Pliotrema annae Weigmann, Gon, Leeney & Temple, 2020

Weigmann, Simon, Gon, Ofer, Leeney, Ruth H., Barrowclift, Ellen, Berggren, Per, Jiddawi, Narriman & Temple, Andrew J., 2020, Revision of the sixgill sawsharks, genus Pliotrema (Chondrichthyes, Pristiophoriformes), with descriptions of two new species and a redescription of P. warreni Regan, PLOS ONE 15 (3), pp. 1-56 : 19-38

publication ID 10.1371/journal.pone.0228791

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Pliotrema annae Weigmann, Gon, Leeney & Temple

sp. nov.

Pliotrema annae Weigmann, Gon, Leeney & Temple sp. nov. .

Proposed English vernacular name: Anna's sixgill sawshark.

Proposed German vernacular name: Annas Sechskiemer-Sägehai.

Local name: Papa Unguja.

Figs 15–25 View Fig 15 View Fig 16 View Fig 17 View Fig 18 View Fig 19 View Fig 20 View Fig 21 View Fig 22 View Fig 23 View Fig 24 View Fig 25 ; Table 3.

Pliotrema warreni: Gubanov View in CoL [ 28]: 221 (in part)?

The holotype and paratype are deposited in the Zoological Museum Hamburg ( ZMH).

Holotype ZMH 26361 , presumably adult female, 981 mm TL fresh, caught on or near Kobela Reef (~ 6º29'35”S 39º22'21”E) in Menai Bay, Unguja Island, Zanzibar, in a demersal longline at ~ 20–25 m (i.e. set depth of the gear; water depth unknown but probably only 2–5 m deeper than this), haul time ~8 am, time of catch unknown but likely during hours of darkness, date 07 March 2019. GoogleMaps

Paratype ZMH 26362, presumably adult female, 980 mm TL fresh, 950 mm TL 70% ethanol preserved, caught off Zanzibar in a longline at ~ 25–35 m depth during hours of darkness, landed on 24 Feb 2017 in Kizimkazi-Dimbani, Zanzibar (two further specimens were landed at the same place but not retained on 23 Jan 2017: gravid female, ~ 980 mm TL, with six eggs and on 25 Jan 2017: female with saw cut off, ~ 580 mm to beginning of saw; both these specimens were also caught in a longline at ~ 25–35 m depth during hours of darkness). Measurements taken from the fresh photographs of the not retained gravid female show that this specimen can be assigned to P. annae sp. nov. based on the main morphometric characteristics, particularly the generally shorter snout.

Diagnosis. A medium-sized six-gilled sawshark with the following characters: barbel origin to anterior nostrils 1.9–2.0 times anterior nostrils to symphysis upper jaw; prenarial length 1.6–1.7 times prebarbel length; preoral length 1.5–1.7 times interdorsal space; pectoral-fin anterior margin 1.4–1.5 times dorsal–caudal space; mouth width 2.7–3.2 times spiracle length. First dorsal fin originates about opposite pectoral-fin free rear tips. Lateral trunk dermal denticles tricuspidate, rather flat and imbricated. Color uniform medium to dark brown dorsally without longitudinal stripes; white ventrally but with few indistinct dark blotches on belly; fins with pronounced white posterior fin margins, particularly caudal and pectoral fins; dorsal rostrum surface with two distinct longitudinal dark stripes, lateral rostral teeth dark-edged. Monospondylous centra 53–54; precaudal diplospondylous centra 46–49; total vertebral centra 154. Pliotrema annae is distinguished from its two congeners by a combination of characteristics, including a generally shorter snout, with head length 34.2–34.5% TL, preorbital length 21.7–22.0% TL, preoral length 24.6–25.1% TL, prebarbel length 12.6–12.7% TL, and barbel origin to symphysis upper jaw 12.1–12.3% TL. Pliotrema annae further differs from its two congeners in lower total large lateral rostral tooth and ventral rostral spine counts, and a rostrum that is slightly constricted between barbel origin and nostrils. Like in P. kajae , the barbels are situated about half way from rostral tip to mouth, with prebarbel length about equidistant from barbel origin to symphysis of upper jaw. In contrast, the barbels are situated about two thirds way from rostral tip to mouth, with prebarbel length about twice distance from barbel origin to symphysis of upper jaw in P. warreni .

Description of the holotype. Values of the paratype are presented in parentheses, more complex differences between holotype and paratype are described separately. Where relevant, ratios are based on horizontal measurements unless otherwise stated. Morphometric measurements and meristics are given in Table 3.

External morphology. Body firm and slender, depressed forward of gills, abdomen subcircular in cross-section, tail subtriangular in cross-section, deepest at abdomen; not tapering gradually and evenly beyond pectoral fins; snout flattened, greatly extended, saw-like; abdomen elongate, horizontal head length 0.6 (0.6) times snout–anterior vent length, pectoral–pelvic space 19.0 (19.9)% TL; pelvic–caudal space 2.7 (2.7) times pelvic-fin length; tail flattened ventrally, elongate, snout–anterior vent length 1.3 (1.3) times anterior vent–caudal tip length; caudal peduncle short, dorsal–caudal space 9.1 (9.0)% TL, caudal peduncle height 4.9 (4.5) times in dorsal–caudal space and width 1.1 (1.1) times in height; ventrolateral keels well developed, extending from somewhat behind level of free rear tip of pelvic fins to beyond origin of ventral lobe of caudal fin, converging strongly near their posterior extremity; no precaudal pit; no median predorsal, postdorsal or preventral caudal grooves ( Figs 15 View Fig 15 and 16 View Fig 16 ).

Head narrow, subtriangular and deepest at sixth gill slit, strongly depressed above eyes, head width 6.4 (6.8)% TL, 1.1 (1.0) times head height. Snout forming a very elongate, bladelike rostrum. Rostrum triangular in dorsal view; slightly constricted between barbel origin and nostrils, sides of rostrum nearly straight from tip to barbel origin but slightly concave in posterior part from barbel origin to origin of orbit; tip narrowly rounded; rostrum extending laterally below eyes as a well-defined suborbital ridge along ventrolateral edge of head, terminating somewhat behind level of posterior edge of spiracle ( Fig 17 View Fig 17 ).

A slender, filamentous, dorsoventrally flattened barbel originating on the ventrolateral margin about half way from rostral tip to mouth on each side, with prebarbel length 1.0 (1.0) times distance from barbel origin to symphysis of upper jaw, 51.1 (50.7)% of preoral length and 12.6 (12.7)% TL. Barbel length 2.2 (2.3) times in prebarbel length and 2.1 (2.2) times in length from barbel origin to symphysis of upper jaw. Preorbital length, horizontally 5.3 (5.1) times mouth width, 14.5 (16.4) times spiracle length, 2.1 (2.1) times first dorsal-fin length, 4.3 (4.3) times rostral width at anterior nostrils; extremely narrow in lateral view; preoral length 24.6 (25.1)% TL, 3.8 (3.7) times head width, 4.9 (4.9) times rostral width at anterior nostrils, 7.4 (7.4) times rostral width at origin of barbels, 2.0 (2.0) times prebarbel length, 1.2 (1.2) times prenarial length, and 1.5 (1.7) times interdorsal space ( Fig 17 View Fig 17 ).

Large lateral rostral teeth of prenarial portion of rostrum variable in length, curved, rather stout, serrated, longest near barbel origin and near apex of rostrum posterior to anteriormost two teeth; longest tooth immediately anterior to barbels only slightly shorter than spiracle length, length 1.0 (1.0)% TL and 0.8 (0.9) times first complete interspace anterior to barbels, width 0.2 (0.2)% TL; anteriormost tooth close to tip of rostrum medium-sized, followed by a tiny tooth and the first large tooth; large teeth shortest near nostrils, longest rostral tooth posterior to nostrils 0.4 (0.3)% TL; large teeth absent behind nostrils but interstitial-like teeth present, short to very short and closely set, partially directed almost ventrally, particularly near mouth. Interspaces between large rostral teeth rather regularly sized, about as long as adjacent teeth, with 0–3 (1–3) smaller, variable interstitial teeth. Rostral tooth counts mostly symmetrical between left and right hand sides; left side with 17 (17) large teeth, right side with 17 (16); anterior to barbels left side with 10 (11) large rostral teeth, right side with 10 (10), posterior to barbels left side with 7 (6) large rostral teeth, right side with 7 (6); anterior to nostrils left side with 15 (15) ventral spines, right side with 15 (15), anterior to barbel origin left side with 9 (10) ventral spines, right side with 9 (10); one enlarged ventral spine, distinctly larger than the other ventral spines, present just in front of each nostril. Large rostral teeth ( Fig 18a and 18b View Fig 18 ) with elongated crown and oval-shaped base, slightly bent to the rear and flattened towards the apex, forming anterior and posterior cutting edges at front and rear, the latter serrated by barbed hooks. Crown base with numerous short longitudinal ridges forming a pronounced transversal crest. Both, anterior and posterior faces of the root are curved outwards from the junction of crown and root towards the base of the root. The basal face shows a deep v-shaped median groove that is antero-posteriorly directed and has an oval-shaped cavity in the center. Large interstitial rostral teeth similar but with somewhat less pronounced serration. Small interstitial rostral teeth ( Fig 18c View Fig 18 ) with blade-shaped crown and without serration. Crown of ventral spines elongated cone-shaped with a pronounced transversal basal ridge, root with roundish and pedestal-like base.

Eyes lateral on head, moderately large, oval, length 2.8 (2.7)% TL; skeletal interorbital space 0.9 (0.9) times eye length, 9.0 (8.7) times in horizontal preorbital length; posterior eye notches and suborbital grooves present. Spiracles moderately large, length 1.5 (1.3)% TL and 0.5 (0.5) times eye length, left spiracle with 10 (11) folds, right one with 10 (11); spiracles strongly crescentic, oblique, directed posteroventrally from top to bottom, located just posterior to posterior eye notch, separated by a narrow but deep vertical groove along posterior margin of orbit, shorter than eye; upper edge below level of top of eye. Gill slits small, upright, weakly pleated, lateral on head, close to ventral surface, extending slightly onto ventral surface, subequal in length, sixth slit arches around pectoral-fin origin. Mouth moderately large, strongly inferior, broadly arched, symphysis about level with posterior edge of eye, width 4.1 (4.3)% TL and 1.6 (1.6) times in head width; upper labial furrows absent, lower furrows very short, 0.3 (0.3)% TL; corner of mouth partly concealed by lateral muscles of jaw ( Fig 19 View Fig 19 ). Teeth unicuspidate, in well-defined series, bases oval and flattened with short but pronounced, narrow median cusp near middle of jaw, no lateral cusps; cusps diminishing in height towards jaw angles, indistinct near jaw corners; about 4–5 series of functional teeth ( Fig 20 View Fig 20 ). Median cusp with labial face slightly convex and with both mesial and distal cutting edges weakly bent mesially and distally in occlusal view, respectively. The mesial and distal crown base parts somewhat curve apically. A pronounced and broad, irregularly shaped apron overlaps the junction of crown and root, building a notch at the junction with both mesial and distal crown base parts. Basal ornamentation, striae, reticulations and folds absent in both upper and lower jaw teeth. The lingual face of the cusp is strongly convex, a well-developed uvula is present at the central crown base. The mesial/distal latero-lingual crown faces curve strongly towards the apex of the crown, forming a sharp notch with the uvula. The root is anaulacorhizid and slightly arched without lobation. The outer surface of the root shows large basal foramina, which are mostly oval-shaped. The inner face of the root shows well-developed foramina along the crown-root junction at each side of the uvula. The basal face of the root is flat, partly showing some outer foramina.

Nostrils small, widely separated, subcircular; nostril width 0.7 (0.7)% TL, 4.7 (4.5) times in internarial width, 6.2 (6.5) times in mouth width, 7.7 (7.7) times in width of rostrum at nostrils; located distinctly forward of level of anterior margin of eye; distance from anterior nostrils to symphysis of upper jaw 1.3 (1.3) times internarial space, distance from barbel origin to anterior nostrils 7.9 (8.3)% TL. Anterior nasal flaps well developed, leaf-like, extended ventrally beyond nostrils; incurrent and excurrent apertures surrounded by pronounced marginal lobes; no nasoral or circumnarial grooves; no dermal lobes ( Fig 19 View Fig 19 ).

Lateral trunk dermal denticles densely set and overlapping, with flat, tricuspidate crowns ( Fig 21 View Fig 21 ). The lateral cusps are rather weakly pronounced but situated quite far anteriorly so that the median cusp is not much longer than the lateral cusps. The median ridge is strongly pronounced and reaches the tip of the median cusp. The lateral ridges are less pronounced and do not reach the tips of the lateral cusps. The surface of the denticles is only weakly structured by reticulations very close to base. Dermal denticles on rostrum fan-shaped, with an obtusely angled, weakly pronounced median cusp and no lateral cusps but with 6–7 strongly pronounced ridges ( Fig 18d–18f View Fig 18 ). The surface of the rostral dermal denticles is only weakly structured by reticulations very close to base.

Pectoral fins very large, anterior margin weakly convex, 13.4 (12.7)% TL and 1.9 (1.9) times inner margin; apex narrowly rounded; posterior margin weakly concave, directed across horizontal axis at about origin of first dorsal fin; inner margin convex and strongly notched basally; free rear tip angular ( Figs 17 View Fig 17 and 22a View Fig 22 ). Pelvic fins large, anterior margin almost straight to slightly convex, 7.1 (7.0)% TL, 1.6 (1.6) times in first dorsal-fin anterior margin, and 1.4 (1.4) times in second dorsal-fin anterior margin; apex narrowly rounded; posterior margin concave; inner margin weakly convex and slightly notched basally; free rear tip broadly rounded; origin distinctly posterior to level free tip of first dorsal fin and well forward of level second dorsal fin origin ( Fig 22a View Fig 22 ).

First dorsal fin broad, semifalcate, anterior margin slightly convex; apex narrowly rounded; posterior margin slanting posteroventrally, slightly convex distally, strongly concave in basal three quarters; inner margin straight, free rear tip narrowly pointed; origin about opposite pectoral-fin free rear tips; insertion and free rear tip clearly anterior to level pelvic-fin origins ( Fig 22a View Fig 22 ). Second dorsal fin somewhat smaller than first but of similar shape, anterior margin weakly convex, apex very narrowly rounded; posterior margin weakly convex distally, strongly concave near basal three quarters; inner margin straight, free rear tip narrowly pointed; origin clearly behind level pelvic insertions; interdorsal space 1.5 (1.4) times first dorsal-fin length, 1.8 (1.6) times dorsal–caudal space; second dorsal-fin inner margin 1.1 (1.1) times subterminal caudal-fin margin ( Fig 22b View Fig 22 ).

Caudal fin short, dorsal margin slightly convex, length 19.1 (19.8)% TL, 1.2 (1.1) times in pelvic–caudal space and 4.6 (5.0) times terminal caudal margin; lower post-ventral lobe absent, upper post-ventral margin slightly convex; terminal lobe well developed, caudal terminal margin slightly concave, apices angular ( Fig 22b View Fig 22 ). Ventral origin of caudal fin situated anteriorly due to low anterior fin ridge ( Fig 22b View Fig 22 ).

Cranium: four anterior-most basiventral cartilages laterally expanded, with curved, dorsally reflected margins. Chondrocranium and cranial nerves highly modified to accomodate the elongated rostrum. Foramen magnum surrounded by crescent-shaped occipital condyles.

Dorsal fenestra of the precerebral fossa spindle-shaped, elongate and long, notched anteriorly and posteriorly ( Fig 12b View Fig 12 ).

Skeletal meristics (from radiographs): monospondylous trunk vertebral centra: 53 (54); diplospondylous precaudal centra: 49 (46); total precaudal centra: 102 (100); caudal centra: 52 (54); total centra: 154 (154).

Coloration. Fresh, prior to preservation (types and unretained specimens, Figs 23 View Fig 23 , 24 View Fig 24 and 25 View Fig 25 ): color uniform medium to dark brown dorsally without longitudinal stripes, white ventrally but with few indistinct dark blotches on belly; fins translucent dusky but with white posterior fin margins, particularly pronounced at the posterior pectoral-fin margin and the upper post-ventral and terminal caudal-fin margins; rostrum translucent dusky, dark edged and with two distinct longitudinal stripes dorsally; lateral rostral teeth dark-edged; ventrolateral keels white. Color in preservative (type specimens, Fig 16 View Fig 16 ): coloration similar to fresh coloration, ventral ground coloration yellowish instead of white as usual but dark blotches still present, ventrolateral keels also yellowish; dark edging of rostrum and lateral rostral teeth, as well as longitudinal dorsal rostral stripes still conspicuous.

Size. A medium-sized sawshark species reaching about 981 mm TL. As one specimen of ~ 980 mm TL (not retained) contained six eggs, the holotype and paratype are presumably also adult.

Distribution. Known only from off Zanzibar in depths of 20 to 35 m ( Fig 14 View Fig 14 ). All four known specimens of this new species were caught in these depths during hours of the darkness / twilight. As both other species of Pliotrema usually occur in much deeper waters, P. annae sp. nov. possibly also occurs in deeper waters during the day but enters shallow water during the night. The area in which the specimens were caught is directly adjacent to a dropoff along the southern tip of Unguja Island. The water depth descends rapidly from ~ 20 m to> 200 m. Accordingly, deep-water sharks such as sixgill sharks and spurdogs are caught, alongside oceanic species such as mako and silky sharks and coastal species such as tiger and bull sharks, smoothhounds, and reef sharks all in the same fishery.

Pliotrema annae sp. nov. possibly also occurs off Kenya and/or Somalia following the short description of P. warreni in Gubanov [ 28]. Pliotrema annae sp. nov. is apparently the only species of the genus occurring in this area.

Etymology. The new species is named after Anna Weigmann Huerta, the niece of the first author, to express its relationship to Pliotrema kajae , named after the first author's daughter Kaja Magdalena Weigmann.

Table 3. Pliotrema annae sp. nov., morphometrics and meristic of the presumably adult female holotype (ZMH 26361, measured in fresh, i.e. defrozen condition) and presumably adult female paratype (ZMH 26362, measured in 70% ethanol preserved). Proportional values are expressed as percentages of total length (TL).

Pliotrema annae sp. nov., Pliotrema annae sp. nov., presumably adult female presumably adult female holotype, ZMH 26361 paratype, ZMH 26362
  mm % TL mm % TL
TL, total length 981.0 100.0 950.0 100.0
PRC, precaudal length, dorsally 795.0 81.0 765.0 80.5
PRVC, precaudal length, ventrally 790.0 80.5 760.0 80.0
PD2, pre-D2-length 645.0 65.7 620.0 65.3
PD1, pre-D1-length 425.0 43.3 415.0 43.7
HDL, head length (to end of last gill slit), horizontally 338.0 34.5 325.0 34.2
HDL, head length (to end of last gill slit), point to point 340.0 34.7 328.0 34.5
PG1, prebranchial length, horizontally 290.5 29.6 290.0 30.5
PG1, prebranchial length, point to point 293.1 29.9 292.0 30.7
PSP, prespiracular length, horizontally 242.8 24.7 243.1 25.6
PSP, prespiracular length, point to point 245.2 25.0 244.1 25.7
POB, preorbital length, horizontally 213.3 21.7 208.9 22.0
POB, preorbital length, point to point 215.1 21.9 210.1 22.1
PP1, prepectoral length, horizontally 329.0 33.5 319.0 33.6
PP2, prepelvic length, horizontally 532.0 54.2 525.0 55.3
SVL, snout–anterior vent length 554.0 56.5 542.0 57.1
IDS, interdorsal space 157.9 16.1 138.1 14.5
DCS, dorsal (D2)–caudal space 89.1 9.1 85.6 9.0
PPS, pectoral–pelvic space 186.0 19.0 189.4 19.9
PCA, pelvic–caudal space 225.3 23.0 201.7 21.2
VCL, anterior vent–caudal tip length 426.0 43.4 411.0 43.3
PRN, prenarial length, horizontally 201.4 20.5 200.4 21.1
POR, preoral length 241.2 24.6 238.0 25.1
EYL, eye length 27.3 2.8 26.1 2.7
EYH, eye height 14.7 1.5 13.4 1.4
ING, intergill length 1st to last slit 39.9 4.1 36.1 3.8
GS1, 1st gill slit height (unspread) 11.4 1.2 11.4 1.2
GS2, 2nd gill slit height 12.0 1.2 12.3 1.3
GS3, 3rd gill slit height 12.1 1.2 12.5 1.3
GS4, 4th gill slit height 11.1 1.1 11.9 1.3
GS5, 5th gill slit height 11.3 1.1 11.8 1.2
GS6, 6th gill slit height 12.7 1.3 12.4 1.3
P1A, pectoral anterior margin length 131.5 13.4 120.3 12.7
P1B, pectoral base length 29.3 3.0 28.2 3.0
P1I, pectoral inner margin length 70.4 7.2 64.6 6.8
P1P, pectoral posterior margin length 105.1 10.7 89.8 9.5
P1H, pectoral height, base end to tip 120.6 12.3 109.3 11.5
P1L, P length anterior base to posterior tip 95.7 9.8 90.1 9.5
CDM, dorsal caudal margin length 187.3 19.1 188.4 19.8
CST, subterminal caudal margin length 23.6 2.4 24.7 2.6
CSW, subterminal caudal width 26.2 2.7 23.7 2.5
CTR, terminal caudal margin length 41.1 4.2 37.9 4.0
CTL, terminal caudal lobe length 55.0 5.6 55.8 5.9
D1L, D1 total length 103.0 10.5 101.6 10.7



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