Pseudopicrocuma japonicum, Akiyama, Tadashi, 2012

Akiyama, Tadashi, 2012, Two new species of Atlantocuma (Crustacea: Cumacea), and a new genus and species from Japan, Northwest Pacific, with observations on the degeneration of mouthparts in ovigerous females, Zootaxa 3400, pp. 20-42 : 32-39

Pseudopicrocuma japonicum sp. nov.

( Figs. 9–13 )

Material examined. Holotype preparatory female, 3.23 mm (NSMT-Cr 22185), off Yakushima-Tanegashima, 29°51.42'N, 130°55.69'E – 29°49.82'N, 130°54.46'E, 1678–1769 m (KT-07-1, St. YT-3), 24 February, 2007. Paratypes; 2 adult males (1 specimen dissected), 2.92 mm, 3.08 mm, (NSMT-Cr 22186), same locality as holotype preparatory female (KT-07-1, St. YT-3); 1 preparatory female, 3.04 mm, 2 adult males, 2.86 mm, 2.88 mm, dissected (NSMT-Cr 22187), off Yakushima-Tanegashima, 30°04.40'N, 130°59.95'E – 30°04.54'N, 130°57.89'E, 566–724 m (KT-07-1, St. YT-1), 24 February, 2007; 1 ovigerous female, 3.43 mm (damaged), 1 preparatory female, 3.20 mm, 2 adult males, 2.93 mm, 3.03 mm, dissected (NSMT-Cr 22188), north of Minami-Ensei Knoll, Okinawa Trough, 29°19.35'N, 127°37.37'E – 29°20.52'N, 127°37.96'E, 1018–1042 m (N295, St. Q-1), 21 November, 2009.

Description. Preparatory females, 2.92–3.23 mm ( Figs 9 , 10 ). Body moderately calcified, with few hairs. Carapace smooth, with no ridges, 0.33 times total body length, 1.8–1.9 times carapace width and 1.4–1.8 times carapace depth; dorsal surface arched; pseudorostrum acute, 0.19–0.21 times carapace length. Width of large eye lobe 0.20–0.25 times carapace width, corneal lens not observable, separated from frontal lobe by slight depressions on each side. Antennal notch very shallow; anterolateral angle ( Fig. 9 C) with 2 teeth directing forward, succeeded by minute teeth; inferior margin smooth. Pereon 0.55–0.76 times carapace length; posterior portion of pereonite 1 covered with well-developed pereonite 2. Pleon slender, 0.44–0.48 times total body length; pleonite 6 slightly exceeding opening of anus, with 2 minute setae on dorsal surface and a pair of perianal setae ( Fig. 10 G).

Antenna 1 ( Fig. 9 D) peduncle article 1 curved, 0.4 times combined length of articles 2 and 3; article 3 1.6–1.7 times article 2. Main flagellum tri-articulate, 0.5–0.6 times article 3 of peduncle; article 1 2.1–2.9 times combined length of articles 2 and 3; accessory flagellum 0.4 times article 1 of main flagellum. Antenna 2 ( Fig. 9 E) bi-articulate, strongly bent between basal and distal articles; basal article broad, with plumose seta near distal end; distal article slender, with simple seta on proximal region. Right and left mandibles ( Fig. 9 F) with 5 and 3 curved setae, respectively; lacinia mobilis tri-dentate; incisor process very weakly curved inward. Labium ( Fig. 9 G) round, without process or seta on distal margin. Maxilla 1 ( Fig. 9 H) outer endite with 12 spiniform setae; inner endite with 1 tridentate and 2 minute setae; palp with 2 filaments. Maxilla 2 ( Fig. 9 I) 2 narrow endites with 3 and 4 setae respectively, broad endite with a row of 12 simple setae on distal portion of inferior margin.

Maxilliped 1 ( Fig. 9 J) branchial lobules absent; basis subequal in length to distal articles together; carpus with 4 broad, serrated setae and 3 simple setae on inner margin, plumose seta on outer margin; propodus with 4 setae on inner distal corner; dactylus with 2 weakly curved simple setae on tip. Maxilliped 2 ( Fig. 9 K) basis 0.8–0.9 times combined length of succeeding 4 articles, with long plumose seta on inner distal corner; merus longer than carpus and subequal in length to propodus, with plumose seta on inner distal corner; carpus with 2 simple setae on inner margin and plumose seta on outer distal corner; propodus with simple seta on inner margin; dactylus minute with robust forked and serrated terminal seta. Maxilliped 3 ( Fig. 10 A) basis 1.0 times remaining distal articles, with plumose seta on inner distal corner and fine hairs on inner margin; outer distal corner of basis not protruding, with 2 long plumose setae; carpus 1.4 times propodus, slightly curved inward, with 2 simple setae on inner margin; propodus 4.9 times dactylus, slightly curved inward, with simple seta on inner and outer margins, respectively; dactylus with simple seta on inner distal corner and 2 simple setae on outer margin; 2 hooked terminal setae, one also robust and serrated. Pereopods 1–3 with well-developed exopods ( Fig. 10 B–D). Pereopod 1 ( Fig. 10 B) basis 0.8–0.9 times distal articles together, with 3 simple setae on inner margin and 1 robust seta and 1 long plumose seta on outer distal corner; carpus 1.7–1.8 times propodus, with 4 simple setae on inner and outer margins, respectively; propodus 2.0–2.3 times dactylus; dactylus with 2 simple terminal setae. Pereopod 2 ( Fig. 10 C) basis 0.6–0.7 times remaining distal articles, with 2 simple setae on inner distal corner; merus subequal in length to carpus; dactylus 2.2–2.3 times carpus. Pereopod 3 ( Fig. 10 D) basis 1.1 times distal articles together, with simple seta on distal corner; carpus 2.1–2.2 times merus and 1.6–1.8 times propodus, with 2 stiff simple setae distally; dactylus with 2 short terminal setae. Pereopod 4 ( Fig. 10 E) basis 0.8 times distal articles together, with a couple of simple setae on lateral margin and 1 simple seta on distal corner; merus 1.2–1.4 times ischium; carpus 1.8–2.3 times merus and 1.9–2.1 times propodus, with 2 long and 1 short simple setae on distal margin. Pereopod 5 ( Fig. 10 F) basis 0.6 times distal articles together; merus 1.2 times ischium; carpus 2.3 times merus and 1.9 times propodus.

Uropod ( Fig. 10 G) peduncle 1.9–2.1 times pleonite 6, 0.56–0.66 times exopod and 0.60–0.66 times endopod, with minute spiniform seta on inner distal corner; exopod 1.00–1.07 times endopod, with 2 terminal setae and 1 subterminal seta on inner margin; endopod uni-articulate, with 7–8 spiniform setae on inner margin and bi-dentate terminal and subterminal setae.

Ovigerous female carrying 10 larvae at 2nd nauplius stage, 3.43 mm ( Figs. 11 , 12 ). Carapace damaged, 0.31 times total body length; dorsal surface markedly elevate posteriorly; eye lobe ( Fig. 11 B) smaller than preparatory females. Pereon 0.76 times carapace length ( Fig. 11 A); pereonite 1 and 2 well developed. Pleon 0.44 times total body length ( Fig. 11 A); pleonite 6 with 4 minute setae on dorsal surface ( Fig. 12 G). No food residue present.

Antenna 1 ( Fig. 11 C) similar to preparatory females. Antenna 2 ( Fig. 11 D) tri-articulate. Mandibles ( Fig. 11 E) wholly decalcified, distal portion small, with reduced setae; lacinia mobilis not distinguishable from the other setae; incisor process very short. Maxilla 1 ( Fig. 11 G) without setae on distal margins of both endites. Maxilla 2 ( Fig. 11 H) without setae on distal margin of broad and narrow endites.

Maxilliped 1 ( Fig. 11 I) carpus with 4 thin, serrated setae and several simple setae on inner margin; 2 terminal setae on dactylus similar to preparatory females. Two terminal setae on maxilliped 2 ( Fig. 11 J) minute. Maxilliped 3 ( Fig. 12 A) basis 1.1 times distal articles together, with 4 stiff plumose setae on inner margin and 2 long plumose setae on outer distal corner; 2 terminal setae on dactylus minute. Pereopod 1 ( Fig. 12 B), dactylus broken; basis with plumose seta and simple seta on inner margin and outer distal corner, respectively. Pereopods 2–5 ( Fig. 12 C–F) similar to preparatory females. Uropod ( Fig. 12 G), peduncle near 2 times pleonite 6, 0.9 times exopod and 0.9 times endopod; thin exopod 0.99 times endopod, with 2 terminal and 1 subterminal setae; endopod with 9 spiniform setae on inner margin; long terminal seta broken.

Adult males, 2.86–3.08 mm ( Fig. 13 ). Carapace length, 0.31–0.33 times total body length; 2.0–2.1 times carapace width, and 1.9–2.0 times carapace depth; dorsal surface weakly arched. Pseudorostrum 0.12–0.15 times carapace length; width of eye lobe 0.27–0.30 times carapace width; corneal lenses absent; antennal notch obsolete ( Fig. 13 C); anterolateral angle and inferior margin smooth, without teeth. Pereon 0.52–0.62 times carapace length. Pleon without pleopods, 0.48–0.51 times total body length ( Fig. 13 A); pleonite 6 similar to females ( Fig. 13 L).

Antenna 1 ( Fig. 13 D) peduncle article 1 0.31–0.42 times combined length of articles 2 and 3, with a few simple setae on distal corner; article 2 with a group of 7–10 aesthetascs; article 3 1.52–1.97 times article 2, with numerous aesthetascs on lateral margin. Main flagellum 4-articulate, 0.36–0.39 times article 3 of peduncle; accessory flagellum as long as article 1 of main flagellum. Antenna 2 ( Fig. 13 E) clasping form, peduncle distal 2 articles fused; flagellum of 4–5 large articles and 2 small articles; articles 2–5 with triangular process on inner margin; small articles with several thin setae.

Maxilliped 3 ( Fig. 13 F) basis 1.2–1.3 times distal articles together, with plumose seta on inner distal corner and fine hairs on inner margin; carpus with 2 simple setae on inner margin; dactylus small, with stiff hooked terminal setae. Pereopods 1–3 with well-developed exopods ( Fig. 13 G–I) Pereopod 1 ( Fig. 13 G) basis 1.0–1.1 times distal articles together, with plumose seta on outer distal corner; carpus 1.6–1.8 times propodus; dactylus with 2 terminal setae. Pereopod 2 ( Fig. 13 H) basis 0.9 times distal articles together; carpus subequal in length to merus; dactylus 2.3–2.8 times carpus. Pereopod 3 ( Fig. 13 I) basis 1.2–1.4 times combined length of distal articles; carpus 1.9–2.1 times merus and 1.5–2.0 times propodus, with 2 stiff setae on distal margin. Pereopod 4 ( Fig. 13 J) basis 0.8 times remaining distal articles, with a couple of simple setae on lateral margin; merus 1.1–1.5 times ischium; carpus 1.9–2.4 times merus and 1.5–2.1 times propodus. Pereopod 5 ( Fig. 13 K) basis 0.5–0.6 times distal articles together; merus 0.9–1.2 times ischium; carpus 2.1–2.4 times merus and 1.5–1.6 times propodus.

Uropod ( Fig. 13 L) peduncle 1.9–2.4 times pleonite 6, 0.55–0.65 times exopod, and 0.58–0.68 times endopod, with minute spiniform seta on inner distal corner; exopod 1.02–1.06 times endopod, with 1 long and 1 short terminal setae; endopod with 14–18 spiniform setae on inner margin and long bi-dentate terminal seta.

Etymology. The species name refers to the type locality, Japan.

Remarks. The new genus Pseudopicrocuma is similar to the genus Picrocuma from the shallow waters of eastern Australia ( Hale, 1936, 1945) in (1) overall shape of carapace, pereon, pleon and pereopods (2) well developed exopods present on maxilliped 3 and pereopod 1–3, (2) males having no pleopods, (3) male antenna 2 peduncle articles 4 and 5 fused, flagellum of clasping form. The former genus is distinguishable from the latter by (1) Antenna 1 main flagellum tri-articulate in female and 4-articulate in males (bi-articulate in both sexes of Picrocuma ), (2) male antenna 1 with many aesthetasc-like sensory setae on peduncle articles 2 and 3 (no aesthetasc-like sensory setae in Picrocuma ) (3) mandibles navicular (basal region somewhat truncate in Picrocuma ), and (4) uropod slender; rami very elongate, nearly 2 times peduncle (strongly constructed; rami much shorter than peduncle in Picrocuma ). Character (2) is rather rare in cumaceans, except for Thalycrocuma sarradini Corbera et al., 2008 from the Lucky Strike hydrothermal vent field in Mid Atlantic, which has sensory setae only on peduncle article 3.

Pseudopicrocuma japonicum is characterized by (1) eye lobe large, without corneal lenses, (2) maxilliped 1 with degenerated branchial lobules, (3) maxilliped 2 with serrated, claw-like stiff terminal seta, (4) maxilliped 3 carpus and propodus slightly curved inward; dactylus minute, with serrated, claw-like stiff terminal seta, (5) uropod rami elongate, terminal setae bi-dentate. In addition, the ovigerous female of Pseudopicrocuma japonicum is characterized by degeneration of mouthparts (1) decalcification of mandibles, (2) reduction or loss of setae on mandibles, maxilla 1 and maxilla 2, (3) reduced terminal setae on maxillipeds 2 and 3.

Distribution. Southeast of Yakushima-Tanegashima, Pacific coast of southern Japan, north of Minami-Ensei Knoll, Okinawa Trough, 566–1679 m.

Figures

FIGURE 9. Pseudopicrocuma japonicum sp. nov., preparatory female. A, lateral view; B, anterior portion of body, from above; C, anterolateral angle D, antenna 1; E, antenna 2; F, right and left mandibles; G, labium; H, maxilla 1; I, maxilla 2; J, K, maxillipeds 1, 2.

FIGURE 10. Pseudopicrocuma japonicum sp. nov., preparatory female. A, maxilliped 3; B – F, pereopods 1 – 5; G, uropod with pleonite 6.

FIGURE 11. Pseudopicrocuma japonicum sp. nov., ovigerous female. A, lateral view; B, anterior portion of body, from above; C, antenna 1; D, antenna 2; E, right and left mandibles; F, labium; G, maxilla 1; H, maxilla 2; J, K, maxillipeds 1, 2.

FIGURE 12. Pseudopicrocuma japonicum sp. nov., ovigerous female. A, maxilliped 3; B – F, pereopods 1 – 5; G, uropod with pleonite 6.

FIGURE 13. Pseudopicrocuma japonicum sp. nov., adult male. A, lateral view; B, anterior portion of body, from above; C, anterior portion of carapace, lateral view; D, antenna 1; E, antenna 2; F maxilliped 3; G – K, pereopods 1 – 5; Q, uropod with pleonite 6.