Moruloidea perionasus, 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 : 350-355

Moruloidea perionasus sp. nov.

Figures 31–34

Material examined. Holotype. Male (7.0 mm, immature), Thistle Cove, WA, 34°0´S, 122°12´E, 11 Apr 1984, 5.0 m, G.C.B. Poore and H.M. Lew Ton ( NMV J39710 ).

Paratypes. SA. 2 males (6.2 immature, 5.5 adult [crushed] mm), north side of West I., Encounter Bay , 35°37´S, 138°36´E, 21 Mar 1985, 5 m, sediment at base of Heterozostera, G.C.B. Poore and H.M. Lew Ton ( NMV J26202 ) . Male (4.6 mm, immature), West I., Encounter Bay, 28 Jan 1990, under boulder fauna, S.A. Shepherd ( SAM C5744 ) .

Description of male. Body 1.8 times as long as greatest width (including anterior and posterior processes), widest at pereonites 1 and 5; dorsal surfaces of pereon, pleon and pleotelson granular. Head anterior margin strongly anteriorly produced to form anteriorly medially indented and bifid process, rostral process and frons distinctly ventral in position; head about 1.4 times as long as pereonite 1 in lateral view; pereonite 1 dorsally with ill-defined transverse band of tubercles, laterally with distinct boss and oblique thick longitudinal ridge; pereonites 2–4 narrower that pereonites 1 and 5, each with transverse row of small low tubercles; pereonite 5 wider than 4 and 6, coxae with prominent boss; pereonites 5–7 without distinct tubercles, pereonite 6 narrower than 7, pereonite 7 narrower than 6. Pleon posteriorly rounded in dorsal view, posterodorsal margin with low tubercles; sublateral pleonal ‘keys’ present. Pleotelson strongly vaulted, posterior margin with strongly produced dorsally arched process dorsal surface of which is provided with irregularly shaped nodules.

Antennule peduncle article 1 2.4 times as long as wide, about 8 times as long as article 2, anterior margin convex, posterior margin straight, angled obliquely distally; article 3 about as 0.5 times as long as article 1, about 3.6 times as long as wide, 4.0 times as long as article 2; flagellum 13-articled, extending to posterior of pereonite 1, about twice as long article 3. Antenna peduncle article 1 short, setose; articles 2 and 3 relatively elongate, article 2 2.5 times as long as wide, article 3 0.6 times as long as article 4, 1.7 times as long as wide; article 3, single long simple seta at superior distal angle; articles 2–4 collinear; article 4 0.8 times as long as article 5, 2.5 times as long as wide, superior margin with scale-setae; article 5 2.6 times as long as wide; flagellum stout, about 0.9 times as long as peduncle, extending to anterior of pereonite 2, with 11 articles.

Epistome anteriorly acute, with median constriction, surface irregular. Mandibles with both incisors unicuspid; left mandible with lacinia mobilis distally narrow, with 3 small cusps, spine row of 4 curved serrate spines; right mandible spine row of 1 broad-based bifid, multidigitate spine and 5 distally serrate spines; molar process round, crushing surface strongly ridged, marginally serrate; with basal group of 3 long plumose setae; palp not observed. Maxillule lateral lobe with 11 terminally acute serrate RS on gnathal surface, twelfth seta set between these. Maxilla lateral and middle lobes each with 6 curved finely serrate RS, mesial lobe with about 12 serrate and biserrate RS. Maxilliped endite lateral margin strongly convex, distal margin with 7 CP RS, 2 cactus setae, distomesial angle with 1 simple RS; distomesial margin with 3 large stout CP RS, increasing in size proximally; mesial margin of palp articles 2–5 with 9, 10, 12 and 8 long simple setae respectively; palp lateral margins without long setae, with 1 short simple seta at distal angle of article 3 and 4.

Pereopod 1 basis about twice as long as greatest width, approximately twice as long as propodus; ischium 1.2 times as long as propodus, 1.9 times as long as greatest width, superior margin with 1 proximal and 1 distal acute short simple RS; merus about 0.4 as long as ischium, 0.6 times as long as greatest width, superior distal angle with 2 acute simple RS inferior distal margin with 2 short bifid and 1 long acute simple; carpus inferior margin 1.2 times as long as merus, distally with 2 short bifid; propodus 1.5 times as long as greatest width, inferior lateral margin with 2 short biserrate RS, inferior margin with 3 stout bifid RS; dactylus 0.7 times as long as propodus, inferior margin with prominent serrate cuticular scales, secondary unguis simple, with distal point. Pereopod 2 basis 3.0 times as long as greatest width, margins with scattered scale-setae, superior margin with weak distal flange; ischium 0.75 times as long as basis, 2.8 times as long as greatest width, superior margin with 1 proximal and 1 distal acute short simple RS, merus about 0.7 times as long as ischium, superior distal angle with 2 short acute RS, inferior margin with 2 short stout acute setae and 1 long simple seta; carpus about as long as merus, superior distal angle with 1 simple seta, inferior margin with 2 acute simple setae, distal angle with 1 RS; propodus about as long as ischium, 1.6 times as long as carpus, superior distal angle with 1 simple and 1 palmate setae, inferior margin with 3 short stout acute RS; dactylus 0.5 times as long as propodus. Pereopods 5–7 similar, basis and ischium relatively longer than for pereopod 2, distal margins of carpus with more and longer RS. Pereopod 7 basis 4.4 times as long as greatest width, inferodistal angle with single simple seta, superior margin with widely-spaced small scale-setae; ischium 0.9 times as long as basis, 5.7 times as long as greatest width, superior margin with 1 proximal short acute RS, merus 0.4 times as long as ischium, superior distal margin with 1 acute RS, inferior distal angle with 1 stout acute seta; carpus about as long as merus, anterodistal angle with 3 long acute finely serrate and 1 simple RS, inferior margin with 2 stout short acute RS, inferior distal angle 3 finely biserrate RS; propodus 1.5 times as long as carpus, 0.7 times as long as ischium, superior distal angle with 2 palmate seta, inferior margin with 3 short stout acute RS; dactylus 0.4 times as long as propodus.

Penes mutually adjacent, twice as long as basal width; mesial margin straight, lateral margin angled mesially, apex bluntly rounded.

Pleopod 1 exopod and endopod with c. 17 and 16 PMS respectively, endopod mesial margin setulose; endopod subtriangular, 0.9 times as long as exopod, 1.5 times as long as greatest width; exopod lateral and mesial margins subparallel, distal margin rounded. Pleopod 2 exopod and endopod with c. 18 and 27 PMS respectively; appendix masculina 11 times as long as wide, slightly wider proximally, weakly sinuate, apex bluntly rounded. Pleopod 3 exopod and endopod with c. 50 and 18 PMS respectively. Pleopod 4 exopod lateral margin with 3 fine simple setae, distal part triangular, both margins with fine setae; endopod without setae. Pleopod 5 exopod with 2 distal bi-lobed scale patches, lateral margin with scattered minute simple setae; endopod with fine setae on distal margin only. Uropod peduncle dorsal surface densely covered with small nodules and minute hemispherical structures; endopod mesial margin straight, lateral margin with distal half angled mesially, distolateral margin subapically excavate; lateral margin entirely fringed with expanded cuticular scales; exopod small, 0.2 as long as endopod and peduncle, setin to anterolateral angle.

Female. Similar to male; ovigerous females not known.

Etymology. From Greek periosus (immense) and nasus (nose), alluding the hugely projecting anterior margin of the head; noun in apposition.

Distribution. Thistle Cove, Great Australian Bight, WA, to Encounter Bay, SA; intertidal to 5 m.

Remarks. This remarkable spindle-shaped isopod is easily recognized by the prominent anterior cephalic and pleotelson projections. No other species in the genus has such ornamentation, and in addition the uropodal exopod is reduced to an inconspicuous small flat stub. These characters distinguish Moruloidea perionasus from all other sphaeromatids except perhaps Bregmotypta Bruce, 1994c , the only genus with similar cephalic and pleotelsonic projections. There are many differences at generic level, but in Bregmotypta the cephalic process is single and the pleotelson has two prominent bosses, while in M. perionasus the anterior process is doubled, and the posterior process is single and elongate.

Character states that support inclusion in Moruloidea are: antenna with expanded and reflexed articles 4 and 5; close-set, terminally rounded short, flat penial processes; appendix masculina arising basally, not distally narrowed and longer that ramus; pereopod 1 much more robust than pereopods 2–7, the propodus of which has a proximal extension; coxae 5 overlapping anteriorly and posteriorly; uropodal rami lamellar with exopod smaller than endopod. Other characters such as mouthparts and pleopods present a consistent appearance with other species of the genus.

The immature specimen was selected as holotype as it was the most intact specimen. The propodus of pereopod 1 in this juvenile lacks the prominent ‘heel’ of the adult male although that part of the inferior margin is weakly produced; the dactylus lacks the scales on the inferior margin.

Figures

Figure 31. Moruloidea perionasus sp. nov. A–D, holotype, remainder male paratype, NMV J26202. A, dorsal view; B, lateral view; C, frons, ventral view; D, pleon, posterior margin, posterior view; E, antennule; F, antenna; G, maxilliped; H, penes.

Figure 32. Moruloidea perionasus sp. nov. Male paratype, NMV J26202. A, right mandible; B, left mandible; C, maxilliped; D, maxilliped endite, distal margin; E, maxilla; F, maxillule; G, pereopod 1, propodus.

Figure 33. Moruloidea perionasus sp. nov. A, pereopod 1 holotype; remainder male paratype, NMV J26202: B, pereopod 2; pereopod 7.

Figure 34. Moruloidea perionasus sp. nov. Male paratype, NMV J26202. A–E, pleopods 1–5; F, uropod; G, detail of uropod dorsal surface.