Comprehensive DescriptionRead full entry
“Notostomus sparsidenticulatus, n. sp.
Figs. 6 and 9
Diagnosis. Integument soft. Carapace greatly inflated; dorsal margin highly arched above level of rostrum. Dorsal carina of carapace sparsely denticulate with 14 small teeth irregularly spaced from level of orbit to near posterior margin. Posterior half of carapace with 5 lateral carinae, including weak infrasubhepatic carina. Rostrum slender, slightly more than half as long as carapace, ascending, extending beyond tips of antennal scale, armed with 13 dorsal teeth and 7 ventral teeth. Stylocerite proximally broad, tapering to short terminal spine, not reaching distal end of proximal antennular peduncle.
Description. Integument soft. Carapace greatly inflated; dorsal margin highly arched above level of rostrum, sharply carinate throughout, sparsely denticulate with 14 small teeth irregularly spaced from level of orbit to near posterior margin. Posterior half of carapace with 5 lateral carinae: gastroorbital carina begins near posterior margin of carapace, its anterior end descending near posterior edge of orbit; infra-gastro-orbital carina extends approximately 2/3 distance between posterior margin of carapace and the prominent posthepatic carina connecting gastro-orbital and subhepatic carinae; sub-hepatic carina extends from strong and prominently flared branchiostegal spine to posterior branchial region; weak infrasubhepatic carina closely approaches subhepatic carina posteriorly and is more evident on left side of body; submarginal carina parallels lower edge of carapace, passing upward to posterior dorsal surface. Suborbital angle bluntly subrectangular. Antennal spine distinct.
Rostrum slender, slightly more than 1/2 as long as carapace, ascending, slightly damaged at apex, extending beyond tips of antennal scale. Upper lateral rostral carina weak, closely paralleling dorsal margin, extending posteriorly to level of orbit; lower lateral rostral carina continuous posteriorly with postorbital margin, with weak posterior extension running toward anterior end of gastroorbital carina but not continuous with it. Rostrum armed dorsally with 13 teeth, 9 of which are closely spaced on thicker descending base of rostrum and 4 more widely spaced on slender portion; ventral margin with 7 teeth, proximal 2 set off from distal 5 by distinct space.
Abdomen carinate dorsally on every somite; dorsal carina of first more than half as long as tergite, measured laterally; dorsal carinae of third, fourth, fifth, and sixth somites terminating in well-developed posteromesial spines, that of third the largest. Telson about 1.8 times length of sixth somite, dorsally sulcate throughout length, armed with 3 pairs of small dorsolateral spines, posteriorly truncate, armed with 2 terminal pairs of spines on either side of median spine. Endo-pod of uropod narrowly oval distally, shorter than telson; exopod slightly overreaching telson, broadly oval distally, with subdistal spine on thickened lateral margin.
Eyes wider than eyestalks, cornea lightly pigmented in alcohol; small distinct papilla on inner surface of stalk.
Stylocerite proximally broad, tapering to short terminal spine, not reaching distal end of proximal antennular segment. Proximal antennular segment excavated below eye, with sharp spine distally on lateral anterior margin; proximal segment longer than second and third segments together. Antennal scale about 2.75 times as long as broad; outer margin thickened, terminating distally in short stout spine slightly exceeding convex end of blade.
Mouthparts (Figures 9c-9g) typical for genus. Third maxilliped reaches beyond outer spine of antennal scale when extended forward by distal 1/5 length of dactylus. Pereopod 1 reaches anteriorly about halfway from end of antennal peduncle to end of antennal scale; pereopod 2 reaches anteriorly slightly beyond reach of pereopod 1; pereopod 3 reaches beyond antennal scale by length of dactylus and distal half of propodus; pereopod 4 reaches beyond antennal scale by length of dactylus and distal 1/4 of propodus; pereopod 5 slightly overreaches end of antennal scale when extended forward.
Integumental tuft organs, noted by Mauch-line et al.  on many pelagic shrimps, including all the oplophorids they examined, are also present in this species. The fourth abdominal somite has a tuft of short setae present in a hollow or depression in the posterior fourth of the dorsal carina. A pair of similar tuft organs is present in the dorsal median proximal area of the telson; the lateral tuft organs on the telson are not evident, although a slightly raised area is visible on either side where they probably would be.
Color in life not known; devoid of all color in alcohol. Integument transparent, so that internal organs and muscles are visible.
Postorbital CL is 36.4 mm; length of rostrum is 20.0 mm. This specimen has the largest CL of any of the oplophorids considered in this study. Since there are no males or ovigerous females, there is no way of determining whether the holotype is in fact a female or an immature specimen.
Material. One specimen, the holotype, of N. sparsidenticulatus was collected to Subantarctic waters south of the Subtropical Convergence. The specimen is deposited in the U.S. National Museum of Natural History, USNM 228471. Specific collection data are as follows: Eltanin cruise 24; sta. 1727; 44°40'S, 145°26’ W; 3-m IKMT; 2050-0 m; July 20, 1966.
Remarks. Notostomus sparsidenticulatus n. sp. differs from the other Notostomus species having five lateral carinae on the posterior lateral surface of the carapace (N. elegans, N. auriculatus, and N. crosnieri), all of which have strong and well-developed lateral carinae on their carapaces and carapaces which are less highly arched, with their dorsal carinae finely and closely denticulate. This species agrees with the otherwise very different N. distirus Chace, 1940 (known from the western North Atlantic off Bermuda), in having the median dorsal carina on the carapace sparsely denticulate.
Etymology. The Latin compound sparsidenticulatus is in reference to the sparse denticulation on the dorsal carina of the carapace of this species.”