Pseudischyrocerus caecus, Souza-Filho & Serejo, 2014

Souza-Filho, Jesser F. & Serejo, Cristiana S., 2014, On the phylogeny of Ischyroceridae (Amphipoda, Senticaudata, Corophiida), with the description of a new genus and eight new species from deep-sea Brazilian waters, Zoological Journal of the Linnean Society 170 (1), pp. 34-85 : 64-68

PSEUDISCHYROCERUS CAECUS SP. NOV. ( FIGS 19–21 )

Etymology

The specific name is derived from the Latin caecus , meaning blind, referring to a unique character within the genus.

Type material

Holotype: One male, Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604 .

Paratypes: One female, Campos Basin , 11 March 2006, 1058 m, ECOPROF, MNRJ 21604 . One male (2.5 mm, dissected and drawn) OCEANPROF II, BC-SUL , # 59 (0–2 CM), Campos Basin , Rio de Janeiro, Brazil, 21°52′59″S, 39°55′32″W, 29 June 2003, 750 m, MNRJ 21225 . One female, OCEANPROF I, BC-NORTE, # 44, Campos Basin , Rio de Janeiro, Brazil, 22°11′44″S, 39°54′46″W, 12 December 2002, 750 m, MNRJ 21226 .

Type locality

Campos Basin, Rio de Janeiro, Brazil.

Diagnosis

Eyes absent. Antennae 1 accessory flagellum 2- or 3-articulate. Coxa 1, shorter than coxae 2–4, anterodistal angle slightly produced. Gnathopod 1 basis slender; carpus longer than propodus. Gnathopod 2 basis moderately stout, posterior margin with two or three long setae; carpus triangular, shallowly lobate, one-third of propodus length; propodus massive, ovate, palm acute, serrate with a rounded and serrate process near hinge of dactylus bearing one facial robust seta; palmar corner defining by a subacute spine and one facial robust setae; dactylus curved, not reaching end of palm. Pereopod 5 basis broad, ovoid, posterior margin excavate, posteroventral corner rounded and produced. Uropod 1 peduncle interamal process one-third of inner ramus length. Uropod 2 peduncle interamal process one-quarter of outer ramus length. Uropod 3 peduncle with two robust setae and two slender setae on distolateral angle, ventral margin with four robust setae; inner ramus with two marginal and one apical setae; outer ramus with two middle robust setae, tip with one subdistal robust seta, and a plate bearing three recurved spines. Telson triangular, wider than long; tip rounded; lateral margins with two pairs of pappose setae and two groups of three robust setae; dorsal margin with two pairs of robust and pappose setae.

Description

Based on holotype male. Head anteroventral margin strongly recessed; lateral cephalic lobe acute; eyes absent. Antennae 1 accessory flagellum 2- or 3-articulate. Epistome acute and upturned. Mandibular palp strong, article 3 spatulate, shorter than article 2. Maxilla 1, inner plate with a single seta; outer plate with seven robust setae; palp article 2 with four robust setae, and three slender facial setae. Maxilla 2, plates with almost the same width and apically setose; inner plate without row of facial setae. Lower lip with developed inner lobes; mandibular process acute. Maxilliped, inner plate rectangular; outer plate reaching one-third of palp article 2, with four medial to distal robust setae; palp 4-articulate; article 3 wider distally than proximally; article 4 with a long distal seta.

Coxa 1, shorter than coxae 2–4, anterodistal angle slightly produced. Coxae 2–4, similar in size, anterior and posterior margins straight, angles rounded and distally with some setules. Coxa 5 with posterior lobe. Coxa 6 wider than long; slightly excavate distally. Coxa 7 shorter than coxa 6, subovate. Gnathopod 1 basis slender; carpus longer than propodus; posterior margin with long pappose setae; propodus setose; palm acute, with some marginal and facial setae; dactylus long, slender, inner margin serrate, outer margin with one plumose seta. Gnathopod 2 basis moderately stout, posterior margin with two or three long setae; carpus triangular, shallowly lobate, one-third of propodus length; propodus massive, ovate, palm acute, serrate with one facial robust seta and a rounded and serrated process near dactylus hinge; palmar corner defined by a subacute spine and one facial robust seta; dactylus curved, not reaching end of palm. Pereopods 3 and 4 similar in shape and size; basis subrectangular; merus, anterodistal angle slightly produced; dactylus slender and shorter than propodus. Pereopod 5 basis broad, ovate, posterior margin excavate, posteroventral corner rounded and produced; merus anterior and posterior distal angles produced, propodus longer than carpus and merus together, with one very long robust seta and one short robust seta. Pereopods 6 and 7 slender, similar; basis subrectangular, posterior margin sinuous; merus and carpus with antero- and posterodistal angle produced; propodus long, three times longer than merus; dactylus about one-third length of propodus, posterior margin with one plumose setae. Pereopod 6 propodus anterior margin with one robust seta and three robust setae on anterodistal angle, posterodistal angle with a tuft of long setae. Pereopod 7 propodus anterior margin with one robust seta on anterodistal angle, posterodistal angle with a tuft of long setae.

Epimera 1 and 2 posteroventral corner rounded. Epimeron 3 posteroventral corner acute, with posterior margin excavated. Uropod 1 not exceeding apex of uropod 2, peduncle longer than rami, inner margin with three robust setae, outer margin with four robust setae; interamal process one-third of inner ramus length; outer ramus with one marginal and four distal robust setae; inner ramus shorter than outer ramus, with four distal setae. Uropod 2 peduncle with one distolateral robust setae; interamal process one-quarter of outer ramus length; inner ramus longer than outer ramus, with two marginal robust setae and three distal robust setae; outer ramus with one marginal robust seta and four distal robust setae. Uropod 3 peduncle longer than rami, broad proximally and narrow distally, with two robust setae and two slender setae on distolateral angle, ventral margin with four robust setae; inner ramus more slender than outer ramus, with two marginal and one apical seta; outer ramus slightly recurved, with two middle robust setae, tip with one subdistal robust seta and a plate bearing three recurved spines. Telson triangular, wider than long; tip rounded; lateral margins with two pairs of pappose setae and two groups of three robust setae; dorsal margin with two pairs of robust and pappose setae.

Sexually dimorphic characters

Pseudischyrocerus caecus sp. nov. presents a weak sexual dimorphism. The female differs mainly in gnathopod 2 less setose and propodal palm lacking process.

Variation

The males of P. caecus sp. nov. show extensive ontogenetic modification in some structures, including the number of articles in the accessory flagellum, gnathopods 1 and 2, basis of pereopod 5, and uropod 3. In juvenile and adult specimens the number of articles in the accessory flagellum varies from two to three; also, one female showed a difference between the right and left side. In juvenile specimens the carpus of gnathopod 1 is about as long as the propodus, the basis of pereopod 5 is slightly concave, and uropod 3 has the peduncle with only one robust distal seta and the rami are naked; however, in adults and hyperadults the carpus of gnathopod 1 is about 1.5 × propodus length, the basis of pereopod 5 is strongly concave, and the uropod 3 peduncle bears four robust setae on the ventral margin, and both rami have two robust setae. The most important modification is observed in gnathopod 2, as in juveniles the propodus is sparsely setose, the palm is serrate and without a palmar corner, whereas in adults it becomes densely setose with a rounded crenulate process near the dactylus hinge. Moreover, in hyperadults a palmar corner is developed and the dactylus is strongly curved, reaching three-quarters of the palm.

Remarks

As a whole, P. caecus sp. nov. differs from the other three species of the genus by the following combination of characters: eyes absent; palm of the male gnathopod 2 with two robust facial setae; and a distinctly more setose telson.

Geographic distribution

South-western Atlantic: Campos Basin, Rio de Janeiro, Brazil.

Figures

Figure 19. Pseudischyrocerus caecus sp. nov. Paratype: male (2.5 mm), OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21225. lAF and rAF from holotype male (6.2 mm), Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604. Scale bars: 0.1 mm.

Figure 20. Pseudischyrocerus caecus sp. nov. Paratype: male (2.5 mm), OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21225. Holotype: hyperadult male (6.2 mm), Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604. Paratype: female, Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604. Paratype: adult male OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21225. Scale bars: 0.1 mm.

Figure 21. Pseudischyrocerus caecus sp. nov. Paratype: male (2.5 mm), OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21225. Holotype: hyperadult male, Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604. Paratype: female, Campos Basin, 11 March 2006, 1058 m, ECOPROF, MNRJ 21604. Scale bars: 0.1 mm.