Akanthophoreus undulatus, Bird, Graham J, 2007

Bird, Graham J, 2007, Family incertae cedis *, Zootaxa 1599, pp. 121-149 : 132-136

Akanthophoreus undulatus n.sp.

Figures 7–10

Material examined. Holotype: 1 non-ovigerous female ( KMNH IvR 500.199), station XR-7, 42°12.87’– 42°12.10’N 145°33.93’– 145°32.05’E, 3853–3858 metres, 17 September 2001. Allotype: 1 preparatory male ( KMNH IvR 500.200), same locality. Paratype: 1 ovigerous female (partially dissected; KMNH IvR 500.201), station TD-4, 39°27.08’– 39°29.15’N 143°37.79’– 143°38.52’E, 3272–3146 metres, 26 September 2001.

Diagnosis. Akanthophoreus with lateral pleonal spurs. Cheliped propodus with dorsal nodules, fixed finger with lateral row of nodules, dactylus crenulate. Pereopods 1–6 basis, merus, carpus and propodus with undulated or crenulated margins. Pereopods 1–3 merus with one thin and one spiniform seta. Dactylus/unguis of pereopods 1–3 at least as long as propodus.

Etymology. From the Latin adjective undulata ‘crenulate’ or ‘wavy’, referring to the pereopods.

Description, non-ovigerous female.

Body ( Fig. 7 A). Slender, 8.3 times as long as broad (extended holotype), length 5.32mm.

Carapace. As long as pereonites 1–2 together (excluding pereonal gap), 1.4 times as long as broad, with parallel margins for posterior two-thirds portion; rostrum a moderately developed sub-triangular process.

Pereonites. Sub-rectilinear with slight bulge over pereopodal insertion. Pereonite 1 slightly narrower posteriorly. Pereonites 1–6 0.58, 0.85, 0.84, 0.84, 0.81 and 0.61 times as long as broad, respectively.

Pleon. As long as preceding two pereonites, 16–18% of body length (of extended and contracted length respectively), all pleonites much wider than long, with seta on epimeral margin; each pleonite sternum produced into lobiform process ( Fig. 7 B), decreasing in size from pleonite 1 to pleonite 5.

Pleotelson ( Figs 7 B–C). As long as two preceding pleonites, shorter than broad, with rounded posterior margin in dorsal view obscuring deflected apex, and lateral margins with an extended, acutely triangular process; two setae on posterior margin and seta anterior of each uropod basal article.

Antennule ( Fig. 8 B). Slender, about 0.8 times as long as carapace. Article 1 just over half total length, 3.3 times as long as broad (mid-length), with disto-outer seta and sensory seta and more proximal group of three sensory setae. Article 2 sub-rectangular, 1.6 times as long as broad, with a long disto-outer seta and three sensory setae. Article 3 less than half length of article 2, with two unequal setae, inner smaller of two. Article 4 slender, 4.5 times as long as broad, about as long as article 2, with four long, quite thick setae, one aesthetasc and at least one sensory seta.

Antenna ( Fig. 8 C). Slender, about 0.75 times as long as antennule. Articles 1–2 short, but article 1 larger than article 2, both with dorsal seta. Article 3 almost half length of antenna, about six times as long as broad, with pseudo-articulation near mid-point, accompanied by a sensory seta, terminally with two long setae and four sensory setae. Article 4 slender, five times as long as broad, with terminal seta; article 5 small, with five unequal setae.

Mouthparts. Labrum ( Fig. 8 D) of sub-conical or sub-triangular lateral profile, with numerous small distal setae. Labium not recovered. Maxilla ( Fig. 8 E) plate-like, elongate, sub-rectangular. Mandibles ( Figs 8 F–I) strong, with dentate incisor and molar with acuminate shape, terminally with about eight unequal spines, two of which are clearly longer than the rest and paired; left mandible with acuminate lacinia mobilis ( Fig. 8 H), with about three cusps or teeth. Maxillule ( Fig. 8 J) palp with two setae and endite with nine strong spiniform setae, some of which are pectinate. Maxilliped ( Fig. 8 K) basis fused and longer than endites, with long seta at base of each palp; endites unfused, each with weakly lobed distal margin, minutely setose lateral processes and distal seta; palp articles 1–3 equally long, article 2 with one outer and three inner setae, article 3 with two large and two smaller setae, article 4 with five unequal setae.

Cheliped ( Figs 7 D–G, Fig. 8 A). Attached via sclerite. Basis with large, rounded posterior margin. Merus sub-triangular, with ventral seta. Carpus twice as long as broad, with small proximal seta, one ventral seta, shield very shallow, without crenulation. Propodus and spine as long as carpus, twice as long as deep, dorsal crest with about five nodules or crenulations and outer ventral margin with short crenulate ridge, with two setae, small outer seta near dactylus. Fixed finger with four relatively delicate teeth on incisive margin, three outer setae and short, blunt terminal spine. Dactylus with dorsal margin crenulate (about ten–12 nodules), more finely so for distal half, with spine on incisive margin.

Pereopod 1 ( Fig. 9 A). Coxa annular, with seta. Basis weakly crenulate outline, with dorsal plumose setae. Ischium with seta. Merus more strongly ribbed than basis, with inner slender seta and outer spiniform seta. Carpus ribbed, with one dorsal and one ventral terminal spiniform seta. Propodus weakly ribbed, with distoventral spiniform seta. Dactylus and unguis together just longer than propodus, unguis longer than dactylus, with spatulate tip.

Pereopod 2 ( Fig. 9 B). Similar to pereopod 1 but carpus with three spiniform setae. Dactylus and unguis only as long as propodus.

Pereopod 3 ( Fig. 9 C). Similar to pereopod 2 but basis slightly longer and without plumose seta.

Pereopod 4 ( Fig. 9 D). With no discrete coxa. Basis strongly ribbed. Merus and carpus strongly ribbed.

Propodus weakly ribbed. Dactylus with double row of spinules on inferior margin.

Pereopod 5 ( Fig. 9 E). Similar to pereopod 4 but basis with three sensory setae.

Pereopod 6 ( Fig. 9 F–G). Similar to pereopod 5 but propodus with additional distal spiniform seta. Pleopod ( Fig. 10 A). Relatively small compared to pereopods but setose, both rami sub-ovate. Endopod

with one inner-distal seta and about 16 distal setae. Exopod with about 30 setae.

Uropod ( Fig. 10 B). Long and slender, as long as pleotelson and two preceding pleonites. Exopod two-articled 0.6 times as long as article 1 of endopod, with one seta on article 1 and two unequal setae on article 2. Endopod two-articled, article 1 just over half total length of endopod, about eight times as long as broad, with one long distal seta and two distal sensory setae, article 2 about nine times as long as broad, with one distal seta and four unequal terminal setae, with one sensory seta.

Ovigerous female: generally as neuter but dorso-ventrally compressed, with four pairs of oostegites; length 5.80 mm.

Preparatory male: ( Figs 7 H–J) generally as neuter/non-ovigerous female, but antennule five-articled, broad; length 4.06 mm.

Remarks. This large abyssal species is very similar to Scoloura phillipsi Sieg & Dojiri, 1991 from the shelf and bathyal of the western U.S. A but differs in having a smaller cephalothorax, coarser and fewer mandible molar spines, a longer cheliped carpus, a longer pereopod 1 dactylus/unguis, but particularly the crenulate pereopod margins. It differs from Akanthophoreus gracilis sensu stricto (= Leptognathia sarsi ) principally by the last character and its more slender cheliped carpus. The large and impressive A. multiserratus from the NE Atlantic also has nodulose/crenulate pereopods, at least on the basis of pereopods 4–6.

It is possible that the earlier records of Leptognathia gracilis from the Kurile-Kamchatka Trench and the Japan Trench ( Kudinova-Pasternak 1970) and Leptognathia longiremis from the Izu-Ogasawara Trench ( Kudinova-Pasternak 1977) refer to this species.

Distribution. Kurile-Kamchatka Trench and the Japan Trench, 3146–3858 metres.

Figures

FIGURE 7. Akanthophoreus undulatus n. sp. A – G, holotype non-ovigerous female. A, habitus; B, pleon / pleotelson, lateral view (pleopods omitted for clarity); C, pleotelson, lateral view, enlarged; D, right cheliped; E, dorsal crest of cheliped propodus and proximal dactylus; F, setae of cheliped propodus and proximal dactylus; G, distal of cheliped fixed finger; H – J, allotype preparatory male. H, habitus; I – J, pleotelson, lateral, to scale and enlarged. Scale bar = 2 mm for A, B, H and I, 0.94 mm for C, D and J, 0.47 for E-G.

FIGURE 8. Akanthophoreus undulatus n. sp. Ovigerous female. A, crenulations of distal propodus / proximal dactylus, dorsal view; B, antennule; C, antenna; D, labrum, lateral view; E, maxilla; F – G, right and left mandibles respectively; H, incisor and lacinia mobilis of left mandible, full profile; I, molar of left mandible, enlarged; J, maxillule endite; K, maxilliped, one palp omitted for clarity. Scale bar = 0.5 mm for B and C, 0.33 mm for K, 0.25 mm for A, D-H and J, 0.125 mm for I.

FIGURE 9. Akanthophoreus undulatus n. sp. Ovigerous female. A – F pereopods 1 – 6 respectively, oostegites excluded for clarity; G, detail of carpal setation, pereopods 4 – 6. Scale bar = 0.5 mm for A-F, 0.25 mm for G.

FIGURE 10. Akanthophoreus undulatus n. sp. Ovigerous female. A, pleopod; B, uropod. Scale bar = 0.5 mm for B, 0.4 mm for A.