Parabetaeus acanthus, Anker, Arthur, 2015

Anker, Arthur, 2015, Description of a new distinctive species of Parabetaeus Coutière, 1897 (Decapoda: Caridea: Alpheidae) from the Indo-West Pacific, Zootaxa 3957 (5), pp. 585-595 : 586-594

publication ID	https://doi.org/ 10.11646/zootaxa.3957.5.7
publication LSID	lsid:zoobank.org:pub:439FD859-085F-4790-B9AA-D12944B6BEA4
DOI	https://doi.org/10.5281/zenodo.6107564
persistent identifier	https://treatment.plazi.org/id/290FEA54-DE26-FFE3-FF4C-FA954167FE49
treatment provided by	Plazi
scientific name	Parabetaeus acanthus
status	sp. nov.

Treatment

Parabetaeus acanthus View in CoL sp. nov.

( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Type material. Holotype: male (cl 3.4 mm), FLMNH UF 36028, Saudi Arabia, Red Sea coast, off Thuwal, Shark Reef, sheltered side of offshore reef, 22.4268°N 38.9963°E, under coral rubble, depth: 5–15 m, coll. A. Anker et al., 18.iii.2013 [fcn BDJRS-2940]; paratype: female (cl 3.0 mm), FLMNH UF 36076, Saudi Arabia, Red Sea coast, off Thuwal, El Fahal, exposed side of offshore reef, 22.2227°N 38.9677°E, under coral rubble, depth: 5–15 m, coll. A. Anker et al., 19.iii.2013 [fcn BDJRS-2967].

Additional material. 1 male (cl 3.9 mm), MNHN-IU-2014-6024, Papua New Guinea, Madang lagoon, sta. PR174, Kranket Island, 05°11.3'S 145°49.5'E, depth: 5–36 m, coll. A. Anker and Z. Ďuriš, 04.xii.2012 [fcn PR174- PZD-540A].

Description. Relatively small species (cl 3.0– 3.9 mm). Carapace with frontal margin slightly convex, without distinct rostrum or rostral projection; orbital teeth well-developed, longer than wide, acute distally; mid-dorsal line with more or less pronounced, anteriorly directed, spine-like, sharp tooth, situated well posterior to base of eyestalks, at about 0.20–0.25 of carapace length; pterygostomial angle rounded, not protruding; cardiac notch deep ( Figs. 1 View FIGURE 1 A–C, K, 4A).

Pleura of first four abdominal somites rounded posteroventrally; fifth pleuron with acutely projecting posteroventral angle; sixth somite with subacute posterior lobe and well-delimited, triangular, distally pointed, articulated plate ( Fig. 1 View FIGURE 1 D). Telson narrow, widest at anterior margin, distally tapering, about 2.5 as long as anterior width; dorsal surface with two pairs of slender spiniform setae inserted at some distance from lateral margin, at about 0.50 and 0.75 telson length, respectively; posterior margin less than half as long as anterior margin, produced into triangular, distally pointed end piece, latter flanked on each side by one pair of stout spiniform setae, mesial much longer and stouter than lateral, one pair of long plumose setae, and some shorter, less conspicuous dorsolateral setae ( Fig. 1 View FIGURE 1 E, F).

Eyes only partly concealed by orbital hoods, with large anterior portion visible in both dorsal and lateral views; eyestalks juxtaposed medially, with very large, globular, well-pigmented cornea ( Figs. 1 View FIGURE 1 A, B, 4A). Epistomial sclerites with small blunt processes.

Antennular peduncles moderately stout; stylocerite slender, with acute tip exceeding distal margin of first article but not reaching mid-length of second article; ventromesial carina with large, anteriorly directed, acute tooth; second article distinctly longer than wide; lateral flagellum biramous; fused portion short, with three joints; accessory ramus long, with four groups of long aesthetascs ( Fig. 1 View FIGURE 1 A, B, G). Antenna with basicerite ending in sharp tooth distoventrally; scaphocerite ovate, somewhat elongate, with broad, anteriorly rounded blade and acute distolateral tooth, latter reaching slightly beyond anterior margin of blade; anterior margin of scaphocerite not exceeding distal margin of antennular peduncles; carpocerite reaching about 0.8 length of scaphocerite ( Fig. 1 View FIGURE 1 A, B).

Mouthparts typical for family. Mandible with broad incisor process distally bearing seven teeth; molar process stout, distally with fields of short setae and some rugosities, palp with two articles ( Fig. 2 View FIGURE 2 A). Maxillule with bilobed palp, each lobe furnished with seta ( Fig. 2 View FIGURE 2 B). Maxilla with rather narrow scaphognathite; dorsal endite with deep cleft; endopod entire ( Fig. 2 View FIGURE 2 C). First maxilliped with moderately developed caridean lobe on exopod; endopod subdivided into one broad proximal article and one slender distal article ( Fig. 2 View FIGURE 2 D, E). Second maxilliped without specific features, as illustrated ( Fig. 2 View FIGURE 2 F). Third maxilliped slender, pediform; coxa with relatively small, distally subacute lateral plate above mastigobranch; antepenultimate article twisted, slender, penultimate article about 4.5 times as long as wide; ultimate article ending in corneous tip, without spiniform setae; arthrobranch small ( Fig. 2 View FIGURE 2 G).

Chelipeds somewhat variable, either equal in size and symmetrical in shape, slender (male holotype and female paratype, Figs. 3 View FIGURE 3 , 5 View FIGURE 5 ), or slightly unequal in size and asymmetrical in shape, noticeably more robust (nontype male, Figs. 4 View FIGURE 4 B–D, 6); both chelipeds capable of folding but apparently carried extended when not in use ( Figs. 5 View FIGURE 5 , 6 View FIGURE 6 ). Right cheliped of male holotype elongate, slender; merus about seven times as long as wide, somewhat twisted, depressed ventrally, distally slightly broadening, armed with two strong sharp teeth distally, one distomesial and one distolateral; carpus relatively short, cup-shaped, with rounded distal lobes; chela slender, with fingers about 1.3 times as long as palm, not gaping, distally crossing when closed; palm about three times as long as high, subcylindrical in cross-section, smooth; cutting edge of pollex with 28 small subtriangular-rounded teeth extending almost along entire length, including one more isolated subdistal tooth; cutting edge of dactylus sharply delimited, unarmed except for two subtriangular teeth at about 0.8 of dactylus length and one smaller subdistal tooth; both fingers furnished with some very conspicuous, long, stiff setae ( Fig. 3 View FIGURE 3 ). Left cheliped of male holotype and right cheliped of female paratype (left cheliped missing) generally very similar to right cheliped of male holotype. Right (major) cheliped of non-type male robust; merus about four times as long as wide, slightly twisted, depressed ventrally, noticeably broader distally, armed with two strong sharp teeth distally, one distomesial and one distolateral; carpus short, cup-shaped, with rounded distal lobes; chela moderately stout, with fingers 0.8 times as long as palm, somewhat gaping, distally crossing when closed; palm about twice as long as high, subcylindrical in cross-section, smooth; cutting edge of pollex with nine subtriangular-rounded teeth extending from base to about 0.6 of dactylus length, and one much larger tooth at about 0.8 of dactylus length; cutting edge of dactylus unarmed except for one large subtriangular-rounded tooth at about 0.7 of dactylus length, opposed to broad hiatus between teeth on cutting edge of pollex; both fingers also furnished with some long stiff setae ( Figs. 4 View FIGURE 4 B,C). Left (minor) cheliped of non-type male noticeably smaller than right (major) cheliped; merus and carpus similar to those of major cheliped; chela moderately stout, with fingers about 1.2 times as long as palm, not gaping, distally crossing when closed; palm about twice as long as high, subcylindrical in cross-section, smooth; cutting edge of pollex with 25 subtriangular-rounded teeth extending along almost entire length, except for one small gap at 0.8 of pollex length; cutting edge of dactylus sharply delimited, unarmed except for two small subtriangular teeth at about 0.7 of dactylus length opposed to small gap between teeth on cutting edge of pollex, and minute subdistal tooth; both fingers also furnished with some long stiff setae ( Figs. 4 View FIGURE 4 D).

Second pereiopod slender; ischium subequal to merus in length; carpus five-articulated, with first article longer than sum of remaining four articles; ratio of carpal articles (from proximal to distal) approximately equal to: 5.4: 1: 0.9: 1: 1.4; chela much longer than distal carpal article, with fingers longer than palm, simple ( Fig. 2 View FIGURE 2 H). Third pereiopod very slender; ischium with two stout spiniform setae on ventrolateral surface; merus about 11 times as long as wide, armed with three stout spiniform setae on ventrolateral surface; carpus much more slender than merus, about 0.8 length of merus, with slender spiniform seta on distoventral margin; propodus with three slender spiniform setae along ventral margin and one much longer distal spiniform setae adjacent to dactylus; dactylus about 0.4 length of propodus, slender, simple, subconical, gradually curving distally, with some curved setae subdistally ( Fig. 2 View FIGURE 2 I). Fourth pereiopod very similar to third pereiopod in general proportions of articles and armature on ischium, merus and propodus ( Fig. 2 View FIGURE 2 J). Fifth pereiopod longer and more slender than third and fourth pereiopods; ischium with one spiniform seta on ventrolateral surface; merus almost 13 times as long as wide, armed with two spiniform setae on ventrolateral surface; carpus about 0.8 length of merus, with slender spiniform seta on distoventral margin; propodus very slender, with five or so very small spiniform setae along ventral margin, one much longer spiniform seta adjacent to dactylus, and at least 10 rows of serrulate setae becoming longer distally; dactylus slightly more than 0.3 length of propodus, similar to that of third pereiopod ( Fig. 2 View FIGURE 2 K).

Male second pleopod with appendix masculina not exceeding appendix interna; apex with single long stiff seta ( Fig. 1 View FIGURE 1 H, I). Uropod with lateral lobe of protopod bearing sharp tooth; endopod and exopod broadly ovate; diaeresis sinuous, with blunt distolateral tooth adjacent to slender spiniform seta, mesial portion rather poorly defined ( Fig. 1 View FIGURE 1 J).

Gill-exopod formula as described for genus (cf. Nomura & Anker 2001).

Colour pattern. Carapace semitransparent, mostly colourless except for few chromatophores in anterodorsal area; abdomen semitransparent with six transverse red bands, one across each somite; antennular peduncles with distinctive reddish-white pattern, stylocerites intense red, flagella reddish; antennae mostly whitish, with some scattered chromatophores on carpocerites; chelipeds reddish except for hyaline-whitish fingers; second to fifth pereopods mostly colourless, with some scattered red chromatophores; tail fan reddish due to abundance of reddish chromatophores ( Figs. 5 View FIGURE 5 , 6 View FIGURE 6 ).

Variation. As noted in the description, the non-type male has relatively stout, unequal, asymmetrical chelipeds ( Fig. 6 View FIGURE 6 ), with a robust major chela armed with 10 large teeth (most distal strongest and separated by broad hiatus) on the cutting edge of the pollex and one large tooth on the cutting edge of the dactylus, and with the fingers distinctly shorter than the palm ( Figs. 4 View FIGURE 4 B, C). In contrast, in the minor chela of the non-type male as well as in the chelae of the male holotype and female paratype, the cutting edge of the pollex is armed with numerous (25–28) smaller teeth, whilst the fingers are noticeably longer than the palm ( Figs. 3 View FIGURE 3 , 4 View FIGURE 4 D). Thus, the minor cheliped of the non-type male is similar in the general shape and dentition of the fingers to the chelipeds of the male holotype or female paratype, differing basically by the proportions of the merus, carpus and palm (compare Figs. 3 View FIGURE 3 and 4 View FIGURE 4 D). The development of the tooth on the mid-dorsal line of the carapace is also variable, with the female paratype having a much smaller tooth ( Fig. 1 View FIGURE 1 K) compared to a very prominent tooth present in both the holotype and the non-type male ( Figs. 1 View FIGURE 1 B, 4A).

Etymology. The new species name (new Latin derived from the ancient Greek word akanthos = thorn or spine) refers to the presence of a conspicuous spine-like tooth on the mid-dorsal line of the carapace; used as a noun in apposition.

Type locality. Thuwal, Saudi Arabian coast of the Red Sea.

Distribution. Indo-West Pacific: presently known only from two distant localities: Thuwal, Saudi Arabia, and Madang, Papua New Guinea.

Remarks. Parabetaeus acanthus sp. nov. can be easily separated from the other three species of Parabetaeus , viz. P. culliereti , P. euryone and P. hummelincki , by the presence of a sharp spine-like tooth on the mid-dorsal line of the carapace, posterior to the base of the eyes (absent in the other species), the distinctively shorter stylocerite, its tip not reaching the mid-length of the first article of the antennular peduncle (vs. overreaching the mid-length of this article in the other species), and the dorsally partly exposed eyes (vs. completely concealed by the carapace in the other species) (cf. Figs. 1 View FIGURE 1 A, B and De Man 1911, 1915; Schmitt 1936; Banner 1953; Nomura & Anker 2001). The new species may also be distinctly smaller than P. culliereti , P. e u r y o ne and P. hummelincki . The three available specimens of P. acanthus sp. nov. are ranging between cl 3.0 and cl 3.9 mm. In contrast, the largest individuals of P. culliereti , P. euryone and P. hummelincki , for instance, may reach cl 7.4 mm, 7.3 mm and 8.2 mm, respectively (see Comparative material and Anker 2011).

In the shape of the frontal margin of the carapace, P. acanthus sp. nov. ( Fig. 1 View FIGURE 1 A, B) is most similar to some specimens of P. culliereti , especially those with the sharp orbital teeth and without a rostrum (cf. Nomura & Anker 2001: figs. 1B, 3A, B). In contrast, P. euryone and P. hummelincki are characterised by the presence of blunt or angular orbital teeth and a triangular rostrum (cf. Nomura & Anker 2001: fig. 3F; Anker 2007: fig. 7a; Anker 2011: fig. 3B). The spination on the third to fifth pereopod, although consistent in the three specimens of P. acanthus sp. nov., is known to be variable in P. culliereti and P. euryone ( Nomura & Anker 2001) and therefore can hardly be used as taxonomic character.

The shape (proportions), size, degree of asymmetry and armature of the chelipeds appear to be variable in P. acanthus sp. nov., as they are in the other species of the genus ( Nomura & Anker 2001; Anker 2007, 2011). The robust major chela, with more or less gaping fingers and armature of the cutting edges consisting of a few large teeth, seems to be present only in some adult males ( Fig. 4 View FIGURE 4 B, C; see also Banner 1953: fig. 6i; Nomura & Anker 2001: fig. 2H). A more or less pronounced polymorphism of the chelipeds is also known in several other alpheid genera, especially in Athanas Leach, 1814 ( Anker 2003a; Anker & Jeng 2007), Salmoneus Holthuis, 1955 ( Anker 2003b) , and Betaeus Dana, 1852 ( Anker & Baeza 2012) . More studies of the reproductive biology and social behaviour of Parabetaeus and other alpheid shrimps are needed to determine whether their cheliped polymorphism is somehow linked to their life style and social structure.