Phalloleucon abyssalis, Mühlenhardt-Siegel, Ute, 2008

Mühlenhardt-Siegel, Ute, 2008, Phalloleucon abyssalis, a new cumacean genus and species (Crustacea: Peracarida: Leuconidae) from the Peru Basin, Zootaxa 1829, pp. 61-68 : 63-64

Phalloleucon abyssalis gen.nov. sp.nov.

( Figs 1–3 )

Type material. Holotype, adult male, 3.1 mm length; SMF-32716; type locality: SE Pacific, Peru Basin, 07° 07’ S 88° 27’ W, 4170 m depth, ATESEPP expedition, RV Sonne cruise 106, Station 2, box corer 1504, top water. 14 January 1996; Ch. Borowski coll.

Diagnosis. The new species has a single pair of pleopods in males and bears penial lobes.

Description. Body ( Figs 1 a–c). Carapace smooth, pseudorostral lobes meeting for a distance in front of eye lobe, ventro-anterior margin of pseudorostrum with four teeth; siphonal tube short, eye lobe rudimentary, no lenses, no middorsal teeth. Antennal notch wide and shallow, not reaching region of anterior margin of frontal lobe; anterolateral corner strongly angular; anteroventral margin of carapace with three teeth; integument weakly calcified.

Five free thoracic segments visible, a little longer than carapace. Penial lobes developed at sternite of fifth pereiomer: two cylindrical appendages, each inserting close to the basis of the walking legs. Pleon longer than carapace and free thoracic segments combined; one pair of pleopods present; telsonic segment short.

Mouthparts not dissected in order to preserve the holotype. Mandible visible within integument (while stored in glycerine), basis appears truncate.

Antenna 1 ( Fig. 2 , A1): RLP: 43/25/32; accessory flagellum two articulate, three quarters of basal article of main flagellum, which has four articles, the last article minute; three aesthetascs on basal article and four aesthetascs on penultimate article of main flagellum.

Antenna 2 ( Fig. 2 , A2): flagellum reaching end of pereionites, two distal peduncle articles with setae irregularly scattered along anterior margin; flagellum articles each with pairs of hair-like curled setae.

Maxilliped 2 ( Fig. 2 , Mxp2): B/R ratio 0.6, relative length of articles I to D: 7/33/24 /23/13. Basis and merus each with strong plumose seta at distal margin; carpus with four pairs of plumose setae along inner margin, propodus with one strong plumose seta at distal part and three simple setae along inner margin.

Maxilliped 3 ( Fig. 2 , Mxp3): B/R ratio 1.2, relative length of articles ischium to dactylus: 5/27/28 /22/17; basis with four long pappose setae at distal outer corner, five shorter pappose setae along inner margin; merus and carpus with strong pappose seta at outer distal corner; carpus with three and propodus with two pappose setae along inner margin; dactylus with one terminal and four subterminal simple setae, exopod present.

Pereiopod 1 ( Fig. 2 , P1): broken after slender basis, which is beset with pappose setae; exopod present.

Pereiopod 2 ( Fig. 3 , P2): B/R ratio 0.8, RLA: 3/19/32 /13/32; basis, ischium, merus and carpus with few pappose setae, dactylus with one long distally annulated terminal (unguis) and three setae subterminally; exopod present.

Pereiopod 3 ( Fig. 3 , P3): B/R ratio 1.5, RLA: 9/24/41 /18/8; basis with two, merus with one pappose setae at distal inner corner and one terminally annulated at distal margin, carpus with two, propodus with one long simple setae at outer distal corner; unguis of dactylus strong, two hair-like short setae subterminally; exopod present.

Pereiopod 4 ( Fig. 3 , P4): B/R ratio 1, RLA: 12/20/41 /15/12; basis with three pappose setae along inner margin, ischium with one long simple seta, merus and carpus with one pappose seta each along margins, carpus with two acuminate, propodus with one long terminally annulate setae; unguis long and strong, dactylus two hair-like short setae subterminally; exopod present.

Pereiopod 5 ( Fig. 3 , P5): B/R ratio 0.4, RLA: 10/18/42 /19/10; carpus longer than basis; pappose setae on basis, merus and carpus, carpus with two, propodus with one long simple, terminally annulate setae; unguis long, terminally annulate, dactylus with two short hair-like setae subterminally.

Uropods ( Fig. 3 , U): peduncle 1.4 times as long as pleonite 6, but 0.5 times as long as endopod, four setae along inner margin. Exopod two articulate, with five long pappose setae along inner margin of second article, distally three terminally annulate setae, exopod only a little shorter than endopod. Endopod two articulate, article 1 with eight stout plumose setae along inner margin, 2.4 times longer than article 2, which has three stout plumose setae along inner margin; two terminal setae, one of them longer than article 2, both annulated terminally.

Female unknown.

Remarks. Phalloleucon abyssalis gen.nov. sp.nov. resembles in terms of the habitus members of the genus Bytholeucon , with a shallow antennal notch, the anterolateral corner strongly angular and the uropod rami subequal in length and the males with one pair of pleopods. It differs from Bytholeucon in the following characters:

• Antenna 1 peduncle curved between article 1 and 2 ( Bytholeucon is geniculate); • The accessory flagellum has two articles (only one article in Bytholeucon );

• The basal articles of the exopods in maxilliped 3 and pereiopod 1 are smooth (serrate or with teeth in Byt-

holeucon);

• Maxilliped 3 without teeth on merus and carpus (at least the carpus has teeth in the three species of Bytho-

leucon );

• Maxilliped 3 basis with four long plumose setae on the outer distal corner (only two long plumose setae in

the three known species of Bytholeucon );

• The males have penial lobes (no penial lobes in Bytholeucon ).

• The penial lobes resemble most closely those of Pseudeudorella redacticruris .

Figures

FIGURE 1. Phalloleucon abyssalis gen. nov. sp. nov., holotype male: Habitus male. Seen from lateral (a and b, both sides), penial lobes and pleopod in higher magnification (c) and anterior part from dorsal (d). The divergence of the pseudorostral lobes (b and c) is an artefact.

FIGURE 2. Phalloleucon abyssalis gen. nov. sp. nov., holotype male: A 1: first antenna; A 2: second antenna; Mxp 2: maxilliped 2; Mxp 3: maxilliped 3; P 1: basis of pereiopod 1 and exopod; P 2: pereiopod 2. Scale bars: 0.1 mm.

FIGURE 3. Phalloleucon abyssalis gen. nov. sp. nov., holotype male: P 3: pereiopod 3; P 4: pereiopod 4; P 5: pereiopod 5; U: pleonite 6 and left uropod. Scale bars: 0.1 mm, if not otherwise indicated.