Paralebbeus pegasus, Ahyong, 2019

Ahyong, Shane T., 2019, Discovery of the sponge-associated caridean genus Paralebbeus in New Zealand and southeastern Australia: P. pegasus sp. nov. (Crustacea: Decapoda: Thoridae), Zootaxa 4652 (2), pp. 375-383 : 376-380

publication ID	https://doi.org/ 10.11646/zootaxa.4652.2.10
publication LSID	lsid:zoobank.org:pub:1A48815D-B23A-40C6-BDBF-2B59A83C008E
persistent identifier	https://treatment.plazi.org/id/3CE92C6D-E993-4BA9-87F2-C075C1094E89
taxon LSID	lsid:zoobank.org:act:3CE92C6D-E993-4BA9-87F2-C075C1094E89
treatment provided by	Plazi
scientific name	Paralebbeus pegasus
status	sp. nov.

Treatment

Paralebbeus pegasus sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

urn:lsid:zoobank.org:act:3CE92C6D-E993-4BA9-87F2-C075C1094E89

Type material. HOLOTYPE: NMNZ Cr 9841, ovigerous female (cl 18.1 mm, pcl 14.2 mm), off Pegasus Bay, South Island, New Zealand, 42°29.6–30.9’S, 173°58.7–58.6’E, 912–1040 m, inside a sponge, GRV James Cook, J 12/016/88, 26 September 1988 . PARATYPE: MNZ Cr 9842, 1 ovigerous female (cl 18.2 mm, pcl 14.3 mm), Canterbury Bight , 44°52–56’S, 173°12’E, 1040–1100 m, FV Ahktuba, sponges & corals, 16 December 1979 .

Other material examined. Australia, Tasmania: NMV J58059 View Materials , 1 View Materials prespawning female (cl 13.2 mm, pcl 9.8 mm), Hill U, 44° 19.6158 –19.7310 ’S, 147° 10.7538 –10.7400 ’S, 1200–1300 m, SS02/2007/13, epibenthic sled, 1 April 2007 GoogleMaps .

Diagnosis. Rostrum with 1–3 dorsal and 2 ventral spines; supraorbital and pterygostomial spine present; margin between antennal spine and pterygostomial spine distinctly convex, with concavity below base of antennal spine. Telson with 3 or 4 pairs of dorsolateral spines. Antennular peduncle reaching to distal 0.8 of antennal scale; article 1 with 3 or 4 distolateral dorsal spines; stylocerite reaching base of article 2. Maxilliped 3 exceeding antennal scale by about two-thirds length of ultimate article; ultimate article with 8–10 corneous distodorsal spinules in approximately ovate arrangement. Pereopods 1–3 with mastigobranch and associated setobranch. Pereopod 1 overreaching antennal scale by almost half length of chela; dactylus terminal claws arising at same level; dactylus and pollex terminal claws each with accessory spine at base. Pereopods 3–5 dactylus stout, length about twice height; biunguiculate, proximal unguis triangular, wider than distal unguis; merus with 1 or 2 articulated distoflexor marginal spines.

Description. Body robust, glabrous, integument soft. Rostrum 0.3–0.4 pcl, relatively straight, descending, reaching to about midlength of antennular peduncle article 1, laterally compressed, tapering to simple acute apex; dorsal margin with 1–3 sharp spines; distal half of ventral margin with 2 spines (distalmost apically bifurcate in paratype); with low lateral carina. Carapace dorsal margin convex in lateral view; postrostral median ridge weakly delineated, unarmed, extending posteriorly to anterior one-third of carapace. Supraorbital spine strong, directed anteriorly, ventrally with U-shaped notch. Anterolateral margin between supraorbital notch and suborbital lobe concave. Suborbital lobe narrowly triangular, apex rounded. Antennal spine slender, without carina, slightly overreaching suborbital lobe. Pterygostomial spine minute, not reaching antennal spine. Anterolateral margin between antennal spine and pterygostomial spine distinctly convex, with concavity below base of antennal spine.

Abdomen rounded dorsally; somite 2 with shallow transverse dorsal groove, posteriorly forming low ridge; somite 3 posterodorsal margin not produced; pleura 1–4 broadly rounded, unarmed; pleuron 5 with posterolateral spine. Abdominal somite 6 length 1.5 × length of somite 5, 1.6–1.8 × height; with blunt posteroventral angle and strong, triangular, posterolateral projection with minute apical spine.

Telson length 2.5–2.8 × greatest width, 1.5 × length of somite 6; margins subparallel in anterior one-third, tapering posteriorly to convex posterior margin; surface with proximomedial tuft of setae and shallow, irregular pitting; with 3 or 4 pairs of dorsolateral spines; with 2 pairs of posterolateral spines (inner longer), 8 or 9 plumose setae and several simple setae.

Thoracic and abdominal sternites unarmed in ovigerous females; in prespawning female thoracic sternites 6–8 and abdominal sternites 1–3 each with transverse pair of median spines, abdominal sternites 4 and 5 each with single median spine, abdominal sternite 6 with low pre-anal tubercle.

Eye subglobular, cornea wider and slightly shorter than stalk; nebenauge absent; maximum corneal diameter 0.15 pcl.

Antennular peduncle reaching to distal 0.8 of antennal scale. Article 1 longer than articles 2 and 3 combined; falling short of midlength of antennal scale; with 3 or 4 distolateral dorsal spines and 1 subdistal ventromesial spine; stylocerite sharp, reaching base of article 2. Article 2 about half-length of article 1; with stout distolateral spine. Article 3 about half-length of article 2; with conical distolateral spine, inclined dorsally. Lateral flagellum with thickened aesthetasc-bearing portion 0.5 pcl.

Antennal scale 0.5 pcl, length 2.5–2.6 × width; lateral margin nearly straight; distolateral spine directed anteriorly, not reaching anteriorly as far as apex of broadly rounded distal margin of blade. Basicerite with slender ventrolateral spine. Carpocerite length 2.5 × width; reaching slightly beyond midlength of antennal scale.

Mouthparts not dissected; mandibular palp 2-articulate.

Maxilliped 3 with 4 articles; exceeding antennal scale by about two-thirds length of ultimate article (= dactylus + propodus); mastigobranch flattened, arcuate, distally hooked. Ultimate article 0.6–0.7 pcl, 2.8–3.7 × length of penultimate article (= carpus); with transverse tufts of setae; with 8–10 corneous distodorsal spinules in approxi- mately ovate arrangement. Antepenultimate article (= fused merus, ischium and basis) flattened dorsoventrally, setose; 1 distolateral spine; 1 small distal, articulated, ventrolateral spine.

Pereopod 1 stout, overreaching apex of antennal scale by almost half length of chela. Chela 2.0–3.2 × carpus length. Dactylus length 0.3–0.4 × palm length, strongly curved distally, terminating in 2 parallel corneous claws, outer slightly longer, each with slender, corneous, accessory spine at base; occlusal margin entire. Pollex terminating in single corneous claw, with slender, corneous, accessory spine at base; occlusal margin entire. Palm length 3.1–3.2 × height; ovate in cross-section. Carpus half palm length. Merus subcylindrical, obliquely articulated with ischium; surfaces sparsely setose; with low proximodorsal tubercle; length 1.8–2.3 × carpus length and 3.2–3.5 × greatest width. Mastigobranch flattened, arcuate, distally hooked; setobranch present.

Pereopod 2 slender, overreaching antennal scale by half-length of chela and carpus combined. Chela small; palm subcylindrical; dactylus 0.5–0.6 × palm length, apex simple. Pollex apex simple. Occlusal margins of fingers entire. Carpus 4 × longer than chela, 7-articulate (third article longest), in following proportions from proximal end: 0.16: 0.08: 0.30: 0.12: 0.10: 0.08: 0.17 (holotype). Merus 0.6–0.7 × carpus length, 1.1–1.3 × ischium length; merus anteriorly extending beyond pereopod 3 merus. Mastigobranch flattened, arcuate, distally hooked; setobranch present.

Pereopods 3–5 long and slender, similar in structure, decreasing in length posteriorly; sparsely setose. Dactylus stout, length about twice height; corneous, biunguiculate, single row of 4 or 5 slender, articulated, corneous spines on flexor margin, proximal unguis triangular, wider than distal unguis; propodus with 2 rows of minute flexor spinules; carpus almost half-length of propodus, unarmed. Merus with 1 or 2 (on pereopod 4 of paratype) articulated distoflexor marginal spines. Ischiobasis half merus length, unarmed. Pereopod 3 overreaching antennal scale by one-third length of propodus; mastigobranch flattened, arcuate, distally hooked; setobranch present. Pereopod 4 reaching anteriorly to apex of antennal scale; mastigobranch absent; setobranch present. Pereopod 5 not reaching anteriorly to apex of antennal scale; propodus with distal brush of grooming setae; mastigobranch and setobranch absent.

Uropodal protopod acutely produced posterolaterally; rami subequal in length, extending posteriorly slightly beyond telson apex when folded; endopod length about 3 × width; exopod with 1 or 2 small articulated spines mesial to smaller distolateral spine; diaeresis sinuous.

Egg size: 3.0 × 1.9 mm, late “black-eyed” stage.

Etymology. Derived from the name of the type locality, Pegasus Bay; used as a noun in apposition.

Remarks. Species of Paralebbeus were previously recorded from scattered localities in the southwestern Indian Ocean, northwestern Australia, Southeast Asia and the northwestern Pacific including Japan ( Fig. 3 View FIGURE 3 ), in each case, associated with deepwater hexactinellid sponges ( Bruce & Chace 1986; Chace 1997; Hayashi & Mitsuhashi 2003; Komai 2013; Xu et al. 2016). The discovery of P. pegasus from New Zealand and Australia represents the first evidence of the genus from the temperate southwestern Pacific, and the southernmost record for the genus worldwide. Paralebbeus pegasus sp. nov. is also apparently associated with sponges, although the specific identity of the host sponge of the holotype was not identified. The occurrence of P. pegasus in both New Zealand and southeastern Australia parallels that of other benthic deep water carideans, such as Leontocaris alexander Poore, 2009 , L. amplectipes Bruce, 1990 , L. yarramundi Taylor & Poore, 1998 , Lipkius holthuisi Yaldwyn, 1960 and Merhippolyte chacei Kensley, Griffin & Tranter, 1987 ( Ahyong 2010a) .

Paralebbeus pegasus is unique in the genus for having movable distolateral spines on the pereopod 3–5 meri ( Fig. 1A View FIGURE 1 , 2 View FIGURE 2 G–I); these meri are unarmed in all other species of Paralebbeus . The rostrum of P. pegasus is also distinctive in its more extensive spination: 1–3 dorsal and 2 ventral spines ( Fig. 1A View FIGURE 1 , F–H). In other species of Paralebbeus , the rostrum is unarmed dorsally and ventrally ( P. zotheculatus , P. zygius ), has a single ventral spine only ( P. jiaolongi ), or has a single dorsal and ventral spine ( P. mollis ). The rostral armature seemingly differs between P. pegasus and P. mollis (1–3/2 versus 1/1), but given the range of variation exhibited by the former, similar variation could be expected in the latter, perhaps resulting in meristic overlap between the species.

Despite its geographical proximity to P. zotheculatus (in northern Australia) ( Fig. 3 View FIGURE 3 ), P. pegasus most closely resembles P. mollis , also a southern hemisphere high latitude species, in having dorsal and ventral rostral spines (albeit in greater number), the strongly convex anterolateral margin of the carapace with a distinct concavity below the antennal spine ( Fig. 1A View FIGURE 1 , F–H), similar distal spination on maxilliped 3 with 8–10 corneous spines arranged in near oval pattern ( Fig. 2A View FIGURE 2 ), and in the paired corneous claws of the pereopod 1 dactylus in which the bases are in-line ( Fig. 2C, D View FIGURE 2 ). Aside from the pereopod 3–5 meral spination, P. pegasus , further differs from P. mollis in the minute (versus prominent) pterygostomial spine (Fig. Fig. 1A View FIGURE 1 , F–H) and proportionally longer pereopod 2 in which the merus, when extended forwards, overreaches the end of the pereopod 3 merus (versus reaching the end) ( Fig. 1A View FIGURE 1 ). In addition, the apical claws of both fingers of pereopod 1 have a slender, moveable accessory spine ( Fig. 2D View FIGURE 2 ), as in P. zotheculatus and P. zygius (see Chace 1997: fig. 24p, q). Paralebbeus mollis apparently lacks the accessory spine on the terminal claw of the pereopod 1 pollex ( Komai 2013) and the condition in P. jiaolongi remains to be confirmed given the rudimentary figures of the pereopod 1 of the holotype ( Xu et al. 2016). As discussed by Komai (2013), most diagnostic distinctions between Lebbeus White, 1847 , and Paralebbeus identified by Bruce & Chace (1986) are not valid, with the single distinguishing feature being the absence of postrostral carapace spines in the latter. The discovery of P. pegasus with pereopod 3–5 meral spines (absent in other species of Paralebbeus ; usually present in Lebbeus ) further reinforces the morphological overlap between Lebbeus and Paralebbeus .

The most significant variation in the present series of P. pegasus is in rostral armature, with fewer spines in the holotype ( Fig. 1A, F View FIGURE 1 ) and the largest number in the paratype ( Fig. 1G View FIGURE 1 ). The distalmost ventral rostral spine in the Australian specimen is bifid ( Fig. 1H View FIGURE 1 ). The basal antennular article has four distodorsal spines in the holotype ( Fig. 1B View FIGURE 1 ), three in the other specimens. A row of four dorsolateral telson spines is present on both sides in the holotype ( Fig. 1E View FIGURE 1 ), three in the paratype, and in the Australian specimen, three on one side and four on the other.

The holotype and paratype of P. pegasus are both ovigerous, and the Australian specimen is a prespawning female as indicated by the less arched carapace, shorter abdominal pleura and spinose abdominal and thoracic sterna. The embryos carried by the ovigerous females are comparatively large (3.0 × 1.9 mm), apparently yolky and at a late stage, with thoracic and abdominal appendages, and stalked, pigmented eyes. Development in P. pegasus is possibly abbreviated, with potentially limited larval dispersal ability.