Research Article
Research Article
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
expand article infoShoki Shiraki, Michitaka Shimomura§, Keiichi Kakui
‡ Hokkaido University, Sapporo, Japan
§ Kyoto University, Nishimuro, Japan
Open Access


We describe a new paranthurid isopod genus and species, Deltanthura 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). Deltanthura and four paranthurid genera (Califanthura Schultz, 1977, Colanthura Richardson, 1902, Cruranthura Thomson, 1946, and Cruregens Chilton, 1882) share neotenous characters, but in Deltanthura 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


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.

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 Tansei-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).


Superfamily Anthuroidea Leach, 1814

Family Paranthuridae Menzies & Glynn, 1968

Deltanthura gen. nov.

New Japanese name. Sankaku-ashitarazu-uminanafushi-zoku


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. Pereopod 7 absent on non-manca individuals. Uropodal exopod elongate triangular, tapering.

Type species

Deltanthura palpus Shiraki, Shimomura & Kakui, by original designation.


The generic name is a combination of the Greek letter delta (δέλτα), which is triangular in shape, referring to the shape of pleotelson, prefixed to anthura, from Greek anthos (a flower) and oura (a tail). The gender is feminine.


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 Deltanthura the mandible is acute, with a 3-articulate palp and maxillipedal endites present, characters that are unique among the neotenous paranthurid genera (Table 1).

Table 1.

Comparison of selected characters among the seven genera in Paranthuridae.

Characters Pseudanthura Richardson, 1911 Paranthura Bate & Westwood, 1866 Califanthura Schultz, 1977 Colanthura Richardson, 1902 Cruranthura Thomson, 1946 Cruregens Chilton, 1882 Deltanthura gen. nov.
Eyes Absent Present/absent Present Present Present Absent Present
Pereonite 7 Not hidden laterally Not hidden laterally Hidden laterally Hidden laterally Not hidden laterally Not hidden laterally Hidden laterally
Pleonites 1–5 Fused Free or fused Fused Indicated by folds 1 free, 2–5 fused Free Fused
Pleonite 6 and telson Fused dorsally Not fused dorsally Not fused dorsally Not fused dorsally Not fused dorsally Not fused dorsally Fused 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 in non-manca individuals Present Present Absent Absent Absent Absent Absent
Uropodal exopod Tapering Oval Oval Oval Oval Oval Tapering
References Poore and Lew Ton (1986) Frutos et al. (2011), Poore (2001) Poore (2001) Poore (2001) Poore (2001) Poore (2001) Present study

Deltanthura gen. nov. does not fit well within the clade (Paranthura + neotenous clade) (cf. Poore 2001), as it has a maxillipedal endite. Rather, Deltanthura 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 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 Deltanthura) are unknown for C. minuta, we refrain from transferring it to Deltanthura.

Deltanthura palpus sp. nov.

[New Japanese name: Sankaku-ashitarazu-uminanafushi] Figs 1, 2, 3, 4

Material examined

Holotype. Japan • 1 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.


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 paranthurid 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.

Figure 1. 

Deltanthura palpus sp. nov., holotype, female, lateral view of fixed specimen. Scale bar: 1 mm.

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.

Figure 2. 

Deltanthura 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 µm (D–H).

Antenna (Fig. 2E) with five peduncular and nine flagellar articles. Peduncular article 1 with outer simple 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 narrow 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.

Figure 3. 

Deltanthura palpus sp. nov., holotype, female. A–F. Left pereopods 1–6. Scale bar: 100 µm.

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.

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 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.

Figure 4. 

Deltanthura 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 µm.

Pleopods 2–5 (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 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.


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 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; Wägele 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 Deltanthura (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).

Key to the genera in Paranthuridae, modified from Poore (2001)

1 Pereopod 7 present in non-manca individuals 2
Pereopod 7 lacking in non-manca individuals 3
2 Pleonite 6 marked off dorsally from telson; uropodal exopod linear or leaf-shaped Paranthura
Pleon and telson fused into single segment; uropodal exopod extremely reduced Pseudanthura
3 Pleonite 6 entirely fused dorsally to telson; pleotelson tapering, triangular; mandible acute, with 3-articulate palp Deltanthura gen. nov.
Pleonite 6 marked off dorsally from telson; pleotelson oval; mandible blunt, without palp 4
4 Pereonite 7 hidden laterally; head as long as wide 5
Pereonite 7 not hidden laterally; head longer than wide 6
5 Pleonites 1–5 separated by integumental folds dorsally; pleonite 1 twice as long as pleonite 2 Colanthura
Pleonites 1–5 fused, rarely with integumental folds dorsally; pleonites 1 and 2 similar in length Califanthura
6 Pleonites 2–5 fused; marine or estuarine; eyes present Cruranthura
Pleonites all free; hypogean or freshwater; eyes lacking Cruregens


We thank the captain and crew of RV Tansei-maru, Dr. Tadashi Akiyama of Okayama University, and other onboard researchers for their efforts in collecting; cruise director Dr. Tatsuo Oji of Nagoya University for organizing cruise KT08-3; and Dr. Matthew H. Dick for reviewing the manuscript and editing our English.


  • Bate CS, Westwood JO (1866) A History of the British Sessile-eyed Crustacea. Vol. 2. John Van Voorst, London, 536 pp.
  • Chilton C (1882) On some subterranean Crustacea. Transactions and Proceedings of the New Zealand Institute 14: 174–180.
  • Frutos I, Sorbe JC, Junoy J (2011) The first blind Paranthura species (Crustacea, Isopoda, Paranthuridae) from the ‘El Cachucho’ Marine Protected Area (Le Danois Bank, southern Bay of Biscay). Zootaxa 2971(1): 17–32.
  • Kensley B (1980) Anthuridean isopod crustaceans from the International Indian Ocean Expedition, 1960–1965, in the Smithsonian Collections. Smithsonian Contributions to Zoology 304(304): 1–37.
  • Kensley B (1981) Amsterdam Expeditions to the West Indian Islands, Report 10. Curassanthura halma, a new genus and species of interstitial isopod from Curacao, West Indies (Crustacea: Isopoda: Paranthuridae). Bijdragen tot de Dierkunde 51(1): 131–134.
  • Kensley B, Heard RW (1991) Studies on the Crustacea from the Turks and Caicos Islands, British West Indies. I. Four new marine isopod crustaceans from the vicinity of Pine Cay. Gulf Research Reports 8(3): 237–257.
  • Leach WE (1814) Crustaceology. Brewster’s Edinburgh Encyclopedia 7: 383–437. [pl. 221]
  • Menzies RJ, Glynn PW (1968) The common marine isopod Crustacea of Puerto Rico: A handbook for marine biologists. Studies on the Fauna of Curacao and other Caribbean Islands 27(104): 1–133.
  • Poore GCB (1984) Colanthura, Califanthura, Cruranthura and Cruregens, related genera of the Paranthuridae (Crustacea: Isopoda). Journal of Natural History 18(5): 697–715.
  • Poore GCB (2001) Families and genera of Isopoda Anthuridea. Crustacean Issues 13: 63–173.
  • Poore GCB (2009) Leipanthura casuarina, new genus and species of anthurid isopod from Australian coral reefs without a “five-petalled” tail (Isopoda: Cymothoida: Anthuroidea). ZooKeys 18: 171–180.
  • Poore GCB, Lew Ton HM (1986) New species of Aenigmathura and Pseudanthura (Crustacea: Isopoda: Paranthuridae) from eastern Australia. Memoirs of the Museum of Victoria 47(1): 59–73.
  • Richardson H (1902) The marine and terrestrial isopods of the Bermudas, with descriptions of new genera and species. Transactions of the Connecticut Academy of Sciences 11: 277–310.
  • Richardson H (1911) Les Crustacés Isopodes du Travailleur et du Talisman; Formes Nouvelles. Bulletin du Muséum National d'Histoire Naturelle 17: 518–534.
  • Schultz GA (1977) Anthurids from the west coast of North America, including a new species and three new genera (Crustacea, Isopoda). Proceedings of the Biological Society of Washington 90(4): 839–848.
  • Shiraki S, Shimomura M, Kakui K (2021) A new species of Expanathura (Crustacea: Isopoda: Anthuroidea) from Iriomote Island, Japan, with a note on male polymorphism. Zootaxa 5047(3): 377–390.
  • Thomson JM (1946) New Crustacea from the Swan River estuary. Journal of the Royal Society of Western Australia 30: 35–53.
  • Wägele JW (1981) Study of the Anthuridae (Crustacea: Isopoda: Anthuridea) from the Mediterranean and the Red Sea. Israel. Journal of Zoology 30(3): 113–159.
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