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"Diagnosis. Rostrum moderately long, about 3/4 length of adult carapace, broadly triangular at base in lateral view, directed generally anterodorsad to acute tip. No sharp dorsal carina on any abdominal somite; third somite with strong posteromesial spine overreaching anterior part of fourth somite, fourth and fifth somites with small posteromesial spine. Posterior margin of tergum of fourth and fifth abdominal somites armed with single small tooth above articular knob; fifth pleuron with sharp tooth on posterior margin. Sixth abdominal somite flattened dorsally, about twice length of fifth. Telson sulcate dorsally, longer than sixth abdominal somite, terminating posteriorly in sharp, laterally spinose endpiece set off from rest of telson by large pair of spines; portion of telson proximal to large paired spines with about 50 small lateral spines in 2 or 3 irregular rows.
Description. Body relatively stout, integument firm, surface smooth. Rostrum moderately long, about 3/4 length of adult carapace, reaching to end of antennal scale, broadly triangular at base in lateral view, directed generally anterodorsad, with weak lateral carina extending from orbit, tip acute; anterior dorsal surface of carapace and rostrum with 14 teeth, 10 of which are on rostrum proper, and ventral edge of rostrum with 6 teeth. A blunt dorsal carina runs backward from the rostrum over the anterior portion of the carapace for a length somewhat shorter than the rostrum itself, becoming obsolete near posterior gastric region. Lower margin of orbit continuous with the strong antennal spine, with no prominence representing the orbital spine. Branchiostegal spine prominent, supported by a blunt carina twice length of spine. Lateral surface of carapace with a low, poorly defined ridge extending obliquely downward from behind antennal spine to hepatic region; a somewhat stronger ridge extends obliquely upward from hepatic region above branchial region, with a short branch upward into cardiac region.
No sharp dorsal carina on any abdominal somite; third somite with a strong posteromesial spine overreaching anterior part of fourth somite, fourth and fifth with small posteromesial spine. Anterior margin of first abdominal pleuron produced into lobe overlapping hind margin of carapace; posterior margin of tergum on fourth and fifth somites armed with single small tooth above articular knob; fifth pleuron with sharp tooth on posterior margin. Sixth somite flattened dorsally, about twice as long as fifth.
Telson shallowly sulcate dorsally, longer than sixth abdominal somite, terminating posteriorly in sharp, laterally spinose endpiece set off from rest of telson by large pair of spines; posterior 2/3 of telson proximal to large spines with about 50 small lateral spines in 2 or 3 irregular rows; posterior endpiece with 8 lateral spines in single row. Exopod of uropod longer than endopod, not reaching tip of telson.
Cornea of eyes wider than stalks, with black pigment; well-developed median tubercle present distally on stalk.
Proximal segment of antennular peduncle longer than second and third segments together, deeply excavated dorsally to receive eye, with prominent lateral spine which is not very acute anteriorly but reaches 1/2 the length of second segment; stylocerite long, reaching to beginning of the lateral spine of first segment, proximally broad, with distinct lobe in posterior upper margin. Antennal scale about 3.5 times as long as broad, with short lateral tooth exceeding end of blade.
Mouthparts (Figures 13d-13h) typical for genus: incisor process of mandible toothed for entire length of cutting edge, palp with 3 articles; 2 inner distal lobes of second maxilla project beyond basal lobe; endopod of first maxilliped composed of 3 segments, the second segment the longest; third maxilliped reaching about 3/4 length of antennal scale when extended forward, exopod present, epipod with podobranch.
Pereopods 1-5 with well-developed exopods which are neither foliaceous nor rigid; pereopods 1-4 with epipods, those on pereopods 1-3 with podobranchs.
Pereopod 1 reaching about to middle of ultimate joint of third maxilliped when extended forward, chelate, carpus simple; pereopod 2 slightly longer than anteriorly extended pereopod 1, chelate, carpus simple; pereopods 3 and 4 longer than pereopod 2, reaching to end of antennal scale when extended forward, dactylus slender, not quite length of propodus, tip acute; pereopod 5 short, reaching to proximal 1/4 of propodus of anteriorly extended pereopod 4, distal 3/4 of flexor margin of propodus with transverse rows of spinules forming brushes, dactylus very short, with rounded tip and long, curved distal setae.
The holotype is an ovigerous female, bearing about 40 large ova; while it is evident that the ova are shrunken, those that were measured were in the range of 4 x 3 mm.
Endopod of first pleopod of male (Figure 14a) with oval process on distal margin bearing very small denticles; appendix masculina on second pleopod of male (Figure 14b) about 1.5 times as long as appendix interna, bearing 15 long spines.
Color in life not known. Preserved specimens are dark orange to pale yellow. Careful examination of the integument reveals no evidence of cuticular photophores.
The smallest juvenile specimen has a CL of 13.2 mm. The smallest male, which has a well-developed appendix masculina, has a CL of 21.2 mm. The smallest female has a CL of 24.5 mm, while the smallest ovigerous female has a CL of 31.4 mm. The largest specimen taken was an ovigerous female of 34.5 mm CL; this specimen is the longest in overall length of all the oplophorids encountered in this study, although the CL is slightly less than that cited for the holotype of Notostomus sparsidenticulatus; the largest specimens of S. eltanini approach the maximum size of specimens of S. braueri recorded from off Oregon [Krygier and Pearcy, 1981].
Material. A total of 14 specimens of S. eltanini, including 2 juveniles, 5 males, 6 females (including 4 ovigerous), and 1 damaged specimen whose sex is not determinable, were collected at three stations in the Pacific sector of the Southern Ocean by the USNS Eltanin and at six stations in the Atlantic sector of the Southern Ocean in open Engel trawls by the German FRS Walther Herwig. Specific collection data are as follows: Eltanin cruise 9--Sta. 743; 33°18'S, 72°21'W; 3-m IKMT; 1830-0 m; September 26, 1963; 2330-0345 hours; 1 juvenile (CL = 16.4 mm).
Eltanin cruise 10--Sta. 846; 57°52'S, 74°43'W; 3-m IKMT; 1866-0 m; November 10, 1963; 2315-0330 hours; 1 juvenile (CL = 13.2 mm). Sta. 877; 55°22'S, 78°08'W; 3-m IKMT; 1940-0 m; November 29, 1963; 2040-0035 hours; 1 male (CL = 31.0 mm). FRS Walther Herwig cruise 36--Sta. 376; 39°55'S, 26°02'W; Engel trawl; 2000-0 m; March 11, 1971; 1835-2338 hours; 3 females (CL = 24.5-33.0 mm), including 1 ovigerous (CL = 33.0 mm). Sta. 384; 39°45'S, 17°40'W; Engel trawl; 2000-0 m; March 13, 1971; 1913-2330 hours; 1 male (CL = 34.0 mm). Sta. 395; 36°49'S, 12°17'W; Engel trawl; 2000-0 m; March 17, 1971; 0020-0518 hours; 3 males (CL = 21.2-32.0 mm), 1 ovigerous female (CL = 32.0 mm). Sta. 412-II; 37°08'S, 05°23'E; Engel trawl; 2200-0 m; March 21, 1971; 1926-2400 hours; 1 ovigerous female (CL = 31.4 mm). Sta. 417; 34°12'S, 16°35'E; Engel trawl; 1550-0 m; March 28, 1971; 0852-1215 hours; 1 ovigerous female (CL = 34.5 mm). Sta. 427; 33°00'S, 07°50'E; Engel trawl; 2000-0 m; March 30, 1971; 1925-2343 hours; damaged specimen, sex not determinable (CL - 33.0 mm).
Deposition of types. The holotype, an ovigerous female (CL = 34.5 mm) from FRS Walther Herwig cruise 36, sta. 417, and the allotype male (CL = 32.0 mm) from sta. 395 are deposited in the Zoologische Museum, Hamburg, K-33244 and K-33245, respectively. All other specimens are deposited in the U.S. National Museum of Natural History, USNM 228472-228479, as paratypes.
Type locality. South Atlantic: 34°12'S, 16°35'E; 1550-0 m.
Range. Known only from the type series collected in Subantarctic waters of the Pacific sector of the Southern Ocean from 33°18'S to 57°52'S between 72°21'W and 78°08'W and in the Atlantic sector from 33°00'S to 39°55'S between 26°02'W and 16°35'E. Systellaspis eltanini is apparently a deep-living species, since it was not collected by any trawls sampling shallower than 1550 m.
Remarks. Figures 14c-14f show the individual rostral variations for those specimens of S. eltanini on which the rostrum is undamaged. It can be seen that the rostral length varies from about half the length of the antennal scale in a juvenile specimen with a CL of 13.2 mm (Figure 14c) to about three-fourth the length of the antennal scale in specimens with a CL of 16.4 mm (Figure 14d), to as long as the antennal scale in specimens with CL of 31.4 mm and 33.0 mm (Figures 14e and 14f). The rostrum is ascending in all specimens at hand, even those damaged distally. The rostral formula, determined from all specimens on which the rostrum is undamaged, is (8-11) /(4-6)
Systellaspis eltanini most closely resembles S. braueri, from which it can be distinguished by the rostral features: in S. braueri, the rostrum is directed generally anteroventrad, less than half as long as the carapace, and with fewer dorsal and ventral teeth. In addition, S. eltanini has a greater number of lateral spines on its telson than does S. braueri, and they are more irregularly arranged into two or three rows. The rostrum of S. eltanini also distinguishes it from the remaining four species in the genus, S. cristata S. debilis, S. lanceocaudata, and S. pellucida. In each of the latter four species, the rostrum trends downward from a dorsal crest above the orbit but is ascendent in its distal half. Other useful diagnostic characters are the following: hind margin of fourth and fifth abdominal somites not bearing a series of denticles (present in S. debilis), fourth abdominal somite not dorsally carinate for its entire length (as it is in S. cristata), longitudinal ridge on the lateral surface of the carapace above the branchial region present (absent in S. pellucida), and a sixth abdominal somite which is flattened dorsally (sulcated in S. lanceocaudata). The absence of cutaneous photophores further separates S. eltanini from S. cristata, S. debilis, and S. pellucida, all of which have numerous cutaneous photophores.
Integumental tuft organs, noted by Mauchline et al.  on many pelagic shrimps, including all oplophorids they examined, are not evident on any of these specimens of S. eltanini, although the hollow or depressions in the posterior portion of the dorsal surface of the fourth abdominal somite, and slightly raised and lighter pigmented areas on the proximal portion of the telson where these organs have been reported can be easily observed. It is suggested that the external tufts of setae have been lost by abrasion in the trawl during collection.
Etymology. The specific epithet eltanini is in commemoration of the USNS Eltanin, which first collected the species in 1963 and whose multidisciplinary research cruises as part of the USARP did much to further our understanding of the oceanography of the waters bordering the Antarctic continent."