Hymenopenaeus fallax, Crosnier, Alain & Dall, William, 2004

Crosnier, Alain & Dall, William, 2004, Redescription of Hymenopenaeus obliquirostris (Crustacea, Decapoda, Penaeoidea, Solenoceridae) and descriptions of two new species of Hymenopenaeus from the Indo­West Pacific, Zootaxa 600, pp. 1-26 : 10-14

Hymenopenaeus fallax sp. nov. ( Figs. 6 ñ8)

Haliporus equalis Rathbun, 1906: 905 [non Bate, 1888].

Hymenopenaeus cf. obliquirostris . — Crosnier, 1989: 47, figs. 2c, 4b (under H. equalis ).

Types. Hawaii: Albatross Exped., Stn 4106, Kaiwi Channel, 613–640 m, 24.07.1902, 1 ɗ paratype 16.3 mm and Ψ holotype, 28.7 mm (USNM 30919); Stn 4029, vic. Kauai Id, 875– 832 m, 24.06.1902, 1 ɗ allotype 18.8 mm (USNM 30918); Stn 3989, vic. Kauai Id, 914– 704 m, 11.06.1902, 1 Ψ paratype 21.8 mm (USNM 30914); Stn 4110, Kaiwi Channel, 821–841 m, 24.07.1902, 1 ɗ paratype, 18.2 mm (USNM 30922); Stn 4153, vic. Modu Manu Id, 1760–1937 m, 5.08.1902, 1 Ψ paratype 24.1 mm (USNM 30924).

Other material examined. Hawaii: Albatross Exped., Kaiwi Channel, 627 m, 4.12.1891, 2 juv. 10.8 and 11.0 mm ( USNM 30909); Stn 3471, Kaiwi Channel, 617 m, 4.12.1891, 2 juv. 10.5 mm ( USNM 30910); Stn 3474, Kaiwi Channel, 686 m, 6.12.1891, 1 ɗ 16.1 mm; 1 Ψ ( USNM 30911) from fish stomach; Stn 3475, Kaiwi Channel, 642 m, 6.12.1891, 1 Ψ 21.0 mm ( USNM 30912); Stn 3988, Kauai Id, 857– 302 m, 11.06.1902, 1 juv. 11.1 mm ( USNM 30913); Stn 4022, vic. Kauai Id, 729– 684 m, 21.06.1902, 2 Ψ 16.9 and 17.4 mm ( USNM 30916); Stn 4028, vic. Kauai Id, 812–875 m, 24.06.1902, 1 Ψ 20.4 mm ( USNM 30917); Stn 4107, Kaiwi Channel, 640–649 m, 24.07.1902, 2 ɗ 14.0 mm and 19.0 mm ( USNM 30920); Stn 4108, Kaiwi Channel, 752–809 m, 24.07.1902, 1 Ψ 12.2 mm ( USNM 30921); Stn 4112, Kaiwi Channel, 818– 791 m, 24.07.1902, 1 Ψ 14.5 mm ( USNM 30923); Stn 4157, vic. Modu Manu Id, 1394–1829 m, 6.08.1902, 1 juv. 12.0 mm ( USNM 30925); Stn 4166, vic. Modu Manu Id, 536–1463 m, 8.08.1902, 1 juv. 10.0 mm ( USNM 30926).

Diagnosis. Body cuticle smooth, without setae. Rostrum bearing 5 or 6 dorsal rostral teeth, none ventral. A postrostral carina, clearly defined, extending for three­quarters the distance between the cervical sulcus and the posterior border of the carapace. Hepatic, antennal, postantennal and branchiostegal spines slender, the last the strongest, with its tip varying from almost reaching to slightly exceeding the anterior edge of the carapace. Eye relatively small, colour a clear brown. Merus of the first pereopods without a fixed spine on the internal edge. Thelycum on sternite XIII, between the fourth pereopods, projecting in the form of the tip of a tongue, very flattened antero­posteriorly; the posterior part of the sternite bears on each side, two well­developed projecting transverse plates. Sternite XIV bears a prominent swelling, more or less in the shape of an escutcheon, and with a median ridge, which does not have a terminal tooth abutting the posterior of sternite XIII. Petasma with a median lobe whose extremity is divided into two elongate lobules, each terminating in a point, separated by a V­shaped opening; anterior lobule very asymmetric, with exterior edge very curved and interior edge almost straight; posterior lobule more symmetrical with the edges slightly curved; below these lobules on the external side, an inferior lobule regularly rounded and scarcely wider than long; lateral lobe showing on the external face an extended distal lobule, roughly ovoid, which partly covers the inferior lobule of the median lobe.

Coloration. Unknown.

Size. The largest female examined had a carapace of 28.7 mm, which corresponds with a total length of about 104 mm.

Etymology. From the Latin fallax , deceptive, evoking the ease with which this species may be confused with H. obliquirostris .

Remarks. This species is close to H. obliquirostris , having a well defined postrostral carina and the merus of the first pereopods lacking a fixed spine, contrary to that seen in other Indo­West Pacific Hymenopenaeus species. The rostrum and spines on the carapace, particularly the branchiostegal spine, closely resemble those of H. obliquirostris .

Hymenopenaeus fallax may be easily separated from H. obliquirostris by comparison of features of the genitalia, particularly the thelycum. Thus the female H. obliquirostris has a strong trihedral dentiform projection on sternite XIII between the fourth pereopods, the edges sharper in juveniles ( Fig. 4 ), whereas H. fallax has a tongue­like projection, flattened antero­posteriorly, directed obliquely towards the rear and more or less rounded ( Fig. 7 ). In H. obliquirostris on sternite XIV, between the fifth pereopods, the escutcheonshaped swelling has a longitudinal median ridge with a strong anterior tooth which abuts the posterior edge of sternite XIII ( Fig. 4 a), whereas in H. fallax the median ridge is strongly convex and stops well short of sternite XIII ( Figs. 7 a, b, c). The posterior edge of sternite XIII with a median depression between two projections is much more developed in H. fallax ( Fig. 7 d) than in H. obliquirostris ( Fig. 4 c).

In the males the distinction is more difficult to make on account of the variability observed. In general the petasma of H. fallax may be distinguished from that of H. obliquirostris by the external edge of the anterior distal lobule of the median lobe being more convex and the inferior lobule situated under the distal lobules much smaller and more rounded. Also, the distal ovoid lobule of the lateral lobe is relatively smaller than in H. obliquirostris . The differences described above are difficult to appreciate without having specimens of both species for comparison. An example of the variation encountered is given in figures 8d and e.

Distribution. This species is not known outside the Hawaiian Islands. It was collected at a depth of 617 m and also between 1760–1937 m.

Figures

FIGURE 4. Hymenopenaeus obliquirostris (Bate, 1881), a – b, Ψ syntype, 24.2 mm, Kermadec Islands, Challenger, Stn 170, 951 m (NHM 1888.22), a, thelycum, ventral view (after Crosnier, 1989), b, longitudinal median section of sternites XIII and XIV (after Crosnier, 1989, modified); c, Ψ 22.3 mm, New Caledonia, HALIPRO 2, Stn BT 42, 1132 – 1160 m, posterior view of sternite XIII (MNHN­Na 15041); d – g, development of the median tooth of sternite XIII with four females of increasing size (top part, side view and rear view), d, Ψ 11.0 mm, New Caledonia, BIOCAL, Stn CP 61, 1070 m (MNHN­Na 15033), e, Ψ syntype 18.3 mm, Kermadec Islands, Challenger, Stn 170, 951 m (NHM 1888.22), f, Ψ syntype 19.7 mm, ibidem (NHM 1888.22), g, Ψ syntype 24.2 mm, ibidem (NHM 1888.22). Scale, a – g, 1 mm.

FIGURE 6. Hymenopenaeus fallax n. sp., anterior region of the body, lateral view, Ψ 21.8 mm, Hawaii, Albatross, Stn 3989, 914 – 704 m (USNM 30914). Scale, 10 mm.

FIGURE 7. Hymenopenaeus fallax n. sp., a – d, Ψ holotype 28.7 mm, Hawaii, Albatross, Stn 4106, 613 – 614 m (USNM 30919), a, thelycum, ventral view (after Crosnier, 1989), b, longitudinal median section of sternites XIII and XIV (after Crosnier, 1989); c, Ψ 24.1 mm, Hawaii, Albatross, Stn 4153, 1760 – 1937 m (USNM 30924), d, posterior view of sternite XIII, Ψ 21.8 mm, Hawaii, Albatross, Stn 3989, 914 – 704 m (USNM 3914). Scale, a – c, 2 mm; d, 1 mm.