Agathotanais hadalis Larsen, 2007, n. sp.
Creators: name: Larsen, Kim
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Agathotanaidae
Agathotanais
Agathotanais hadalis

description: Agathotanais hadalis n. sp.
Figures 1–5
Material examined. Holotype, non-ovigerous female (KMNH IvR 500.163), station XR12, 41°37.67’– 41°37.08’N, 146°54.19’– 146°52.72’E. 5473–5484 metres, 22–23 September 2001. Paratypes: 5 non-ovigerous females, 5 males, 3 mancae (KMNH IvR 500.164) station TD-8, 39°15.54’– 39°17.01’N, 144°45.37’– 144°42.46’E. 5762–5733 metres, 29 September 2001.
Diagnosis (both genders). Pereonites 1, 2 and 6 shoulders weakly demarcated. Pereonite 6 short, almost trapezoid. Pereopod 1–3 propodus with two dorsal spines.
Etymology. Name derived from the deep-sea habitat.
Description. Adult female.
Body (Fig. 1 A,B). Nine times as long as wide. Lateral shoulders weakly defined.
Cephalothorax. With smooth lateral edges in dorsal view. Longer than wide. Shorter than pereonites 1 and 2 combined.
Pereonites. Pereonites 1 and 6 wider than long. Pereonite 2 square. Pereonites 3–5 longer than wide.
Pleon. Short (including pleotelson only 0.15 times as long as total body length). All pleonites subequal. Pleotelson almost as long as all pleonites combined, acorn-shaped, apex rounded and covered by dorsal plate.
Antennule (Fig. 1 C). Shorter than carapace, with three articles. Article 1 longer than rest of antennule combined, with outer medial process (only visible in dorso/ventral view) carrying simple and setulate setae. Article 2 less than one-third as long as article 3, with one simple and setulate distal setae. Article 3 longer than half of article 2, with five simple distal setae and one aesthetasc.
Antenna (Fig. 1 D). Uniarticulated, shorter than antennule article 3, with one distal seta.
Mouthparts. Labrum (Fig. 2 A) large, only marginally narrower than clypeus, distal edge setose. Mandibular molar indistinct and membranous. Left mandible (Fig. 2 B) lacinia mobilis absent, incisor blunt without denticles. Right mandible (Fig. 2 C) incisor slightly narrower than on left mandible, otherwise without denticles. Labium (Fig. 2 D) lobes setose, with spiniform outer process and medial setulose seta. Maxillule (Fig. 2 E) endite with ten spiniform distal setae; palp longer than endite, with two long terminal setae. Maxilla (Fig. 2 F) triangular. Maxilliped (Fig. 2 G) endites without setae. Palp (twisted during dissection) article 1 naked, article 2 and 3 with three setae on inner margin, article 4 only 0.5 times as wide and half as long as article 3, with five setae. Epignath (Fig. 2 H) naked, widest at basis, terminal setae present but naked.
Cheliped (Fig. 1 E). Basis naked, only twice as long as merus. Merus prominent, with one medial seta. Carpus marginally shorter than propodus including fixed finger, with two medio-ventral setae and one dorsal seta in each end. Propodus with one seta at dactylus insertion. Fixed finger with one ventral seta and three setae on inner margin, inner margin with one prominent distal tooth. Dactylus as long as fixed finger, with one small dorsal-proximal seta.
Pereopod 1 (Fig. 3 A). Coxa rounded, with one seta. Basis as long as combined length of merus, carpus and propodus, with one dorso-medial setulated seta. Ischium with one simple seta. Merus more than 0.5 times as long as carpus, widening distally, with two simple setae. Carpus less than one-third as long as basis, with three distal setae. Propodus longer than carpus, with one ventro-distal seta and two dorsal spines. Dactylus and unguis combined as long as propodus and not fused.
Pereopods 2–3 (Fig. 3 B,C). As pereopod 1 except merus with only one seta.
Pereopod 4 (Fig. 3 D). Basis longer than the three succeeding articles combined, with three setulated setae. Ischium with two setae. Merus almost as long as carpus, widening distally, with two spiniform setae. Carpus shorter than half as long as basis, with one simple and three spiniform setae. Propodus longer than carpus, with two spiniform setae and blunt dorsal spine. Dactylus and unguis combined longer than propodus, not fused, and unguis with ventral serration.
Pereopod 5 (Fig. 3 E). As pereopod 4 except: ischium apparently with only one seta.
Pereopod 6 (Fig. 3 F). As pereopod 4 except: basis with only two setulate setae. Pleopods not present in females.
Uropod (Fig. 1 F). Marginally shorter than pleotelson. Basal article naked, about one third as long as endopod, exopodal spur reduced to little more than a blunt process with two setae. Endopod uniarticulated, fused with basal article, with one subdistal and two to four distal setae.
Description of the adult male (where different from female).
Body (Fig. 4 A, B). Pleon as wide as pereon and pleotelson.
Antennule (Fig. 4 C). Thicker than that of female. Article 1 shorter than rest of antennule. Article 4 longer than in female, with sharply decreasing width midlength.
Antenna (Fig. 4 D). Longer than that of female, with medial abrupt decrease in width.
Pereopods (Fig. 5 A–F). Except for the odd setae, the pereopods are identical to those of the female.
Pleopods (Fig. 5 G). All pairs subequal, rectangular and coalesced, with six or seven simple setae.
Remarks. Kudinova-Pasternak (1970) recorded the species Agathotanais splendidus and A. ingolfi from the Kamchatka Trench and as A. hadalis looks indeed very similar to A. ingolfi, it is likely that the records of A. ingolfi sensu Kudinova-Pasternak, 1970 refer to A. hadalis. However, this cannot be assured without access to the material collected by Kudinova-Pasternak (which is reported lost by Błażewicz-Paszkowycz pers. comm.). Agathotanais hadalis differs from the original A. ingolfi sensu Hansen, 1913 by the short, almost trapezoid pereonite 6; the inconspicuous pereonite 1, 2 & 6 corners and the two dorsal spines on pereopod 1– 3 propodus. Also the pereonites 1, 2 and 6 shoulders are less demarcated in A. hadalis than A. ingolfi.
It is established that an easy way to recognize the males of Agathotanais (and many other Tanaidomorpha) is by the presence of pleopods and thicker antennules (Lang 1971b; Bird & Holdich 1988; Larsen 1999b). One additional character seems to be that the male antennule distal article is subdivided by an abrupt decrease in width or even fusion-line. This character is not previously described but was somewhat illustrated by Lang (1971b:64,fig.4) and Bird & Holdich (1988:1599,fig.3a). The male antenna is about one-third longer than that of the female.
description: Published as part of Larsen, Kim, 2007, Family Agathotanaidae Lang, 1971 a *, pp. 41-60 in Zootaxa 1599 on pages 42-48, DOI: 10.5281/zenodo.178729