Colomastix scorpio Guedes-Silva, Souza-Filho and Tavares, 2024

Guedes-Silva, Elkênita, Souza-Filho, Jesser F. & Tavares, Marcos, 2024, Three new species of Amphipoda (Crustacea: Peracarida) from the remote oceanic island of Trindade, off the coast of south-eastern Brazil, Journal of Natural History 58 (45 - 48), pp. 2075-2098 : 2077-2081

Colomastix scorpio Guedes-Silva, Souza-Filho and Tavares sp. n.

( Figures 2–5 )

Type material

Holotype, 1 male (1.7 mm, dissected and drawn, 1 slide), MZUSP 45089 , PROTRINDADE, Trindade Island , off Espírito Santo, Brazil, Paredão, diurnal scuba diving, 19 m depth, 20.527° S, 29.304°W, J.B. Mendonça col., 19 June 2012.

Diagnosis

Head subequal in length to pereonites 1 and 2 combined. Interantennal plate with anteroventral angle not projecting far beyond anterodorsal angle. Antenna 2 peduncle segments 3–5 lacking triangular spinules on lateral margins. Mandibles, maxillae, and outer plates of maxilliped not reduced. Maxilliped basal shell not expanded to form ventral keel. Gnathopod 1 elongate, simple. Gnathopod 2 male propodus with three large subacute (triangular) processes, one defining palmar corner. Pleopods 1–3, inner and outer rami with unequal number of articles. Urosome segment 1 not elongate. Uropod 1 outer ramus reduced, about 1/3 of inner ramus length; inner ramus with a tip resembling a ‘venom gland and stinger of a scorpion’ in lateral view. Telson with two recurved downward spines in lateral view, disto–ventrolateral margin serrate.

Description

Head

Head 1.2× longer than deep, subequal in length to pereonites 1–2 combined; rostrum subacute; interantennal plate with anteroventral angle not extending far beyond anterodorsal angle, anterior margin almost straight, smooth, with two spines each on dorsal and ventral angle. Antenna 1 peduncle article 1, mesial margin with three robust setae; article 2 anterior margin with one robust seta, posterior margin with three robust setae. Antenna 2 peduncle articles 3–5, both anterior and posterior margins without robust setae. Mouthparts other than maxilliped moderately reduced. Maxilliped inner plates completely fused, basal shell not expanded to form a ventral keel.

Pereon

Coxa 1 anteroventral angle slightly narrowly produced. Coxae 1–4 without small anteroventral cusp or serration. Coxal gills 2–5 gradually increasing in size, gill 6 smaller than gill 5. Gnathopod 1 elongate, slender; propodus with a tuft of pectinate apical setae. Gnathopod 2 basis broadly expanded distally, anterior margin entire, with anterodistal rounded process; ischium with inner anterodistal lobe slightly expanded; carpus much shorter than propodus (0.3×), inner ventral surface without patch of setae; propodus greatly enlarged, suboval, inner ventral surface without patch of setae, setae elongate, slender, palm not excavate, with three dissimilar, unequally spaced subtruncate processes, palmar corner defined by the largest process, middle process shorter than the others, subtruncate, apical margin smooth, process near dactylar hinge broad, subtriangular; dactylus, insertion on propodus apically, strongly curved, lacking process on posterior margin, tip blunt, subacute. Pereopods 3–4 basis subrectangular, lacking anterodistal lobe. Pereopods 5–6 basis slightly expanded. Pereopod 7 basis subrectangular, propodus, anterior margin lacking robust setae.

Pleon

Pleopods 1–3 rami with 3 articles. Uropod 1 outer ramus reduced, 0.3× of inner ramus length; inner ramus modified, expanded proximally, tapering distally, dorsal margin with a process on its first third, with tip resembling a venom gland and stinger of a scorpion in lateral view. Uropod 2 both rami, ventral margin lacking setae; outer ramus with outer lateral margin serrate on distal half; inner lateral margin with strong spine; inner ramus outer lateral margin serrate, inner margin finely setose. Uropod 3 peduncle 1.2× longer than wide; outer ramus slightly shorter than inner ramus, leaf-like. Telson narrowly subrectangular, distolateral angle with two recurved downward spines in lateral view, disto-ventrolateral margin serrate.

Female

Unknown.

Etymology

From the Latin ‘scorpio’ (= scorpion), in allusion to the tip of the inner ramus of the uropod 1 that resembles a scorpion’s stinger. The specific epithet is treated as a noun in apposition.

Type locality

Paredão, 20.527°S, 29.304°W, 19 m, Trindade Island, off Espírito Santo, Brazil.

Remarks

Colomastix scorpio sp. n. closely resembles C. irciniae LeCroy, 1995 , in having the interantennal plate with anterodorsal and anteroventral angles extending forward subequally; mandibles, maxillae and outer plates of the maxilliped not reduced; maxilliped basal shell not expanded to form a ventral keel; gnathopod 1 elongate and simple, gnathopod 2 with palm tridentate; urosome 1 not elongate and uropod 1 with outer ramus less than half length of the inner ramus. However, the new species differs in the head subequal in length to pereonites 1–2 combined; antenna 2 peduncular, articles 3–5 devoid of triangular robust setae on the ventrolateral margins; pleopods 1–3 with the inner ramus 3-articulate; tip of uropod 1 inner ramus similar to a ‘scorpion gland of venom and stinger’; and ventrodistally a pair of strong, curved hooks continued by a few acute teeth.

Four other species of Colomastix are known to occur in Brazilian coastal waters to date ( C. iemanja Silvany and Senna, 2019 ; C. marielle Silvany and Senna, 2019 ; C. trispinosa Silvany, Alves and Senna, 2019 and C. tubulosa Silvany and Senna, 2019 ), from which C. scorpio sp. n. can be readily differentiated by having the male gnathopod 1 fully developed and elongate, instead of vestigial.

Figures

Figure 2. Colomastix scorpio sp. n. Habitus, holotype (1.7 mm), Ilha da Trindade, Brazil, 19 m depth, 20.527°S, 29.304° W, MZUSP 45089. Scale bar = 0.1 mm.

Figure 3. Colomastix scorpio sp. n. Holotype (1.7 mm), antennae and mouthparts, Ilha da Trindade, Brazil, 19 m depth, 20.527°S, 29.304°W, MZUSP 45089. Abbreviations: A, antenna; Hd, head; Md, mandible; Mx, maxilla; Mxp, maxilliped. Scale bars = 0.1 mm.

Figure 4. Colomastix scorpio sp. n. Holotype (1.7 mm), gnathopods 1–2 and pereopods 3–7, Ilha da Trindade, Brazil, 19 m depth, 20.527°S, 29.304°W, MZUSP 45089. Abbreviations: Gn, gnathopod; P, pereopod. Scale bars = 0.1 mm.

Figure 5. Colomastix scorpio sp. n. Holotype (1.7 mm), uropods 1–3 and telson, Ilha da Trindade,Brazil, 19 m depth, 20.527°S, 29.304°W, MZUSP 45089. Abbreviations: T, telson; Ur, uropods. Scale bars = 0.1 mm.