Exosphaeroma alveola, Bruce, 2003

Bruce, N. L., 2003, New genera and species of sphaeromatid isopod crustaceans from Australian marine coastal waters, Memoirs of Museum Victoria 60 (2), pp. 309-369 : 333-339

Exosphaeroma alveola sp. nov.

Figures 18–22

Material examined. Holotype. Male (6.5 mm), near mouth of Moona Moona Creek, Jervis Bay, NSW, 34°04.5´S, 150°41.0´E, 23 Jan 1982, 4.5 m, on test of ascidian Herdmania, P.B. Berents ( AM P51055 ).

Paratypes. NSW. 3 males (6.0 mm), 2 females (non-ovigerous 3.5, 4.2 mm), E of Fairy Bower , Manly, 33°48´S, 151°17´E, 22 Nov 1984, 6 m, sand between rocks, J. Just ( AM P41189 ) . 2 females (non-ovigerous 4.3, 4.4 mm), Edwards Beach , Middle Harbour, Sydney, 33°49.4´S, 151°15.1´E, 17 Mar 1985, under rocks at low tide, N.L. Bruce ( AM P41389 ) . Male (7.1 mm), same as previous, 23 Mar 1985 ( AM P41382 ) . 5 males (4.6–[6.7 dissected] mm), 11 females (non-ovigerous 3.0– 4.6 mm), same data as holotype ( AM P51056 ) . Male (5 mm, rolled), Murrumbulga Point, Twofold Bay, 37°05´S, 149°54´E, 17 Sep 1985, intertidal rock platform, P.A. Hutchings and S.J. Keable ( AM P41201 ) . 2 males (5.5, 6.6 mm), Quarantine Bay , Murrumbulga Point, Twofold Bay, 37°05´S, 149°54´E, 17 Sep 1985, subtidal breakwater, P.A. Hutchings and S.J. Keable ( AM P41202 ) . 2 females (5.5, 3.0 mm), Murrumbulga Point , Twofold Bay, 37°05´S, 149°54´E, 9 Oct 1985, subtidal rock, P.A. Hutchings and S.J. Keable ( AM P35955 ) . Tas. 4 females (4.0– 5.5 mm), 3 females (?3.8, 4.0, 4.3 mm), Governor I., Bicheno, 41°52´S, 148°19´E, 29 May 1984, 30 m, on bryozoan, ( NMV J26419 ) .

Description of male. Body heavily calcified, 1.7 times as long as greatest width, dorsum noticeably flattened, lateral margins distinctly thickened, approximately straight in dorsal view, diverging, widest at pereonite 6; dorsal surfaces minutely punctate. Head about 1.3 times as long as pereonite 1, dorsally deeply corrugated; pereonite 1> 2>3=4>5<6<7; pereonite 7 laterally narrower than 6, not forming part of body outline, laterally wholly overlapped by coxae of pereonite 7. Pleon laterally about as long as pereonite 7 in lateral view (flexure makes this difficult to measure accurately), with median weakly elevated region, with evident sublateral ‘keys’. Pleotelson strongly vaulted, posterior margin produced to bluntly rounded apex; ventral margin anteriorly excavate; dorsal margin mesially raised, with 2 obscure punctate submedian ridges uniting at about midpoint, expanding at posterior margin.

Antennule peduncle article 1 1.4 times as long as wide, about twice as long as article 2, anterior margins convex, distal one-third somewhat produced; article 3 about two-thirds as long as article 1, 3.7 times as long as wide, 1.3 times as long as article 2; flagellum 7-articled, extending to posterior of pereonite 1, about 1.5 times as long article 3; antennule peduncles prominently visible in dorsal view. Antenna relatively robust, peduncle articles 1 and 2 short, article 1 anterior margin with mass of setae, combined lengths of articles 1 and 2 about equal to that of article 5; article 3 about 0.8 times as long as article 4; article 4 about 0.6 as long as article 5, articles 3–5 collinear; flagellum about 0.8 times as long as peduncle, extending to posterior margin of pereonite 1, with 12 articles.

Epistome prominently visible in dorsal view, anteriorly truncate, anterior lateral margins straight, diverging to midpoint, then narrowing to medial constriction; ventral surface pitted, centrally depressed. Left mandible incisor with 4 cusps, lacinia mobilis with 3 cusps, spine row of 8 curved serrate spines; right mandible with 3 indistinct cusps, spine row of 2 broad-based multidigitate spines, 8 serrate spines; molar process round, crushing surface strongly ridged; palp article 2 longest, article 2 distolateral margin with 9 stout and prominently biserrate setae; article 3 with 12 prominently biserrate setae, 2 terminal setae being longest. Maxillule mesial lobe with 4 long, strongly CP RS and 1 simple slender seta, lateral lobe with 11 RS on gnathal surface, twelfth seta set between these; gnathal RS variously serrate, submesial RS being most strongly serrate. Maxilla lateral lobe and middle lobe each with 9 curved finely serrate RS respectively, mesial lobe with about between 12–18 serrate and biserrate RS (number could not be clearly observed), proximal seta longest. Maxilliped endite lateral margin strongly convex, distal margin with 1 simple RS at sublateral angle, 5 curved CP RS, 2 short straight CP RS; distomesial margin with 3 large stout CP RS, increasing in size proximally; palp articles 2–5 with about 11, 14, 16 and 14 setae respectively.

Pereopod 1 basis about 2.7 times as long as greatest width, 1.7 times as long as propodus; margins without setae, inferodistal angle with single seta; ischium 0.6 times as long as basis, about as long as propodus, twice as long as greatest width, superior margin with scattered scale-setae, with 2 prominent mesial acute simple setae, one proximal and 1 at midpoint, inferior margin without setae; merus short, about half as long as ischium, about 0.8 times as long as greatest width, superior distal angle with 2 short RS, inferior margin with dense setulose fringe, with 1 apically bifid RS at distal angle; carpus 0.8 as long as wide, inferior margin with dense setulose fringe, distally with 1 apically bifid RS; propodus 2.0 times as long as greatest width, about as long as ischium, inferior margin setulose, with 3 apically bifid setae; dactylus 0.6 times as long as propodus, unguis inferior margin with prominent serrate cuticular scales, secondary unguis recurved, blunt, simple. Pereopods 2–7 subsimilar, slender. Pereopod 2 basis 3.3 times as long as greatest width, inferior margin with 2 minute widely spaces setae; inferodistal angle with single simple seta, superior margin proximally with 2 palmate setae, with widely spaced small setae; ischium 0.9 times as long as basis, 3.3 times as long as greatest width, superior margin with 3 prominent acute RS, one set proximally, 2 set at midpoint, slender seta distally, inferior margin setulose at distal angle only; merus about half as long as ischium, superior distal angle with 2 apically serrate RS, inferior margin with dense setulose fringe with 4 short setae and 1 long simple seta; carpus slightly (1.1) times longer than merus, 1.9 times as long as greatest width, anterodistal angle with 1 short RS, distal half of inferior margin densely setulose; propodus 1.4 times as long as ischium, superior distal angle with 1 palmate seta, inferior margin with dense setulose fringe, with 6 simple setae none of which greatly exceed length of setulose fringe; dactylus about half as long as propodus. Pereopods 5–7 similar, longer and with more RS than pereopods 1 and 2. Pereopod 7 basis 4.8 times as long as greatest width, inferior margin without setae, superior margin with numerous widely spaced small setae, distally with 1 palmate seta; ischium 0.8 times as long as basis, 3.6 times as long as greatest width, proximal superior margin setulose with 4 prominent acute RS, inferior distal angle with 1 short simple setae; merus about half as long as ischium, superior distal angle with 2 short acute distally serrate RS, inferior margin with dense setulose fringe with 1 distally bifid RS; carpus 1.3 times as long as merus, anterodistal margin with 6 acute biserrate and 1 simple RS, inferior margin with dense setulose fringe, inferior distal angle with 1 simple and 2 stout biserrate RS; propodus about as long as ischium, 4 times as long as wide, inferior margin setulose but less dense than merus and carpus, distally with 2 short simple RS, superior distal angle with 1 simple and 1 palmate seta; dactylus 0.4 as long as propodus.

Penes 3.4 times as long as basal width; separated by about half basal width of penial process, straight with subacute apex.

Pleopod 1 exopod and endopod with c. 33 and 17 PMS respectively, exopod proximolateral RS prominent; endopod about as long as exopod, 1.7 times as long as greatest width. Pleopod 2 exopod and endopod with c. 34 and 22 PMS respectively; appendix masculina 18 times as long as wide, straight, distally glandular in appearance, apically acute, extending beyond endopod by 0.4 of its length. Pleopod 3 exopod and endopod with c. 37 and 14 PMS respectively; exopod transverse suture entire. Pleopod 4 rami without folds, distally with 1 PMS; exopod transverse suture entire, distal margin with 2 short PMS, lateral margin proximal to suture with continuous evenly spaced fine simple setae. Pleopod 5 with both rami lacking folds, endopod lateral margin with evenly spaced fine simple setae; exopod transverse suture entire, with 3 scale patches, 2 distal to suture, lateral margin with numerous evenly spaced simple setae. Uropod rami subequal in length, rami not extending beyond posterior margin of pleon, exopod with lateral margin convex with apex laterally falcate, endopod distally subtruncate with distolateral angle produced.

Female. Slightly smaller than males; body shape generally similar to that of male, dorsal surface markedly more ornamented.

Size. Males 4.6–6.6 mm, females 3.0– 4.6 mm.

Etymology. From Greek alveus (cavity, pit), alluding the pitted surfaces of this species.

Distribution. Southern NSW, Tas.; from ascidians, bryozoans, under rocks and in sand from intertidal to 6 m in NSW, 30 m in Tas.

Remarks. Although the large uropods and coarsely pitted dorsal surfaces of this species immediately separates it from all other species, Exosphaeroma alveola is strikingly similar to the South African E. planum Barnard, 1914 in the shape of the pleotelson and uropods, pleotelson ornamentation and the somewhat flattened body shape. In contrast to E. planum the posterior margin of the pleotelson extends well beyond the uropods.

Four Southern Hemisphere species of Exosphaeroma have similar pleotelson ornamentation, with the anterior dorsal surface with two submedian ridges and the posterior part being somewhat produced, with a median ridge. These species are E. antikraussi Barnard, 1940 , E. kraussi Tattersall, 1913 , E. varicolor Barnard, 1914 (also recorded from Australia by Hale, 1929) all from South Africa, and E. montis (Hurley and Jansen, 1978) comb. nov. (Appendix) from New Zealand.

Most species of Exosphaeroma have a group of long, simple setae at the midpoint of the superior margin of the ischium and at the distal margin of the merus of the pereopods. This is shown by the type species ( Brandt and Wägele, 1989), E. agmokara sp. nov., E. bruscai (Espinosa-Peréz and Hendrickx, 2002) and E. amplicauda ( Stimpson, 1857) ( Kussakin, 1979) , but has rarely been illustrated for other species. In the present species these setae are absent.

Figures

Figure 18. Exosphaeroma alveola sp. nov. A, B, E, G, holotype, remainder as indicated. A, dorsal view; B, lateral view; C, lateral view female; D, dorsal view, head and pereonite 1, female; E, frons; F, pleon and pleotelson, female; G, pleon, posterior margin, ventral view.

Figure 19. Exosphaeroma alveola sp. nov. A, antennule; B, antenna; C, left mandible; D, left mandible, distal part; E, right mandible, distal part; F, mandible palp; G, maxillule; H. maxillule, gnathal end, lateral lobe; I, maxillule, lateral lobe; J, penial processes.

Figure 20. Exosphaeroma alveola sp. nov. A, maxilliped; B, maxilla; C, pereopod 1; D, pereopod 1, dactylus; E, pereopod 2; F, pereopod 7, f, RS from carpus superior distal angle.

Figure 21. Exosphaeroma alveola sp. nov. A–E, pleopods 1–5.

Figure 22. Exosphaeroma alveola sp. nov. SEMs. Female, AM P51056. A, head; B, pleon, dorsal view; C, right mandible, spine row; D, right mandible, molar; E, maxillule, lateral lobe; F, maxillule, mesial lobe; G, pereopod 1, dactylus; H, pleopod 5, exopod.