Colomastix trispinosa, Silvany & Alves & Senna, 2019

Silvany, Liz, Alves, Jessika & Senna, André R., 2019, First record of the suborder Colomastigidea (Amphipoda) from Brazilian waters, with description of a new species of Colomastix Grube, 1861, Zootaxa 4563 (1), pp. 149-162 : 150-161

Colomastix trispinosa sp. nov.

Figs (1–7)

Etymology. The name of this species is derived from the Latin tri (three) and spinatus (spinose) and refers to the trispinose telson apex of the male, which closes resembles Colomastix tridentata Lecroy, 1995 , named after the same character.

Type locality. Marine State Park of Pedra da Risca do Meio, (3°36’06”S, 38°24’27”W), Ceará, Brazil.

Material examined. Holotype. Adult male (dissected and drawn), 3.4 mm, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W), 21 April 2013, associated with sponge Angelas sp. and Monanchora arbuscula (MNRJ-Porifera 17350, 17351), UFBA 2171 .

Paratypes. Adult male (dissected and drawn), 3.6 mm, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W), 13 April 2013, associated with sponge Angelas sp. (MNRJ-Porifera 17355), UFBA 2170 . Adult female (dissected and drawn), 3.0 mm, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W), 13 April 2013, associated with sponge Angelas sp. (MNRJ-Porifera 17355), UFBA 2172 . Adult female (dissected and drawn), 3.4 mm, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W) 13 April 2013, associated with sponge Angelas sp. (MNRJ-Porifera 17355), UFBA 2173 . Adult female, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W), 13 April 2013, associated with sponge Angelas sp. (MNRJ-Porifera 17355), UFBA 2174 . 1 adult male, 2 adult females, Marine State Park of Pedra da Risca do Meio, Ceará state, Brazil (3°36’06”S, 38°24’27”W), 21 April 2013, associated with sponges Angelas sp. and Monanchora arbuscula (MNRJ-Porifera 17350, 17351), UFBA 2175 .

Diagnosis. Rostrum acute; inter-antennal plate, anteroventral angle extending far beyond anterodorsal angle, anterior margin concave (straight to slightly concave in female); antenna 1, peduncle article 1 with three setae on dorsomedial margin; antenna 2, peduncle article 3 with one distomedial seta adjacent to small process (with two setae and lacking process in female); maxilliped inner plate, basal shall not expanded to form ventral keel; propodus 3–7 with four setae on flexor margin; pleopod 1–3, rami 4-articulate; gnathopod 1 vestigial (elongate, simple in female); gnathopod 2 of male, basis expanded distally, propodus enlarged, palm tridentate; gnathopod 2 of female, dactylus insertion terminal, with pleated subtruncated apex; uropod 1, inner ramus curved dorsally, broadly expanded proximally, tapering distally to slender acute bifurcate apex, both branches of bifurcation straight; uropod 3, rami with all dorsal margins lined with setae, inner ramus longer and wider than outer ramus, apex rounded, setae on dorsal inner margin stout, much larger than all other setae on both rami; telson, flat dorsally, subtriangular, with castelloserrations on distal margins, apex sharply upturned, with three subtriangular teeth (not upturned in female).

Description: Based on holotype male, 3.4 mm, UFBA 2171 and paratype male, 3.6 mm, UFBA 2171.

Head. Head as long as deep, subequal in length to pereon segments 1 and 2 combined, approximately 1/7 length of body; rostrum acute; inter-antennal plate, with anteroventral angle acutely produced in lateral and ventral view, extending beyond anterodorsal angle, the latest rounded in lateral view, anterior margin slightly concave, anteroventral margin serrated; eyes not protruding laterally in dorsal view, consisting of 15–18 well-separated ommatidia. Antennae 1–2 subequal in length, approximately 1/3 length of body; marginal robust setae short. Antenna 1, ratio of peduncle articles 1–3 1:1:0.5; peduncle article 1, dorsomedial margin with 3 stout setae, and ventromedial margin with 2 distal setae, proximal most setae stout and the distalmost slender; peduncle article 2, ventromedial margin with 3 subequal setae; peduncle article 3 slightly smaller than other two, ventromedial margin with 5 distal slender setae, distalmost 2 setae much bigger than other 3, ventrolateral margin with 2 slender distal seta; flagellum short, 2-articulate, with many long setae, approximately 1/4 length of peduncle article 3. Antenna 2, ventrolateral margins of peduncle articles 3–5 lined with small, closely appressed, triangular setae; peduncle article 3 with 2 distomedial setae adjacent to small process, proximal seta stouter than distal, and with tip extending far beyond tip of process; peduncle, article 4, dorsomedial margin irregular, with 5 similar stout setae unequally spaced, ventromedial margin straight, with 4–5 similar slender setae subequally spaced; article 5, dorsomedial margin irregular, with 4 pairs of subequal robust setae, ventrolateral margin straight, with 5–8 slender setae; flagellum short, 3-articulate, with many long setae, approximately 1/3 length of peduncle article 5; accessory flagellum absent. Mouthparts other than maxilliped greatly reduced. Maxilliped outer plates reduced; inner plate completely fused, suboval; basal shell flattened distally, not projecting to form ventral keel.

3.0 mm, Marine State Park of Pedra da Risca do Meio, (3°36’06”S, 38°24’27”W), Ceará state, Brazil, UFBA 2172. Scale Bars: 0.5 mm for fHb.

Pereon. Pereonites 1–7 slightly increasing in size, corresponding approximately to half-length of body. Coxa 1 much smaller than others, anteroventral angle rounded, without anteroventral cusp, anterior margin convex, posterior margin thin, posteroventral corner produced and rounded. Coxae 1–4 slightly increasing in size, subequal in depth. Coxae 2 and 3 with small anteroventral acute cusp. Coxa 4 anterior and posterior margin convex, anteroventral and posteroventral angles rounded. Coxae 5–7 decreasing in size, gradually becoming slightly shallower, anteroventral and posteroventral margins convex, anteroventral and posteroventral angles rounded and ventral margin concave to straight. Coxal gills 2–6 gradually increasing in size, ranging from 1/4 length of basis on gnathopod 2 to 2/3 length of basis on pereopod 6. Gnathopod 1 vestigial, approximately 1/4 the length of gnathopod 2; basis longer than all the other articles combined, anteroventral corner with a wrinkled surface; all other articles subequal in length; propodus with a wrinkled surface, rounded, palm undifferentiated; dactylus reduced, seta shaped. Gnathopod 2 basis broadly expanded distally, very produced; ischium anterodistal corner with a notch; merus with a medial concavity, and distoventral corner with a notch and 2 elongate setae; carpus posteroventral lobe setose; propodus greatly enlarged, facially setose, approximately 1/3 the length of gnathopod 2, with long dorsal and ventral setae, dorsal setae longer than others, palm not excavate with 3 dissimilar unequally spaced processes, 2 proximal most processes acute, proximal most bigger, distalmost third process larger than other two, trapezoid in medial view and acute in lateral view; dactylus, apically inserted on propodus, with medial concavity and irregular inner margins. Pereopods 3–7, basis not distally enlarged; merus anterodistal margin with a stout seta; carpus with row of very small setae and one slender seta on distal flexor margin; propodus flexor margin with 4 poorly developed setae, distalmost smaller than others, setae with apical accessory seta. Pereopods 3–4 ischium anterior margin irregularly produced. Pereopods 5–7 ischium posterior margin irregularly produced.

Pleon about 1/4 the length of body. Pleopods 1–3 peduncular articles robust, equal in width, those of pleopods 1–2 subequal in length, 1/4 longer than that of pleopod 3, each with pair of coupling setae on distomedial margin; all rami 4-articulate, each article with pair of long, plumose setae, inner ramus subequal to first 3 articles of outer ramus in length, article 1 of inner ramus with 1 short plumose seta on medial margin. Urosome about 1/9 the length of body. Urosomite 1 slightly shorter than fused urosome segments 2+3; urosome segments 1 and 2+3 about as long as deep. Uropods 1–3 gradually decreasing in size, ratio 1:0.8:0.5. Uropod 1, peduncle subequal in length to inner ramus, dorsal inner and outer margins lined with very small subequal setae, setae slightly longer on distodorsal inner corner, one stout and long seta on distodorsal outer corner, distodorsal corners both rounded; inner ramus curved dorsally, broadly expanded proximally, tapering distally to slender acute bifurcate tip, both apices of bifurcation straight, ventral margin not straight, and without setae on any margin; outer ramus approximately 2/3 the length of inner ramus, lanceolate, slender, dorsal inner and outer margins setose, setae similar to those of peduncle. Uropod 2, peduncle subequal in size to rami, dorsal inner and outer margins lined with small subequal setae, setae on distodorsal corner of inner margin slightly longer than others, ventral margin lined with very small setae; rami subequal in size, lanceolate, dorsal inner and outer margins setose, proximal half of setae gradually increasing in size distally, distal half of setae gradually decreasing in size distally, ventral margins lined with very small setae, similar to those on ventral margin of peduncle. Uropod 3, peduncle stout, length less than twice of width, subequal in length to inner ramus, distal margin and dorsal inner and outer margins lined with small subequal setae, slightly smaller than those of rami, dorsodistal corner produced with subacute angle; inner ramus longer and wider than outer, with a rounded expansion proximally, tip rounded, dorsal inner margin lined with dissimilar stout setae, proximal half of setae gradually increasing in size, distal half of setae gradually decreasing in size, dorsal outer margins lined with small subequal setae, similar to those on outer ramus; outer ramus lanceolate, 6/7 the length of inner ramus, dorsal inner and outer margins setose. Telson flat dorsally, subtriangular, approximately 2/3 the length of uropod 3, lateral margins with 9–11 well-defined castelloserrations about 50% of distal length of lateral margins, lined with extremely small setae; tip sharply upturned, with 3 subtriangular spines.

Sexual dimorphic characters (based on female paratypes UFBA 2172 and 2173). Head. Similar in length to pereonite 1; inter-antennal plate anterior margin straight, without serrations under ventral tooth. Antenna 1–2, flagellum 4-articulate. Antenna 1, article 1 with additional 4 setae on ventromedial margin, besides the 2 distal setae present in male; article 2, ventromedial setae longer than in male; article 3 with 3 stout setae on ventromedial margin. Antenna 2, article 3 lacking small distal process and with two, instead of one, distomedial setae; article 4 with no marginal setae, only with 4 pairs of setae in double row on medial surface, and 2 distal setae; article 5 with 4 pairs of setae in double row on medial surface, and 3 distal slender setae on both dorsal and ventral medial margins. Mandibles and maxillae unreduced, typical of genus. Maxilliped inner plate subtriangular, bigger than in male; outer plates not reduced; basal shell distally rounded.

Pereon. Coxa 1 not reduced, posteroventral corner not produced. Coxae 2–3 anteroventral corner produced and rounded, without cusps. Coxa 3 posteroventral corner rounded, without cusp. Gnathopod 1, elongate, simple; propodus with 7 plumose apical setae; dactylus slender, tip spatulate, laminar. Gnathopod 2, basis slightly expanded distally; carpus subequal in length to propodus, propodus and carpus slightly enlarged; propodus lacking palmar process; dactylus tip pleated, subtruncate. Oostegites narrowly subovate, with 17–20 marginal setae, tips of setae curled.

Urosome. Uropod 1, peduncle artcile much longer than rami, dorsal outer and inner margins and distal margin lined with small setae. Uropod 2, inner ramus longer than outer ramus; rami dorsal outer and inner margins and ventral margins lined with small setae. Uropod 3 similar to male, but peduncle article less robust, inner ramus less expanded, and inner ramus longer in relation to outer ramus. Telson castelloserrations more square-shaped, tip not upturned.

Variation. Antenna 2, article 4, ventromedial margin straight, with 5 similar slender setae subequally spaced in holotype, and 4 in paratype UFBA 2170 ; article 5, ventrolateral margin with 5 slender setae in holotype, and 8 in paratype UFBA 2170 .

Distribution. The new species is known exclusively from the type locality Marine State Park of Pedra da Risca do Meio, (3°36’06”S, 38°24’27”W), Ceará state, Brazil ( Fig. 8 ).

Remarks. The trapezoid process on the palm of propodus of gnathopod 2 and the morphology of the inner ramus of uropod 1 serves to distinguish Colomastix trispinosa sp. nov. from all others known species of Colomastix . Additionally, the well-developed seta on the peduncle dorsodistal outer corner of uropod 1 distinguish Colomastix trispinosa sp. nov. from all other Colomastix species from the Atlantic. Colomastix trispinosa sp. nov. is also the only Atlantic species to have a pleated apex in the dactylus of gnathopod 2 of the female.

Colomastix trispinosa sp. nov. closely resembles C. tridentata . Both species have an acute rostrum, gnathopod 2 with a tridentate palm, four setae on flexor margin of pereopod propodi, pleopods 1–3 with 4-articulated rami, similar morphologies of bifurcated apex of inner ramus of uropod 1, a telson with castellated margin and trilobed upturned apex, and similar morphologies of coxal gills. However, Colomastix trispinosa sp. nov. differs from C. tridentata in a number of characters. First, in Colomastix trispinosa sp. nov. the anteroventral angle of the interantennal plate projects far beyond anterodorsal angle and there are ventral serrations on the anterior margin, whereas in C. tridentada the anteroventral angle projects only slightly beyond the anterodorsal angle and there are no serrations; in addition, the shape of the coxal plates and the number and placement of setae on the antennae differ between these two species, including the presence of three setae on the dorsomedial margin of peduncle article 1 of antenna 1 in dorsal view of Colomastix trispinosa sp. nov., as opposite to four setae in C. tridentata ; besides that, peduncle articles 3–4 of antenna 2 of Colomastix trispinosa sp. nov. are straight dorsally, whereas in C. tridentata they are faintly serrate; the gnathopod 2 of Colomastix trispinosa sp. nov. has three process, two acute and one trapezoid, and the dactyl has an irregular posterior margin, whereas C. tridentata has three acute processes in the palm of gnathopod 2 and only one small process in the posterior margin of dactyl; there are small accessory apical setae on the pereopod propodi of Colomastix trispinosa sp. nov., whereas C. tridentata has no accessory setae; the bifurcate tip of the inner ramus of uropod 1 of C. tridentata has a subterminal lateral concavity that is absent in Colomastix trispinosa sp. nov. and although the telson morphology of these two species is very similar, Colomastix trispinosa sp. nov. lacks two dorsolateral pairs of setae present in C. tridentata .

Some other characters also distinguish the females of the two species. The anterior margin of the inter-antennal plate is straight in Colomastix trispinosa sp. nov. and concave in C. tridentata ; the setae that forms the brush of the pectinate terminal setae of gnathopod 1 are much longer in Colomastix trispinosa sp. nov. than in C. tridentata ; the tips of the marginal setae of the oostegites are not curled in C. tridentata ; and besides the dorsolateral pair of setae, the telson of C. tridentata also have a pair of dorsal apical setae, absent in Colomastix trispinosa sp. nov.

The pleated tip on the dactyl of gnathopod 2 of the female is a characteristic of Colomastix trispinosa sp. nov. shared only with five other species, C. plumosa, Ledoyer, 1979 , from Madagascar, C. azumai Hirayama & Kikuchi, 1980 , C. littoralis Ariyama, 2005 , C. semiplumosa Ariyama, 2005 , all from Japan, and C. thomasi LeCroy, 2009 from Australia. However, Colomastix trispinosa sp. nov. can be distinguished from all of these by the tip morphology of the inner ramus of uropod 1 in the male, and by the presence of pectinate terminal setae in gnathopod 1 of the female, which are simple in the other species.

Males of five other species of Colomastix ( C. castellata Barnard, 1932 ; C. subcastellata Hurley, 1954 ; C. janiceae Heard & Perlmutter, 1977; C. camura LeCroy, 1995 and C. tridentata LeCroy, 1995 ) have distinctly castellate telson margins. Colomastix trispinosa sp. nov. can be distinguished from the first of these species by having completely fused inner plates on the maxilliped and a subtriangular telson, and from the second specie by having a strong distomedial process on peduncle article 3 of antenna 2, fused maxilliped inner plates, a basal shell of the maxilliped that is not expanded to form a ventral keel, a vestigial male gnathopod 1, a terminal dactyl on gnathopod 2 of the female and pectinate lateral margins of telson. Colomastix trispinosa sp. nov. can be distinguished from the last three of these species by the absence of any dorsal setae in the telson. Additionally, the female of C. cornuticauda LeCroy, 1995 also have castellate telson margins, but it differs from Colomastix trispinosa sp. nov. by the presence of two dorsolateral pairs of setae in the telson.

The morphology of the male uropod 1 inner ramus is unlike that of any previously described species of Colomastix , although it bears a strong resemblance to that of C. irciniae LeCroy, 1995 , C. janiceae LeCroy, 1995 and C. tridentata . However, compared to that of Colomastix trispinosa sp. nov., C. irciniae has a narrower tip of the inner ramus of uropod l and a hook in one branch of the bifurcation. This hook is also present in C. janiceae , and separates it from Colomastix trispinosa sp. nov. Differences between Colomastix trispinosa sp. nov. and C. tridentata are discussed above.

Figures

FIGURE 8. Type locality of Colomastix trispinosa sp. nov., Marine State Park of Pedra da Risca do Meio, (3°36’06”S, 38°24’27”W), Ceará state, Brazil.