Atlantocuma ojii, 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 : 27-30

Atlantocuma ojii sp. nov.

( Figs. 5–8 )

Diagnosis. Carapace elevated only in ovigerous female; pseudorostrum length 0.16–0.20 times carapace in preparatory females; anterolateral angle with about 3 teeth; inferior margin not serrated in preparatory female, serrated for entire length in ovigerous female. Pereopod 1 carpus 1.7–2.0 times propodus. Uropod peduncle 2.6–2.9, 2.9–3.3 times pleonite 6, 2.2–2.4, 2.5–2.8 times endopod, in preparatory and ovigerous females, respectively; exopod with 1–2 spiniform setae on inner margin, except for subterminal one. Pseudorostrum in adult male truncate, anterolateral angle without teeth. Uropod peduncle 3.7 times pleonite 6, 2.0 times endopod in adult male.

Material examined. Holotype preparatory female, 4.70 mm (NSMT-Cr 22182), Shima Spur, southern coast Honshu, 34°00.72ˏN, 136°53.28ˏE – 34°01.55ˏN, 136°52.98ˏE, 781–789 m (KT-08-3, St. SM-1-2), 4 March 2008. Paratypes; 7 preparatory female, 5 specimens dissected, 4.48–4.78 mm, 5 ovigerous females, dissected, 4.50–4.77 mm, (NSMT-Cr 22183), same locality as holotype female (KT-08-3, St. SM-1-2); 3 adult males (1 specimen damaged), dissected, 3.85–4.16 mm (NSMT-Cr 22184), Shima Spur, 34°00.53ˏN, 136°52.49ˏE–34°00.02ˏN, 136°52.32ˏE, 810–861 m (KT-10-16, St. SK2), 14 August, 2010.

Description. Preparatory females, 4.48–4.78 mm ( Figs. 5 , 6 ). Body moderately calcified, with few hairs. Carapace ( Fig. 5 C) slender, 0.27–0.29 times total body length, 1.97–2.13 times carapace width and 1.80–1.97 times carapace depth; pseudorostrum pointed, 0.18–0.20 times carapace length; width of triangular eye lobe ( Fig. 5 B) 0.12–0.14 times carapace width; antennal notch shallow; anterolateral angle with 3 teeth; inferior margin smooth ( Fig. 5 C). Pereon 0.51–0.60 times carapace length ( Fig. 5 A); posterior portion of pereonite 1 covered by pereonite 2. Pleon 0.52–0.56 times total animal length ( Fig. 5 A); combined length of carapace and pereon shorter than pereonites 1–5 together.

Antenna 1 ( Fig. 5 D) peduncle article 1 thick and curved, 0.6–0.8 times combined length of articles 2 and 3, with fine hairs on ventral surface; article 3 0.9–1.1 times article 2. Main flagellum 3-articulate, 1.0–1.1 times article 3 of peduncle, with 2 aesthetascs and 2 long setae on tip; article 1 0.8–0.9 times combined length of articles 2 and 3; article 3 minute; accessory flagellum uni-articulate, 0.4–0.5 times article 1 of main flagellum. Antenna 2 ( Fig. 5 E) tri-articulate; basal article with a plumose seta on distal end; median and distal articles with simple seta. Right and left mandibles ( Fig. 5 F) with 4 setae; lacinia mobilis long and slender; incisor process directed inward. Arrangement of setae on maxilla 1 and 2 ( Fig. 5 G, H) normal for the genus.

Maxilliped 1 ( Fig. 5 I) basis longer than distal articles together, with 4–5 rudimentary branchial lobules; basis longer than combined length of distal articles; carpus with 6 broad, serrated setae and 5 simple setae on inner margin, with 1 plumose seta on outer margin; propodus with 4 setae on inner distal corner; dactylus with 2 thin terminal setae. Maxilliped 2 ( Fig. 5 J) basis 0.9–1.0 times combined length of succeeding 4 articles, with 1 plumose seta on inner margin and 1 plumose seta on inner distal corner; carpus shorter than merus, with 1 simple and 1 plumose setae on inner margin; dactylus with 2 minute terminal setae. Maxilliped 3 ( Fig. 5 K) basis 1.6–1.8 times remaining distal articles, with 2 long plumose setae on outer distal corner and fine hairs on inner margin; carpus with 3 simple setae on inner margin. Pereopod 1 ( Fig. 6 A) basis 1.1–1.2 times length of distal articles together, with 1 robust spiniform seta and 1 minute spine on inner distal corner, carpus 1.7–2.0 times propodus, propodus 1.7–2.0 times dactylus; dactylus with stiff terminal seta. Pereopod 2 ( Fig. 6 B) basis 0.7–0.9 times remaining distal articles, with a couple of simple setae on lateral margin; carpus 1.2–1.4 times merus; dactylus 1.1–1.3 times carpus. Pereopod 3 ( Fig. 6 C) basis 1.1 times distal articles together, with a couple of simple setae on lateral margin; carpus 2.0–2.1 times propodus. Pereopod 4 ( Fig. 6 D) basis 0.8 times distal articles together, with a couple of simple setae on lateral margin; carpus 2.1–2.4 times propodus. Pereonite 5 ( Fig. 6 E) basis 0.6 times distal articles together; carpus 2.3–2.5 times propodus.

Uropod ( Fig. 6 F) peduncle 2.6–2.9 times pleonite 6, 2.16–2.36 times exopod and 2.17–2.41 times endopod, with minute spiniform setae on inner distal corner; exopod 1.00–1.07 times endopod, with spiniform setae on inner margin except for subterminal one; endopod uni-articulate, with 8–10 spiniform setae on inner margin.

Ovigerous females, 4.50–4.77 mm ( Fig. 7 ). Carapace markedly elevate ( Fig. 7 C); Carapace length 0.27–0.29 times total body length, 1.5–1.7 times carapace width and 1.6–1.7 times depth; pseudorostrum 0.16–0.19 times carapace length; width of eye lobe 0.09–0.10 times carapace width; antennal notch shallow; anterolateral angle and inferior margin serrated with 25–27 teeth ( Fig. 7 C). Pereon 0.56–0.68 times carapace ( Fig. 7 A). Pleon 0.54 times total body length. No food residue present.

Antenna 1 ( Fig. 7 D) peduncle article 1 0.6–0.7 times combined length of articles 2 and 3; article 3 0.9–1.1 times article 2; main flagellum 1.0–1.1 times article 3 of peduncle. Main flagellum article 1 0.8–0.9 times combined length of articles 2 and 3; accessory flagellum uni-articulate, 0.4–0.5 times article 1 of main flagellum. Mandibles ( Fig. 7 E) decalcified and flattened, setae on inner margin reduced; lacinia mobilis not identifiable. Maxilla 1 and 2 with reduced simple setae ( Fig. 7 F, G). Maxilliped 1 ( Fig. 7 H) slender; carpus with thin serrated setae on inner margin. Maxilliped 2 ( Fig. 7 I) slender, basis 1.2–1.3 times combined length of next 4 articles; carpus with 2 thin short simple setae on lateral margin.

Maxlliped 3 ( Fig. 7 J) basis 1.2–1.3 times distal articles together, with 6–8 plumose setae on inner margin; merus with 1 plumose seta on inner distal corner. Pereopods 1–5 ( Fig. 7 K–O) similar to preparatory females. Uropod ( Fig. 7 P) peduncle 2.9–3.3 times pleonite 6, 2.4–2.8 times exopod, 2.5–2.8 times endopod; exopod 0.92–1.07 times endopod, with 1–2 spiniform setae on inner margin except for subterminal one; endopod with 8–11 spiniform setae on inner margin.

Adult males, 3.85–4.16 mm ( Fig. 8 ). Body slender, weakly calcified. Carapace 0.26–0.27 times total body length, 2.3 times greatest width and 2.0–2.1 times depth (fig. 8A, B). Dorsal surface weakly arched; pseudorostrum ( Fig. 8 B) truncate, 0.07–0.08 times carapace length; antennal notch well marked; anterolateral angle and inferior margin smooth, without teeth; width of eye lobe 0.16–0.18 times carapace width.

Antenna 1 ( Fig. 8 D) peduncle article 1 0.46–0.57 times combined length of articles 2 and 3; article 3 0.9–1.1 times article 2. Main flagellum 4-articulate, as long as article 3 of peduncle; accessory flagellum uni-articulate, 1.0–1.1 times article 1 of main flagellum. Antenna 2 ( Fig. 8 E) peduncle article 4 and 5 with numerous thin long setae; flagellum 0.8–0.9 times peduncle, of 11 articles, terminal one minute.

Maxilliped 3 ( Fig. 8 F) basis 1.7–1.8 times distal articles together, with fine hairs on inner margin. Pereopods 1–4 with well-developed exopods. Pereopod 1 ( Fig. 8 G) basis 1.2–1.3 times distal articles together; carpus 1.8–1.9 times propodus, with 8–11 simple setae on lateral margin and distal corner. Pereopod 2 ( Fig. 8 H) basis 1.0–1.2 times remaining distal articles; carpus with 7 simple setae. Pereopod 3 ( Fig. 8 I) basis 1.3–1.5 times distal articles together; carpus with 6–7 simple setae. Pereopod 4 ( Fig. 8 J) basis 1.0–1.2 times distal articles together; carpus with 7 simple setae. Pereonite 5 ( Fig. 8 K) basis 0.7 times distal articles together; carpus with 7–8 simple setae.

Uropod ( Fig. 8 L) elongate, peduncle 3.7 times pleonite 6, 1.95–1.98 times exopod, 1.98–2.03 times endopod; exopod 1.02–1.03 times endopod, with 2– 3 spiniform setae except for subterminal one; endopod with 15–16 spiniform setae on inner margin.

Etymology. The species name is dedicated to Dr. Tatsuo Oji, director of the R/V Tansei-maru cruises during which all Atlantocuma specimens examined in the present study were collected.

Remarks. Atlantocuma ojii sp. nov. resembles Atlantocuma tenue Jones, 1984 , from deep Atlantic and the Southeast Pacific, 587–5000 m, in the shape of carapace in preparatory and ovigerous females. However, the former species is distinguished from the latter by (1) pereopod 1 carpus 1.7–2.0 times propodus, dactylus less than 2 times dactylus (carpus about 1.5 times propodus, propodus 2 times dactylus in A. tenue ), (2) uropod peduncle 2.6–3.3 times pleonite 6 (2.4 times pleonite 6 in A. tenue ), (3) uropod exopods with 1–3 spiniform setae on inner margin except for subterminal one (no setae in A. tenue ), (4) pseudorostrum of adult males truncate (pointed in A. tenue ).

The new species also resembles Atlantocuma ramses Muihlenhardt-Siegel, 2005 , but can be distinguished by (1) maxilliped 2 merus shorter than carpus (subequal in length in A. ramses ), (2) long plumose seta absent on merus of maxilliped 2 (present in A. ramses ), (3) basis of maxilliped 3 in females 1.2–1.8 times distal articles together (1.96 times in A. ramses ), (4) anterolateral angle of adult male without teeth (with a tooth in A. ramses ).

Atlantocuma ojii is distinguishable from A. gamoi , collected from the same locality, by (1) carapace of preparatory female elevated, (2) inferior margin of carapace in ovigerous females serrated (not serrated in A. gamoi ), (3) combined length of carapace and pereon shorter than length of pleonite 1–5 together (longer in A. gamoi ), and (4) uropod exopod with 2–3 spiniform setae on inner margin (1 spiniform seta in A. gamoi ). Degeneration of mouthparts, and morphology of maxilliped 3 in ovigerous females show the same trends as A. gamoi .

Distribution. Southern coast of Honshu, Northwest Pacific, 781– 861 m.

Figures

FIGURE 5. Atlantocuma ojii sp. nov., preparatory female. A, lateral view; B, anterior portion of body, from above; C, carapace, lateral view; D, antenna 1; E, antenna 2; F, right and left mandibles; G, maxilla 1; H, maxilla 2; I – K, maxillipeds 1 – 3.

FIGURE 6. Atlantocuma ojii sp. nov., preparatory female. A – E, pereopods 2 – 5; F, uropod with pleonite 6.

FIGURE 7. Atlantocuma ojii sp. nov., ovigerous female. A, lateral view; B, anterior portion of body, from above; C, carapace, lateral view; D, antenna 1; E, right and left mandibles; F, maxilla 1; G, maxilla 2; H – J, maxillipeds 1 – 3; K – O, pereopods 1 – 5; Q, uropod with pleonite 6.

FIGURE 8. Atlantocuma ojii 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.