Mollisquama mississippiensis, Grace & Doosey & Denton & Naylor & Bart & Maisey, 2019

Grace, Mark A., Doosey, Michael H., Denton, John S. S., Naylor, Gavin J. P., Bart, Henry L. & Maisey, John G., 2019, A new Western North Atlantic Ocean kitefin shark (Squaliformes: Dalatiidae) from the Gulf of Mexico, Zootaxa 4619 (1), pp. 109-120 : 110-112

Mollisquama mississippiensis sp. nov.

Figures 1 , 2 , 3 , 4 , 5 , 6 ; Table 1 , 2

urn:lsid:zoobank.org:act:2BBDBBA6-3A9C-40F0-8E37-B852D26439C6

Mollisquama sp. ( Grace et al. 2015)

Mollisquama aff. parini Dolganov 1984 ( Del Moral-Flores et al. 2015)

Mollisquama parini Dolganov 1984 ( Weigmann 2016)

Mollisquama sp. ( Denton et al. 2018)

Mollisquama parini Dolganov 1984 ( de Figueiredo Petean & de Carvalho 2018)

Holotype: — TU 203676, central Gulf of Mexico, NOAA Ship PISCES survey 7620101001, station 053, 4 February 2010, 142.0 mm total length, 14.6 g, immature male.

Diagnosis. Differs from the only other described species of Mollisquama , M. parini (Zoological Institute, St. Petersburg, Russia, ZIL-45988), in having a putative pit organ centrally placed just posterior to the lower jaw margin, photophores irregularly distributed along many areas of the body, a series of 16 ventral-abdominal photophore aggregations, upper teeth without a labial-surface ridge ( M. parini has a labial-surface ridge), and lower teeth with a weak or absent basal sulcus ( M. parini has a deep basal sulcus). The distinguishing external features the pit organ and photophore aggregations were clearly discernable when the new species was captured ( Grace et al. 2015) and after preservation. These features were not reported as present on M. parini .

Description. Gross Morphology. Resembles M. parini in general shape, fin placement, fin shapes, and pectoralarea pocket glands (distinguishes Mollisquama spp. from all other elasmobranchs). Total vertebrae 73; 37 monospondylous precaudal centra and 36 diplospondylous caudal centra ( Fig. 3 ). A putative pit organ 2.5 mm posterior to the lower jaw margin center with a radiating arrangement of bordering dermal denticles (five radiating dermal denticles in first proximal row, Fig. 4A ); rounded center protuberance (0.5 mm diameter) equal in height to bordering denticles and ringed with approximately 20 low nodules, two half-circle wedges at center separated by a groove. Along the ventral-abdominal surface a series of 16 photophore aggregations extend from approximately 5.0 mm posterior of lower jaw to anterior of pelvic fin origin ( Fig. 1B ), anterior to posterior numbering 2, (followed by the healed vitelline scar), 2, 2, 3, 2, 1, 1, 1, 1, 1; aggregations completely covered by dermal denticles oriented on an rostral-caudal axis, at aggregation centers numerous dark clusters of photophores surrounded by a lighter-grey area with fewer photophores; additional photophores irregularly distributed along many other areas of the body.

Cylindrical body tapers towards a slender caudal peduncle, nearly circular in cross section, followed by a bilobed homocercal caudal fin with rounded apexes. Wide head considerably deeper than the rest of the body with a broadly-rounded bulbuous snout (in profile) with a subterminal mouth. Head width greatest just posterior to spiracles. Oral furrows extend past mouth corners to below spiracles. Orbits elliptical and positioned level with nostrils and anterior to and just ventral of spiracles. Five small gill slits surrounded by light cream-colored distinct bar, posterior gill slit over pectoral fin origin. Distinct, cream-colored blotch at dorsal and ventral-posterior margin of pectoral fin base. Pocket gland opening above pectoral fin base and approximately half the length of the pectoral fin base, opening surrounded by 14 shallow dermal folds with lighter blue-grey corners, gland interior lined with numerous dark villi. Two low dorsal fins positioned above the pelvic fin. Spines absent on all fins and no anal fin, caudal keels or precaudal pits. Dermal denticles spade-shaped with type-I scale morphology ( Reif 1985), more prevalent overlapping at fin bases, covering the body except for posterior margins of fin tips, relatively translucent with four rows of ectodermal pits and a darker pedicle center ( Fig. 4B ). Body color coal grey with brown undertones, slightly counter-shaded (dark dorsally and lighter ventrally). Fins dark with distinctly lighter ceratotrichia fringes along posterior margins (<2.0 mm length). Lateral line darker than background body color. Lighter pigmentation around and within mouth.Additional diagnosis of features and morphometric values are found in Grace et al. (2015) and Denton et al. (2018), and specimen photographs taken just after capture are found in Grace et al. (2015).

Dentition. Dignathic heterodonty with upper teeth narrow and conical without a labial-surface ridge and lower teeth broad and bladelike ( Fig. 2 ). Upper and lower teeth decrease in size toward mouth corners. Symphyseal teeth present in both upper and lower jaws; lower jaw symphyseal tooth with flanking shoulders below the cusp that overlaps adjacent teeth. Upper teeth with a broad-forked root and cusps slightly curved posteriorly. For lower teeth the root height is approximately 50% of the total tooth height and most cusp tips curve toward jaw corners. For lower teeth the basal sulcus is absent or weakly present ( Denton et al. 2018). Dental formula 10-1-10 / 15-1-15 ( Denton et al. 2018).

Habitat. The new species was captured with a midwater trawl (07:01 U.S. Central Standard Time, 4 February 2010, 2 h trawling effort) during a cetacean research project to assess predator/prey trophodynamics for sperm whales ( Physeter macrocephalus ) of the Gulf of Mexico (NOAA Ship PISCES survey PC10-01; location 26 18.55 oN /-087 25.75 oW, Fig. 7 ). Trawl fishing depths were from 5 m of surface to a maximum trawl fishing depth of 580 m over 3,038 m bottom depth; the sea bottom was a relatively flat abyssal plain without significant bathymetric features. Environmental sampling was conducted within 10 nautical miles of the trawl location. Surface/maximum trawling depth environmental data was; temperature 21.5 oC /7.2 oC, oxygen saturation 6.6 mg /l/ 4.0 mg/l, and salinity 36.5 psu/34.9 psu. Other fauna captured included 44 species identified to lowest taxon (3.3 kg total catch weight, 731 specimens); 29 finfish taxa, 15 invertebrate taxa. Grace et al. 2015 includes a comparative discussion of the considerably-different collection locations of Mollisquama spp. (e.g., M. mississippiensis sp. nov. captured above an abyssal plain 3,038 m depth influenced by the relatively warm Gulf Stream; M. parini captured above an extensive seamount ridge 330 m depth that is influenced by the relatively cold sub-Antarctic Humboldt Current).

Figures

FIGURE 1. Mollisquama mississippiensis sp. nov., TU 203676 illustrated to scale in (A) lateral and (B) ventral view.

FIGURE 2. Mollisquama mississippiensis sp. nov., upper tooth lateral view (tooth #4 right); lower tooth labial-surface view (tooth #4 right).

FIGURE 3. Mollisquama mississippiensis sp. nov. CT scan of vertebral column (http://sharksrays.org/).

FIGURE 4. (A) Putative pit organ of Mollisquama mississippiensis sp. nov. in the photo center (0.5 mm diameter); anterior is the photo upper margin. (B) SEM micrograph of Mollisquama mississippiensis sp. nov. dermal denticles; anterior is to the left.

FIGURE 5. Mollisquama mississippiensis sp. nov. right pocket gland anatomy at maximum dimensions (a single synchrotron scan layer); total length approximately 7.0 mm x 1.5 mm width; anterior is to the right.

FIGURE 6. Mollisquama mississippiensis sp. nov. spiral valve detail (a single synchrotron scan layer); anterior is to the right.

FIGURE 7. Mollisquama mississippiensis sp. nov. capture site (*).