Paradesmosoma australis, 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 : 180-181

Paradesmosoma australis sp. nov.

Figures 4–7

Material examined. Holotype. Female , preparatory, NMV J18608 ; Type locality. - Australia, Vic., S of Point Hicks (38°17.70'S, 149°11.30'E), depth 400 m, WHOI epibenthic sled, RV Franklin, 24 Jul 1986 (stn. SLOPE 40 ).

Diagnosis. Body length about 4.4 times longer than width of pereonite 2. Palp of left mandible with 2 articles, article 2 length 2.10 width, tapering to distal end, terminally 1 small seta, margins hirsute. Pereonite 1 length 1.36 pereonite 2 length. Coxae 1–4 faintly produced, without setae. Pleotelson anteriorly widest, about as wide as long, posterolateral spines present, lateral margins slightly convex, posterior margin slightly rounded. Uropods uniramous, endopod length 4.82 protopod length, 10.25 times longer than wide.

Description. Habitus: body 2.6 mm long, 4.36 times longer than width of pereonite 2. Pereonite 1 width 1.44 times cephalon width in dorsal view. Pereonite 1 length 1.36 pereonite 2 length, 0.97 pereonite 2 width. Pereonite 5 anterior margin straight, lateral margins slightly concave. Coxae 1–4 faintly produced, without setae. Pleotelson anteriorly widest, about as wide as long, posterolateral spines present, lateral margins slightly convex, posterior margin slightly rounded.

Antennula: About 0.26 mm long, length about 0.10 body length, with 5 articles. Article 1 with 1 small slender seta and 4 small broom setae. Article 2 length 3.70 width, 1.48 article 1 length; marginally with 2 slender setae, distally with 2 long articulated broom setae. Article 3 with 2 slender setae, article 4 distally with 1 broom seta, distal article with 1 aesthetasc, 1 broom seta and 2 long slender setae. Antenna (fig. 5): broken off.

Mandible: Palp of 2 articles. Article 1 without setae, article 2 length 2.1 width, tapering to distal end, terminally 1 small seta, margins hirsute. Incisior process with 3 teeth. Lacinia mobilis of left mandible with 3 teeth, right mandible not dissected from specimen. Spine row containing 8 spines. Molar process large, with 12 slender setae. Maxillula: Inner lobe not dissected from specimen. Outer lobe broken off from inner lobe, marginally with 6 ventral setae and 6 dorsal setae, terminally with 12 strong spines. Maxilla: Medial lobe as long, slightly broader than other lobes, terminally with 3 slender setulate setae, marginally with 14 setae, setae inserting near base longest. Outer lobe terminally with 3 long slender setulate setae, dorsal margin with 5 pairs of fine setae. Maxilliped: Epipodite length 3.31 width, length 1.17 endite length, outer margin hirsute. Endite with 2 coupling hooks, with numerous fine setae. Edge of endite and palp articles 1–3 fringed with row of fine setae and 1 seta on distal corner. Palp article 2 with 6 setae on inner margin, article 3 with 12 setae on inner margin, article 4 with 3 setae, article 5 with 4 setae. Article 1 length 0.37 width, article 2 length 1.03 width, article 3 length 0.85 width, article 4 length 1.5 width, article 5 length 1.50 width.

Pereopod I: Basis length 2.57 width, near coxa with 1 distally slender plumose seta, 5 simple slender setae and proximal to ischium 1 slender seta. Ischium length 2.43 width, ventrally with row of 6 simple setae, dorsolaterally with row of 7 simple setae. Merus length 0.72 width, distodorsally 1 simple slender seta, ventrally with a row of 5 simple setae, 2 distally setulate setae and 1 stout unequally bifid seta. Carpus length 1.44 width, with dorsolateral row of 5 simple slender setae, distoventrally with claw-seta and a ventral row of setae of irregular size and type: 3 robust unequally bifid setae and 5 slender setae (1 slender seta inserting proximal to propodus). Propodus broadest at articulation to carpus, tapering towards dactylus, length 3.05 width, ventrally fringed with fine setae and 12 small setae inserted in cuticular membrane. Dactylus length 5 times width, mediodistally with 3 small setae. Unguis (claw) of 1 conate setae, 3 slender setae inserting ventrally. Pereopod II: Similar to pereopod III, different from pereopod IV. Basis length 3.04 width, marginally with 7 slender setae and 1 small broom seta, proximal to ischium ventrally with bunch of 5 distally slender plumose setae. Ischium length 3 times width, ventrally with row of 23 distally slender plumose setae, dorsally with 5 setae. Merus length 1.86 width, with dorsolateral row of 9 long simple setae, ventrally with 6 simple slender setae and 2 distally setulate setae. Carpus length 3.05 width, with ventral row of 8 robust unequally bifid setae increasing in length towards propodus, distal seta of row as long as propodus, dorsally with row of 12 simple setae. Propodus length 4.18 width dorsally, ventrally 4 small slender setae, dorsally 7 setae. Dactylus length 5.60 width, mediodistally with 3 small seta. Unguis (claw) of 1 long conate seta, 2 slender setae inserting ventrally. Pereopod IV: Basis marginally with 8 distally slender plumose setae. Ischium length 1.77 width, ventrally with row of 24 distally slender plumose setae and dorsally 3 slender setae. Merus length 1.67 width, with 9 simple slender setae and ventral row of 13 distally slender plumose setae. Carpus length 2.41 width, with dorsal row of 16 slender setae and a ventral row of 33 distally slender plumose setae. Propodus length 1.66 width, dorsally with 24 simple slender setae, ventrally with row of 25 distally slender plumose setae, distally 2 small slender setae. Dactylus width 0.13 propodus width, length 1.5 width, 3 small setae mediodistally. Unguis (claw) with 1 conate seta, 2 slender setae ventrally. Pereopod VI: Similar to pereopod V and pereopod VII. Basis length 1.93 width, with few small slender setae and 1 long slender seta ventrally proximal to ischium. Ischium length 2.15 width, ventrally with 1 simple seta, distodorsally 2 simple slender setae. Merus length 1.21 width, with 2 ventral setae, distodorsally 1 simple slender seta. Carpus length 3.53 width, ventrally with row of 6 long distally setulate setae and 1 short unequally bifid seta, dorsally with row of 7 simple slender setae. Propodus length 3.91 width, ventrally with row of 11 long distally setulate setae, dorsally with row of 4 simple slender seta, distally 1 small broom seta. Dactylus length 6.75 width, proximal to unguis (claw) 4 simple slender setae. Unguis (claw) of 1 long conate seta.

Pleopod 2 (operculum): Length 0.93 width, lateral margins slightly convex, distal margin deeply concave, with 4 small simple setae. Pleopod 3: Endopod length 1.62 width, distally with 3 long plumose setae. Exopod length 0.75 of endopod length, margins hirsute, distally with 1 small seta. Pleopod 4: Endopod oval-shaped, length 2.31 width. Exopod length 5 width, distally 1 long plumose seta, outer margin hirsute.

Uropods Uniramous. Endopod length 4.82 protopod length, 10.25 times longer than wide, marginally with 2 small broom setae, distally with 4 slender setae and 5 broom setae. Protopod length 1.7 width, with 3 simple slender setae.

Etymology. Australis (Latin) , means “from the south”. The name refers to the fact that this species is the first record of the genus Paradesmosoma from the southern hemisphere.

Distribution. South-eastern Australia, off Vic.

Discussion. The new species is assigned to the genus Paradesmosoma Kussakin, 1965 based on the characteristic shape of pereopod IV, the kind of setation of this pereopod, carpus and propodus “paddle-like” and surrounded by numerous distally slender plumose setae (occurring in Paradesmosoma only) and the characters of pereopod I: carpus less enlarged than propodus, with ventral row of irregular setae of varying types. P. australis sp. nov. is most similar to P. orientale Kussakin, 1965 in the shape of palp article 2 of the mandible. As in P. orientale , palp article 2 is about 2.17 times longer than wide and tapers to the distal end which is tipped by a small simple setae. In contrast to P. orientale , the lateral margins of this article are hirsute in P. australis . According to Kussakinʼs (1965) drawings, neither P. orientale nor P. conforme Kussakin, 1965 possesses posterolateral spines on the pleotelson. P. australis has posterolateral spines on the pleotelson. Unlike in the two species from the northern hemisphere, the propodus of pereopod I is posteriorly widest in P. australis and tapers toward the dactylus.

Figures

Figure 4. Paradesmosoma australis sp. nov. Holotype female. NMV J18608. (A) Lateral and (B) dorsal views.

Figure 5. Paradesmosoma australis sp. nov. Holotype female. NMV J18608. Antennae, mouthparts and pereopod I.

Figure 6. Paradesmosoma australis sp. nov. Holotype female. NMV J18608. Pereopods II–V.

Figure 7. Paradesmosoma australis sp. nov. Holotype female. NMV J18608. Pereopods VI and VII, pleopods (Op, Plp 3, Plp 4, Urp).