Scyracepon pseudoliomerae, An & Zheng & Liang & Paulay, 2020

An, Jianmei, Zheng, Wanrui, Liang, Jielong & Paulay, Gustav, 2020, Three new species of Scyracepon Tattersall, 1905 (Isopoda: Bopyridae) from Pacific islands, with comments on the rarity of bopyrids parasitizing brachyurans, Zootaxa 4851 (1), pp. 151-162 : 158-160

Scyracepon pseudoliomerae n. sp.

Fig. 5

Material examined. Holotype female, paratype male, UF Arthropoda 42204, infesting right branchial chamber of Pseudoliomera sp., ( Xanthidae ), UF Arthropoda 412, Mariana Islands, Guam Island, Haputo Point, outer reef slope, under rocks, 13.58583°N, 144.83217°E, 15 meters, 17 July 2000, coll. L. Kirkendale.

Description. Holotype female length 3.58 mm, maximum width 2.27 mm, head length 0.88 mm (including frontal lamina), head width 0.96 mm. Body broad and bulging, oval in outline, with moderate dextral distortion, all segments distinct ( Fig. 5A ).

Head with bilobate anterior margin, with well-developed frontal lamina ( Fig. 5A ), without eyes. Antennula of two articles; antenna of four articles, with terminal two setose. Barbula with three slender, pointed, falcate projections on each side, entire near center ( Fig. 5B ). Maxilliped with triangular palp, inner margin fringed with many setae, plectron long, pointed and extending laterally ( Fig. 5C ).

Pereon broadest across third pereomere ( Fig. 5A ). Pereomeres 1–4 with suboval or triangular dorsolateral bosses, 2 and 3 with tergal projections ( Fig. 5A ). Pereomeres 2 and 3 with slight median swelling, last four with prominent middorsal projections, increasing in size posteriorly ( Fig. 5A ). Brood pouch ventrally vaulted, completely closed. First oostegite with 2 or 3 small, simple tubercles on internal ridge, anterior margin smooth and curved, posterior margin fringed with setae, posterolateral point blunt and projecting laterally ( Fig. 5D, E ). Pereopods increasing in size posteriorly, bases lacking carinae ( Fig. 5F, G ), carpi and propodi each with triangular projection along ventral margin; dactyli small, pointed ( Fig. 5F, G ).

Pleon of six segments, first five bearing lateral plates and biramous pleopods ( Fig. 5A ). All lateral plates and exopodites of pleopods with digitate margins, decreasing in size and width posteriorly. Endopodites of pleopods oval and much smaller than exopodites. Uniramous uropods resembling lateral plates ( Fig. 5A ).

Paratype male length 1.77 mm, maximum width 0.75 mm, head length 0.23 mm, head width 0.31 mm, pleonal length 0.54 mm. All pereomeres distinct ( Fig. 5H, I ).

Head oval, with black eyes near curved posterior margin ( Fig. 5H ). Antennula of 2 articles; antenna of 4 articles; terminal articles of both setose ( Fig. 5J ).

Pereon segments much wider than head, 4 th broadest; lateral margins bending ventrally ( Fig. 5I ). First two and last two pereopods slightly smaller than pereopods 3–5. Propodi of all pereopods with sharp, ventral tooth, increasing in size posteriorly ( Fig. 5 K–M). All pereomeres with midventral projections ( Fig. 5I ), these small and round on first pereomere, bilobate on pereomeres 2–7 ( Fig. 5I ).

Pleon of six pleomeres clearly demarcated on ventral surface; dorsally first pleomere free, pleomeres 2–3 separated by obscure suture line, pleomeres 4–6 fused, ending in median anal cone ( Fig. 5H, I ). Five pairs of rudimentary pleopods ( Fig. 5I ), no uropods.

Etymology. The specific name pseudoliomerae refers to the host genus.

Remarks. Among all the species of Scyracepon only three others have middorsal projections on the last four pereomeres: S. hawaiiensis , S. quadrihamatum and S. polynesiensis n. sp. The present specimens are most similar to S. hawaiiensis , a species that infests Thyraplax cooki (Rathbun, 1906) (Goneplacidae) and is recorded from a depth of 277–284 fathoms ( Richardson, 1910). The posterolateral point of the oostegite 1 of the new species projects laterally, while in S. hawaiiensis it does not. The middorsal projections on the last four pereomeres of the new species are subequal, but in S. hawaiiensis the last is larger, curved and sharply pointed. The head of the male of the new species has a curved posterior margin while that of S. hawaiiensis is straight. The first three pleomeres are free in the new species, but all pleomeres are fused in S. hawaiiensis . Although the morphological difference between these two species are relatively minor, major differences in host and depth also suggests that they represent distinct species. This conclusion needs to be tested with additional samples and molecular data.

Both S. pseudoliomerae and S. polynesiensis parasitize crabs of the family Xanthidae , and have females with middorsal projections on the last four pereomeres. They can be distinguished from each other by the anterior margin of the head (head of S. polynesiensis with smooth and almost straight anterior margin; but those of S. pseudoliomerae deeply bilobate), and by the posterior margin and internal ridge of oostegite 1 (first oostegite of S. polynesiensis with two nearly equal segments, internal ridge with a large digitate projection, and 3–5 small tubercles, posterolateral point sharp and projecting posteriorly; those of S. pseudoliomerae with 2–3 small, simple tubercles on internal ridge, posterolateral point blunt and projecting laterally). Females of S. quadrihamatum are readily differentiated from those of the other species by the very elongate middorsal projection of the last pereomere that extends to the end of the body, while males have all pleomeres fused.

Figures

FIGURE 5. Scyracepon pseudoliomerae n. sp. Holotype female (A–G) A. Dorsal view; B. Right side of barbula; C. Left maxilliped, external view; D. Left oostegite 1, external view; E. Left oostegite 1, internal view; F. Left pereopod 2; G. Left pereopod 5; paratype male (H–M); H. Dorsal view; I. Ventral view; J. Left antennae; K. Right pereopod 1; L. Right pereopod 3; M. Right pereopod 5. Scale-bars: A = 1mm; B = 0.47 mm; C, H, I = 0.39 mm; D, E = 0.59 mm; F, G, J–M = 0.21 mm.