Atlantocuma gamoi, 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 : 21-27

publication ID	https://doi.org/ 10.5281/zenodo.209717
DOI	https://doi.org/10.5281/zenodo.6166752
persistent identifier	https://treatment.plazi.org/id/CE5887C6-9D02-DF31-E791-F278E6C1FD3B
treatment provided by	Plazi
scientific name	Atlantocuma gamoi
status	sp. nov.

Treatment

Atlantocuma gamoi View in CoL sp. nov.

(Figs. 1–4)

Diagnosis. Carapace elevated in preparatory and ovigerous females; pseudorostrum 0.16–0.18 times carapace in females; anterolateral angle with 3–4 teeth; inferior margin not serrated. Pereopod 1 carpus 1.5–1.8 times propodus. Uropod peduncle 2.1–2.3, 2.6–2.8 times pleonite 6, 1.9–2.0, 2.2–2.4 times endopod in preparatory and ovigerous females, respectively; exopod without spiniform setae on inner margin except for subterminal one. Pseudorostrum in adult male truncate; anterolateral angle without teeth. Uropod peduncle 2.8–3.0 times pleonite 6, 1.7–1.8 times endopod in adult male

Material examined. Holotype. Preparatory female, 4.24 mm (NSMT-Cr 22180), Shima Spur, southern coast of Honshu Island, 34°00.72ˏN, 136°53.28ˏE – 34°01.55ˏN, 136°52.98ˏE, 781–789 m (KT-08-3, St. SM-01-2), 4 March 2008. Paratypes, 6 preparatory females, 5 specimens dissected, 4.07–4.29 mm, 6 ovigelous females, 4.20–4.42 mm, 5specimens dissected, 4 adult males (1 specimen damaged), 3.76–3.95 mm, 3 specimens dissected (NSMT-Cr 22181), same locality and date as holotype specimen (KT-08-3, St. M-01-2).

Description. Preparatory females. 4.07–4.29 mm (Figs. 1, 2). Body moderately calcified, with few hairs. Carapace smooth, with no ridges or carina, 0.30–0.31 times total body length, 1.86–1.95 times width and 1.64–1.74 times depth. Integument with small scale-like sculpture. Pseudorostrum, 0.16–0.18 times carapace length. Width of triangular eye lobe 0.12–0.15 times carapace width; antennal notch well defined; anterolateral angle with 3–4 teeth directing forward (Fig. 1C, D); inferior margin smooth, without teeth. Pereon 0.57–0.60 times carapace length; pereonite 1, narrow tightly jointed to carapace; pereonite 3 well developed; pereonite 3–5 small. Pleon slender, 0.51–0.52 times total length; combined length of carapace and pereon longer than pereonites 1–5 together; posterior end of pleonite 6 slightly exceeding opening of anus ( Fig. 2 View FIGURE 2 E).

Antenna 1 (Fig. 1E) peduncle article 1 thick and curved, 0.7–0.9 times combined length of articles 2 and 3, with rows of fine hairs on ventral surface; article 3 0.96–1.13 times article 2. Main flagellum tri-articulate; article 1 0.8–0.9 times combined length of articles 2 and 3; article 3 minute, with 2 aesthetascs and 2 long setae; uniarticulate accessory flagellum 0.4–0.5 times article 1 of main flagellum. Antenna 2 (Fig. 1F) tri-articulate; basal article with a plumose seta on distal margin; distal article with simple seta on lateral margin and a few setae on apical end. Mandibles (Fig. 1G) with 4 setae, respectively; lacinia mobilis slender, bi-dentate; incisor process directing inward. Labium (Fig. 1H) pointed distally, with 1 bi-dentate seta and 1 simple seta on tip. Maxilla 1 (Fig. 1I) outer endite with 12 spiniform setae; inner endite with 1 tri-dentate, 1 bi-dentate and 1 simple seta; palp with 2 filaments. Maxilla 2 (Fig. 1J) with 5 setae on 2 narrow endites, respectively; broad endite with a row of about 15 thin simple setae on inferior margin.

Maxilliped 1 (Fig. 1K, L) with 5 rudimental branchial lobules; basis longer than combined length of distal articles; carpus with a row of 6 broad, serrated setae and 3–4 simple setae on inner margin, with plumose seta on outer margin; propodus with 4 setae on inner distal corner; dactylus with 2 minute terminal setae. Maxilliped 2 (Fig. 1M) basis as long as succeeding 4 articles together, with 2 plumose seta on inner margin; carpus shorter than merus, with 1 simple and 1 plumose setae on inner margin; propodus with 2 simple setae on inner margin; dactylus minute, with 2 terminal setae. Maxilliped 3 (Fig. 1N) basis 1.6–1.7 times remaining distal articles, with 2 long plumose seta on outer distal corner, with fine hairs on inner margin; carpus 1.3–1.4 times propodus, with 3 simple and 0–1 plumose setae on inner margin: propodus with 2 simple setae on inner margin distally. Pereopod 1 (Fig. 1O) basis 1.2–1.3 times distal articles together, with 1 robust seta on inner distal corner, carpus 1.5–1.8 times propodus; propodus 1.8–2.0 times dactylus; dactylus with 1 stiff, simple terminal seta. Pereopod 2 ( Fig. 2 View FIGURE 2 A) basis 0.8–0.85 times remaining distal articles, with a couple of simple setae on lateral margin; carpus 1.1–1.5 times merus; dactylus 1.1–1.2 times carpus, with 5 robust setae on lateral margin and distal end. Pereopod 3 ( Fig. 2 View FIGURE 2 B) basis 1.0–1.2 times distal articles together, with a couple of simple setae on lateral margin; carpus 1.7–2.2 times propodus; terminal seta fused with dactylus. Pereopod 4 ( Fig. 2 View FIGURE 2 C) basis 0.7–0.8 times distal articles together, with a couple of seta on lateral margin; carpus 1.9–2.1 times propodus. Pereonite 5 ( Fig. 2 View FIGURE 2 D) basis 0.6 times distal articles together; carpus 1.9–2.2 times propodus; terminal seta defined at base.

Uropod ( Fig. 2 View FIGURE 2 E) peduncle 2.1–2.3 times pleonite 6, 1.83–1.97 times exopod and 1.88–2.03 times endopod, with 1 minute spiniform seta on inner distal corner; exopod 1.01–1.05 times endopod, with robust simple seta terminally and with 2 simple setae subterminally; endopod uni-articulate, with 5–7 spiniform setae on inner margin; terminal seta robust.

Ovigerous females, 4.20–4.22 mm ( Fig. 3 View FIGURE 3 ). Carapace 0.29–0.31 times total body length, 1.5–1.7 times carapace width and 1.4–1.1.6 times depth; dorsal surface markedly elevate posteriorly; pseudorostrum 0.16–0.18 times carapace length; width of eye lobe 0.10–0.12 times carapace width; antennal notch and anterolateral angle similar to preparatory females; inferior margin smooth. Pereon 0.60–0.69 times carapace; 1st segment well developed. Pleon slender, 0.50–0.51 times total body length. No food residue present.

Antenna 1 ( Fig. 3 View FIGURE 3 D) peduncle article 1 0.6–0.7 times combined length of articles 2 and 3; article 3 1.05–1.12 times article 2; main flagellum 1.0 times article 3 of peduncle; main flagellum article 1 0.9–1.0 times combined length of articles 2 and 3; accessory flagellum 0.4 times article 1 of main flagellum. Antenna 2 similar to preparatory females. Mandibles ( Fig. 3 View FIGURE 3 F) wholly decalcified and flattened; setae on inner margin and lacinia mobilis reduced. Maxilla 1 ( Fig. 3 View FIGURE 3 G) with minute setae on both outer and inner endites. Maxilla 2 ( Fig. 3 View FIGURE 3 H) broad and narrow endites with minute setae.

Maxilliped 1 ( Fig. 3 View FIGURE 3 I) slender; serrated setae on inner margin of carpus thinner than preparatory females. Maxilliped 2 ( Fig. 3 View FIGURE 3 J) slender; stiff plumose seta on inner distal corner of basis absent. Maxilliped 3 ( Fig. 3 View FIGURE 3 K) basis 1.7–1.9 times distal articles together, with 7–9 stiff plumose setae on inner margin; merus with 1 plumose seta on inner distal corner. Pereopods 1–5 ( Fig. 3 View FIGURE 3 L–P) similar to preparatory females. Uropod ( Fig. 3 View FIGURE 3 Q) peduncle elongate, 2.6–2.87 times pleonite 6, 2.12–2.35 times exopod, 2.22–2.37 times endopod; exopod 1.01–1.05 times endopod; endopod with 5–7 spiniform setae on inner margin.

Adult males, 3.76–3.95 mm ( Fig. 4 View FIGURE 4 ). Body slender, weakly calcified. Integument of carapace covered with scale-like sculptures ( Fig. 4 View FIGURE 4 D). Carapace length 0.29–0.30 times total body length, 2.1–2.2 times greatest width and 1.9–2.0 times depth. Dorsal surface of carapace weakly arched; pseudorostrum truncate, 0.068–0.079 times carapace length; antennal notch shallow; anterolateral angle ( Fig. 4 View FIGURE 4 C) and inferior margin smooth, with no teeth; width of eye lobe 0.17–0.20 times carapace width.

Antenna 1 ( Fig. 4 View FIGURE 4 E) peduncle article 1 0.5–0.6 times combined length of articles 2 and 3; article 3 1.2–1.3 times article 2. Main flagellum 4-articulate, 0.8–0.9 times article 3 of peduncle; articles 1, 3 and 4 with 2 aesthetascs, respectively; accessory flagellum uni-articulate, 0.9–1.0 times article 1 of main flagellum. Antenna 2 ( Fig. 4 View FIGURE 4 F) peduncle article 4 and 5 subequal in length, with numerous long sensory setae; flagellum of 10 articles of normal size and 1 minute terminal one, 0.7–0.9 times peduncle.

Maxilliped 3 ( Fig. 4 View FIGURE 4 G) basis 1.7 times distal articles together. Pereopods 1–4 basis massive, with welldeveloped exopods. Pereopod 1 ( Fig. 4 View FIGURE 4 H) basis 1.3 times distal articles together; carpus 1.6–1.7 times propodus, carpus with 5–6 simple setae on lateral margin and distal corner. Pereopod 2 ( Fig. 4 View FIGURE 4 I) basis 1.0–1.1 times remaining distal articles; carpus with 3–4 setae. Pereopod 3 ( Fig. 4 View FIGURE 4 J) basis 1.3–1.4 times distal articles together; carpus with 2–3 simple setae. Pereopod 4 ( Fig. 4 View FIGURE 4 K) basis 1.0–1.1 times distal articles together; carpus with 2–3 simple setae. Pereopod 5 ( Fig. 4 View FIGURE 4 L) basis 0.7–0.8 times distal articles together.

Uropod ( Fig. 4 View FIGURE 4 M) elongate, peduncle 2.8–3.0 times pleonite 6, 1.70–1.72 times exopod, 1.70–1.75 times endopod; exopod 0.99–1.03 times endopod, with subterminal spiniform seta on inner margin; endopod with 13–15 spiniform setae on inner margin.

Etymology. The species name is dedicated to Dr. Sigeo Gamô, in his honor of contribution to cumacean taxonomy.

Remarks. The present new species resembles A. tenue Jones, 1984 from the deep Atlantic in which carapace of the ovigerous female is elevated, however, it can be distinguished from the latter by (1) carapace of preparatory females also elevated, (2) maxilliped 3 basis less than 2 times remaining articles (3 times in A. tenue ), (3) uropod endopod with 5–7 spiniform setae (12–13 in A. tenue ), and (4) male pseudorostrum truncate (pointed in A. tenue ).

Atlantocuma gamoi is also similar to A. ramses, Miuhlenhardt-Siegel, 2005 from the deep Atlantic, 5415 m, but is distinguished from the latter by (1) uropod peduncle length less than 3 times pleonite 6 (3.25 times in A. ramses ), (2) uropod endopod of females with 5–7 spiniform setae (9 setae in A. ramses ) (3) maxilliped 2 merus longer than carpus (subequal in length in A. ramses ), (4) maxilliped 2 merus without long setae (with 1 long plumose seta in A. ramses ), (5) carapace of adult males without tooth on anterolateral angle (with a tooth in A. ramses ).

The ovigerous females are characterized by a degeneration of the mouthparts (1) wholly decalcified mandibles, (2) reduced number and size of setae on inner margin of mandibles, maxilla 1 and 2, and maxilliped 2, and (3) maxilliped 1 and 2 slender. Other noteworthy characters of the ovigerous females are elevation of carapace, and maxilliped 3 with stiff plumose setae on inner margin.

Distribution. Southern coast of Honshu, Northwest Pacific, 781– 789 m.