Pseudomesus pitombo, 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 : 23-33

publication ID	https://doi.org/ 10.5281/zenodo.274018
DOI	https://doi.org/10.5281/zenodo.5662160
persistent identifier	https://treatment.plazi.org/id/BE0F0011-FFEE-FFA6-FF3A-FBFBFBF2FE21
treatment provided by	Plazi
scientific name	Pseudomesus pitombo
status	sp. nov.

Treatment

Pseudomesus pitombo View in CoL sp. nov.

( Figs 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype: 1 ɗ (adult, 1.5 mm), Angola Basin, 16°18.1`S, 005°27.2`E – 16°19.3`S, 005°527.2`E, RV Meteor (48/1), station 348, 5390– 5387 m, ZMH K–41066.

Paratypes: 1 Ψ (preparatory, 3.4 mm), Angola Basin, 18°18.3`S, 004°41.3`E – 18°19.4`S, 004°41.9`E, RV Meteor (48/1), station 340, 5395 m, ZMH K–41067. 1 Ψ (juvenile, 1.8 mm), Angola Basin, 17°06.2`S, 004°41.7`E – 17°07.5`S, 004°42.3`E, RV Meteor (48/1), Station 344, 5415 m, ZMH K–41068.

Diagnosis. Mandible with palp; carpus and propodus of pereopods 2–4 long and slender (length> 6.5 width); coxa 1 in female strongly produced, visible in dorsal view.

Description. Habitus of male holotype ( Fig. 1 View FIGURE 1 A–B): Body approximately 1.5 mm long (measured without appendages), length 6.9 times pereonite 2 width. Surface alveolar structured, with few simple setae. Pereonites 1–4 increasing in length caudally; pereonite 2 widest, width 2.2 times length, about 1.2 times pereonite 1 width. Pereonite 1 about 3.5 times wider than long, 0.6 times pereonite 2 length; pereonite 3 almost twice as long as wide, width 0.8 times pereonite 2 width; pereonite 4 width times 1.5 length, lateral margin convex. Pereonites 5–7 decreasing in length caudally. Pereonite 5 longest, length 3.5 times pereonite 1 length, as long as wide, width increasing caudally like in pereonites 6–7; anterior margin slightly concave, lateral margin straight. Pereonite 6 as wide as pereonite 2, lateral margins of pereonites 6–7 straight. Coxae 1–7 visible in dorsal view; coxa 1 tipped with a robust spine, coxae 2–4 each with slender seta. Pleotelson ( Fig. 1 View FIGURE 1 C) 0.2 times body length, 1.3 times wider than long, almost as wide as pereonite 2; anterior margin straight, posteriorly strongly bended, with two posterolateral spines, 0.7 from anterior margin, acute-angled, caudally bended. Anus laterally and caudally covered by anus valves. Uropods inserting closely to anus valves, covering them partially.

Cephalothorax ( Fig. 1 View FIGURE 1 D) 1.3 times longer than wide, triangular, mediofrontally vaulted, posterior margin strongly convex.

Antennula like in female.

Antenna ( Fig.1 View FIGURE 1 E) robust, about 0.6 mm long; length 0.4 times body length, with six peduncular and 17 flagellar articles. Peduncular articles 1–4 short, articles 1, 2 and 4 of similar size, almost rectangular, article 3 length 1.7 times article 4 length, with 1 simple seta; article 5 length 2.4 times width, with 1 small seta distally; article 6 somewhat shorter than article 5, as long as article 1–4 together, length 2.3 times width, with 1 long and 2 short broom setae and 3 simple slender setae of varying size distally. Flagellar articles 1–17 decreasing in width and length distally; article 1 length 2.4 times article 2 length, as long as wide. Articles 1–10 with row of long, simple setae; some articles with 1–3 fine simple setae; article 17 with 5 long and 4 short slender setae terminally.

Pereopod 1 ( Fig.1 View FIGURE 1 A) more robust than pereopods 2–7; basis length 5.8 times width; with 1 small seta ventrally. Ischium 0.6 times basis length, 3.2 times longer than wide; with 1 small seta distodorsally. Merus about half of ischium length, 1.4 times longer than wide; with 2 setae of different size dorsally, with a ventral hook.

Carpus length 3 times merus length, 4.4 times longer than wide; with row of fine hairs inserted in cuticular membrane and 3 robust unequally bifid setae ventrally. Propodus length 1.1 times carpus length, about 4 times longer than wide; with 1 simple seta distodorsally and a row of fine hairs inserted in cuticular membrane ventrally, with 2 short simple setae distally. Dactylus length 0.6 times propodus length, 5.3 times longer than wide; with 3 simple setae medially; unguis with 1 short robust cuspidate seta dorsally and 2 slender setae of same length ventrally.

Pereopods 2–4 ( Fig. 2 View FIGURE 2 B–D): basis of pereopods 2 and 3 missing; pereopod 4 basis length 6.8 times width; with 1 broom seta dorsally. Ischium of pereopods 2–4 length 4.3 times width; with 1 slender seta distodorsally, pereopod 4 with a proximal hook. Merus length 1.8 times width; with 1 long slender seta dorsally, pereopod 2 additionally with 1 short seta distally, pereopods 2–3 with 1 small, simple seta ventrally. Pereopods 2– 3 carpus length 6.5 times width, pereopod 4 carpus length 8.8 times width; pereopods 2–4 with 3–4 slender simple setae dorsally, decreasing in length distally, with row of fine hairs inserted in cuticular membrane ventrally, with 3–6 robust unequally bifid setae increasing in length distally. Propodus length about 6.8 times width; with 1–3 short simple setae dorsally, pereopods 2 and 3 with row of fine setules inserted in cuticular membrane and 2–3 short robust unequally bifid setae ventrally. Dactylus of pereopods 2–3 length 6 times width, of pereopod 4 length 5 times width; pereopod 2 and 4 with 2–4 small setae medially; claw of pereopods 2–4 length 0.3 times dactylus length, with 2 short cuspidate setae and 2 slender simple setae in between.

Pereopods 5–7 ( Fig. 2 View FIGURE 2 E–G) more slender than pereopods 1–4; basis of pereopod 6 missing, of pereopod 5 damaged proximally. Pereopod 7 basis length 7.1 times width, pereopod 5 and 7 with 1 slender simple seta and 2 broom setae dorsally, and with 1 short simple seta and 1 broom seta ventrally. Ischium of pereopod 5–7 length 4.3 times width; with 1 slightly produced hook dorsally and with 1 fine simple seta ventrally. Merus length twice width; with 1–2 dorsal and 1 ventral fine simple seta. Carpus length 7 times width; carpus and propodus with row of long and slender natatory setae; with 11 natatory setae on carpus and propodus; ventral row reduced; carpus of pereopod 6 with 4 long natatory setae ventrally, pereopods 5–7 additionally with 2 robust, composed setae and 1–2 slender simple setae ventrally. Propodus length 8.6 times width; with 5–6 long slender natatory setae ventrally and 3 somewhat shorter simple setae distally. Dactylus length 7 times width; unguis of pereopod 7 with 1 robust cuspidate seta dorsally and 1 slender somewhat longer seta ventrally.

Pleopod 1 ( Fig. 1 View FIGURE 1 F) long, proximally slender, width increasing distally. Lateral margins slightly concave with 1 fine seta; distal margin slightly concave, with some fine setae.

Protopodit of pleopod 2 ( Fig. 1 View FIGURE 1 G) length 2.6 times width; with 4 slender, simple setae distolaterally. Endopodite inserting 0.3 of distal tip; stylet length 0.8 times protopodite length, distal part slender, width 0.2 times proximal part width. Exopodite small, without setation.

Uropods ( Fig. 1 View FIGURE 1 C) like in female.

Descriptive notes on males. Habitus ( Fig. 1 View FIGURE 1 A–B) more slender than in female, coxae 1–5 more produced, coxae 1–7 visible in dorsal view. Pereonites 2 and 6 widest; pleotelson with 2 posterolateral spines. Cephalothorax longer than wide, anterior margin mediofrontally vaulted. Antenna ( Fig. 1 View FIGURE 1 E) more robust, flagellum setose, with 17 flagellar articles. Pereopods 5–7 ( Fig. 2 View FIGURE 2 E–G) with long natatory setae on dorsal margin of carpus and propodus; ventral row reduced.

Description of paratype female. Habitus ( Fig. 3 View FIGURE 3 A, C): Body 3.4 mm long, 5.3 times longer than width of pereonite 1; surface with few single setae. All pereonites free, dorsoventrally not considerably flattened; pereonites 1–4 decreasing in width and increasing in length caudally; pereonite 1 width 4.6 times length; pereonite 2 width 2.5 times length, pereonite 3 twice as long as wide; pereonite 4 width 1.6 times length. Pereonites 5–7 of same width, decreasing in length caudally; pereonite 5 longest, length 3.1 times pereonite 1 length, almost as long as wide, increasing in width caudally. Coxae 1 and 5–7 visible in dorsal view; coxa 1 tipped with 1 fine seta. Pleotelson ( Fig. 6 View FIGURE 6 H) length 0.2 times body length; 1.4 times longer than wide; width 0.8 times pereonite 1 width; anterior margin straight, posterior margin strongly bended. Anus laterally covered by anus valves; uropods inserting closely to the anus valves, covering them partially.

Cephalothorax ( Fig. 3 View FIGURE 3 A, C) free, oval shaped; length 1.2 times width, about 0.2 times body length. Anterior margin almost straight, posterior margin strongly convex.

Antennula ( Fig. 4 View FIGURE 4 C) 0.3 mm long; length 0.1 times body length, with 5 articles. Article 1 short, with 1 short broom seta and 1 seta broken off; article 2 length 1.6 times article 1 length, with 1 long broom seta distally. Article 3 length 0.3 times article 2 length. Article 4 length 0.25 times article 2 length, with 2 small simple setae. Terminal article minute; length 0.2 times article 2 length, with 3 long slender setae and 1 aesthetasc.

Antenna ( Figs 3 View FIGURE 3 B, 4A) about 1.4 mm long, length 0.4 times body length, with 6 peduncular and 10 flagellar articles. Peduncular articles 1–4 short, articles 1, 2 and 4 of similar size; article 3 length twice article 4 length, with 1 small seta; articles 1–4 together as long as article 5. Article 5 length 4 times width, with 2 short setae distally. Article 6 length 1.3 times article 5 length, 6 times width, with 2 broom setae and 3 simple setae of varying size distally. Length of flagellar articles 1–10 decreasing distally; articles 1–9 with up to 4 fine setae distally, article 10 with 5 long slender setae terminally.

Palp of left and right mandible ( Fig. 4 View FIGURE 4 D–E) not reaching tip of incisor. Articles 1 and 2 of same length, article 2 of right mandible with 1 slender seta; article 3 length 0.25 times article 2 length, with few short setules. Incisor of right and left mandible with 2 teeth. Lacinia mobilis of left mandible with 3 teeth; setal row with 17 slender setae, of right mandible with 13 slender setae. Molar of left mandible almost as long as palp, with 16 slender simple setae, of right mandible with 14 slender simple setae.

Maxillula lost during dissection.

Outer margin of maxilla ( Fig. 4 View FIGURE 4 F) outer and inner lobe with some slender setae of varying size. Outer and medial lobe with 2–3 robust long setae, distal margin of inner lobe with several fine setae, surface of medial and inner lobe with few fine setae.

Right and left maxilliped ( Fig. 4 View FIGURE 4 G) connected by 2 retinacula. Epipodite triangular, surface smooth, length 3.2 times width, almost reaching palpal article 3. Palpal article 1 length almost half of article 2 length; article 2 almost as long as wide, with several slender setae, decreasing in length distally; article 3 somewhat shorter than article 2, somewhat wider than long, with 6 slender setae; article 4 length 0.7 times article 3 length, half as long as wide, with 4 slender simple setae; article 5 half of article 4 width, terminally with 5 fine setae. Endite with several slender setae laterally and distally. Protopodite oval, width 1.5 times length.

Pereopod 1 ( Fig. 5 View FIGURE 5 A) more robust than pereopods 2–7; basis lost during dissection. Ischium length 3 times width; with 1 robust seta distodorsally, length twice merus length. Merus length 1.2 times width; with 1 robust and 1 more slender seta dorsally, with a row of fine setules inserted in cuticular membrane and 2 robust unequally bifid setae ventrally; merus half of carpus length. Carpus length 3.2 times width; with 1 short seta distodorsally, with a row of fine setules inserted in cuticular membrane and 3 robust unequally bifid setae ventrally increasing in length distally; carpus length 1.3 propodus length. Propodus length 3.3 times width; with 1 short slender seta distodorsally, ventral margin with row of fine hairs inserted in cuticular membrane and 2 simple setae or varying size distally. Dactylus as long as propodus, length 5 times width; with 3 fine, simple setae medially; unguis length 0.4 times dactylus length; with 2 robust cuspidate setae and 2 slender setae in between.

Pereopods 2–4 ( Fig. 5 View FIGURE 5 E): pereopods 2 and 3 missing in adult female, described from juvenile. Pereopod 4 basis length 7.3 times width; with few short simple setae and strongly produced dorsal hook proximally; basis length 1.5 ischium length. Ischium length 6.3 times width; with 1 short dorsal and ventral seta and 1 dorsal hook; length twice as long as merus. Merus length twice width; with 1 slender seta on dorsal and ventral margin; merus length 0.4 times carpus length. Carpus length 5.2 times width; with 1 slender simple seta distodorsally, with row of fine setules inserted in cuticular membrane and 2 robust unequally bifid setae ventrally; carpus length 1.6 times propodus length. Propodus length 4.2 times width; with 1 long slender seta distodorsally, with row of fine hairs inserted in cuticular membrane and 3 short unequally bifid setae ventrally. Dactylus length half of propodus length, 5.5 times width, with 2 fine short setae medially; unguis length almost half of dactylus length; with 2 robust cuspidate setae, ventral one somewhat shorter than dorsal seta, with 1 slender seta in between.

Pereopods 5–7 ( Fig. 6 View FIGURE 6 A, C): pereopod 6 missing (drawn from juvenile). Pereopod 5 basis length 5 times width, in pereopod 7 length 6.5 times width; pereopod 5 with a distinct ventral hook, pereopod 7 with 1 broom seta medially and 1 short simple seta ventrally. Pereopod 5 ischium length 6.1 times width; with 1 ventral broom seta and few small simple setae; pereopod 7 ischium length 4.4 times width. Pereopod 5 and 7 merus length 1.8 times width; with 1–2 small simple setae on ventral and dorsal margin. Pereopod 5 carpus length 7.1 times width, in pereopod 7 length 5.1 times width; pereopod 5 with 2 short simple setae distodorsally, with 3 simple setae increasing in length distoventrally; pereopod 7 with 2 small simple setae distodorsally and with 1 long slender seta distoventrally. Pereopods 5 and 7 propodus with 1–2 slender setae of varying size dorsally and with 3 slender simple setae ventrally. Pereopod 5 dactylus length 8.3 times width, in pereopod 7 length 6.5 times width. Pereopods 5 and 7 unguis length half of dactylus length; pereopod 5 with 2 long slender setae dorsally and 1 somewhat shorter seta ventrally; pereopod 7 with 1 robust cuspidate seta dorsally and 2 slender, somewhat shorter setae ventrally.

Pleopod 2 (operculum, Fig. 6 View FIGURE 6 D) as long as wide; surface smooth; with 4 short simple setae distally. Lateral margins strongly curved, more straight distally.

Pleopods 3–5 ( Fig. 6 View FIGURE 6 F–G): Pleopod 4 lost during dissection. Exopodite of pleopod 3 small, triangular, with few fine setae on inner margin; endopodite length 3 times exopodite length, 1.5 times width, distally with 3 short plumose setae. Pleopod 5 oval-shaped, without setation; protopodite length 1.6 width, endopodite length 3.2 protopodite length, 1.6 endopodite width.

Uropods ( Fig. 6 View FIGURE 6 E) uniramous, small. Length 0.2 times pleotelson length, not overlapping pleotelson´s posterior margin. Protopodite length 1.6 times endopodite length, with 5 slender setae. Endopodite length 1.5 times width, terminally with 1 long, slender seta and 1 somewhat shorter broom seta.

Descriptive notes on juvenile paratype. Habitus ( Fig. 3 View FIGURE 3 D–E): pereonite 7 incompletely developed; pereopod 7 missing. Only coxae 5 and 6 visible in dorsal view. Pleotelson length 0.25 times body length. Cephalothorax length 0.2 times body length.

Antennula ( Fig. 4 View FIGURE 4 B) article 2 with 2 broom setae. Antenna ( Fig. 3 View FIGURE 3 D–E) with 9 flagellar articles.

Pereopods 1–3 ( Fig. 5 View FIGURE 5 B–D): Pereopod 1 carpus with only 1 unequally bifid seta ventrally, setal row and unequally bifid setae absent on ventral margin of merus. Pereopods 2–3: basis of pereopod 3 damaged. Pereopod 2 basis length 3.4 times width, with 4 short setae ventrally, length 1.3 times ischium length. Pereopods 2 and 3 ischium length about 3.6 times width. Merus length twice ischium length; with 1 long, slender seta distodorsally and 1 short simple seta distoventrally. Carpus length 2.6 times merus length; pereopod 2 carpus length 4.4 times width, in pereopod 3 about 5.3 times width, pereopod 2 and 3 with row of fine setules inserted in cuticular membrane and 1 robust unequally bifid seta ventrally; carpus length 1.6 propodus length. Propodus length 3.6 times width, with 1–2 slender setae distodorsally; row of fine setules inserted in cuticular membrane and 2 robust unequally bifid setae ventrally; pereopod 2 additionally with 1 slender simple seta medioventrally; propodus length 1.3 times dactylus length. Pereopod 2 dactylus length 4.7 times width; pereopod 3 dactylus more slender, length 6 times width; pereopods 2 and 3 with 2–3 fine setae medially. Pereopod 2 unguis length 0.2 times width, with 2 cuspidate setae and 2 somewhat longer slender setae in between; pereopod 3 unguis length almost half of dactylus length, with 2 cuspidate setae and 2 slender setae in between.

Pereopod 6 ( Fig. 6 View FIGURE 6 B) more slender than pereopod 2 and 3; basis damaged proximally, with 1 short broom seta ventrally. Ischium length 3.6 times width, 1.6 of merus length. Merus length 2.3 times width, with 1 short simple seta distodorsally and distoventrally; merus half of carpus length. Carpus length 5.7 times width, with 1 short simple seta distodorsally and 1 long more robust seta distoventrally; carpus length 1.4 times propodus length. Propodus length 4 times width, with 2 slender simple setae of varying size dorsally and ventrally; propodus length 1.2 times dactylus length. Dactylus 6.7 times width; unguis about half of dactylus length, with 1 robust cuspidate seta dorsally and 2 slender setae ventrally.

Type locality. South-eastern Atlantic Ocean, Angola Basin.

Distribution. Only known from type locality.

Etymology. Pitombo comes from a Bantu dialect spoken in Angola and means “bulge at head”. The name refers to the shape of the male cephalothorax.

Remarks. Pseudomesus pitombo sp. nov. is assigned to the genus Pseudomesus Hansen, 1916 by means of the following synapomorphies: antennula with 5 articles, terminal article minute; pleotelson enlarged, uropods uniramous, endopodite short; pereopod 1 shorter and more robust than pereopod 2; sexual dimorphism strongly developed.

The new species mostly resembles the male of Pseudomesus brevicornis Hansen, 1916 (redescribed by Svavarsson, 1984). Besides the lack of the mandibular palp, P. brevicornis can be distinguished from the new species as follows: Pereopod 5 with 15 (18) natatory setae on dorsal margin of carpus (propodus); carpus and propodus of pereopods 2 and 5 more robust.

As there were only three specimens of P. p i t o m b o sp. nov. in the samples, and the preparatory female is considerably damaged, the male is designated as the holotype of this new species.