Pseudomesus satanus, Kaiser, Stefanie & Brix, Saskia, 2007

Kaiser, Stefanie & Brix, Saskia, 2007, Two new species of the genus Pseudomesus Hansen, 1916 (Isopoda, Asellota) from the Southern hemisphere: Pseudomesus pitombo sp. nov. and Pseudomesus satanus sp. nov., Zootaxa 1658, pp. 21-38 : 33-37

Pseudomesus satanus sp. nov.

( Figs 7–9 )

Material examined. Holotype: Ψ (preparatory, 1.7 mm), Australian continental slope, 38°23.95'S, 149°17.02'E, RV Franklin, Station SLOPE 67, 1277– 1119 m, leg. G.C.B Poore, NMV J18597 .

Diagnosis. Body length 6.2 times longer than width of pereonite 2. Cephalothorax with 2 cephalic spines and a row of small setae on frons. Antennula with 5 articles, article 2 length 3.4 times width, 1.5 times article 1 length; with serration resembling 4 “teeth” and with 3 broom setae distally. Pleotelson inflated dorsally, length subequal width, lateral margins convex, tapering to posterior margin. Uropods uniramous, bulbous, not overlapping posterior margin of pleotelson, overlapping anus valves; endopod length 1.5 times protopod length, 1.9 times longer than wide.

Description. Habitus of female holotype ( Fig. 7 A): Body 1.7 mm long (measured without appendages), length 6.2 times pereonite 2 width. Pereonite 1 width 1.1 times cephalothorax width in dorsal view. Frons clypeal furrow present, 2 cephalic spines and a row of small setae on frons. Pereonite 1 length 0.8 times pereonite 2 length, 1.1 times pereonite 2 width. Pereonite 5 anterior and lateral margins straight. Coxae 1–4 slightly produced, without setae. Pleotelson dorsally inflated, length 1.2 times width, posterolateral spines absent. Lateral margins convex, tapering towards posterior margin.

Antennula ( Fig. 7 B) about 0.25 mm long, length 0.2 times body length, with 5 articles. Article 1 with 3 broom setae. Article 2 length 3.4 times width, 1.5 times article 1 length; with serration resembling 4 “teeth” and 3 broom setae distally (1 broken off). Article 3 with 1 small “tooth”; article 4 with 1 broom seta; terminal article with 1 aesthetasc and 2 slender setae terminally.

Antenna ( Fig. 7 C) about 1 mm long, length 0.8 times body length; with 6 peduncular and 9 flagellar articles. Article 5 with 2 broom setae and 2 simple setae. Article 6 with 1 large and 3 small broom setae and with 1 slender and 2 small setae distally. Flagellar articles 1–8 with 2 slender setae each; terminal article with 4 long slender setae distally.

Mandibles ( Fig. 7 E): left mandible was not dissected from the holotype. Palp articles 1 and 2 of right mandible without setae; apical article with 9 ventral setae, distal one longest. Incisor with 1 strong tooth. Lacinia mobilis with 3 small teeth; spine row with 5 spines. Molar with 10 slender setae.

Inner lobe of Maxillula ( Fig. 7 F) slightly smaller than outer lobe (lost during dissection). Outer lobe length 4.1 times width, dorsal margin with 6 pairs of fine setae, ventral margin with 6 small simple setae, terminally with 11 strong spines (4 of them with setules).

Medial lobe of Maxilla ( Fig. 7 G) shorter than outer lobes; without setae terminally, with 7 fine setae marginally. Outer lobe length 6.8 times width, with 3 setae terminally.

Left and right maxilliped ( Fig. 7 D) connected by 2 retinacula. Epipodite length 3.6 times width, length 1.1 times endite length. Endite with numerous fine setae marginally and terminally. Edge of endite and palpal articles 1 and 2 fringed with a row of fine setae and 1 seta on tip. Article 1 length 0.6 times width; article 2 length 1.1 times width; article 3 length 0.9 times width, inner margin with 5 setae, outer margin with 2 setae; article 4 length 1.3 times width, with 3 setae; article 5 length 2 times width, with 3 terminal setae.

Pereopod 1 ( Fig. 8 A) basis length 3.8 times width; with 1 broom seta and 1 small seta marginally and with 1 simple seta distoventrally. Ischium length 2.5 times width; with 1 composed seta dorsally and 1 small seta ventrally. Merus length 1.5 times width; with 1 composed and 1 simple seta distodorsally and with 2 unequally bifid distally setulate setae and 1 comb of fine setules in cuticular membrane ventrally. Carpus length 4.4 times width; with 1 small seta distodorsally and with 3 unequally bifid distally setulate setae and 3 combs of fine setules inserted in cuticular membrane ventrally. Propodus length 2.9 times width; with 1 small seta distodorsally and with few small slender setae, fringed with fine setules inserted in cuticular membrane, ventrally. Dactylus length 4.2 times width; with 3 small slender setae medially; unguis with 1 robust cuspidate and 1 conate seta and with 2 slender setae in between.

Pereopod 2 ( Fig. 8 B) similar to pereopods 3 and 4 ( Fig. 8 C, 9A). Basis length 3.5 times width; with 1 small broom seta dorsally and 3 small setae ventrally. Ischium length 2.8 times width; with dorsal hook and 1 small seta ventrally. Merus length 1.2 times width; with 1 seta distodorsally (broken off) and 1 small seta distoventrally. Carpus length 4.4 times width; with 2 slender simple setae dorsally and with 5 robust unequally bifid setae and 6 combs of fine setules inserted in cuticular membrane ventrally. Propodus length 2.9 times width; with 1 small broom seta distodorsally and with 2 robust unequally bifid setae fringed with fine setules inserted in cuticular membrane ventrally. Dactylus length 4.2 times width; with 3 small slender setae medially; unguis with 1 conate seta dorsally and 2 slender setae ventrally.

Pereopod 5 ( Fig. 9 B) similar to pereopods 6 and 7 ( Fig. 9 C–D). Basis length 5.3 times width; with 3 broom setae dorsally, with 2 small seta ventrally. Ischium length 3.5 times width; with 1 dorsal hook. Merus length 2 times width; with 2 robust setae distodorsally and with 1 small seta distoventrally. Carpus length 5.6 times width; with 1 small broom seta and 1 small seta distodorsally and with 2 long slender setae and 3 combs of fine setules inserted in cuticular membrane ventrally. Propodus length 5.1 times width; with 1 small broom seta and 1 long slender seta distodorsally and with 4 slender setae of varying size and 1 comb of fine setules inserted in cuticular membrane ventrally. Dactylus length 5 times width; unguis with 1 long conate seta dorsally and 2 slender setae ventrally.

Pleopod 2 (operculum, Fig. 8 D) length 1.1 times width; margins rounded, with 4 slender setae on distal margin.

Endopod of pleopod 3 ( Fig. 8 E) length 1.2 times width; with 3 long plumose setae distally. Exopod length 0.6 times endopod length; inner margin hirsute, with 1 small seta distally.

Endopod of Pleopod 4 ( Fig. 8 F) oval-shaped, length 2.3 times width. Exopod length 3.9 times width; outer margin with row of fine setae, with 1 long plumose seta distally.

Uropods ( Fig. 8 G) uniramous, bulbous, not overlapping posterior margin of pleotelson, overlapping anus valves. Endopod length 1.5 times protopod length, 1.9 times longer than wide; with 3 broom setae, 5 slender simple setae of varying size terminally. Protopod length 1.5 times width, with 3 slender setae.

Type locality. Australian continental slope, South Pacific.

Distribution. Only known from type locality.

Etymology. The name satanus (masculine) refers to the devil-like cephalic spines at the cephalothorax of the new species.

Remarks. Pseudomesus satanus sp. nov. is assigned to the genus Pseudomesus due to the elongated body (more than 6 times pereonite 2 width), the enlarged dorsally inflated pleotelson, the extremely short uropods and the characters of the pereopod 1. This new species is most similar to P. p i t o m b o sp. nov., but can be distinguished from the latter by the following characters: cephalothorax width 1.5 times length, anterior margin medially vaulted, with two cephalic spines and a row of small setae on frons; article 4 of antennula with 1 long broom seta; antenna with 9 flagellar articles; exopodit of maxilliped reaching fourth palpal article. Both species can be distinguished from the remaining species of the genus by the presence of a well developed mandibular palp.

Figures

FIGURE 7. Pseudomesus satanus sp. nov., holotype female (NMV J 18597). A, habitus dorsal view. B, antennula. C, antenna. D, maxilliped. E, right mandible. F, maxillula. G, maxilla. Scale bar: A = 1 mm; B – G = 100 µm.

FIGURE 8. Pseudomesus satanus sp. nov., holotype female. A – C, pereopods 1 – 3. D, pleopod 2 (operculum). E – F, pleopods 3 – 4. G, uropod. Scale bar = 100 µm.

FIGURE 9. Pseudomesus satanus sp. nov., holotype female. A – D, pereopods 4 – 7. Scale bar = 100 µm.