Neotanais micromopher Gardiner 1975

Neotanais micromopher

Neotanais americanus Beddard, 1886a: 118 [in part, specimen from North Atlantic only]; 1886b: 124 [in part, specimen from North Atlantic only].

DIAGNOSES.—Stages Other Than Copulatory Males: *Pereonites all noticeably wider than long and rectangular in shape from above. *Pleonites rounded or almost flat midventrally in lateral view. *Pleotelson fused to pleonite 5; *short, about twice as wide as long; *posterior margin slightly concave on either side. Carapace smooth dorsally, almost lacking in surface relief; a single anterolateral and a single posterolateral seta present. Cuticular surface largely covered by minute hairs, animals appearing pubescent under proper illumination. *Chela bearing very blunt or even flat-topped, irregular teeth distally on fixed finger; dactylus strongly curved compared to many species; dorsal propodal keel very low and short. Pereopods II–IV with a single, long, terminal propodal spine bearing relatively large and irregularly spaced teeth; pereopod VII totally lacking short, subterminal propodal spines. Dactylar spines of pereopods II–IV less than one-fourth length of dactylus and inserted subterminally.

Copulatory Males: *Pereonite 2 bearing very prominent lateral spurs anteriorly unlike any other known species of Neotanais; pereonites 3–7 wider than long and gradually rounded anterolaterally. Pleonites wider than pereonite 7; epimeres expanded and angular laterally, sternites rounded midventrally or slightly flattened anteriorly in lateral view. Pleotelson: As in other stages but not posteriorly concave. *Chelipedal carpus: Slender, strongly curved, and bearing at least 3 or 4 very short dorsal setae and 1 or 2 slender ventral setae far forward on article. Both types of chelae (A and B) with fine dorsal crenations or scales and a slight depression on propodal keel. *Chela of primary male (chela type A) dentition as in Figure 10A,B,D; *chela of secondary male (chela type B) dentition as in Figure 10C,E.

DESCRIPTION OF INTERMEDIATE (?) FEMALE HOLOTYPE (WHOI B. Sta. 64).—Body (Figures 2B, 3B): 7.6 mm long and 5.8 times longer than wide. Covered with very short, fine hairs (Figure 12A) of varying density giving animal a pubescent appearance under magnification.

Carapace (Figure 4A–C): 1.2 times longer than wide. Without significant dorsal surface sculpturing; anterolateral keels very slightly raised, oblique furrows shallow; respiratory chambers and chelipedal coxae not well developed laterally in dorsal view. Only 1 anterolateral and 1 posterolateral seta present. Rostrum very low, hardly developed at all, sides sloping toward ocular lobes only very slightly convex.

Pereonites: Appear considerably wider than long and generally rectangular in dorsal view. Pereonite 5, 1.4 times wider than long. Pereonite 2 not tapering evenly anteromedially but slightly angular anteriorly with very low anterolateral “shoulders” (Figure 5C).

Pleonites (Figures 3B, 4A,H, 5A, 6A): Pleonite 1 slightly narrower than pereonite 7 (see copulatory male) but slightly wider than pleonite 5, giving pleon a slightly tapered appearance. Epimeres almost evenly rounded laterally in dorsal view. Sternites slightly flattened but almost evenly rounded midventrally in lateral view.

Pleotelson (Figures 3A, 5A,H, 6A): Short, considerably wider than long, width-length ratio, 2.0; posterior edges noticeably concave on either side in dorsal view; *fused to pleonite 5, with fusion most distinct ventrally.

First Antenna (Figure 5J; see also Figure 6C): Article 1, 3.8 times longer than wide.

Second Antenna: As in Figure 6D.

Labrum: As in Figure 6C.

Right Mandible (Figure 7A): Incisive spines 1 and 2 both serrate along each side, the second spine along the outer one-third only; third spine serrate at tip.

Left Mandible (Figure 7B): Incisive spines as on right side. Lacinia mobilis with 3 sharply acute teeth; posterior lobe partially cleft.

Labium: As in Figure 7E.

First Maxilla: As in Figure 7C.

Second Maxilla (Figure 8D): Medial setal row with 11 slender, heavily setulated setae with stout bases. The single spine next to this row with or without terminal setules.

Maxilliped (Figure 9A,B): Setal formula of palp, (0,0,5+1,7,14).

Epignath: As in Figure 9H.

Cheliped (Figure 9J,K): Carpus bearing about 9 dorsal setae of moderate length. Propodus with low dorsal keel; fixed finger bearing about 15 small, rounded, brown denticles proximally and about 5 large, brown, very irregular, and relatively flat-topped teeth distally. Dactylus with about 7 low, variable, brown teeth with sharp points along cutting edge, the most proximal tooth being much shorter and more perpendicular to the dactylus than the others; dactylus strongly curved.

Pereopods II–IV (Figure 12A–C,G): Short, terminal propodal spine only slightly curved and bearing 4 to 7 stout teeth. Short, straight, stout, subterminal carpal spine bearing numerous fine teeth. Long, terminal propodal spine single, with relatively large, irregular teeth, and present on pereopod II only. Setal formula (5,4,5,4), (6,7,3,6), and (7,7,3,6), respectively. Dactylar spine very short, only about 0.2 times the length of dactylus, inserted subterminally on dactylus, and tip tapering relatively abruptly.

Pereopods V–VII (Figure 12D–F): Short, subterminal propodal spines of pereopod VII absent. Setal formulae (6,6,5,6), (6,6,5,6), and (5,6,3,4), respectively. Dactyli of all bearing large terminal teeth.

Pleopods (Figure 10L): Terminal endopodal setal row distinct from lateral setae. Setal formula (0,0) (3,8,3) (0,1;0,10,1).

Uropods (Figure 6A): With 9 endopodal articles on each side.

DESCRIPTION OF SECONDARY COPULATORY MALE ALLOTYPE (male AP from WHOI B. Sta. 64).—Body (Figures 2A, 3A): 8.1 mm long and 5.9 times longer than wide.

Carapace: 1.4 times longer than wide. Narrower anteriorly than in other stages, giving appearance of being more elongated. Respiratory chambers moderately, and chelipedal coxae strongly, expanded laterally. Rostrum strongly pointed, much more so than in other stages, and with sides markedly concave. Oblique furrows moderately deep. An inverted U-shaped line connects posteromedial angles of chelipedal coxae. Height of carapace proportionately shallower anteriorly than in female, probably due to rudimentary nature of the mouthparts (Figure 4E). Anterolateral keels small and difficult to see in dorsal view; 1 anterolateral and 1 posterolateral seta present.




Pereonites: Although wider than long as in other stages, decidedly not quadrangular; pereonites 3–7 gradually rounded anteriorly on each side, areas over pereopods widest. Anterior margin of pereonite 2 straight on each side and prolonged laterally into prominent, acutely angled “shoulders.”

Pleonites (Figures 3A, 5B,I, 6B): Pleonite 1 considerably wider than pereonite 7 and somewhat wider than pleonite 5. Pleonite 5 considerably wider than pleotelson. Epimeres markedly angular and somewhat tapered laterally in dorsal view. Sternites rounded or slightly anteriorly flattened midventrally in lateral view.

Pleotelson (Figures 3A, 5B,I, 6B): Short, similar to that of other stages; 1.7 times wider than long. Posterior margin convex rather than concave as in other stages. Ventral surface bearing a raised, horseshoe-shaped protuberance below anal fusion.

First Antenna (Figure 6E): Article 1, 5.6 times longer than wide.

Second Antenna: As in Figure 3F.

Labrum (Figures 4D,E, 7F): Without hairs.

Mandibles (Figures 4D,E, 7F, 8A–C): Both similar in form; strongly reduced. Fused with carapace dorsally and posteriorly. Pars incisiva remains as small ventromedial protuberance. Pars molaris absent.

Labium (Figure 7F): Very flat, apparently more so than in other stages. Although strongly reduced, all 3 lobes clearly recognizable.

Second Maxilla (Figure 8E–G): Strongly reduced; a few irregular and variable hairs, spines, and knobs present.

Maxilliped (Figure 9D,E): Coxa fused to basis. Coxa and basis, including endite, without setae. Setal formula of palp, (1,0,1+1,0,12).

Cheliped (Figures 2A, 3A, 10C,E): Carpus slender, strongly but gradually curved; with at least 3 or 4 short dorsal setae centrally and 1 or 2 moderately long, slender ventral setae distally. Chela (type B): Dorsal surface of propodus finely crenate in lateral view or slightly scaly in dorsal view. A very slight dorsal depression centrally located on propodal crest (characteristic of all copulatory males of this species). Fixed finger with 1 low tooth about midway along its length. Dactylus with a low rise just proximal to a large, distally directed tooth with slightly expanded flat tip; tooth located about midway along dactylus. Dactylus strongly medially directed (in Figure 10C both fingers are drawn in the same plane, hence dactylus appears much longer—its true length—than in life).

Pereopods II–VII (Figure 13A–G): Anterior propodal setae of pereopods II–IV moderately slender and bearing numerous fine setules. Setal formulae of pereopods II–IV, (5,4,5,4), (7,7,3,5), and (7,8,3,5). Long, terminal propodal spine single, present on pereopods II–IV (cf. holotype), and bearing 15 to 20 moderately large, irregular teeth on one side and about 3 such teeth on the other. Short, terminal propodal spine of pereopods II–IV slender, practically straight, and bearing very fine teeth or setules. Short, subterminal carpal spine of pereopod II stout and almost straight. Short, subterminal propodal spines of pereopod VII absent as in other stages.

Pleopods (Figure 10M): Setal formula, (0,0) (3,11,5) (0,2;0,9,5).

Uropods (Figure 6B): With 9 endopodal articles on each side.

INTRASPECIFIC VARIATION.—Neotanais micromopher provided the basis for a detailed study of intraspecific variation in the genus Neotanais. The differences among many individuals are discussed at length below (p. 175); however, a description of chela type A of primary copulatory males is given here for purposes of identification. (Body lengths of individuals at WHOI Benthic Stations 64 and 76 are listed in Tables 16 and 17). Chela Type A (primary copulatory males; Figure 10A,B,D): Similar to chela type B, but one large tooth present on fixed finger. One small to moderately large, proximal tooth and one large, more distally located tooth on dactylus. Dactylus more or less parallel to fixed finger in lateral view although directed outward in dorsal view (chela in Figure 10D tipped to right, hence minimizing the latter angle).

Male AQ (body length, 7.6 mm) from Sta. 64 has a normal type A chela on the left side. But the dactylus on the right side bears a flat-tipped, distally directed tooth (Figure 11A) similar to that of a secondary male. However, the tooth is short and the overall length of the dactylus relative to the fixed finger is similar to that of the left side. The two low protuberances proximal to the large dactylar tooth are more distinct than those on primary males (cf. Figure 10A,B).

A male (body length, 7.0 mm) from WHOI B. Sta. 66 is very similar in all respects, but the two proximal dactylar protuberances are even more distinct and both chelae have the same aberrant form. A third specimen (body length, 8.4 mm), from Noratlante Sta. 019, has chelae in which the fixed finger resembles that of a primary male (Figure 10A) and the dactylus that of the secondary male in all respects (Figure 10C). The significance of these unusual males is discussed under “Development”

A single individual, a manca 2, has been collected from eastern Atlantic waters (Noratlante Sta. 111, B016). This specimen (body length, 3.5 mm) is identical with western Atlantic specimens except for a somewhat convex posterior pleotelsonal border in dorsal view. This difference is not unreasonable, however, since the animal is very young, and this much variation has been observed over long distances in other species. This animal was also found at a depth (4729 m) considerably greater than the deepest western Atlantic collection (3828 m) of this species.

DISTRIBUTION.—Neotanais micromopher has been collected in the western North Atlantic from the Greenland area to the Cape Hatteras, North Carolina, region at depths of about 2270 to 3830 m. A single collection has been made in the eastern Atlantic—in the Bay of Biscay, at 4729 m.

MATERIAL.—See Table 2.

LOCATION OF MATERIAL.—NMNH: holotype (USNM 143132); allotype (USNM 143133); WHOI 64 developmental series including MI (CL, CM), M2 (CF, CG), Juv (BD, BG, BL, BX), P 1 (E, BH), P 2 (B, D), ?I (C), Cop (AB, BA), P (AA, AD), 1°Cop (AV, AQ), 2°Cop (AR, AS, AT) (USNM 143134); Albatross 2221 (USNM 43234); Albatross 2570 (USNM 141450); CMS 2072 (USNM 143135); CMS 2073 (USNM 143136); CMS 2118 (USNM 143137); CMS 2125 (USNM 143138); 2144 (USNM 143139); CMS 2145 (USNM 143140); CMS 2154 (USNM 143141); CMS 2164 (USNM 143142); CMS 2188 (USNM 143143); Noratlante 019, E003 (USNM 143145); Noratlante 042, E006 (USNM 143144); Noratlante 111, B016 (USNM 143146). BMNH: Challenger 45 (Reg. No. 1889.4. 2′/107, microslide). UCZM: Ingolf 22; WHOI 66; WHOI 72.

DERIVATION OF NAME.—Referring to the anterolateral spurs borne on pereonite 2 of the copulatory males. From the Greek mikros (little), omos (shoulder), and phero (to bear).