.7 times length of merus, with three spines on lateroventral margin; merus longest article, 1.1 times length of carpus; carpus becoming wider distally; chela with fingers subequal in length to palm, fingers closing completely, not gaping, tips crossing (Fig. 4B, C).

Second pair of pereiopods slender; ischium 1.2 times as long as merus, with three spines on ventrolateral margin; merus simple; carpus 5-articulated, first carpal article longer than half-length of carpus, remaining carpal articles subequal in length; chela simple, with fingers about half length of palm (Fig. 3E). Pereiopods 3–5 simple, increasing in length posteriorly, carpi longest articles in third and fourth pereiopods, propodus longest in fifth; ischia unarmed; meri unarmed, slender; propodi unarmed, with some stiff setae; brush on propodus of P5 reduced to distal tuft; dactylii simple, slender, curved, about 0.35 length of propodi in third and fourth pereiopods, about 0.25 length of propodus in fifth pereiopod (Figs. 1, 3F–H, 4D–F).

Second pleopod with endopod bearing appendix interna and appendix masculina (Fig. 4G). Appendix masculina straight, stout, apical portion with four slender spinules oriented laterally; appendix interna subequal in length to appendix masculine, curved mesially, with coupling hooks on apical portion. Holotype with approximately 70 eggs, ovoid in shape, measuring 0.5 x 0.35 mm.

Etymology. The specific epithet is derived from the type locality, Caye Chapel, Belize.Distribution. Presently known only from the type locality, a marine cave off Caye Chapel, Belize. Habitat. Caye Chapel Cave is located 0.5 km east (seaward) of the northern tip of Caye Chapel, Belize. The

entrance consists of two vertical shafts located about 15 m apart on a seagrass bed in 3 m depth. At a depth of 8 m in the cave, the two entrance shafts join in a low room from where a sandy restriction under a ledge leads to a large descending rift, well decorated with stalactites and floored with white sandy sediments. At 35 m depth, the rift

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levels off and begins to ascend to a point at which the cave ends in collapse 150 m from the entrance. The water is clear with visibility about 20–30 m. The deeper waters of the cave appear relatively more sterile in comparison with regions closer to the entrance where encrusting sponges, orange mysids, and red shrimps (possibly Janicea or Parhippolyte) are conspicuous. Speleonectes cokei Yager, 2013, previously known only from Caye Caulker Cave, is the second species of Remipedia to be collected from a completely submarine cave. The harpacticoid copepod Novocrinia trifica Huys & Iliffe, 1998, from the new family Novocriniidae and the calanoid copepod Enantiosis

belizensis Fosshagen, Boxshall & Iliffe, 2001, from the family Epacteriscidae, as well as representatives of the primitive calanoid genera Ridgewayia Thompson & A. Scott, and Pseudocyclops Brady have been recorded from this cave (Audun Fosshagen, pers. comm.).

Remarks. Triacanthoneus chapelianus sp. nov. can be distinguished from the other four known species of the genus by the position of the dorsolateral teeth on the carapace, which are in a submarginal position posterior to the extra-corneal (orbital) angle (Figs. 2A, B); in the other four species, these teeth are in a more or less hepatic position (cf. Anker 2010; Alvarez et al. 2012). Other characters of the new species are a reduced cardiac notch on the posterodorsal margin of the carapace and the presence of a U-shaped notch on the posterior margin of the telson (Fig. 2E).

FIGURE 1. Triacanthoneus chapelianus sp. nov., ovigerous female, holotype (CNCR 28284): A, total lateral view; B,

photograph of a preserved individual. Scale bar = 1 mm.

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FIGURE 2. Triacanthoneus chapelianus sp. nov., ovigerous female, holotype (CNCR 28284): A, carapace, dorsal view; B,

carapace, lateral view; C, detail of rostrum and submarginal dorsolateral teeth; D, telson and uropods, dorsal view; E, detail of

posterior margin of telson. Scale bars = A, B, D, 1 mm; C, 0.5 mm; E, 0.25 mm.

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FIGURE 3. Triacanthoneus chapelianus sp. nov., ovigerous female, holotype (CNCR 28284): A, antennular flagella; B, detail

of accessory branch of lateral antennular flagellum; C, detail of tip of accessory branch of lateral antennular flagellum; D,

major cheliped; E, second pereiopod; F, third pereiopod; G, fourth pereiopod; H, fifth pereiopod. Scale bars = A, B, C, 0.5 mm;

D–H, 1 mm.

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FIGURE 4. Triacanthoneus chapelianus sp. nov., ovigerous female, holotype (CNCR 28284): A, third maxilliped; B, minor

cheliped; C, detail of chela of minor cheliped; D–F, detail of propodi and dactylii of third through fifth pereiopods; G, second

pleopod showing endopod, appendix masculina, and appendix interna (exopod missing). All scale bars = 1 mm.

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The holotype of T. chapelianus sp. nov., described as an ovigerous female, has a well-developed appendix masculina on the second pleopod, a characteristic already reported for the three species of Triacanthoneus

described by Anker (2010) (T. toro, T. pacificus, T. alacranes), but not found in all specimens of the type series of T. akumalensis, where one ovigerous individual, designated as “female” did not have appendix masculina, while another “ovigerous specimen” had a well-developed appendix masculina (Alvarez et al., 2012).

Egg size is remarkably uniform in Triacanthoneus regardless of the two types of habitats: the eggs of the shallow coastal species T. toro and T. alacranes measure 0.65 x 0.36 mm and 0.6 x 0.38 mm, respectively (Anker 2010); while they measure 0.5 x 0.33 mm in T. akumalensis and 0.5 x 0.35 mm in T. chapelianus, the two cave species (Alvarez et al. 2012; present study). This suggests that the larval development of the cavernicolous species of Triacanthoneus is not advanced as observed in many other cave shrimps.

Although all species of Triacanthoneus are found in coastal areas, T. toro, T. pacificus and T. alacranes were collected in shallow/intertidal habitats in substrates with sand, seagrasses or rubble (Anker 2010), whereas, in contrast, T. chapelianus and T. akumalensis were collected in marine caves at shallow depths, 8–10 m for the former, and moderate depths, 25–40 m for the latter (Alvarez et al. 2012; present study).

Key to the species of Triacanthoneus (modified from Anker, 2010)

1. Orbital margin of carapace forming acute tooth-like projection, dorsolateral teeth slightly anterior to mediodorsal tooth. . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Triacanthoneus alacranes Anker, 2010

- Orbital margin of carapace without tooth-like projection, dorsolateral teeth clearly anterior to mediodorsal tooth . . . . . . . . . . 2

2. Eyes not visible in dorsal view covered by carapace, tip of rostrum reaching midportion of third antennular article . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Triacanthoneus akumalensis Alvarez, Iliffe, Gonzalez & Villalobos, 2012

- Eyes visible in dorsal view, tip of rostrum reaching midportion of second antennular article . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3. Dorsolateral teeth of carapace in a submarginal position near orbital margin; posterior margin of telson with distinct medial U-

shaped notch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Triacanthoneus chapelianus n. sp.

- Dorsolateral teeth of carapace in hepatic position; posterior margin of telson straight, without U-shaped notch . . . . . . . . . . . . 4

4. Major chela with fingers longer than palm, ventral tooth of rostrum directed forwards . . . . . .Triacanthones toro Anker, 2010

- Major chela with fingers shorter than palm, ventral tooth of rostrum directed downwards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Triacanthoneus pacificus Anker, 2010

Acknowledgments

Cave collections in Belize in 1989 were supported by a grant from the Smithsonian Institution’s Caribbean Coral Reef Ecosystems Program awarded to T. M. Iliffe. Serban Sârbu helped with cave diving collections and sorting of specimens. Frank Bounting of the Belize Diving Services at Caye Caulker provided logistical and cave diving assistance. We gratefully acknowledge the Belize Department of Archeology and its Commissioner, the late Harriot W. Topsey, for granting us permission to carry out these investigations. The first author gratefully acknowledges the support of CONACYT grant 155644 “Processes that create and maintain the biodiversity in an extreme environment: the Anchialine systems of Yucatan”. The manuscript was improved with the revisions made by A. Anker and M.R. McClure.

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ALVAREZ ET AL.94 · Zootaxa 3768 (1) © 2014 Magnolia Press