Oecidiobranchus nowrae, Brix, 2006

Brix, Saskia, 2006, A new genus and new species of Desmosomatidae (Crustacea: Isopoda: Asellota) from the deep sea of south-eastern Australia, Memoirs of Museum Victoria 63 (2), pp. 175-205 : 185-186

Oecidiobranchus nowrae sp. nov.

Figures 8–10

Material examined. Holotype. Male , 1.4 mm, NMV J18606 . Australia, NSW, 65 km E of Nowra (34°55.52'S, 151°22.20'E), 2055 m depth, G.C.B. Poore et al., RV Franklin, 23 Oct 1988 (stn. SLOPE 63 ).

Diagnosis. Body length 3.83 times longer than width of pereonite 2. Pereonite 1 length 1.10 pereonite 2 length, similar to pereonite 2 width. Pereonite 5 anterior margin slightly convex, lateral margins straight. Lacinia mobilis of left mandible with 5 teeth. Coxae 1–4 produced, tipped with stout setae. PI carpus length 1.41 width, distodorsally with 1 long robust simple seta, ventrally with the large claw-seta and a row of distally setulate setae and setal combs inserted in a cuticular membrane, propodus length 2.61 width, more enlarged than carpus. Pleotelson with posterolateral spines.

Description. Habitus: body 1.4 mm long (measured without appendages), 3.83 times longer than width of pereonite 2. Pereonite 1 width 1.13 times cephalon width in dorsal view. Pereonite 1 length 1.10 pereonite 2 length, similar to pereonite 2 width. Pereonite 5 width 1.36 length, anterior margin slightly convex, lateral margins straight. Coxae 1–4 produced, tipped with stout setae. Pleotelson length 0.71 width, posterolateral spines present. Lateral margins convex, posterior margin rounded.

Antennula: 0.31 mm long, length 0.22 body length, with 5 articles. Article 1 with 3 broom setae. Article 2 length 1.53 width, 2.36 article 1 length; distally with 3 broom setae and 1 small seta. Article 3 with 1 slender seta, article 4 with 2 small broom setae, distal article with 1 aesthetasc, 1 broom seta and 4 long slender setae. Antenna: About 1 mm long, length about 0.71 body length, with 22 articles. Articles 3 with 3 small setae, article 4 with 3 small setae. Article 5 with 4 slender setae and distally 1 broom seta. Article 6 with 6 slender setae. Flagellum basally swollen (sexual dimorphism), articles with 1 or 2 slender setae each, distal article with 5 long slender setae.

Mandible: Article 2 of palp ventrodistally with 4 small setae, dorsally with rows of fine setae, apical article with 6 setae, distal one longest. Incisior process with 3 teeth. Lacinia mobilis of left mandible with 5 teeth. Right mandible not dissected from specimen. Spine row containing 5 spines. Molar process with 6 fine slender setae. Maxillula: Inner lobe slightly smaller than outer lobe, terminally with 5 setae. Outer lobe dorsally with 4 fine setae, terminally with 11 strong spines (4 spines with setules). Maxilla: Not dissected from specimen. Maxilliped: Epipodite length 3.13 width, length 1.43 endite length. Endite with 2 coupling hooks, terminally with 1 conate seta and numerous fine setae. Outer edge of endite and palp articles 1–3 fringed with numerous fine setae, distal corners tipped with 1 seta. Palp article 3 with 6 setae on inner margin, article 4 with 2 setae and article 5 with 4 setae. Article 1 length 0.5 width, article 2 length 1.16 width, article 3 length 1.07 width, article 4 length 1.1 width, article 5 length 1.6 width.

Pereopod I: Enlarged, chelate. Basis length 4.53 width, marginally with 1 small broom seta and 5 simple setae, proximal to ischium ventrally 1 long simple seta. Ischium length 1.87 width, distodorsally 1 simple seta, ventrally 2 simple setae. Merus length 1.13 width, ventrally 2 setal combs inserted in a cuticular membrane, distally 1 distally setulate and 1 simple seta, distodorsally 2 setae. Carpus length 1.41 width, distodorsally 1 long robust simple seta, ventrally with the large claw-seta and a row of distally setulate setae and setal combs inserted in a cuticular membrane. Propodus length 2.61 width, more enlarged than carpus, ventral and dorsal margin convex, distodorsally 2 small setae, ventrally fringed with fine setae and 9 small setae inserted in a cuticular membrane. Dactylus length 7.50 width, folding to propodus, mediodistally with 3 small setae. Unguis (claw) of dactylus with 1 cuspidate and 1 conate seta, 2 slender setae medially. Pereopod III: Pereopod II missing from specimen, pereopod III similar to pereopod IV. Basis length 5.70 width, marginally with 4 broom setae, 5 small slender setae and proximal to ischium ventrally 1 large simple seta. Ischium length 2.25 width, distodorsally 1 long simple seta and distoventrally 1 long simple seta. Merus length 2.50 width, dorsally with 2, ventrally with 1 simple seta. Carpus length 4.30 width, with ventral row of 4 long slender setae, dorsally with row of 4 setae. Propodus length 3.50 width, ventrally with row of 5 slender setae, dorsally with 4 slender setae and 1 small broom seta. Dactylus length 4 times width, mediodistally with 3 small slender seta. Unguis (claw) of 1 conate seta, 2 slender setae inserting ventrally. Pereopod V: Similar to pereopod VI and VII. Basis length 4 times width, marginally with 3 simple slender setae and 3 broom setae. Ischium length 2.64 width, dorsally with 4 slender setae, ventrally with 2 small slender setae. Merus length 1.89 width, 1 small slender seta distodorsally and 1 small slender seta distolaterally. Carpus length 3 times width, ventrally with row of 5 long slender setae, and distodorsally 1 small broom seta. Propodus length 3.4 width, ventrally with a row of 6 long slender setae, dorsally with 7 long slender setae and 2 unequally bifid setae (1 midway, 1 distally). Dactylus length 4 times width, mediodistally with 3 small slender setae, unguis (claw) of 1 long conate seta, 2 slender setae inserting ventrally.

Pleopod 1: Length 2.04 width. Outer margins straight, terminal margin rounded, with 3 small setae on each side. Pleopod 2: Sympod oval-shaped, length 2.24 width. Outer margin distally with 1 small seta. Endopod inserting 0.56 of sympod length. Pleopod 3: Endopod length 1.4 width, distally with 3 long plumose setae. Exopod length 0.52 of endopod length, terminally tapering, with 1 simple seta, outer margin hirsute. Pleopod 4: Endopod oval-shaped, length 1.92 width. Exopod missing.

Uropods: Uniramous. Endopod length 2.33 protopod length, 3.5 times longer than wide, distally with 3 broom setae, 1 small seta and 4 slender setae. Protopod length 1.5 width, with 3 simple slender setae.

Etymology. Nowrae (Lat.) means “from Nowra”. The name refers to the sampling area on the southern Australian continental slope 65 km E of Nowra.

Distribution. Off NSW, Australia.

Discussion. Oecidiobranchus nowrae sp. nov. is assigned to the genus Oecidiobranchus Hessler, 1970 on the basis of the small and rounded breathing chamber. The male of the new species differs from the other two species of the genus in the characters of pereopod I. Unlike O. plebejum Hansen, 1916 and O. nanseni Just, 1980 , O. nowrae possesses a ventral row of distally setulate seta on the carpus. Furthermore, the new species possesses posterolateral spines at the pleotelson. Neither O. plebejum , nor O. nanseni possess posterolateral spines at the pleotelson.

Figures

Figure 8. Oecidiobranchus nowrae sp. nov. Holotype male. NMV J18606. (A) Lateral and (B) dorsal views, antennae.

Figure 9. Oecidiobranchus nowrae sp. nov. Holotype male. NMV J18606. Mouthparts, pereopods I–V.

Figure 10. Oecidiobranchus nowrae sp. nov. Holotype male. NMV J18606. Pereopods VI and PVII, pleopods (Plp 1, 2, 3, 4, Urp).