Argeiopsis Kensley, 1974

An, Jianmei, Zhang, Pengchi & Paulay, Gustav, 2017, A new genus and two new species of Argeiinae (Crustacea: Isopoda: Bopyridae) from the Indo-west Pacific, Journal of Natural History 51 (7 - 8), pp. 405-420 : 413-416

Genus Argeiopsis Kensley, 1974

Type species: Argeiopsis inhacae Kensley, 1974 , by monotypy Argeiopsis guamensis sp. nov.

( Figures 3 and 4 )

Material examined

UF Arthropoda 42224: holotype ♀, allotype ♂, infesting Synalpheus cf . stimpsonii (de Man, 1888) ( UF Arthropoda 2135); Mariana Islands, Guam Island, Tumon , Gun Beach, fore reef, 13.5° N, 144.8° E, host commensal on the crinoid Phanogenia gracilis , 30 m, 1 June 2000, coll . Lisa Kirkendale .

Description of holotype female ( Figure 3 )

Length 4.23 mm, maximum width 3.84 mm, head length 0.77 mm, head width 1.08 mm. Body outline triangular, almost symmetrical ( Figure 3 (a,b)).

Head quadrate with short frontal lamina, wider than long. Black eyes on the boundary between head and frontal lamina ( Figure 3 (a)). Antennule of two articles; antenna of three articles; both with broad, bulging bases and with setose terminal articles ( Figure 3 (c)). Barbula with two pairs of falcate lateral projections on each side, flat near centre ( Figure 3 (d)). Maxilliped articulated, with setose palp ( Figure 3 (e)).

Pereon broadest across third pereomere ( Figure 3 (a)). Small coxal plates on first four pereomeres on right, and on first two pereomeres on left ( Figure 3 (a)). Dorsolateral bosses on first four pereomeres on both sides, but tergal projections only on second and third right pereomeres. Brood pouch widely open ( Figure 3 (b)). First oostegite ( Figure 3 (f,g)) with two articles subequal in length; posterolateral point of distal segment rounded; internal ridge almost unornamented, except for a conspicuous incision. Pereopods increasing in size posteriorly ( Figure 3 (h,i)); bases of first three pereopods with lobes along flexor margins.

Pleon of six pleomeres; first five pleomeres clearly demarcated on right side but only faintly demarcated on left. Lateral plates absent. Five biramous, unequal pleopods present, exopodites much larger than endopodites ( Figure 3 (b,j)). Endopodite of first pleopod globose, others plate-like; left pleopods much larger than those on right. Sixth pleomere with biramous uropods, also with much larger exopodite than endopodite.

Description of allotype male ( Figure 4 )

Length 2.56 mm, maximum width, across pleon 5, 1.06 mm, head length 0.43 mm, head width 0.71 mm, pleonal length 0.63 mm.

Head oblong, with triangular posterior margin ( Figure 4 (a)). Small black eyes close to posterior margin ( Figure 4 (a)). Antennule of three articles, bases stout, distal article setose. Antennae of three articles, bases slender, terminal two articles setose ( Figure 4 (b,c)).

All pereon segments distinct. First four pereomeres subequal in width, lacking midventral projections ( Figure 4 (b)). First pereopods each with much larger dactylus and much shorter carpus than those of other six. Posterior six pereopod pairs subequal in size and structure ( Figure 4 (d,e)). All propodi and carpi with setae on inner surface ( Figure 4 (d,e)).

Pleon fused into a single piece; only first pleomere of left side discernible from sharp marginal angle ( Figure 4 (a)). Anal cone on the ventral surface near the posterior margin of pleon ( Figure 4 (b)).

Etymology

The specific name guamensis refers to the type locality of Guam Island .

Remarks

As with the other two species of Argeiopsis , females of the new species have biramous pleopods and uropods, lacking lateral plates, and have a widely open brood pouch, whereas males have fused pleons. Based on the descriptions given by Kensley (1974) and Adkison et al. (1982), the new species is most similar to Argeiopsis inhacae Kensley, 1974 , but differs in the following characters (character states in A. inhacae given in parentheses): female: (1) first oostegite with curved posterior margin, posterolateral point rounded, extending posteriorly, (with straight posterior margin, posterolateral point somewhat pointed, extending laterally); (2) pleomeres partly fused, (pleomeres distinct); male: (1) head separated from first pereomere (fused with first pereomere); (2) pleon nearly as wide as seventh pereomere (pleon much narrower than seventh pereomere).

The new species can be distinguished from Argeiopsis kensleyi Boyko & Kazmi, 2005 by the structure of the first oostegite, maxilliped, and barbula of the female. In the female of A. kensleyi a posterolateral point is absent on the first oostegite, the maxilliped palp lacks setae, and the barbula has one pair of projections on each side ( Boyko and Kazmi 2005).

The host, Synalpheus stimpsonii (de Man, 1888) , is known to be part of a species complex that has not yet been revised ( Hultgren et al. 2014).

Key to species of Argeiopsis

1. First oostegite without posterolateral point, maxilliped with curved, non-setose palp........................................................................................................................................... A. kensleyi First oostegite with posterolateral point, maxilliped with long setose palp ............. 2

2. Posterolateral point of first oostegite directed laterally .................................. A. inhacae Posterolateral point of first oostegite directed posteriorly....... A. guamensis sp. nov.

Figures

Figure 3. Argeiopsis guamensis sp. nov. Holotype female: (a) Dorsal view. (b) Ventral view. (c) Right antenna and antennule. (d) Right side of barbula. (e) Right maxilliped, external view. (f) Right oostegite 1, external view. (g) Right oostegite 1, internal view. (h) Left pereopod 1. (i) Left pereopod 7. (j) Ventral view of pleon (endopodites shaded). Scale = 1 mm (a, b), 0.18 mm (c, h, i), 0.39 mm (d), 0.32 mm (e, f, g), 0.40 mm (j).

Figure 4. Argeiopsis guamensis sp. nov. Allotype male: (a) Dorsal view. (b) Ventral view. (c) Left antenna and antennule. (d) Left pereopod 1. (e) Left pereopod 4. Scale = 1 mm (a, b), 0.29 mm (c, d, e).