Hemiarthrus alphei, An & Chen & Paulay, 2020

An, Jianmei, Chen, Ruru & Paulay, Gustav, 2020, Three new species of abdominal shrimp parasites (Crustacea: Isopoda: Bopyridae Hemiarthrinae) from the Indo-West Pacific, Zootaxa 4845 (2), pp. 264-274 : 270-272

publication ID	https://doi.org/ 10.11646/zootaxa.4845.2.7
publication LSID	lsid:zoobank.org:pub:ED92874B-EBFF-4A77-A9C8-B654F30BA28C
DOI	https://doi.org/10.5281/zenodo.4407347
persistent identifier	https://treatment.plazi.org/id/03808789-FFCB-A474-FFCD-ADBFC92182C7
treatment provided by	Plazi
scientific name	Hemiarthrus alphei
status	sp. nov.

Treatment

Hemiarthrus alphei View in CoL n. sp.

Figs 4 View FIGURE 4 , 5 View FIGURE 5

Material examined. Holotype female, ovigerous, 1.97 mm, paratype male, 1.06 mm, UF Arthropoda 15685 ( Fig. 4C, D View FIGURE 4 ), French Polynesia, Society Island, Moorea, N end of Temae, near lighthouse, outer reef slope, 29 meters, from within rubble, 17.479°S, 149.7643°W, coll. J. Poupin, 17 October, 2008. Infesting ovigerous Alpheus crinitus Dana, 1852 (species complex) UF Arthropoda 15684 ( Fig. 4A, B View FIGURE 4 ). GoogleMaps

Description. Holotype female (UF 15685) length 1.97 mm; head length 0.57 mm; head width 0.8 mm; pleon length 0.86 mm. Body extremely asymmetrical, 45°dextral distortion; no pigmentation ( Fig. 5A View FIGURE 5 ).

Head oval, anterior margin deeply bilobate anteriorly, posterior margin rounded ( Fig. 5A View FIGURE 5 ). Eyes absent. Both antennulae and antennae rudimentary, with one article, without setae ( Fig. 5C View FIGURE 5 ). Barbula ( Fig. 5D View FIGURE 5 ) with three slender falcate pointed lateral projections on each side. Maxilliped ( Fig. 5E View FIGURE 5 ) with two segments, anterior segment subtriangular and much larger than irregularly-shaped posterior one, without palp, plectron slender.

Pereon broadest across seventh pereomere ( Fig. 5A View FIGURE 5 ). Pereomeres 3–7 separated along middle region but fused along both sides. Coxal plates absent. Brood pouch enclosed by oostegites, open medially ( Fig. 5B View FIGURE 5 ). First oostegites highly asymmetrical; left one ( Fig. 5F, G View FIGURE 5 ) with two subequal articles, internal ridge entire, with blunt posterolateral point; right one ( Fig. 5H, I View FIGURE 5 ) with anterior article approximately three times longer than posterior article, internal ridge entire, with sharp posterolateral point. Seven pereopods on right side of pereon, but only first pereopod discernible on left side. Pereopod with stout basis, small meri and carpi, short but pointed dactyli ( Fig. 5J View FIGURE 5 ).

Pleon of five pleomeres, extending away from pereomere 7 in dorsal view ( Fig. 5A View FIGURE 5 ). First four pleomeres with uniramous, symmetrical lateral plates and four pairs of similar, uniramous pleopods. Terminal pleomere extending to form rounded pleotelson, terminating in sharp point ( Fig. 5B View FIGURE 5 ).

Paratype male ( UF 15685 ) length 1.06 mm; maximum width (across pereomere 5) 0.39 mm; head length 0.15 mm; head width 0.20 mm, pleon length 0.31 mm. All pereomere regions distinct; pleon fused ( Fig. 5K, L View FIGURE 5 ) .

Head elliptical, with rounded anterior margin, posterior margin fused with first pereomere; irregular dark eyes near posterolateral corners ( Fig. 5K View FIGURE 5 ). Antennulae and antennae with three and five articles respectively, terminally setose; antennae prominently extending beyond head, visible in dorsal view. ( Fig. 5L, M View FIGURE 5 ).

Pereon with seven segments ( Fig. 5K View FIGURE 5 ). Pereomeres 3–5 subequal in width, lacking midventral projections, with patches of pigmentation on pereomeres 4–5 ( Fig. 5K View FIGURE 5 ). Pereopods subequal, except last pair slightly larger than others ( Fig. 5L, N, O View FIGURE 5 ).

Pleon fused into single piece ( Fig. 5L View FIGURE 5 ), inflated, with scattered black pigmentation on dorsal surface. Pleopods and uropods absent.

Etymology. The specific name, alphei , refers to the host genus, Alpheus .

Remarks. This new species is placed in Hemiarthrus because the female has 5 pleomeres, four pairs of uniramous lateral plates and uniramous pleopods, and only one pereopod on the long side. It can be distinguished from the other species of Hemiarthrus by the barbula of the female having three pairs of falcate pointed lateral projections, pleomeres having well-developed, symmetrical lateral plates, and the pleon ending in a sharp point. The present species is most similar to H. synalphei , but it can be distinguished from H. synalphei (character states in H. synalphei given in parentheses) because the barbula of the female has three pairs of lateral projections (only two pairs); the pleotelson is short and oval (long and cylindrical); and the head of the male is fused with pereomere 1 (head separated from pereomere 1); it lacks sucker discs on the oostegite (with sucker discs on the oostegite).

Hemiarthrus surculus , H. synalphei and H. alphei infest alpheid shrimp, H. abdominalis infests pandalid and hippolytid shrimp, while H. nematocarcini is parasitic on nematocarcinid shrimp. Chopra (1923) thought Palaemon specimens parasitized by bopyrids are difficult to identify owing to the fact that the parasite inhibits sexual activity and prevents the full manifestation of secondary sexual characters, and females never carry eggs. Rajkumar et al., (2011) found that infestation with Epipenaeon ingens had a significant effect on reproduction in Metapenaeopsis stridulans . But the host of H. alphei was ovigerous, suggesting that hosts can remain reproductive after bopyrid infestation.