Acrobelione halimedae, Boyko & Williams & Shields, 2017

Boyko, Christopher B., Williams, Jason D. & Shields, Jeffrey D., 2017, Parasites (Isopoda: Epicaridea and Nematoda) from ghost and mud shrimp (Decapoda: Axiidea and Gebiidea) with descriptions of a new genus and a new species of bopyrid isopod and clarification of Pseudione Kossmann, 1881, Zootaxa 4365 (3), pp. 251-301 : 260-262

Acrobelione halimedae n. sp.

Fig. 3

Material examined. Singapore: Mature non-ovigerous holotype female (7.5 mm), ex right branchial chamber of female Austinogebia spinfrons (8.6 mm CL), Sta. 6, Pulau Tekong (type locality) ( ZRC 1990.4330 ).

Etymology. This species is named for the tapered and marginally constricted lateral plates and pleopods that are reminiscent of the “segmented” appearance of species in the algal genus Halimeda J. V. Lamoroux, 1812 (e.g., H. cylindracea Descaisne, 1842 ) with subquadrate or cylindrical plates. In Greek mythology, Halimeda was a Nereid, the daughter of Nereus and Doris.

Distribution. Singapore.

Host. Austinogebia spinfrons (Haswell, 1881) (type host).

Description. Female ( Fig. 3 A, B ), body length 8.0 mm, maximal width 6.4 mm, head length 1.5 mm, head width 1.9 mm. No body pigmentation. Pereon weakly sinistral (15°) with coxal plates and pereomeres of right side slightly larger on segments 1–4 ( Fig. 3 A ). Head slightly wider than long, with thin frontal lamina ( Fig. 3 A ), deeply embedded medially in first pereomere; eyes lacking.

Antennules of three articles each, antennae of four articles each ( Fig. 3C ).

Maxilliped with rounded distal end and subacute recurved spur; palp present as setose, non-articulated lobe ( Fig. 3E ).

Barbula with 2 pairs of irregular lateral projections with numerous short, finger-like marginal lobes; medial margin with few finger-like, short fleshy projections ( Fig. 3D ).

First oostegite anterior lobe rounded, external posterior face with patch of irregular low, fleshy lobes, inner ridge with numerous small rounded projections along ¾ of length; distal lobe subtriangular, slightly recurved ( Fig. 3F, G ). Fourth and fifth oostegites with fringe of setae on posterior margin ( Fig. 3B ).

Pereon composed of 7 pereomeres ( Fig. 3 A ), first 2 markedly curved and rounded at lateral margins, third and fourth nearly laterally straight, rounded at lateral margins except for one side of pereomere 7 which has a posterolateral point ( Fig. 3J ), last 3 slightly curved posteriorly at truncate lateral margins; broadest across pereomere 4, gradually tapering anteriorly and posteriorly; Pereomere 1 with convex posterior margin; posterior margins of pereomeres 2 and 3 nearly straight; posterior margins of pereomeres 4–7 convex ( Fig. 3 A ). Pereomeres 1–4 with rounded coxal plates, no dorsolateral bosses. Pereomere 4 bilobed laterally, remainder undivided with rounded coxal plates.

First pair of pereopods near anterolateral margin of head; pereopods evenly spaced. Pereopods subequal in size ( Fig. 3H, I ), carpi and meri fused, small tubercles present on lateral faces of some ischia; basis with ridge of larger tubercles ( Fig. 3H, I ).

Pleon with 5 distinct pleomeres plus small pleotelson ( Fig. 3 A ), pleomeres resembling posterior three pereomeres, but with tapered lateral plates. Lateral plates present distally on pleomeres as elongate, tapered lobes with numerous constrictions along length ( Fig. 3 A, J, K ); lateral region of pleomeres with few, low warty lobes on margins and surface ( Fig. 3 A, K ). First five pleomeres with pair of tapered, elongate, biramous pleopods with lateral constrictions as seen in lateral plates ( Fig. 3L ); pleopods extending beyond lateral plates and visible in dorsal view, mostly on left side of body ( Fig. 3 A ), all endopods and exopods subequal in size and shape ( Fig. 3B ).

Pleotelson not easily seen in dorsal view ( Fig. 3 A ), bearing pair of uniramous uropods with endopod and exopod subequal in size, both resembling lateral plates and pleopods in having numerous marginal constrictions ( Fig. 3 A, L ).

Male unknown.

Remarks. All species of Acrobelione have females with the barbula possessing lateral projections with numerous short, finger-like lobes on the margins, and lateral plates and pleopods with numerous constrictions along their lengths, as well as pereopods with scattered tubercles on the ischia and a ridge of pronounced tubercles on the bases. This new species is most similar to A. langi ( Van Name, 1920) (see also Bourdon 1981b) but differs from it in the shape of the female’s head (flat frontal margin in A. halimedae n. sp. vs. distinctly medially produced in A. langi ) and the overall body shape (nearly circular in A. halimedae n. sp. vs. ovate in A. langi ). The material (2 females and 2 males) of A. langi examined by Bourdon (1981b) came from hosts collected at the same time and from the same locality as the unique holotype but were not seen by Van Name (1920) and are not type specimens. Acrobelione anisopoda Bourdon, 1981b was described from an immature female and mature male (type host and locality: Gebiacantha talismani (Bouvier, 1915) from off Príncipe, Gulf of Guinea); both show characters of species in Acrobelione , but the female does not have well developed tubercles on the pereopods nor laterally constricted lateral plates or pleopods. However, these differences may be due to the specimen’s immaturity. A key to species in the genus based on mature females is given below, including type host and type locality data.

Although not common, Acrobelione has species known from both gebiidean and axiidean hosts (An et al. 2009). However, Bourdon (1981b) erred when he listed Acrobelione reverberii ( Restivo, 1970) as occurring on U. pusilla because the 66 individuals said by Bourdon (1981b: 120, footnote) to be from this upogebiid host are clearly stated by Restivo (1968) to be from C. truncata . Likewise, the listing by Markham (2001) of A. reverberii occurring on U. pusilla is erroneous; his supposed source for that data ( Restivo, 1970) does not list any host other than Callianassa truncata . Restivo (1968), although listing a “nuova specie” from U. pusilla , also lists one from C. truncata , and this is the correct data that should be associated with A. reverberii .

Figures

FIGURE 3. Acrobelione halimedae n. sp., mature holotype female (ZRC 1990.4330), ex Austinogebia spinfrons (Haswell, 1881). A, dorsal overview of female; B, ventral overview of female; C, right antennule and antenna; D, left barbula; E, right maxilliped, outer view; F, right oostegite 1, internal view; G, right oostegite 1, outer view; H, right pereopod 1; I, left pereopod 7; J, right pereomere 7 (Per7) and right lateral plate 1 (Lp1); K, left lateral plate 1; L, ventral view of fifth pleopods (Ple5) and uropods (Uro).Scale bars:A, B, E, F = 1 mm; C = 125 µm; D, = 250 µm; G–L = 500 µm.