Comprehensive Description

provided by Smithsonian Contributions to Zoology
Neotanais americanus Beddard, 1886

Neotanais americanus Beddard, 1886a: 118 [in part, South American specimen only]; 1886b:124, pl. 26: figs. 4–6 [in part, South American specimen only].

Neotanais serratispinosus Norman and Stebbing.—Hansen, 1913:18, pl. 1: figs. 6a,b; pl. 2: figs. 1a–c [in part, only manca 2 and copulatory female].

Neotanais serratispinosus (Norman and Stebbing).—Lang, 1956b:469, figs. Al–14 [in part, female only].

Alaotanais serratispinosus Norman and Stebbing, 1886:111, pl. 2S: fig. 1 [in part, specimen from Valorous Sta. 15 only].

DIAGNOSES (Atlantic populations only; see section on Pacific specimen under intraspecific variation below).—Stages Other Than Copulatory Male: *Pereonites 4–6 almost square in dorsal view (depending on degree to which animal is stretched), with areas of pereopodal attachment sometimes being visible from above. *Pleotelson short, about twice as wide as long, border slightly convex on either side posterior to uropods (in marked contrast to Neotanais micromopher. *Pleonites with low, posteriorly directed, and often rounded midventral spurs in lateral view; rounded laterally in dorsal view and bearing occasional short hairs laterally on epimeres. Cheliped with about 10 dorsal carpal setae; *propodus with substantial dorsal crest; the distal teeth generally rounded (cf. teeth in Neotanais micromopher); dactylus with about 3 brownish convexities or teeth pointed to various degrees. *Carapace with few prominent features: anterolateral keels, oblique furrows, respiratory chambers, and chelipedal coxae in dorsal view insignificantly developed; I or 2 short anterolateral and posterolateral setae present. Propodal and carpal setae of pereopods II–VII strongly developed and spinelike, at least those of pereopods II–IV with easily visible teeth; dactyli of pereopods II– IV often bearing slender distal teeth ventrally (in North Atlantic populations) similar to those of pereopods V–VII, the only instance of such serration known in the Neotanaidae (teeth sometimes invisible from certain angles); long, terminal propodal spines of pereopods II–IV very often with fewer widely spaced teeth than in other species; *short, terminal propodal spine of same legs with curved tip and 4 to 6 large, triangular teeth borne almost at right angles to axis of spine; *short, subterminal carpal spine of pereopod II almost straight and bearing 4 or 5 teeth of moderate size.

Copulatory Males (Gay Head-Bermuda Transect): *Pereonites 4–6 sloping gradually anteromedially from area of pereopodal coxae in dorsal view. *Pleonites rounded laterally with sides sloping forward from epimeres more gradually anteriorly than posteriorly as seen from above; *sternal spurs more pronounced midventrally than in other stages and slightly less posteriorly directed. *Carapace bearing relatively sharp rostrum, very distinct oblique furrows, and a series of other furrows (see Figure 17E); *chelipedal coxae prominent, anterior sides not quite parallel; number of setae on carapace and *shape of pleotelson shared with other stages. *Chelipedal carpi strongly bent but heavy, those of males with chela type B having a pronounced posterior hook at bend; bearing about 10 dorsal setae; *posterior ventral carpal seta thin and posteriorly directed, anterior seta straighter and thick, brown, and with broad base. Chela type A (primary male) with *dorsal keel of propodus thin and frayed along its distal half; *both fingers moderately bent medially; *dentition as in Figure 19E. Chela type B (secondary male) as in type A except *fixed finger strongly bent medially and *dentition as in Figure 19F.

DESCRIPTION OF PREPARATORY FEMALE 2 A (WHOI B. Sta. 76).—Body (Figure 17E): 6.9 mm long and 6.5 times longer than wide.

Carapace: Smooth, devoid of appreciable relief dorsally, lateral keels not flared dorsally, and oblique furrows faint. Anterolateral setae not observed (see “Intraspecific Variation,” below); 2 posterolateral setae present on each side.

Pereonites: Appearing relatively square in dorsal view (many specimens appear much more nearly square than shown in Figure 17E); attachments of pereopods barely visible dorsally (see “Intraspecific Variation,” below); bearing only occasional very short hairs laterally. Sternites with faint ridge midventrally.

Pleonites (Figures 17A, 18A): Rounded laterally in dorsal view; width of pleonites decreasing anteroposteriorly, giving slightly tapered appearance to pleon in dorsal view; short, scattered, epimeral hairs present dorsally. Sternites each gradually sloping downward posteriorly (in lateral view), forming very low spurs.

Pleotelson (Figure 17H): Considerably wider than long, width-length ratio, 2.0.

First Antenna: First article 3.7 times longer than wide.

Right Mandible (see Figures 17I,J; 18A): First 2 incisive spines serrate on both sides, third spine with “comb” of teeth distally.

Left Mandible (Figure 18B): Incisive spines as in right mandible. Lacinia mobilis with 3 large, pointed teeth; posterior lobe uncleft.

First Maxilla: As in Figure 18C.

Second Maxilla: Forked spines on fixed endite bifid. Twelve setae present in medial row along with 2 stout spines.

Maxilliped: 6 setae on coxa. Setal formula of palp, (1,0,6+1,4+4,8).

Cheliped (Figures 18I, 19A): Carpus bearing 10 long dorsal setae. Propodal crest of appreciable size. Fixed finger bearing about 30 denticles anteriorly on cutting edge; distal teeth rounded and brown. Setae on chela long and thick. Dactylus with only 3 low, brown swellings proximally on cutting edge. Dactylar seta long and thick.

Pereopod II (Figure 20A,B): Setae generally low in number and large in size, anterior setae of propodus and carpus spinelike. Setal formula, (3,3,7,4). Short, terminal propodal spine strongly curved distally and bearing 4 or 5 heavy, triangular teeth oriented at right angles to axis of spine. Two long, terminal propodal spines with teeth large and scattered along spine. First (distal) seta in anterior propodal row long, heavy, spinelike, and bearing sizable teeth; remaining setae with somewhat smaller teeth. Short, subterminal carpal spine straight, thick, and with about 4 irregular teeth on either side. First seta in anterior row especially thick and dentate. Dactylus bearing slender teeth or setules on either side distally and ventrally; spine 0.4 times as long as article.

Pereopods III–VII: Pereopods III and IV also with 2 long, terminal propodal spines identical to those of pereopod II. Setae of pereopods V–VII also thick. Setal formula of pereopod V, (6,4,5,7). Row of short, subterminal propodal spines on pereopod VII not observed in this specimen; 2 other specimens (same stage) from this station with 5 and 7 spines; dentition of these spines similar to those of most species.

Pleopods (Figure 20J): Setal formula, (1,3) (3,5,5) (0,2;0,8,2). Protopodal setae short and slender.

Uropods (Figure 20I): Endopods slender; exopods 0.9 times length of first endopodal article.

DESCRIPTION OF SECONDARY COPULATORY MALE A (WHOI B. Sta. 76).—Body (Figure 17E): 5.9 mm long and 6.0 times longer than wide.

Carapace: 1.6 times longer than wide. Rostral area acute, anterolateral keels moderately developed; oblique furrows deep and proceeding posteriorly to a deep transverse furrow; 2 short furrows extending lateral to transverse furrow on either side. Anterolateral setae 1 and 2 in number on either side; posterolateral setae of similar number but of greater length.

Pereonites: 3–7 narrow anteriorly, sloping gradually anteromedially anterior to pereopods and sloping abruptly posteriorly to legs. Genital cones prominent.

Pleonites (Figures 17E, 18H): Rounded laterally in dorsal view. Pleonite 1 wider than pleonite 5, giving pleon a slightly tapered appearance. Dorsal epimeral hairs scattered, single, and short. Sternites expanded into bluntly tipped midventral spurs considerably longer than those of other stages.

Pleotelson (Figure 17F): 1.9 times wider than long in dorsal view. Anal area distorted. Ventral surface with median angularity.

First Antenna: First article 5.2 times longer than wide.

Mandibles: Incisive tips elongate, pressed closely to labrum, and with rudimentary incisive spines.

Second Maxilla: Bearing prominent setulated setae representing movable endite and 2 or 3 groups of smaller and irregular setae.

Maxilliped: Four setae on coxa; setal formula, (0,0,0,10,9).

Cheliped (Figures 19F,H): Carpus strongly bent (right angle) with a slight posterior convexity just below bend; proximal ventral seta weak and recurved, distal seta strong, brown, and with expanded base; about 8 to 10 dorsal setae present (broken in this specimen). Dorsal keel of propodus thin and with irregularly serrate edge. Median propodal seta stout and brown. Fixed finger strongly medially bent. Most proximal tooth flat-topped, wide, and followed by about 5 variously shaped blunt teeth, the last of which is taller and leans distally. Setae as in Figure 19F. Dactylus relatively straight in dorsal view; proximal teeth 2 in number and moderate in size. Distal tooth much larger, triangular, and strongly medially bent; medial seta weak. Surface of dactylus “beaded” lightly in places.

Pereopods II–VII (Figure 20G,H): Pereopod II similar to that of female but setae not as stout; setal formula, (3,4,6,2). Long, terminal propodal spines 2 in number and with sharp, fine, tightly packed teeth. Short spines on both propodus and carpus different from those of other stages: short, terminal propodal spine of pereopods II–IV slender, straight, and with a row of many, moderately sized teeth along one entire side; short, subterminal carpal spine of pereopod II also straight and with similar teeth along distal two-thirds of spine only. Dactylus of pereopods II–IV without distal serrations (cf. other stages). Pereopod VII with 3 exceedingly short, thin, rudimentary spines distally on propodus (remnant of short, subterminal spine row of other stages).

Pleopods: Setal formula, (2,1?) (3,7,5) (0,2;0,7,3). Terminal endopodal setae 1.6 times longer than endopod.

Uropods: With 9 endopodal articles (one side only, other broken). First endopodal article bearing a number (about 15) of broom setae on dorsolateral side (not figured).

INTRASPECIFIC VARIATION IN THE NORTH ATLANTIC.—Stages Other Than Copulatory Male: a. Specimens from Gay Head-Bermuda Transect (WHOI B. Sta. 64): Representative body lengths (numbers of individuals considered are in parentheses): manca 1 (1), 2.3 mm; juvenile (9), 3.5 to 6.2 mm; preparatory female 2 (8), 5.8 to 6.6 mm; copulatory female (10), 6.3 to 7.9 mm; preparatory male (1), 6.7 mm. The anterolateral and posterolateral setae on the carapace both vary between one and two. Some animals have a few heavily toothed spines on the external endite of the first maxilla (Figure 18D). The number of spines (8) as found on female A described above is aberrant (Figure 18C); other individuals have 10. The denticles on the propodal finger of the cheliped vary considerably in height (Figure 19A,B,D); the teeth on the dactylus often are anteriorly directed, pointed, and of variable number (Figure 19A–D). The dactyli of pereopods II–IV sometimes lack setules. The long, terminal propodal spines of these legs sometimes have more closely packed teeth than those of female A (Figure 20E). There is some indication that lack of dactylar setules and the presence of more closely packed teeth may be common at deeper stations.

b. Copulatory Female from Ingolf Sta. 22, Davis Strait: The length is 6.7 mm. The midventral points of the pleonites are more blunt than those of other specimens. All significant features, however, are similar to female A described above. The Noratlante specimens from the same general area lack the dactylar setules on pereopods II–IV.

c. Juvenile from Valorous Sta. 15, Southeast of Greenland: This animal was one of three specimens on which Norman and Stebbing (1886) erected Neotanais serratispinosus. It is the one illustrated in their plate 23 and apparently it was used as the basis of their written description. It agrees with female A down to the smaller details such as the presence of distal serrations on the dactyli of pereopods II–IV. Its body length is 4.2 mm. See “Remarks,” below.

d. Preparatory Female from the Bay of Biscay: This preparatory female (length 7.2 mm) almost perfectly resembled the described female from the Gay Head-Bermuda Transect in all details including carapace setation; shapes of carapace, pereonites, pleonites, and pleotelson; and dentition of the long and short specialized spines and the dactyli of pereopods II–IV. It differed in having two small feathered hairs on each pleonal epimere.

e. Specimens from the Canary Islands: Two specimens were collected by the Discovery in the vicinity of the Canary Islands. These have been assigned to Neotanais americanus because they resemble this species more closely than others. It is difficult to say much about the manca 1 (body length, 4.5 mm). The juvenile (body length, 7.2 mm) differs from the holotype (off Uruguay) in having more pronounced spurs midventrally on the pleon, similar to the North American animals. It differs from most North American specimens in lacking dactylar serrations on pereopods II–IV, and the proportions of the pleotelson more nearly resemble those of the South American holotype. The body lengths of both specimens are longer than for equivalent stages of North American populations. The long, terminal propodal spines of pereopods II–IV have small and more numerous teeth that are set more closely together than in other populations examined. The setal formula of pereopod II is (1,4,3,3). The short, terminal propodal spine of pereopod II bears only a couple of pointed teeth on each side. The carapace bears a single anterolateral seta and a single posterolateral seta. The penultimate dorsal seta on the chelipedal carpus is much longer than the other setae in this row. The depths at which these animals were collected are within the range in which one would expect to find Neotanais americanus.

Copulatory Males: Representative Body Lengths (WHOI B. Sta. 64; numbers of individuals considered are in parentheses): Primary copulatory male (3), 5.7 to 7.2 mm; secondary copulatory male (4), 7.7 to 8.6 mm.

Cheliped Type A (primary male B, WHOI B. Sta. 76): The carpus is similar to that of animals with chela type B but lacks the posterior convexity below the proximal bend. The fixed finger is strongly bent medially and bears two moderate teeth proximally, the first of which is medially directed, and one high, narrow tooth distally following two low convexities. The dactylus bears two prominent teeth: the proximal tooth is narrow and round-tipped, the distal tooth triangular and bluntly tipped.

Cheliped Type B: The posterior convexity of the carpus is often more prominent than in the described male (e.g., Figure 19K). The fixed finger always has a broad proximal tooth separated from the other teeth by a gap, but the other teeth vary in shape and in size. The proximal dactylar teeth are sometimes fused (Figure 19I) and usually are two in number but occasionally there are three (Figure 19J).

Carapace: The posterolateral setae are notably longer and heavier in some specimens than in the described male (e.g., WHOI B. Sta. 80 and Eastward Sta. 5474 from deep water).

Pereopods II–IV: Dactylar setae are sometimes present as in the other stages at WHOI B. Sta. 76.

INTRASPECIFIC VARIATION IN THE SOUTH ATLANTIC.—Juvenile Holotype from Challenger Sta. 323: The length of this specimen is 6.1 mm. Several figures of this specimen, inadequately illustrated by Beddard (1886b), are presented here. The pereonites are not as square in dorsal view as in female A (described above), but the variation is not appreciably greater than that among the other animals from WHOI B. Sta. 76 (cf. Figure 17A–C). Pereonite 2 has a more marked anterior depression than female A. The pleonal hairs are longer but this condition was also observed on the Ingolf specimen from the Davis Strait. The pleotelson is only 1.6 times wider than long. The pleonal sternites are blunt medially, but this also was noted in the Ingolf specimen from the North Atlantic (Figure 18F).

The tip of the most distal incisive spine on the right maxilla is cleft only once (Figure 17K). In the Antarctic specimen from IWSOE Sta. 44 (see under specimen from Weddell Sea, below), which in all other respects is identical with the holotype, this spine is serrate terminally, similar to the North Atlantic specimens; however, the animals from the Argentine Basin (Vema 17–81) are closer to the holotype in this feature than to North Atlantic specimens or to the Antarctic specimen (Figure 17L–N).

The chela is like that of the North Atlantic populations (Figure 19B), as is peropod 11 (Figure 20F), except that the dactylar spines on some legs are longer. The dactylus is without serration distally and the teeth on the long, terminal propodal spines are not widely spaced. The pleopodal setal formula is (2,2) (2,3,4) (0,2;0,4,2). The shape of the pleopods is like that of female A, described above.

Specimens from Argentine Basin: Four additional specimens are known from Vema 17–81 at 5330 m. They agree with the Challenger holotype in almost all characters. The third right incisive mandibular spine of the three oldest specimens were compared (Figure 17L–N) and found to be consistently similar to that of the holotype but unlike the North Atlantic and Weddell Sea specimens. There are two or three anterolateral setae and two posterolateral setae on the carapace of these animals.

The specimens include a preparatory female 1 with faint male gonopore anlagen, a manca 1, and an animal with no secondary sexual characters except very faint gonopore anlagen and a length almost as great as that of the preparatory female 1.

Specimens from Weddell Sea, Antarctica: The specimens from IWSOE Sta. 0008 resemble the holotype in the midventral shape of the pleonal sternites (lateral view) and in the shape of the pleotelson (dorsal view). Pereonites 4–6 are notably square in dorsal view, and each of the pleonal epimeres bears one or two feathered setae. The setal formula of pereopod II of the copulatory female is (5,5,6,7), with the short, terminal propodal spine bearing three large, slightly forwardly directed teeth; the two long terminal spines have slender teeth. There are 12 short, subterminal propodal spines on pereopod VII. The carapace bears a single long anterolateral and posterolateral seta on each side.

The third incisive spine of the right mandible is serrate terminally in the juvenile at IWSOE Sta. 44 as in North Atlantic populations. That of the copulatory female from IWSOE Sta. 0008 is similar terminally but also has serrations similar to those of the other incisive spines along the outer third of the inner side.

The specimen from IWSOE Sta. 0019 has two long anterolateral and three posterolateral setae on its carapace. The areas over the pereopods on the pereonites are wider than in the other specimens, and the pereonites bear long, lateral hairs. This specimen has feathered pleonal hairs as do the others. Whether it belongs to the same species as the other specimens is not clear. More material will be required to determine its relationships clearly.

INTRASPECIFIC VARIATION IN THE PACIFIC.—Preparatory Female 2 from Anton Bruun Sta. 179 (4823 to 4925 m), off Peru: This animal resembles Neotanais americanus from the Gay Head–Bermuda Transect in the following ways: (1) pereonite shape in dorsal view; (2) carapace shape; (3) shape of chela; (4) third incisive spine of right mandible with same serrations distally (Figure 17O); (5) pereopod II with 2 long, terminal propodal spines and the teeth loosely spaced; (6) short, terminal propodal spine with 3 or 4 large, triangular teeth; (7) short, subterminal carpal spine similar (if with only 2 or 3 somewhat smaller teeth); (8) 1 dactylus apparently bearing a few setules distally, but cuticle blistered and difficult to determine this precisely.

The following differences from the North Atlantic specimens were observed: (1) the midventral silhouette of the pleonites is much smoother (but not round—Figure 18G); (2) the pleonites bear feathered setae laterally (Figure 17D); (3) the distalmost setae in the anterior rows of pereopods II–IV are not as thick or the setules as long; and (4) the dactylar spines on pereopods II–IV sometimes are considerably longer and more tapered distally.

These differences, especially the first three, may be significant; however, in light of the large number of similarities to North Atlantic populations, this specimen is assigned to Neotanais americanus. Unfortunately, the pleotelson and uropods are missing.

DISTRIBUTION.—Neotanais americanus has been found from Greenland to the Antarctic in the western Atlantic and from the Bay of Biscay and Canary Islands in the eastern Atlantic. On the Gay Head– Bermuda Transect it is a deepwater species, having been collected from about 2800 to 5020 m. In the Antarctic, at IWSOE Stas. 0001 and 0008, it has been found in depths as shallow as 513 m. One specimen collected off Peru has been assigned to this species.
bibliographic citation
Gardiner, Lion F. 1975. "The systematics, postmarsupial development, and ecology of the deep-sea family Neotanaidae (Crustacea: Tanaidacea)." Smithsonian Contributions to Zoology. 1-265. https://doi.org/10.5479/si.00810282.170