Colomastix tubulosa, Silvany & Senna, 2019

Silvany, Liz & Senna, André R., 2019, Three new species of Colomastix Grube, 1861 (Amphipoda: Colomastigidea) from Todos-os-Santos Bay, northeastern Brazilian coast, with identification keys to Atlantic Ocean species, Zootaxa 4629 (4), pp. 519-554 : 540-548

Colomastix tubulosa sp. nov.

Figs (13–17)

Etymology. The name of this species is given after the tubular-like structure at the apex of inner ramus of uropod 1 of male. It derives from the Latin tubulosae, meaning tubular. This character is unique to this species.

Type locality. Bimbarras Island (12°43’32.131”S, 38°37’52.162”W), Bahia state, Brazil.

Examined material. Holotype. Adult male (dissected and drawn) 2.9 mm, Bimbarras Island (12°43’32.131”S, 38°37’52.162”W), Bahia state, Brazil, unidentified sponge, 20 August 2005, UERJ 105 .

Paratypes. Jevunile male (dissected and drawn) 3.0 mm, data same as holotype, UERJ 107 . Adult male (dissected and drawn) 2.6 mm, data same as holotype, UERJ 106 . Adult female (dissected and drawn) 3.2 mm, data same as holotype, UERJ 109 . Juvenile male (dissected) 2.8 mm, data same as holotype, UERJ 108 . Adult female (dissected) 3.0 mm, data same as holotype, UERJ 110 . 9 adult female and 5 adult female, data same as holotype, MOUFPE 18759 . 1 adult male and 16 subadult males, data same as holotype, MOUFPE 18760 . 97 juveniles, data same as holotype, MOUFPE 18761 . 1 adult male, 2 juvenile males, 1 adult female, and 5 juveniles, Dentão Rock, (12°50’02.4”S, 038°31’32.0”W), Bahia state, Brazil, in, Sponge 3— Desmapsamma anchorata + Ircinia , 4–6 m depth, 20 May 2017, UERJ 111 .

Diagnosis. Rostrum acute; interantennal plate, anteroventral angle projecting slightly beyond anterodorsal angle (projecting much beyond in female and juvenile male), anterior margin concave; antenna 1, peduncle article 1 with three setae on dorsomedial margin; eyes, ommatidia set in pairs, closely set together; antenna 2, peduncle articles 3–5 ventrolateral margin lined with small, equally-spaced setae, peduncle article 3 with single, distomedial welldeveloped seta and adjacent process; maxilliped, inner plate completely fused, basal shall not expanded to form ventral keel; gnathopod 1 vestigial (elongate, simple in female and juvenile male); gnathopod 2, basis expanded distally, propodus greatly enlarged, palm tridentate, distalmost process with anterior margin irregular; gnathopod 2 of female, insertion of dactylus terminal, dactylus apex pleated; gnathopod 2 of juvenile male, propodus not greatly enlarged, lacking palmar processes, dactylus apex pleated; pereopods 3–7, propodus with 1–2 setae on flexor margin; pleopods 1–3, outer ramus 4-articulate, inner ramus 3-articulate; uropod 1, inner ramus with a subterminal long seta, and distal 1/4 of lateral margins closing upon itself, forming a tube with a terminal concavity, outer ramus expanded, with distomedial well-developed seta; uropods 2–3, rami with distomedial well-developed seta, inner ramus expanded; uropods 1–3 of juvenile male rami lanceolate, simple, with distomedial well-developed seta, inner ramus slightly expanded; uropods 1–3 of female, rami lanceolate, simple, uropod 3, inner ramus much longer than outer, expanded, dorsal inner margin lined with stout, well-developed setae; telson flat to slightly convex dorsally, subovate (subtriangular in female).

Description. Based on holotype male, 2.9 mm, UERJ 105 and paratype adult male, 3.2 UERJ 107.

Head. Head as long as deep, subequal in length to pereonites 1 and 2 combined, approximately 1/8 length of body; rostrum acute; interantennal plate with anteroventral angle extending slightly beyond anterodorsal, anterodorsal and anteroventral angles acute in lateral view, anterior margin concave and somewhat irregular, without serrations or ventral teeth; eyes not protruding laterally in dorsal view, ommatidia set in pairs, from 9–23 pairs, separation of ommatidia somewhat variable, but usually closely set together. Antennae 1–2 subequal in length, approximately 1/5 length of body. Antenna 1, ratio of peduncle articles 1–3 1:0.7:0.5; peduncle article 1, dorsomedial margin with 3 setae, ventromedial margin with 1 small medial seta and 2 distal setae; peduncle article 2, with no setae on dorsomedial margin and ventromedial margin with 1 medial small seta and 1 distal well-developed setae; peduncle article 3, ventromedial margin with 1 fine medial seta, and 2 distal stout setae; flagellum short, 3-articulate, with few relatively short setae. Antenna 2, ventrolateral margins of peduncle articles 3–5 lined with small, closely appressed setae; peduncle article 3 with 1 distomedial well-developed stout seta another small seta adjacent to small distomedial process; peduncle article 4, dorsomedial margin with 3 equidistant stout setae with a blunt apex, ventromedial margin with 1 apically blunt seta, and 1 distomedial fine seta; peduncle article 5, dorsomedial margin with 2 pairs of apically blunt setae; flagellum short, 3-articulate with few relatively short setae. Mandibles and maxillae reduced. Maxilliped, basal shell rounded distally, not expended to form ventral keel, somewhat reduced; inner plate completely fused, subtriangular; outer plates, left somewhat reduced; palp article 2 with 1 distomedial small seta; palp article 3, medial surface with many fine setae, 2 stout, long setae, outer margin with 1 long, stout seta at joint with dactylus.

Pereon. Corresponding to little more than half-length of body. Coxae 1–4 subequal in depth, slightly increasing in size, ventral margins nearly straight to slightly convex, produced anteriorly with small anteroventral cusp (except coxa 1), posterior margin with a small depression and posteroventral angle broadly rounded; coxae 5–7 much shallower, decreasing in size, ventral margins convex, anteroventral and posteroventral angles rounded. Coxal gills 2–5 gradually increasing in size, ranging from 1/3 length of basis on gnathopod 2 to slightly longer than half-length of basis on pereopod 5; coxal gill 6 slightly smaller than coxal gill 5. Gnathopod 1, vestigial, approximately little more than 1/4 of gnathopod 2, with a wrinkled surface; basis length slightly smaller than all the other articles combined; propodus slightly shorter than carpus, palm undifferentiated, without setae; dactylus differentiated. Gnathopod 2, basis broadly expanded distally; merus, distoventral margin with 3 elongate well-developed setae, and a few smaller setae; carpus approximately 1/3 length of propodus, distoventral surface with some fine setae, and distoventral margin with elongate, well-developed, minutely pectinate setae; propodus greatly enlarged, approximately 1/3 length of gnathopod 2, ventral margin lined with elongate, well-developed, minutely pectinate setae, sometimes set in pairs, ventromedial surface with much smaller, fine setae, dorsolateral surface with some well-developed distal setae, distalmoust setae longer, palm tridentate, two proximalmost processes smaller and subtriangular, distalmost process much broad and with irregular anterior margin; dactylus stout, terminal, extending posteriorly approximately 2/3 length of propodus, with 2 small setae medially on posterior margin, next to small concavity. Pereopods 3–7, basis somewhat expanded distally; merus anterodistal angle with a well-developed seta; carpus with 1–2 small setae on distal flexor margin; propodus flexor margin with 1–2 well-developed setae.

Pleon. Corresponding to 1/4 length of body. Pleopods 1–3 peduncular articles robust, subequal in width and length, each with pair of coupling setae on distomedial margin; outer ramus 4-articulate; inner ramus 3-articulate, subequal to first 3 articles of outer ramus in length; each article of all rami with pair of long, plumose setae and article 1 of inner ramus with additional short, plumose seta. Urosome about little more than 1/10 length of body. Urosomite 1 much longer than fused urosomes 2+3; urosome 1 longer than deep, fused urosomes 2+3 about as long as deep. Uropods 1–3 gradually decreasing in size, ratio 1:0.8:0.5, both rami with subterminal, medial, well-developed, long seta. Uropod 1, peduncle slightly longer than inner ramus in length, with only 1 stout, long seta on distodorsal inner margin; inner ramus expanded proximally, tapering distally, with distal 1/4 of lateral margins closing upon itself, forming a tube with a terminal concavity, with some short, fine seta along the tube, and subterminal, medial seta inserted at the base of the tube, longer than in all others rami of uropods 1–3; outer ramus about 3/4 length of inner ramus, wide, with a subrounded apex. Uropod 2, peduncle shorter than rami, distodorsal outer margin with line of small setae; both rami with a very acute upwardly turned apex; inner ramus shorter than outer, wide, with a slender dorsal margin, tapering distally, with dorsal inner and outer margins lined with very small setae; outer ramus, dorsal outer and inner margins lined with setae, setae on dorsal inner margin stouter than all other setae on uropods 1–3, setae on medial region stouter than setae on proximal and distal region. Uropod 3, peduncle shorter than rami, without setae; inner ramus slightly longer than outer, wide, with a rounded apex, dorsal inner and outer margins lined with setae, setae on inner margin stouter; outer ramus, dorsal outer margin lined with small setae. Telson, convex dorsally, subovate, about 2/3 length of uropod 3; distolateral margins lined with minute setae; lateral borders much thinner than medial region of telson, resembling a translucent, rigid membrane; pair of small, dorsolateral setae on each side halfway between base and apex, and pair of small, stout, middorsal distal setae; apex rounded.

Differences due to developmental stages (based on paratypes: juvenile male, 3.2 mm, UERJ 107 and juvenile male, 3.0 mm, UERJ 108)

Head. Head width 1.5 × length, slightly longer than first pereonite in length (much smaller than in male), approximately 1/9 length of body (smaller than in adult male); rostrum subacute (acute in adult male); interantennal plate with anteroventral angle extending slightly beyond anterodorsal, anterodorsal and anteroventral angles sub- eacute in lateral view (acute in adult male), anterior margin slightly concave (less concave than in adult male). An- tenna 1, ratio of peduncle articles 1–3 1:0.8:0.4; marginal setae stouter than in adult male. Antenna 2, setae stouter than in mature male, flagellum 2-articulate (3-articulate in mature male). Mandibles and maxillae unreduced, typi- cal of genus.

Pereon. Gnathopod 1, elongate, simple; propodus with 6 elongate, apically curved, pectinate terminal setae; dactylus slender, apex spatulate, laminar. Gnathopod 2, all articles less robust than in mature male, especially propodus and datylus; basis expanded distally, but less than in adult male; merus with 3 fine setae and two more distal stout, well-developed setae on distoventral margin; carpus little more than 1/2 length of propodus, distoven- tral surface with many fine setae, and distoventral margin with elongate, stout, minutely pectinate setae; propodus enlarged (but much less than in adult male), approximately 1/3 length of gnathopod 2, ventromedial margin lined with elongate, well-developed, minutely pectinate setae, ventromedial surface covered with much smaller, fine setae (much more setose than in adult male), distodorsal surface with some stout setae, distalmoust setae longer, palm with irregular margin and without any process; dactylus terminal, extending posteriorly little less than 1/2 length of propodus, apex minutely pleated and setose.

Pleon. Corresponding to 1/6 length of body. Urosome about 1/11 length of body (much smaller than adult male). Urosomite 1 subequal in length to fused urosomes 2+3 (shorter than in mature male), about as long as deep (longer than deep in adult male). Uropod 1, peduncle shorter than rami, dorsal inner and outer margins lined with setae; rami lanceolate, with subterminal, medial, well-developed seta, and subterminal weak constriction followed by small expansion before acute upwards apex, dorsal inner and outer margins lined with setae; inner ramus expanded, apex not highly modified. Uropod 2, peduncle shorter than rami, with distal and dorsal outer margins lined with setae; rami subequal in size, lanceolate, both with a very acute apex and a subterminal, medial, well-developed seta, dorsal outer margin lined with setae; inner ramus wide, tapering distally, setae on dorsal inner margin larger than those on outer margin and both margins of outer ramus, setae on medial region stouter than setae on proximal and distal regions. Uropod 3, both rami lanceolate; inner ramus expanded but without subrounded apex, setae on dorsal inner margin stouter than all other setae of uropods 1–3 and than in adult male. Telson, about 5/6 length of uropod 3, lateral and middorsal setae stouter than in adult male, lacking lateral, translucent rigid membrane.

Sexual dimorphic characters (based on paratypes: adult female, 3.2 mm, UERJ 110 and adult female 2.8 mm, UERJ 111)

Head. Head width 1.5 × length, subequal to first pereonite in length (smaller than in adult male, subequal to juvenile male); interantennal plate with anteroventral angle extending much beyond anterodorsal angle, anterior margin deeply concave and angulate in almost 90º, anteroventral and anterodorsal angle acute in lateral view. Antennae 1–2, setae stouter and longer than in adult male, flagellum 2-articulate (3-articulate in mature male). Antennae 2, stout seta adjacent to small process with apical accessory seta (absent in male). Mandibules and maxillae not reduced, typical of genus. Maxilliped, wright outer plate more reduced than the left, as opposite to male.

Pereon. Coxae 1–5 slightly longer relative to width than in male, and somewhat more acute anteriorly. Gnathopod 1, elongate, simple; propodus with 7 elongate, apically curved, plumose terminal setae; dactyus slender, laminar, apex spatulate. Gnathopod 2, basis slightly expanded distally; carpus somewhat enlarged, slightly longer than propodus, with many fine setae on medial surface, additionally to long, stout, minutely pectinate setae on distoventral margin (also present in male); propodus somewhat enlarged, lacking palmar process, with stout, long setae, usually set in pairs along ventral margin, three stout, long apical setae, fine smaller setae on medial surface, and two stout long setae on dorsal margin; dactylus slender, approximately 3/4 length of propodus, apex pleated, acute. Oostegites subovate, with 13–17 marginal, apically curled setae. Oostegite 2, approximately 1/4 longer than basis of gnathopod 2, length:width ratio 3:1.

Pleon corresponds to little less than 1/3 length of body. Urosome. About 1/9 length of body. Uropods 1–3 similar to that of juvenile male, but peduncles and rami are more slender. Besides, uropod 2 peduncle is subequal to inner ramus and lacks setae (shorter in juvenile male), peduncle of uropod 1 is subequal to inner ramus in length (shorter in juvenile male), and there is no subterminal, medial, well-developed, long seta. Telson subtriangular, straight dorsally, narrower than in male, lateral, translucent rigid membrane present, but narrower than in adult male.

Adult body length. 2.6 mm– 3.2 mm

Host. Desmapsamma anchorata + Ircinia sp.

Distribution. This species was found at Bimbarras Island (12°43’32.131”S, 38°37’52.162”W) and Dentão Rock (12°50’02.4”S, 038°31’32.0”W), both localities from the TSB, state of Bahia.

Remarks. Colomastix tubulosa sp. nov. can be distinguished from any other species in the genus by the tubelike apex of the inner ramus and greatly expanded outer ramus of uropod 1, the slender expansion of inner ramus of uropod 2, the morphology of the distalmost palmar process of gnathopod 2, and the thin lateral borders of the telson in adult male. It can also be distinguished from Colomastix iemanja sp. nov. and Colomastix marielle sp. nov. by the ommatidia set in pairs. Other than Colomastix tubulosa sp. nov., C. heardi also has the inner ramus of uropod 1 with distal margins closing upon itself and forming a terminal concavity. However, in C. heardi it forms a bulbous structure in the apex and lacks setae, while in Colomastix tubulosa sp. nov. it forms a tube-like structure, with one well-developed, long seta at the base, and fine dorsal setae along the “tube”. Although a tridentate palm of gnathopod 2 is highly common amongst Colomastix , the broad distalmost palmar process with an irregular anterior margin is unique to Colomastix tubulosa sp. nov.

Amongst all species from Atlantic Ocean, Colomastix tubulosa sp. nov. is the only one with a subterminal seta on each ramus of uropods 1–3. Besides, as cited before in the Remarks section for Colomastix iemanja sp. nov., the female of these two species are the only ones in the Atlantic to have a pleated apex on the dactylus of gnathopod 2. However, the specific morphology of this structure differs in the two species, and it is apically subtruncate in Colomastix iemanja sp. nov., while in Colomastix tubulosa sp. nov. it is acute.

The developmental differences found between adult and juvenile males of Colomastix tubulosa sp. nov. are very similar to those found in Colomastix iemanja sp. nov., C. azumai and C. litorallis , as demonstrated in the Remarks session for Colomastix iemanja sp. nov. Additional to those changes, Colomastix tubulosa sp. nov. also has an expansion of inner ramus of uropod 2 from juvenile to adult male. Colomastix tubulosa sp. nov. can be differentiated from Colomastix iemanja sp. nov. as also demonstrated in the Remarks for Colomastix iemanja sp. nov. Colomastix tubulosa sp. nov. can be distinguished from C. azumai and C. litorallis especially by the tridentate palm of gnathopod 2, which has only two processes in C. azumai and C. litorallis , and the number of articles of inner ramus of pleopods 1–3, which is 3-articulate in Colomastix tubulosa sp. nov., and 4-articulate in the latter two species. And even though some males of Colomastix have an expanded inner ramus of uropod 3, the broadly rounded apex of Colomastix tubulosa sp. nov. is quite uncommon, present only in C. azumai and C. litorallis .

The holotype UERJ 105 and the paratype UERJ 106, the only adult males examined, were lacking coxae 1–7, thus coxae descriptions were based on juvenile male paratype (UERJ 107). However, this is not expeted to be a problem, since coxae morphology do not appear to be variable between juvenile and adult ( LeCroy 1995).