Agathotanais cilacapicus, Chim & Tong, 2021

Chim, C. K. & Tong, Samantha J. W., 2021, Three new species of agathotanaids (Tanaidacea: Paratanaoidea: Tanaidomorpha) from the lower bathyal zone off southwestern Java, Indonesia, Indian Ocean with notes on the global distribution and diversity of Agathotanaidae, Zootaxa 5004 (1), pp. 67-106 : 70-76

Agathotanais cilacapicus n. sp.

( Figs 5A , 6–9 )

Agathotanais sp. SJ#1: Chim & Bird (in press)

Material examined. Holotype, non-ovigerous female (2.8 mm), in one vial ( ZRC 2020.0311 ), about 80 km south of Cilacap , Java, Indonesia, Indian Ocean, station CR42 (8°20.609’S, 108°43.036’E), 2355 m, box corer, layer 0–2 cm, sieve mesh size 300 μm, SJADES cruise, 31 March 2018.

Paratypes: female with brooding pouch (3.2 mm), in one vial ( ZRC 2020.0312 ) and non-ovigerous female (3.2 mm), dissected and mounted on 19 slides ( ZRC 2020.0313 ), layer 2–5 cm, sieve mesh size 300 μm; one manca III (2.0 mm) in one vial ( ZRC 2020.0314 ) and four mancae II (1.4 mm), in one vial ( ZRC 2020.0315 ), layer 0–2 cm, sieve mesh size 250 μm; other collection data same as holotype .

Diagnosis. Pleonal segments weakly segmented. Labium with large and elongated medial projection. Left mandible lacinia mobilis short and blunt. Pereopods 4–6 propodus with claw-like spiniform seta on outer margin distally. Uropod endopod biarticulate, article-2 not fused to article-1.

Description. Non-ovigerous female (habitus and uropods based on holotype ZRC 2020.0311, others based on paratype ZRC 2020.0313).

Body ( Figs 5A , 6A–B ) slender, subcylindrical, about nine times longer than wide, and densely covered with setules. Cephalothorax about 18% of body length, 1.5 times longer than wide, lateral margins straight, subrectangular in dorsal view; rostrum short and rounded; eye lobes absent.

Pereon about 66% of body length; pereonite-1 widest, almost as wide as cephalothorax, trapezoidal, wider than long; pereonites 2 and 3 of subequal length, hexagonal, longer than wide; pereonites 4 and 5 longest, hexagonal, longer than wide; pereonite-6 shortest, trapezoidal, wider than long; lateral shoulders strongly defined.

Pleon about 16% of body length, narrower than pereon; all five pleonites of subequal length, each 0.3 times as long as wide, fused but with very weak indication of segmental articulations in dorsal view; pleonite-5 with one simple seta on each lateral side; pleotelson ( Fig. 6D ) fused to pleonite-5, about 44% of pleon length, as wide as pleonites, subpentagonal from dorsal view, apex posterior margin straight bearing three pairs of simple setae.

Antennule ( Fig. 7A ) densely covered with setules, about 0.9 times as long as cephalothorax, with three articles; article-1 longest, about 62% of total length, with three simple setae medially and six (four simple and two plumose) setae distally; article-2 shortest, about 12% of total length, with two simple and one plumose setae distally; article-3 subconical, about 26% of total length, with six simple setae, one plumose seta and one aesthetasc distally.

Antenna ( Fig. 7B ) densely covered with setules, with one short subtriangular article bearing one short and one long simple setae distally ( Fig. 9A ).

Mouth parts densely covered with setules. Labrum ( Fig. 7C ) hood-shaped. Left mandible ( Fig. 7D ) incisor with several blunt teeth; lacinia mobilis short and wide. Right mandible ( Fig. 7 D`) incisor bifurcate. Labium ( Fig. 7E ) with one pair of lobes, each with one setulose projection medially ( Fig. 9B ) and laterally ( Fig. 9B ). Epignath and maxilla lost during dissection. Maxillule ( Fig. 7F ) endite with nine spiniform setae; palp with two terminal setae. Maxilliped ( Fig. 7G ) bases not fused distally, each with one simple seta distally; endite with one simple seta distally; palp article-2 with two simple and one setulose setae distally; article-3 with three setulose setae distally; article-4 with one simple and five setulose setae distally.

Cheliped ( Fig. 8A ) slender and densely covered with setules; basis attached directly to cephalothorax ventromedially ( Fig. 6C ), subrectangular, about 1.5 times longer than wide; merus about 0.8 times as long as basis, with one simple seta ventrally; carpus trapezoidal, about 2.3 times longer than basis, with one simple seta dorsomedially, one simple seta dorsodistally and one short ventromedial process bearing two simple setae; propodus about 1.2 times longer than carpus, ventral margin straight, palm with one simple seta on inner margin distally and one simple seta at dactylus insertion, fixed finger with one simple seta ventrally, one small tooth dorsodistally and three simple setae on outer margin near cutting edge, terminal spine acute distally; dactylus and unguis together as wide as but slightly shorter than fixed finger; dactylus with one simple seta on inner margin dorsoproximally and two spiniform setae on outer margin near cutting edge; unguis acute distally.

Pereopod-1 ( Fig. 8B ) attached to pereonite most anteriorly; slender and densely covered with setules; coxa with one simple seta; basis about 8.8 times longer than wide, lateral margins parallel; ischium short, less than 0.1 times as long as basis, with one simple seta ventrodistally; merus about 0.3 times as long as basis, with two simple setae ventrodistally; carpus about 1.4 times longer than merus, with two simple setae ventrodistally and one longer simple seta dorsodistally; propodus about 1.3 times longe than carpus, with three minute spiniform setae dorsodistally and one simple seta ventrodistally; dactylus and unguis naked, slender and slightly curved, combined length about as long as propodus; unguis about 1.2 times longer than dactylus, with blunt tip.

Pereopod-2 ( Figs 8C , 9D ) similar to pereopod-1 but attached to pereonite less anteriorly; carpus and propodus each with one additional simple seta on inner margin distally.

Pereopod-3 ( Fig. 8D ) similar to pereopod-2 but attached to pereonite less anteriorly; basis with two additional plumose setae; dactylus and unguis combined length about 0.7 times as long as propodus; unguis as long as dactylus.

Pereopod-4 ( Fig. 8E ) attached to pereonite slightly posteriorly; slender and densely covered with setules; coxa with one simple seta; basis about 7.3 times longer than wide, with two plumose setae dorsoproximally and two plumose setae ventrodistally; ischium short, less than 0.1 times as long as basis, with two simple setae ventrodistally; merus about 0.2 times as long as basis, with two simple setae ventrodistally; carpus about 1.3 times longer than merus, with two simple and one spiniform setae distally; propodus about 0.7 times as long as carpus, with a dorsodistal rounded process bearing one setulose spiniform seta and two ventrodistal setae (one claw-like spiniform and one setulose spiniform setae); dactylus and unguis, slender and straight, combined length about 1.8 longer than propodus; unguis setulose, about 1.9 times longer than dactylus, with sharp tip.

Pereopod-5 ( Fig. 8F ) similar to pereopod-4 but attached to pereonite more posteriorly; carpus with only one simple and one spiniform setae distally.

Pereopod-6 ( Fig. 8G ) similar to pereopod-5 but attached to pereonite most posteriorly and basis with only one plumose seta dorsally and one plumose seta ventrally.

Pleopods absent.

Uropod ( Fig. 6D ) short and does not extend beyond pleotelson posterior; basal article naked; endopod biarticulate and about 1.3 times longer than basal article, article-1 fused to basal article and with two plumose setae distally, article-2 about 0.7 times as long as article-1 and with seven simple setae distally; exopod fused with basal article forming a small and rounded process bearing two simple setae distally.

Etymology. The specific epithet is an adjective referring to the type locality Cilacap town. It agrees with the masculine gender of the genus Agathotanais (see Larsen 1999).

Distribution and habitat. Only from the type locality, at depth of 2355 m, 0–5 cm top layer of soft sediment.

Remarks. Agathotanais cilacapicus n. sp. clearly belongs to the genus Agathotanais based on the (1) extensive covering of body and appendages with setules; (2) hexagonal pleotelson with a long apex and straight posterior margin; (3) three-articled antennule; (4) reduction of antennae; (5) relatively small lacinia mobilis on left mandible; (6) long lateral projection on labium lobe; (7) direct attachment of cheliped to cephalothorax ventrally. Interestingly, A. cilacapicus (five of eight specimens, including the holotype) and Metagathotanais share the unusual character of nearly fused or fused pleonal segments, which is not present in other members of the family Agathotanaidae . In these two taxa, both endopod and exopod are fused to the uropodal basal article. However, the uropod endopod is uniarticulate in Metagathotanais but biarticulate in A. cilacapicus . Furthermore, the exopod is entirely absent in Metagathotanais due to complete fusion while it is present as a small process in A. cilacapicus . The uropod of A. cilacapicus is most similar to that of A. misakiensis Kakui & Kohtsuka, 2015 ( Table 4). Other notable similarities between these two species include the (1) short and blunt lacinia mobilis that is fused to the body of left mandible; (2) chetotaxy on maxillipeds (i.e. one seta on endite, one seta on basis, three setae on palp article-2, three setae on palp article-3, six setae on palp article-4); (3) presence of a row of minute spiniform setae on pereopods 1–3 propodus dorsodistally; (4) presence of one claw-like spiniform seta on outer margin of pereopods 4–6 propodus distally; (5) number of plumose setae on pereopod bases. However, the two species differ in A. cilacapicus having (1) a much smaller body size; (2) a slightly more elongated body; (3) a much larger and elongated medial projection on the labium; (4) a simple seta on cheliped carpus dorsomedially; (5) less complex spiniform setae on pereopods 1–3 propodus dorsodistally; (6) only one (P4) or two (P5–6) simple and one spiniform setae on pereopods 4–6 carpus. Furthermore, these two species were found in very different biogeographical realms— A. cilacapicus in the lower bathyal depths (2355 m) of the equatorial Indian Ocean and A. misakiensis in the upper bathyal depths (211–493 m) of the temperate North Pacific Ocean (Misaki, Japan).

Figures

FIGURE 5. Agathotanaids of Southwest Java, Indonesia: (A) Agathotanais cilacapicus n. sp.; (B) Bunburia javanica n. sp.; (C) Paranarthrura sundanensis n. sp..

FIGURE 6. Agathotanais cilacapicus n. sp. Southwest Java, Indonesia. Non-ovigerous female holotype (ZRC 2020.0311): habitus, (A) dorsal and (B) lateral views; (C) cephalothorax, ventral view; (D) pleotelson and uropods, ventral view. Scale bars: 0.5 mm (A, B); 200 µm (C); 100 µm (D).

FIGURE 7. Agathotanais cilacapicus n. sp. Southwest Java, Indonesia. Non-ovigerous female paratype (ZRC 2020.0313): (A) antennule, left; (B) antenna, left; (C) labrum; mandibles, (D) left and (D`) right; (E) labium; (F) maxillule; (G) maxillipeds. Asterisk indicates missing part. Scale bars: 100 µm.

FIGURE 8. Agathotanais cilacapicus n. sp. Paratype female: (A) cheliped, left; (B–G) pereopods 1–6, left. Asterisk indicates missing part. Scale bar: 100 µm.

FIGURE 9. Agathotanais cilacapicus n. sp. Paratype female: (A) terminal setae on antenna; medial (B) and lateral (C) projections on labium; (D) dorsodistal spiniform setae on pereopod-2 propodus. Scale bar: 50 µm.