Stylomesus sarsi, Merrin & Poore, 2003

Merrin, K. L. & Poore, G. C. B., 2003, Four new species of Ischnomesidae (Crustacea: Isopoda: Asellota) from off south-eastern Australia, Memoirs of Museum Victoria 60 (2), pp. 285-307 : 301-307

publication ID	https://doi.org/ 10.24199/j.mmv.2003.60.27
persistent identifier	https://treatment.plazi.org/id/671587C8-306C-550C-FC8C-71D3FD92C244
treatment provided by	Felipe
scientific name	Stylomesus sarsi
status	sp. nov.

Treatment

Stylomesus sarsi View in CoL sp. nov.

Figures 16–20 View Figure 16 View Figure 17 View Figure 18 View Figure 19 View Figure 20

Material examined. Holotype. Tasmania., continental slope (40°45´S, 149° 09.3´E – 40° 46.54´S 149°00.27´E), 3000– 2400 m, WHOI epibenthic sled, P. Hutchings et al., RV Franklin, 10 Dec 1986 (stn FR1086–4), AM P63900 (male, 5 mm). GoogleMaps

Paratypes. Collected with holotype, AM P63901 (1 female, 5 mm; 1 male, 5 mm) .

Other material. Australia, Tasmania., 48 km ENE of Cape Tourville (42˚00.25´S, 148˚43.55´E), 1264– 1130 m, gravel with lumps of sandy mud aggregate (stn SLOPE 81 ), NMV J20299 View Materials (2 females, 1 male, 1 fragment) . Tasmania., continental slope, 40°45´S, 149°09.3´E – 40°46.54´S, 149°00.27´E, 3000– 2400 m, (stn FR1086-4), AM P63902 (17 females, 8 males, 22 fragments). NSW, 67 km ENE of Nowra (34˚41.97´S, 151˚22.44´E), 1896– 1642 m (stn SLOPE 59 ), NMV J20294 View Materials (8 females, 2 fragments). Off Nowra (34˚58.40´S, 151˚23.20´E), 1750– 1650 m, (stn SLOPE 15 ), NMV J20291 View Materials (1 fragment) GoogleMaps . Vic., 67 km S of Point Hicks (38˚23.95´S, 149˚17.02´E), 1277– 1119 m, fine mud (stn SLOPE 67 ), NMV J20296 View Materials (7 females, 1 fragment). 76 km S of Point Hicks (38˚29.33´S, 149˚19.98´E), 1840– 1750 m, sandy mud, fine shell (stn SLOPE 69 ), NMV J20297 View Materials (12 females, 2 males, 7 fragments), NMV J20298 View Materials (4 females, 2 males, 1 fragment). 96 km S of Point Hicks (38˚40.29´S, 149˚18.06´E), 2900– 2900 m, compacted clay (stn SLOPE 66 ), NMV J20295 View Materials (8 females, 8 fragments). S of Point Hicks (38˚25´S, 149˚0´E), 1500 m, compacted clay (stn SLOPE 27 ), NMV J20293 View Materials (12 females, 2 males, 7 fragments). S of Point Hicks (38˚25.90´S, 148˚58.60´E), 1850 m, muddy, sandstone (stn SLOPE 25 ), NMV J20292 View Materials (1 male) .

Diagnosis. Body granulate, about 7 times as long as wide. Head+pereonite 1 bearing 2 anterolateral extensions supporting antennae. Pereonites 1 and 2 with pair of stout anterolateral spines. Pereonites 2–4 each with pair of elevated dorsal bosses. Pereonites 4 and 5, about 1.4 and 4.5 times length of pereonite 2 respectively. Pleotelson longer than wide, with wide medial ridge. Antenna 2 articles 2 and 3 length subequal, article 3 about quarter length of article 4, flagellum of 26 articles, each setose. Mandible molar quadrangular, with broad face. Maxilliped with fringe of fine simple setae on basis, palp article 1 widest, with each article narrower than the previous. Pereopod 1 merus with 2 robust setae on distal inferior margin, carpus width generally subequal throughout length, 0.4 length of basis, bearing 1 long robust seta and 3 smaller, robust flagellate setae. Pereopods 2–7 slim, carpus with finely serrate distal margin. Uropod with 2 articles, article 2 0.8 times length of article 1.

Description of male holotype. Body length 6.5 times maximum width of pereonite 3. Body cuticle highly granulated, calcified and brittle, with all pereonites bearing short simple setae. Head+pereonite 1 1.7 times as wide as long, with 2 anterolateral projections of head supporting antennae. Ratio of lengths of pereonites 2: 3: 4: 5: 6: 7+pleon, 1.0:1.0:1.4:4.5:0.9:2.8. Pereonites 1 and 2 with pair of stout anterolateral spines. Pereonite 2 slightly narrower than pereonite 1, pereonites 2–4 widths subequal (excluding anterolateral spines), 5–7 decreasing posteriorly Pereonites 2–4 each with pair of raised dorsal bosses. Pleotelson oval in dorsal view, length 1.1 times width, with wide, medial longitudinal ridge; posterior margin with 2 subventral lobes.

Antenna 1 article 1 broad, roughly oval, bearing 1 simple seta; article 2 length 2.2 as long and 0.25 times as wide of article 1, bearing 3 long flagellate setae and 5 shorter simple setae. Antenna 2 of 31 articles; article 1 small, lacking setae, with a lateral protrusion; article 2 granulated, 5.5 times as long as article 1, with 6 simple setae; article 3 short, 1.7 times as long as article 1 with 1 simple setae; article 4 5.6 times length of article 1, with 7 simple setae; article 5 longest, 8.0 times as long as article 1, with many simple and 2 distal brush setae; flagellum of 26 articles decreasing in length, each setose.

Mouthparts (of male paratype). Mandible incisor process with 5 cusps; lacinia mobilis with 4 cusps; spine row of 4 spines; molar wide, rectangular, with broad, distal grinding surface with 3 fine simple setae on face and proximally 6 fine simple setae. Maxilla 1 with mesial lobe 0.6 times width of lateral lobe; both lobes with numerous fine simple setae on inferior and superior margins; mesial lobe distal margin with 1 short dentate and 1 simple setae; lateral lobe with 12 distal, robust, dentate setae. Maxilla 2 lateral lobe with several rows of microtrichs on superior margin; middle lobe 0.9 times width of lateral lobe, no ornamentation, both lateral and middle lobes with 4 distal pectinate setae of different lengths; mesial lobe with many microtrichs and fine simple setae covering surface, 2 long, pectinate setae set medially on inferior margin, and distally, 3 dentate, 2 small pectinate and 6 simple setae. Maxilliped coxa small, rectangular; basis 1.8 times as long as widest point, with fringe of fine simple setae on superior margin and in its surface, endite with 3 coupling hooks and distally 3 fan and 3 simple setae. Palp tapering, 2.4 times length of basal endite; palp article 1 shortest, almost rectangular bearing 2 simple setae; article 2 0.5 times as wide as maximum width of basal endite and width equal to and 1.4 times length of article 1, with 2 simple setae and few fine simple setae; article 3 as wide as and 1.8 times as long as article 1, with 1 simple setae and 1 stronger distal seta on inferior margin and numerous fine simple setae; article 4 1.6 times length of article 1, narrower than article 3, with 2 distal simple setae and numerous fine simple setae; article 5 narrower than article 4, 1.3 times the length of article 1, with 1 thick distal seta and 4 slightly thinner simple setae. Epipod length 2.8 times width, 1.1 times basis length, with proximal end square, distal tip curved inward and a few microtrichs.

Pereopod 1 basis 0.1 body length; ratio of lengths of articles, basis–dactylus, 1.0:0.4:0.2:0.4:0.3:0.2; basis with 8 simple setae; ischium with 3 simple setae; merus with 2 simple and on inferior distal margin, 1 simple and 2 long, robust setae; carpus width subequal throughout, inferior margin with 3 flagellate robust setae and 1 long robust seta; propodus width subequal throughout, with 4 simple setae on superior margin, 1 simple seta on surface and inferior margin with 2 flagellate, robust and 1 long simple seta; dactylus with 4 short simple setae on distal superior margin.

Pereopods 2–7, basis 0.2 body length; ratio of lengths of articles, basis to dactylus, 1.0:0.5:0.3:0.6:0.4:0.2.

Pereopod 2 basis with 12 simple setae; ischium with 8 simple setae; merus with 4 simple setae; carpus with 5 simple setae on superior margin and on inferior margin 5 flagellate robust and 1 long, robust seta, distal margin finely serrate; propodus with 3 simple setae on superior margin, 6 flagellate robust setae with small fringed scale-setae between each on inferior margin; dactylus with 2 short distal setae.

Pereopod 3 basis with 10 simple setae; ischium with 10 simple setae; merus with 6 simple setae; carpus with 7 simple setae on superior margin and at least 5 flagellate robust setae on inferior margin, distal margin finely serrate; propodus with at least 2 simple setae, inferior margin with 7 flagellate robust setae with fringed scale-setae between each and 1 brush seta on distal superior margin; dactylus with 4 small distal simple setae.

Pereopod 4 basis with 15 simple setae; ischium with 13 simple setae; merus with 8 simple setae; carpus with at least 8 simple setae and inferior margin with 8 flagellate robust setae, distal margin finely serrate; half of propodus intact with superior margin with 3 simple setae and inferior margin with 4 flagellate robust setae with fringed scale-setae between them.

Pereopod 5 basis with 13 simple setae; ischium with 11 simple setae; merus with 8 simple setae; carpus with at least 8 simple setae and at least 4 flagellate robust setae on inferior margin; propodus with 6 simple setae, 10 flagellate robust setae with fringed scale-setae between them and 1 brush seta on distal superior margin; dactylus superior margin with 2 small simple setae.

Pereopod 6 basis with 13 simple setae; ischium with 9 simple setae; merus with 9 simple setae; carpus superior margin with 6 simple setae and inferior margin with 1 simple and 4 flagellate robust setae, distal margin finely serrate; propodus with 4 simple setae on superior margin, 6 flagellate robust setae with fringed scale-setae between each on inferior margin and 1 brush seta on distal superior margin; dactylus with 3 small simple setae.

Pereopod 7 basis with at least 8 simple setae; ischium with 3 simple setae; merus with 5 simple setae; carpus with 3 simple setae on superior margin, 2 flagellate setae on inferior margin and distal margin finely serrate; propodus with 3 simple setae on superior margin and on the inferior margin, 4 flagellate robust setae with some fringed scale-setae between; dactylus with 4 small distal simple setae.

Pleopod 1 length 2.6 times maximum width; margins indent at 0.6 of length from proximal end; 5 simple setae near a small transverse ridge near distal margin; 6 simple setae on right and 5 simple setae on left of distal margin; prominent distolateral horns. Pleopod 2 sympod length 2.2 times maximum width; lateral margins curved, with few simple setae and 6 distolateral, plumose setae; exopod short, 0.1 times sympod length, rounded distally; stylet 0.4 length of sympod tapering to a point; sperm duct 0.5 length of stylet. Pleopod 3 exopod length 0.7 times endopod length with a fringe of fine simple setae on surface and extended from superior margin. Pleopod 4 length 1.8 times width.

Uropod straight, 0.6 times length of pleotelson; article 1 with 2 simple setae; article 2 tapering, 0.8 times length of article 1, with 3 simple setae.

Female. Pereopod 1 shorter and more robust than in male; ratio of lengths of articles, basis–dactylus, 1.0:0.4:0.2:0.5:0.4:0.2; basis with 8 simple setae; ischium with 3 simple setae; merus with 2 simple setae on distal superior margin and 2 long robust setae on distal inferior margin; carpus slightly broader at proximal end, 1 long robust seta on superior margin, inferior margin with 1 simple seta, 5 robust flagellate setae and 1 long robust seta; propodus with 5 simple setae and 2 flagellate, robust setae on inferior margin; dactylus narrower than propodus, with 4 short simple distal setae.

Operculum slightly wider than long, length 0.9 times maximum width; curves to slight keel at apex, with few simple setae on lateral margins, plumose setae and microtrichs on posterior margin. Pleopod 3 similar to male, exopod length 0.8 times endopod. Pleopod 4 length 1.6 times width, with 3 slight dents on lateral margin.

Distribution. South-eastern Australia, from Nowra, New South Wales, to Cape Tourville, Tasmania; 1119–3000 m depth.

Etymology. In honour of the Norwegian carcinologist, Georg

Ossian Sars (1837–1927), the first person to describe taxa of Ischnomesidae .

Remarks. Stylomesus sarsi is the first species of Stylomesus recorded from Australian waters. It resembles Stylomesus natalensis Kensley, 1984 from south-western Indian Ocean off South Africa. Both species have granulate integuments, short anterolateral spines on pereonites 1 and 2 and in both the mandible molars have a broad distal surface. However, S. sarsi can be distinguished from S. natalensis by the lack of tubercles set medially on pereonites 1 and 2, less elongate pleotelson, and longer flagellum of antenna 2. The maxilliped palp of S. sarsi has setae present on all articles, while on S. natalensis , setae are present only on the last three articles.