Type Species: Ione indecora Markham, 1988, by original designation.

Emended Diagnosis: Female. Body somewhat longer than broad, only slightly distorted, subquadrilateral in outline. Head greatly expanded into lateral flap; barbula with two processes on each side. Maxilliped with prominent palp and long slender plectron. Oostegite 1 with tuberculate internal ridge and broad, curved posterolateral projection. Brood pouch closed. Pereopods 1–4 all about same size, pereopods 5–7 progressively larger, pereopod 7 with very long basis. Pleon with six distinct pleomeres: pleomeres 1–5 produced into long slender biramous pleopods and uniramous lateral plates; pleomere 6 with uniramous or biramous uropods. Male. Body more than three times as long as broad. Head distinct from pereon, not abruptly narrower than pereon. Second antennae long and extended beyond margin of head. No midventral tubercles on pereon or pleon. Pereopods all about the same size, but dactyli smaller and bases larger from anterior to posterior. Pleon of six pleomeres, progressively narrower posteriorly, with final three either simple or greatly extended into complex lateral plates. Pleopods lacking or extremely reduced. Uropods present, elongate, or reduced. Host species in Albunea (Albuneidae).

Discussion: Some of the characters of the male, particularly those of the head and first three pereomeres, are unknown for A. yoda

Material Examined: Infesting right branchial chamber of paratype female Albunea groeningi Boyko, 2002 (11.2 mm CL). Kaohsiung, Taiwan, Republic of China, 22;dg37;prN, 120;dg15;prE, 25 m, 07 June 1992, coll. T.-Y. Chan: 1 female, holotype (NTOU H-1992-6-7a); 1 damaged male, allotype (NTOU A-1992-6-7a).

Description of Holotype Female (fig. 1): Body length 8.6 mm, maximal width 5.6 mm, head length 1.8 mm, head width 3.7 mm, pleon length 2.3 mm, body distortion 10;dg, dextral. All body regions and segments distinct. Body outline ovoid, broadest anteriorly (fig. 1A, B); no pigmentation.

Head deeply set into pereon, nearly straight across anterior margin, pentagonal in outline exclusive of lateral extensions, lacking frontal lamina. Long, extended, blunt-ended anterolateral projections of head forming slightly convex anterior margin, nearly covering margins of pereomere 1. Eyes lacking. Antennules and antennae (fig. 1C) of three and five articles respectively, each article much smaller distally than the preceding one, terminal articles sparsely setose distally. Maxilliped (fig. 1D) with anterior article much larger than posterior one and offset laterally from it, anterior margin deeply notched and bearing sparse fringe of setae; palp (fig. 1E) distinctly articulating with maxilliped, arising from anterior margin near medial corner and curved anteromedially. Plectron of maxilliped (fig. 1F) long and slender, pointing straight forward. Barbula (fig. 1G) with two broad unornamented bluntly rounded projections on each side pointed straight backward, median region simple.

Pereomeres all of about same length, posterior margins of first two strongly undulate, others variable but only slightly convex anteriorly. Coxal plates completely covering both sides of each pereomere, those on longer side of body about twice as wide as those on shorter side. Tergal projections on anterolateral corners of pereomeres 2–4. Oostegites strongly overlapping each other and completely enclosing brood pouch. First oostegite (fig. 1H, I) approximately twice as long as broad, semicircular anteriorly, with broad, short, straight posterolateral projection; internal ridge crooked, deeply digitate. No setae on posterior margins of fifth oostegites. Pereopods (fig. 1J–L) all visible dorsally, none extending beyond body margins, all articles, especially carinate bases, larger posteriorly; each propodus (fig. 1K) produced anteriorly into extended cuplike structure deeply grooved to receive distal part of dactylus.

Pleon of six pleomeres distinct both dorsally and ventrally; pleomeres 1–4 dorsally produced into dorsally extending lobe on each side, some lobes rounded and others variously divided; pleomeres 1–3 have deeply digitate crooked margins ventrally. Extended uniramous lateral plates on pleomeres 1–5, those on short side of body much more extended; lateral plates 1–4 with strongly serrated edges, lateral plate 5 appearing as simple stubby club. Five pairs of biramous pleopods, their rami all approximately the same size and structure as lateral plates, those on short side extended laterally, those opposite reflexed over ventral surface of pleon. Uniramous uropods of same size and structure as pleopodal rami.

Description of Allotype Male (specimen damaged, lacking head and pereomeres 1–3) (fig. 2): Total body length unknown; maximal width 0.87 mm, pleon length 1.27 mm. Body long and slender, sides nearly parallel. Pereomeres and pleomeres deeply divided laterally (fig. 2A, B). Small spots of pigmentation on dorsal surface of pereomere 5 and ventral surfaces of pleomeres 1–3.

Pereomeres connected only across median half of each, their sides bluntly rounded. No midventral tubercles. Pereopods long and slender, many extending well beyond margins of body. All pereopods with all articles distinct, size decreasing posteriorly (fig. 2C, D); carpi each with tuft of long setae distally.

Pleon of six pleomeres, first two similar in size and shape to pereomeres, third one with sharply angled sides, pleomeres 4–6 extended into long lanceolate lateral plates, those of pleomere 5 double, others single; pleomere 6 ending in narrow and slightly extended anal cone. Pleopods definitely present as ventral globose swellings on pleomere 4 with ambiguous structures (possibly pleopods) on pleomeres 5 and 6 (fig. 2E).

Etymology: Specific name yoda after the Jedi Master Yoda of the Star Wars saga, in recognition that the slightly curved long lateral extensions of the female's head resemble the head shape of Yoda with his long drooping ears.

Discussion: This is the first record of infestation of Albunea groeningi which is currently known to range from southern Japan southward in a narrow band to Western Australia and Victoria, Australia, to a depth of 45.7 m (Boyko, 2002); the paratype host of Albunione yoda was collected at a depth of 25 m. To date three species of the genus Albunea have been recorded as hosts of bopyrids, all of which belong to the genus Albunione. Albunione indecora (Markham, 1988) infests Albunea paretii Guérin-Méneville, 1853, in the Caribbean Sea, and Albunione australiana Markham and Boyko, 1999, infests Albunea microps Miers, 1878, off the coast of Queensland, Australia. As with A. yoda the other two parasites are known from only a small portion of their hosts' ranges. Characters that females of all three species share are: body nearly straight, broadest near anterior end; head greatly expanded into distinctive lateral flaps (a synapomorphy for this genus), eyes lacking; barbula with two simple projections on each side; maxilliped with extended palp and sharp slender plectron; both sides of all pereomeres completely covered by coxal plates, those on longer side much wider; first oostegite semicircular anteriorly, produced into short blunt point posterolaterally, with deeply divided internal ridge; pereopods much larger posteriorly, each with carpus produced into distal cup for receiving end of dactylus; all pleonal appendages tightly compacted and extending laterally, their rami with digitate margins.

Males of all three species are long and slender, with pereomeres and pleomeres deeply separated, all pereopods of nearly the same size, with six pleomeres having pleopods either absent or very reduced in number. Albunione yoda differs from the other two species in the lateral extensions of the female's head, which are relatively narrower than in the other species; its maxillipedal palp is uniquely articulating and forward, not medially projecting; the projections on the barbula are blunt rather than pointed; the inner margin of the first oostegite is deformed concavely; the proximal regions of some of its pleomeres are deeply divided; and its uropods are uniramous, not biramous. In many features of the female, A. yoda resembles A. indecora more than A. australiana including the shapes of the head, maxilliped, and pereopod 7, although its first oostegite is much more like that of the female of A. australiana The male of A. yoda in having some of its pleomeres produced into distinctive long lateral projections, is much more like that of A. indecora rather than A. australiana whose male completely lacks such projections. Also, like A. indecora, A. yoda possesses a reduced number of pleopods. The male of A. yoda differs from those of both previously described species in having some pereopodal carpi and meri fused and in bearing a very prominent anal cone.

Comparison of males and females of all three species indicates that A. indecora and A. yoda more closely resemble each other than either does A. australiana and should be regarded as sister species. Interestingly, the relationships among the species of Albunione parallel those of their hosts. Each of the three host species, Albunea paretii, A. microps and A. groeningi belong to different species groups within the genus Albunea (Boyko, 2002). A. microps belongs to a group of three species (also including A. elioti Benedict, 1903, and A. galapagensis Boyko, 2002) which is the sister group to most other Albunea species (Boyko, in prep.). These similar phylogenetic patterns of relationship imply a strong degree of coevolution between the hosts and their parasites.

Placement of Albunione: The type species, A. indecora was originally described as a species of Ione Latreille, 1818, but showed anomalies of structure and host selection that prompted its being named I. indecora (Markham, 1988). Upon reconsideration of the species (Markham and Boyko, 1999), we decided that it could not be retained in Ione, but kept it in the subfamily Ioninae, of which Ione is the type genus. No other member of that subfamily is known to infest any anomuran host, most being parasites of brachyurans and several of thalassinideans, which were at one time placed in the Anomura, but are now excluded from that infraorder (e.g., Martin and Davis, 2001).

Codreanu (1967) erected the Pseudioninae, but did not give many characters useful in the separation of this subfamily from the Ioninae. In fact, the only invariable difference he cited was in the form of the male pleopods, which were present (i.e., not reduced) in the Ioninae, but reduced (“more or less”) in the Pseudioninae. In his key to subfamilies of the Bopyridae, Bourdon (1968) distinguished between females of “Groupe CEPON” (= Ioninae) and “Groupe PSEUDIONE” (= Pseudioninae) by stating that in the former the pleonal lateral plates are always very elongate, their margins digitate or strongly tuberculate, with at least the first ones directed toward the front of the body. In contrast, females of Pseudioninae have lateral plates with nearly smooth margins and all are directed laterally or posteriorly; further, their coxal plates are but little developed and all alike, and the frontal laminae of their heads are reduced (translated and slightly paraphrased from the French). By the criteria given by Codreanu (1967) and Bourdon (1968), it appears that Albunione should be considered a member of the Pseudioninae, even though the females of the genus have lateral plates with more or less digitate margins. As a member of the Pseudioninae, Albunione infests anomuran hosts as is typical of members of that subfamily. Females of Albunione are primarily distinguishable from all others in the Bopyridae by the unique lateral enlargements of their heads, and also by the posterior enlargements of the distal regions of their lateral plates. Males of Albunione indecora and A. yoda (but not A. australiana) have posterior pleomeres uniquely produced laterally.

Because the reduction and fusion of body regions and appendages are considered to reflect more advanced evolution in genera of the Bopyridae (Markham, 1986), it would appear that Albunione with both sexes having distinctly separated pereomeres and six pleomeres, and the females of some species having biramous pleopods, is among the more primitive genera. Still, it is not the most primitive, because some females have nonarticulating maxilliped palps and only five pairs of oostegites, and males show some fusion of pereopodal articles and lack nearly all pleopods.