Zoosyst. Evol. 98 (1) 2022, 109-115 | DOI 10.3897/zse.98.81772 yee BERLIN A new neotenous genus and species, Deltanthura palpus gen. et sp. nov. (Isopoda, Anthuroidea, Paranthuridae) from Japan, with a revised key to the genera in Paranthuridae Shoki Shiraki!, Michitaka Shimomura’, Keiichi Kakui® 1 Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan 2 Seto Marine Biological Laboratory, Kyoto University, Nishimuro 649-2211, Japan 3 Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan http://zoobank.org/CBDFBS5FE-1734-4B4A-96AB-C87BDA85E6F2 Corresponding author: Shoki Shiraki (white-treeQ703@eis.hokudai.ac.}p) Academic editor: Sammy De Grave # Received 7 February 2022 # Accepted 15 March 2022 # Published 31 March 2022 Abstract We describe a new paranthurid isopod genus and species, De/tanthura palpus gen. et sp. nov., collected from a depth of 805-852 m off the southern coast of Mie prefecture, Japan. Deltanthura is similar to Pseudanthura Richardson, 1911 in having a triangular pleotelson, acute mandible with a 3-articulate palp, a maxillipedal endite, and a tapering uropodal exopod, but differs in having eyes and neotenous characters (reduced pereonite 7 and pereopods 7 lacking). De/tanthura and four paranthurid genera (Califanthura Schultz, 1977, Colanthura Richardson, 1902, Cruranthura Thomson, 1946, and Cruregens Chilton, 1882) share neotenous characters, but in De/tanthura the mandible is acute, with a 3-articulate palp and maxillipedal endites are present. Califanthura minuta Kensley & Heard, 1991 may belong in Deltanthura as they share the triangular pleotelson and tapering uropodal exopod, but we refrain from transferring it to Deltanthura as its description lacks the other diagnostic characters of Deltanthura. We provide a revised key to all genera in Paranthuridae Menzies & Glynn, 1968. Key Words Califanthura, Cymothoida, deep sea, neoteny, Peracarida, taxonomy Introduction Species in the anthuroid isopod family Paranthuridae Menzies & Glynn, 1968 have the mouthparts acutely produced; the palm of pereopod 1 lacks a proximal tooth; and statocysts are absent (Poore 2001). Paranthuridae comprises six genera: Paranthura Bate & Westwood, 1866, Pseudanthura Richardson, 1911, Califanthura Schultz, 1977, Colanthura Richardson, 1902, Cruranthura Thomson, 1946, and Cruregens Chilton, 1882. The latter four are neotenous genera in which non-manca individuals lack pereopod 7, as is the case for manca- stage individuals, and share the character combination of having a blunt mandible lacking a palp and an extremely reduced pereonite 7. On the basis of morphological observations, Poore (1984) hypothesized that (1) the four neotenous genera comprise a monophyletic group (hereafter, the “neotenous clade”); (2) Paranthura is the sister group to the neotenous clade, as species in both groups lack maxillipedal endites; and (3) Pseudanthura is the most basal genus in Paranthuridae. We collected a paranthurid individual lacking pereopod 7 from off the southern coast of Mie, Japan, but unlike the four known neotenous paranthurid genera, its mandible bears an acute incisor and 3-articulate palp, and its maxilliped bears an endite. Here we describe the Species as new, establish a new genus for it, and provide a revised key to the genera in Paranthuridae. Copyright Shiraki S et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 110 Materials and methods A single specimen was collected in 2008 from Shima Spur off the southern coast of Mie prefecture, Japan, with a 3-m beam trawl at a depth between 805 and 852 m, during the cruise KT 08-3 of RV Yansei-maru. The specimen was fixed in 5—10% borate-buffered formalin in seawater and preserved in 70% ethanol. The methods for dissection, observation, drawing, and measurement were as described in Shiraki et al. (2021). Body length was measured from the tip of the anterolateral lobe of the head to the tip of the telson, and body width at the widest portion of pereonite 4. The specimen examined is deposited in the collections of the Seto Marine Biological Laboratory (SMBL-V0645). Systematics Superfamily Anthuroidea Leach, 1814 Family Paranthuridae Menzies & Glynn, 1968 Deltanthura gen. nov. http://zoobank.org/04EA59DC-C5AD-486B-A3CB-AA7076F SABES New Japanese name. Sankaku-ashitarazu-uminanafushi-zoku Diagnosis. Eyes present. Pereonite 7 reduced and hidden laterally. Pleonites 1-5 fused but with sutures. Pleonite 6 entirely fused dorsally to telson; pleotelson triangular, without statocyst. Mandible acute, with 3-articulate palp. Maxilliped with 4-articulate palp; endite present. Pereo- pod 7 absent on non-manca individuals. Uropodal exopod elongate triangular, tapering. Type species. De/tanthura palpus Shiraki, Shimomura & Kakui, by original designation. Etymology. The generic name is a combination of the Greek letter de/ta (0€\ta), which is triangular in shape, referring to the shape of pleotelson, prefixed to anthura, from Greek anthos (a flower) and oura (a tail). The gen- der is feminine. Remarks. Like Pseudanthura and Paranthura, Deltanthura has an acute mandible with a 3-articulate palp, but it differs from the former two genera in having pereonite 7 reduced and in lacking pereopods 7. Deltanthura and four paranthurid genera share neotenous characters (reduced pereonite 7 and pereopods 7 lacking), but in De/tanthura the mandible is acute, with a 3-articulate palp and maxillipedal endites present, characters that are unique among the neotenous paranthurid genera (Table 1). Deltanthura gen. nov. does not fit well within the clade (Paranthura + neotenous clade) (cf. Poore 2001), as it has a maxillipedal endite. Rather, De/tanthura seems to be more closely related to Pseudanthura, as these two share multiple character states such as a triangular pleotelson; elongate triangular, tapering uropodal exopod:; and maxillipedal endite. If this latter hypothesis is correct, the neotenous condition in Paranthuridae may not have had zse.pensoft.net Shiraki, S. et al.: A new paranthurid genus and species from Japan a single origin. In addition to the five neotenous genera now known in Paranthuridae, three neotenous genera are known in anthuroid isopods (Poore 2009): the monotypic genera Exallanthura Kensley, 1980 and Leipanthura Poore, 2009 in Anthuridae Leach, 1814; and the genus Curassanthura Kensley, 1981 in Leptanthuridae Poore, 2001. We note that Poore (2009) pointed out that the Exallanthura females sensu Kensley (1980) may actually have been manca individuals. The neotenous species Califanthura minuta Kensley & Heard, 1991 from the British West Indies may belong in Deltanthura gen. nov. It has the triangular pleotelson and tapering uropodal exopod (Kensley and Heard 1991) that occur in Deltanthura but not in other Califanthura species. However, as the shape of mandible and the presence or absence of the maxillipedal endite (characters diagnostic for De/tanthura) are unknown for C. minuta, we refrain from transferring it to De/tanthura. Deltanthura palpus sp. nov. http://zoobank. org/290406E3-4688-4CC7-8A3F-DC 104E7C7BBF [New Japanese name: Sankaku-ashitarazu-uminanafushi| Figs 1-4 Material examined. Holotype. JAPAN ¢ | female lacking oostegites, body length 7.03 mm, body width 0.91 mm; Mie prefecture, off the southern coast, Shima Spur, Stn. SM-01-(1); 34°00.83'N, 136°53.79'E to 34°01.42'N, 136°51.80'E; depth 805-852 m; 4 Mar. 2008; Tadashi Akiyama leg.; SMBL-V0645, 12 slides and 1 vial. Etymology. The specific name, palpus (Latin: palp), is a singular noun in the nominative case, referring to the presence of a mandibular palp, a unique trait in paranthu- rid neotenous genera. Description of holotype female. Body relatively slender (Figs 1, 2A—C), length 7.69 times width. Head (Fig. 2A) length 1.02 times head width, roughened, irregular dorsally; rostrum protruding as much as anterolateral lobes; eyes dorsolateral, with scattered ommatidia. Pereonites 1-7 (Fig. 2A, B) roughened, irregular dorsally, with length ratio 1.00:1.02:1.26:1.19: 1.08:0.78:0.18; pereonite 7 (Fig. 2B, C) reduced, hidden laterally, lacking pereopod 7. Pleonites 1—5 (Fig. 2B, C) fused but with sutures, length 0.06 times body length. Pleonite 6 entirely fused dorsally to telson (Figs 2B, C, 4H); pleotelson triangular, length 1.04 times width, with four dorsal and six apical simple setae. Antennula (Fig. 2D) with three peduncular and six flagellar articles. Peduncular article 1 with one inner and two outer plumose sensory setae; article 2 with inner simple seta; article 3 with three inner and one outer simple setae. Flagellar articles 1 and 2 naked; article 3 with distal aesthetasc and three distal simple setae; article 4 with distal aesthetasc; article 5 with distal aesthetasc and simple seta; article 6 with four distal simple setae. Antenna (Fig. 2E) with five peduncular and nine flagellar articles. Peduncular article 1 with outer simple Zoosyst. Evol. 98 (1) 2022, 109-115 Table 1. Comparison of selected characters among the seven genera in Paranthuridae. Characters Pseudanthura Paranthura Bate Califanthura Colanthura Cruranthura Cruregens Deltanthura Richardson, & Westwood, Schultz, 1977 Richardson, Thomson, 1946 Chilton, 1882 gen. nov. 1911 1866 1902 Eyes Absent Present/absent Present Present Present Absent Present Pereonite 7 Not hidden Not hidden Hidden laterally Hidden laterally Not hidden Not hidden — Hidden laterally laterally laterally laterally laterally Pleonites 1-5 Fused Free or fused Fused Indicated by 1 free, 2-5 Free Fused folds fused Pleonite 6 and Fused dorsally Not fused Not fused Not fused Not fused Not fused Fused dorsally telson dorsally dorsally dorsally dorsally dorsally Mandible Acute Acute Blunt Blunt Blunt Blunt Acute Mandibular palp 3-articulate 3-articulate Absent Absent Absent Absent 3-articulate Maxillipedal endite Present Absent Absent Absent Absent Absent Present Pereopod 7 Present Present Absent Absent Absent Absent Absent in non-manca individuals Uropodal exopod Tapering Oval Oval Oval Oval Oval Tapering References Poore and Lew Frutos et al. Poore (2001) Poore (2001) Poore (2001) Poore (2001) ‘Present study Ton (1986) (2011), Poore (2001) Figure 1. De/tanthura palpus sp. nov., holotype, female, lateral view of fixed specimen. Scale bar: 1 mm. seta; article 2 with two distal simple setae; article 3 with two inner simple setae; article 4 with two distal plumose sensory setae and three simple setae; article 5 with four distal plumose sensory setae and four inner simple setae. Flagellar articles 1-9 with four, four, seven, four, three, three, two, four and zero distal simple setae, respectively. Mandible (Fig. 2F) with 3-articulate palp. Palp article 1 naked; article 2 with distal simple seta; article 3 with eleven simple setae. Molar absent. Incisor acute. Maxilla (Fig. 2G) slender, with twelve teeth and nar- row lamella. Maxilliped (Fig. 2H) with 4-articulate palp. Palp articles 1 and 2 long, 3 and 4 short, with one, four, one, and three simple setae, respectively. Endite present, reaching middle of article 2, with distal simple seta. Epipod oval. Pereopod 1 (Fig. 3A) subchelate, robust. Basis with three dorsal plumose sensory setae and ventrodistal seta (tip broken). Ischium with one outer and one ventrodistal simple setae. Merus with two dorsal, one outer, and one ventral simple setae. Carpus strongly protruding ventrodistally, with three inner mid-ventral spiniform setae and four simple setae. Propodus broad, with two inner proximal spiniform setae, and one outer, four dorsal, and one distal simple setae. Palm with five outer spiniform setae and seven simple setae. Dactylus and unguis fused, with two ventral and five middle simple setae. Pereopod 2 (Fig. 3B) narrow. Basis with two dorsal plumose sensory setae, two simple setae, and dorsal seta (tip broken). Ischium with three simple setae. Merus with two dorsal and two ventrodistal simple setae. Carpus triangular, longer than wide, with three ventrodistal simple setae and ventrodistal seta (tip broken). Propodus with dorsal plumose sensory seta, three ventral spiniform setae, and two dorsal and three ventral simple setae. Dactylus with ventrodistal thick seta and three ventral, three ventrodistal, and four inner distal simple setae. Unguis naked. Pereopod 3 (Fig. 3C) similar to pereopod 2 except in number of setae. zse.pensoft.net 112 Shiraki, S. et al.: A new paranthurid genus and species from Japan Figure 2. De/tanthura palpus sp. nov., holotype, female. A. Dorsal view of head and pereonite 1; B. Dorsal view from pereonite 2 to telson; C. Lateral view; D. Left antennula; E. Left antenna; F. Right mandible; G. Right maxilla; H. Right maxilliped. Scale bars: 1 mm (A-C); 100 um (D-H). Pereopods 4—6 (Fig. 3D—F) narrower than pereopod 2, but similar to it except in number of setae and shape of carpus. Carpus rectangular, with ventrodistal spiniform seta. Pleopod 1 (Fig. 4A) protopod with inner simple seta and outer seta (tip broken). Exopod operculiform, distal zse.pensoft.net margin serrate, with 15 marginal plumose setae and four simple setae on surface. Endopod 0.53 times longer than exopod, with three distal simple setae. Pleopods 2—5S (Fig. 4B—E) similar to one another. Protopod with one or two simple setae. Exopod with five to seven distal plumose setae and outer simple (pleopods Zoosyst. Evol. 98 (1) 2022, 109-115 113 Figure 3. Deltanthura palpus sp. nov., holotype, female. A-F. Left pereopods 1-6. Scale bar: 100 um. 2-4) or plumose (pleopod 5) seta. Endopod with three distal plumose setae. Uropod (Fig. 4F, G) with protopod bearing two outer and one inner plumose setae and outer simple seta. Exopod elongate triangular, tapering, with five (right) and 10 (left) simple setae. Endopod with two distal projections, five outer and three distal plumose sensory setae, and 12 distal simple setae. Remarks. Our specimen lacks oostegites and an appendix masculina, but its pereon is expanded ventrally (Fig. 1), leading us to conclude that it is a female prior to spawning, rather than a manca-stage individual. The zse.pensoft.net 114 Shiraki, S. et al.: A new paranthurid genus and species from Japan D Figure 4. Del/tanthura palpus sp. nov., holotype, female. A-E. Left pleopods 1—5 (most setal ornamentation omitted); F. Right uropod; G. Left uropodal exopod; H. Telson. Scale bars: 100 um. strongly reduced pereonite 7 also supports this conclusion; this segment is not as reduced as in the mancae of non- neotenous species (cf. Frutos et al. 2011: fig. 2C, D; Wagele 1981: fig. 9M). This is the fifth neotenous genus known in Paranthuridae. Deltanthura palpus gen. et sp. nov. differs from Califanthura minuta, which may belong in De/tanthura zse.pensoft.net (see Remarks above for the genus), in the following characters (character state of C. minuta in parenthesis): body length 7.03 mm (1.60 mm); carpus of pereopod 1 strongly protruding ventrodistally (not protruding); endopod of pleopod 1 short, about half length of exopod (elongate, slightly shorter than exopod); and uropodal endopod with two distal projections (no projections). Zoosyst. Evol. 98 (1) 2022, 109-115 115 Key to the genera in Paranthuridae, modified from Poore (2001) 1 rerecpods/ Dresemt lit THONAM Ae IMO VIOUS cot... 02a cnt aactfh ins oe Xone stg caensncan vosmee thoes