Akanthophoreus imputatus, Bird, Graham J, 2007

Bird, Graham J, 2007, Family incertae cedis *, Zootaxa 1599, pp. 121-149 : 128-132

Akanthophoreus imputatus n.sp.

Figures 4–6

Material examined. Holotype: 1 non-ovigerous female ( KMNH IvR 500.196), station XR-12, 41º37.67’– 41º37.08’N 146º54.19’– 146º52.72’E, 5473–5484 metres, 4 m ORE beam trawl, 23 September 2001.

Paratypes: 1 non-ovigerous female ( KMNH IvR 500.197), same locality; 1 non-ovigerous female, 1 ovigerous female ( KMNH IvR 500.198), station TD-8, 39º15.54’– 39º17.01’N 144º45.37’– 144º42.46’E, 5762–5733 metres, 4 m ORE beam trawl, 29 September 2001.

Diagnosis. Akanthophoreus with pereonites all shorter than broad. Pleotelson without lateral spurs. Cheliped carpus and pereopods 1–6 merus, carpus and propodus with numerous spinules. Cheliped propodus and dactylus without crenulation; carpus with weak shield. Dactylus/unguis of pereopods 1–3 0.75 times as long as propodus.

Etymology. From the Latin adjective imputatus ‘unpruned’ or ‘untrimmed’, referring to the cheliped carpus and pereopods.

Description, non-ovigerous female.

Body ( Fig. 4 A). Fairly slender, 6.75 times as long as broad (Holotype), cuticle with honeycomb ornamentation, length 3.05–3.52 mm.

Carapace. Just longer than pereonites 1–2 together (excluding pereonal gap), 1.3 times as long as broad, with slightly convex lateral margins for posterior two-thirds portion; rostrum a very slight sub-triangular process.

Pereonites. With nearly parallel or weakly convex lateral margins. Pereonite 1 very slightly narrower posteriorly. Pereonites 1–6 0.48, 0.72, 0.66, 0.67, 0.70, and 0.46 times as long as broad, respectively.

Pleon. Just shorter than pereonites 5–6, 14.4% of body length, all pleonites much wider than long, with long seta on epimeral margin; each pleonite sternum fairly high, rounded or sub-triangular in lateral profile ( Fig. 4 B).

Pleotelson. Longer than two preceding pleonites, shorter than broad, with rounded posterior margin in dorsal view obscuring deflected apex; four setae (two sensory) on posterior margin.

Antennule ( Figs 4 C–E). Slender, about 0.7 times as long as carapace. Article 1 just over a half of total length, 2.6 times as long as broad (mid-length), with disto-outer seta more proximal group of three sensory setae. Article 2 sub-rectangular, 1.5 times as long as broad, with one long disto-outer seta, three sensory setae and one smaller inner seta. Article 3 less than half length of article 2, with two unequal setae. Article 4 twice as long as article 3, 2.8 times as long as broad, with four long, quite thick setae, one shorter seta and one aesthetasc.

Antenna ( Fig. 4 F). Slender, about 0.73 times as long as antennule. Articles 1–3 short, but article 2 larger than article 3, both with dorsal setae, two on article 2. Article 4 over half length of antenna, about five times as long as broad, with pseudo-articulation near mid-point, accompanied by a sensory seta, terminally with two long setae and at least three sensory setae. Article 5 slender, three times as long as broad, with terminal seta. Article 6 small, with six unequal setae.

Mouthparts. Labrum ( Fig. 5 A) of sub-conical or sub-triangular lateral profile, finely setose, distally. Labium ( Fig. 5 B) typical of genus, with numerous small setules. Maxilla ( Fig. 5 C) tongue-shaped, with small terminal seta. Mandibles ( Figs 5 D–E) strong, with dentate incisor and molar with acuminate shape, terminally with about ten unequal spines, longer apically; left mandible with strong lacinia mobilis. Maxillule ( Fig. 5 F) palp with two setae and endite with nine spiniform setae, at least one of which is pectinate. Maxilliped ( Fig. 5 G) 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 process and distal-medial seta; palp with stout articles 1–3, article 2 with three inner and one outer seta; article 3 with two long and two smaller setae; article 4 with three long and two smaller setae.

Cheliped ( Figs 5 H). With distinct pre-basal sclerite attachment. Basis with rounded free posterior margin and outer seta. Merus sub-triangular, with ventral seta. Carpus stout, 1.7 times as long as broad, with distinct, but shallow, shield, two ventral setae, several small dorso-proximal setae and one dorso-distal seta. Propodus and terminal spine just longer than carpus, 0.45 times as deep as long, dorsal crest with several small setae ( Fig. 5 I), inner face with comb of four spiniform setae and group of smaller setae, and one outer seta near articulation with dactylus. Fixed finger with two ventral setae, and three unequal setae near incisive margin, the latter with three irregularly-shaped teeth. Dactylus strong, without crenulation, with spine on incisive margin and small inner seta.

Pereopod 1 ( Fig. 6 A). Coxa annular, with seta. Basis about 3.4 times as long as broad, with dorso-distal sensory seta. Ischium with one seta. Merus twice as long as broad, ventral margin with a few spinules, with inner slender seta and outer spiniform seta nearly reaching end of carpus. Carpus just longer than merus, rectangular, 2.3 times as long as broad, ventral margin with numerous spinules, with two long spiniform pectinate setae (dorsal and ventral). Propodus slender, 1.3 times as long as carpus, ventral and dorsal margins with rows of small spinules, with disto-ventral spiniform seta, dorso-distal seta and terminal fringe of small setae. Dactylus and unguis together 0.75 times as long as propodus, dactylus with accessory seta, unguis as long as dactylus, with spatulate tip.

Pereopod 2 ( Fig. 6 B). Similar to pereopod 1 but basis without sensory seta. Merus and carpus shorter and carpus with three spiniform setae.

Pereopod 3 ( Fig. 6 C). Similar to pereopod 2 but basis slightly shorter.

Pereopod 4 ( Fig. 6 D). With no discrete coxa. Basis slightly longer than in pereopod 3. Ischium with two unequal setae. Merus ventral margin with small spinules, with two spiniform setae. Carpus rectangular, longer than merus, ventral margin with small spinules, with three long spiniform setae and one smaller rod-like dorsal seta. Propodus just longer than carpus, with two long ventro-distal spiniform setae and one dorso-distal spiniform seta. Dactylus and unguis ( Fig. 6 G) just longer than propodus, dactylus with double row of spinules on inferior margin.

Pereopod 5 ( Fig. 6 E). Similar to pereopod 4, basis with two sensory setae.

Pereopod 6 ( Fig. 6 F). Similar to pereopods 4–5 but propodus with two additional dorso-distal spiniform setae.

Pleopod ( Fig. 6 H). Relatively small compared to pereopods, both rami sub-ovate. Endopod with one distal and six terminal setae. Exopod two-articled, with eleven terminal setae and one on small article 1.

Uropod ( Fig. 5 J). As long as pleotelson and preceding pleonite 5. Basal article about twice as long as broad. Exopod two-articled, half 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, nearly twice as long as basal article, just over four times as long as broad, with three distal seta (two sensory), article 2 0.8 times as long as article 1, about five times as long as broad, with five unequal terminal setae, with two sensory setae.

Ovigerous female. Generally as non-ovigerous female ( Fig. 4 G), but pereon more dorso-ventrally compressed, pereonites 2–3 proportionately longer, with four pairs of oostegites; length 3.06 mm.

Remarks. Akanthophoreus imputatus n.sp. is a relatively ‘non-descript’ and stout species, with setose pereopods. It generally resembles A. longiremis sensu Lilljeborg , (= sensu Hansen , = sensu Lang ) from the NE Atlantic, but the spinules on the propodus of pereopods 1–3 are smaller and more numerous and the pleonal sternal processes are less well-developed. It is distinguishable from the previous species, A. crassicauda n.sp., by its longer uropods and more setose chelipeds and pereopods. A close relative, or even conspecific taxon, remains undescribed from the abyssal Arctic Ocean (Bird ined.), although the ‘re-description’ of A. longiremis given by Guerrero-Kommritz (2004) may also be this species.

Distribution. Kurile-Kamchatka Trench and the Japan Trench, 5473–5762 metres.

Figures

FIGURE 4. Akanthophoreus imputatus n. sp. A – F, non-ovigerous female. A, habitus; B, pleon, lateral view (pleopods and uropod rami omitted for clarity); C, right antennule; D, same, lateral view, setation simplified for clarity; E, antennule terminal setation; F, antenna; G, ovigerous female, habitus. Scale bar = 1 mm for A, B and G, 0.25 mm for C-F.

FIGURE 5. Akanthophoreus imputatus n. sp. Non-ovigerous female. A, labrum, lateral; B, labium; C, maxilla; D – E, left and right mandibles respectively; F, maxillule endite; G, maxilliped, one palp omitted for clarity; H, right cheliped; I, left cheliped propodal dorsal crest and dactylus; J, uropod. Scale bar = 0.36 mm for H and J, 0.25 mm for A-G and I.

FIGURE 6. Akanthophoreus imputatus n. sp. Non-ovigerous female; A – F, pereopods 1 – 6, respectively; G, dactylus / unguis of pereopods 4 – 6; H, pleopod. Scale bar = 0.25 mm for A-H.