Petalophthalmus lobatus, Forman & Schnabel, 2021

Forman, Jeffrey S. & Schnabel, Kareen E., 2021, Two new species of Petalophthalmus and Ipirophthalmus (Crustacea: Mysida: Petalophthalmidae), from New Zealand, Zootaxa 5061 (3), pp. 451-475 : 461-468

Petalophthalmus lobatus sp. nov.

( Figs. 8–14 )

Petalophthalmus sp. MNZ.— Webber et al. 2010: 219 (list, part).

Material examined. Type material. Holotype. NIWA 135622 , adult female (7.5 mm CL, 34.5 mm TL), Chatham Rise, FV Arrow, stn Z18642, -44.567, 176.710, 04/11/1986, 1070– 1079 m, plankton net . Allotype. NIWA 147408 , adult male (7.1 mm CL, 32.0 mm TL), Chatham Rise, FV Arrow, stn Z18637, -44.512, -177.990, 909– 931 m, plankton net . Paratypes. NIWA 147401 , adult female (6.7 mm CL, 30.1 mm TL), Challenger Plateau, FV Will Watch, stn Z18656, -39.888, 168.014, 15/07/1990, 905– 932 m, plankton net . NIWA 135623 , juvenile male (5.1 mm CL, 21.9 mm TL), Chatham Rise, FV Arrow, stn Z18642, -44.567, 176.710, 04/11/1986, 1070– 1079 m, plankton net .

Additional material. NIWA 147403 , adult female (7.9 mm CL, 39.0 TL) stn Z18641, -44.145, 176.767, 4/11/1986 , 673–673, plankton net. NIWA 147399 , adult female (7.6 mm CL, 34.8 TL) stn Z18643, -44.625, 176.268 , 5/11/1986, 1000–1030, plankton net. NIWA 10754 , adult female (7.2 mm CL, 33.7 TL) stn S200, -43.050, 173.862 , 1/11/1979, 1400– 1400 m, hyperbenthic sled. NIWA 147422 , juvenile male (6.4 mm CL, 28.4 TL) stn P971, -41.198, 177.327 , 18/06/1980, 2200– 2200 m, hyperbenthic sled. NIWA 147406 , adult female (unmeasurable) stn Z18648, -44.098, 179.812 , 29/11/1986, 600– 643 m, plankton net. NIWA 147400 , 2 juvenile females (3.6 mm CL, 14.8 mm TL, 4.0 mm CL, 16.9 mm TL), stn Z18655, -39.851, 168.026 , 15/07/1990, 886– 914 m, plankton net. NIWA 147402 , adult female without marsupium (6.1 mm, 30.9 mm TL), stn Z18644, -44.4617, -178.6500 , 23/11/1986, 968– 968 m, plankton net. NIWA 147405 , juvenile female (1.8 mm CL, 8.7 mm TL), stn Z18653, -39.520, 178. 247 . 08/10/1990, 740– 764 m, plankton net. NIWA 147407 , juvenile male (5.2 mm CL, 22.3 mm TL), stn Z18639, -44.130, 178.527 , 02/11/1986, 937– 955 m, plankton net. NIWA 147404 , adult male (7.0 mm CL, 35.1 mm TL), TAN1101/05, -42.651, 177.767 , 04/01/2011, 1176– 1246 m, from orange roughy stomach.

Etymology. Species name derived from the Latin adjective lobātus meaning lobed, referring to the enlarged ventilation lobes on the 7 th oostegites.

Diagnosis. Rostrum short, anteriorly produced, acute. Eyes elongate, flattened laterally, small ocular papilla on mesial margin, cornea absent. Carapace with last 2 thoracic somites exposed dorsally. Mandibular palp apical article with 9 long, strong curved spines. First thoracopods without exopod and basal lobe, with epipod. Second thoracopods without basal lobe; ischium lobe overreaching merus. Third and fourth thoracopods endopods reduced to rudimentary lobes in females and short, 3-articulate, rudimentary lobes in adult males. Fifth thoracic endopod fully developed, slender. Sixth to eighth thoracic endopods long and thin. Seventh oostegites with ventilation lobe enlarged, posteriorly produced with set of long straight pappose setae on the inner margin and a set of shorter curved setae on the outer margin. Male pleopods biramous, female pleopods 2-articulate, uniramous except for very mature specimens where the first pleopod develops a small endopod on the first article. Telson armed with three pairs of long robust serrate setae and one short median seta; lateral margins armed with 25–28 small cuspidate setae along the posterior 0.60 of telson.

Description. Body moderately robust, cephalothorax 0.32 × TL, pleon 0.53, telson 0.15, carapace 0.23. Sixth pleon width 0.43 of length. Pleonite 1–4, subequal in length, 0.15× TPL, pleonite 5 0.18 × TPL, pleonite 6 0.24 × TPL ( Fig. 8A , 14 ).

Carapace ( Fig. 8A, B ) cuticle thin, posterior margin concave exposing the last two thoracic somites; rostrum triangular in lateral view, short, sharp, anteriorly produced but not overreaching rostral plate; dorsal tubercle directly behind the base of rostrum; border between rostrum and rounded anterolateral corner concave, small, raised triangular tooth where carapace joins the rostral plate; anterolateral corner rounded with small lobe; anteroventral corner with small lobe curving down and slightly inwards; ventral border of carapace extends along to the basis of the fifth thoracopod rising slightly upwards to a short slightly produced and rounded posterolateral lobe; deep cervical sulcus runs from the dorsal to ventral margins ( Fig. 8C ).

Eyes ( Fig. 8D, E ) without stalk, no visual elements, flattened laterally, small ocular papilla on medial margin in proximal 1/3.

Antennule peduncle ( Fig. 8D ) very long, slender, 1.1 × length of carapace, 3-articulate; first article longest, armed with 4 dorsomedial setae, 1 cuspidate seta near the dorsodistal margin, and several long setae surrounding distal margin, 1.7 × longer than second, 3.4 × longer than third; second article distal margin surrounded by long setae; third article with 3 setae on dorsodistal lobe. Outer flagellum thinner and shorter than inner flagellum, a longitudinal crista on the first article. In mature males outer flagellum swollen, densely covered in setae, wider than inner flagellum.

Antenna peduncle ( Fig. 8F ) 3-articulate, shorter than scale; first article short, one acute process on inner margin; second article slender, long; third article similar in length and size to second, 6 long setae on distal margin; flagellum short, with 5 annulations in holotype (up to 12 in larger females and about 60 in mature males). Antennal scale lanceolate, without apical suture, slender, 7.3 × longer than wide, longer than second article of the antennular peduncle, setose all around.

Mandibular palps ( Fig. 9A ) very long and prehensile, 3-articulate; first article short; second article twice as long as third, 9 strong setae along ventral margin, 9 smaller setae on ventromesial margin, dorsoproximal lobe with small cuspidate seta, ventral margin lined with a row of about 15 very fine simple setae; third article long and narrow, armed with 9 very long, strong, curved setae, 4 inner, 2 ventral, and 3 at the apex. Right mandible ( Fig. 9B ) incisor process comprised of 4 spines and chitinous ridge; molar process with 2 non-chitinous ridges (not shown). Left mandible ( Fig. 9C ) incisor process with two proximally close-set spines, a chitinous ridge, and a small distal spine; lacinia mobilis trifid and chitinous; molar process with 2 non-chitinous ridges and a row of setae (not shown).

Labrum ( Fig. 9D ) quadrangular with short anterolateral lobes, small tuft of short setae on mid posterior margin.

Maxilla ( Fig. 9E ) exopod elongate, extending to half-length of second article of endopod, outer margin lined with long pappose setae, naked only on the inner proximal half; endopod 2-articulate, first article outer margin bilobed, second article 3 × as long as broad, armed on outer margin with long pappose setae, a single longer pappose setae on distal margin, inner margin naked.

Maxillule ( Fig. 9F ) small, upper lobe armed distally with 9 strong cuspidate serrate setae arranged in a combination of 2 singles, 2 pairs, and 3 singles, each seta armed with about 10 serrations, lower lobe armed distally with 4 pappose setae.

First thoracopod ( Fig. 10A ) with long, slender epipodite, subequal in length to endopod, without exopod; endopod robust; basis without lobe, numerous tufts of setae on inner margin; preischium small; inner margin of ischium produced into a conical lobe with a strong terminal seta, ventral margin lined with about 20 simple setae; merus slightly larger than ischium; carpopropodus swollen, almost twice the length of merus; dactylus terminating in long curved nail.

Second thoracopod ( Fig. 10B, C ) longer than first, without exopod and epipod; ischium lobe oblong, reaching just beyond distal margin of merus, about 3 × as long as broad, margin of lobe naked along proximal 1/7 of the lower margin and proximal 2/3 of dorsal margin, otherwise a series of small cuspidate setae interspersed with longer cuspidate setae which increase in length towards distal margin; merus rectangular, about 3.5 × as long long as broad, armed with 6 large cuspidate setae on dorsomedial margin and a series of short and long setae on lower margin; carpopropodus about 2 x as long as broad, 4 cuspidate setae on dorsal margin, 4 long cuspidate setae on dorsomedial margin, curving downward and distally, lower margin with irregular row of long and short setae, tuft of fine simple setae at distal, medial end; dactylus fused with nail to form a long, curved claw with long simple setae on proximal inner and outer margins. Rudimentary oostegite present.

Third and fourth thoracic endopods absent in females ( Fig. 10D ), rudimentary in adult males, reduced to 2 small articles ( Fig. 11 E , third thoracopod only).

Fifth thoracopod long and slender ( Fig. 11A ). No setae except for distal tuft of dense setae; preischium and ischium subequal and together subequal to merus; carpus 2.5 × merus length and subequal to propodus.

Sixth to eighth thoracopods ( Fig. 11B–D ) long and slender, with simple setae. Sixth endopod preischium 0.3 × length of ischium; ischium and merus subequal in length; carpus 1.4 × merus and 1.2 × propodus; dactylus 0.3 × propodus. Seventh endopod preischium 0.6 × length of ischium; ischium 0.4 × merus; merus 1.6 × carpus; carpus subequal to propodus; dactylus 0.3 × propodus. Eighth endopod preischium 0.4 × length of ischium; ischium 0.3 × merus; merus 2 × carpopropodus; dactylus 0.4 × carpopropodus. Exopods of thoracopods similar, 13–18-articlulate ( Fig 10D , 11A–D ). First articles in males much broader than in females, increasing in size as male matures, 15–17 articles, endopods rudimentary, 2–3-articulate ( Fig. 11 E, F ).

Male penis (at base of eighth thoracopod) moderately elongated, tapering distally ( Fig. 11F ).

Marsupium ( Fig. 10 B, D , 11A–D ) composed of seven pairs of oostegites, first pair rudimentary, second to sixth pair similar, seventh pair smaller and with prominent posteriorly directed and curved ventilation lobe in the distodorsal margin. The distal margin of ventilation lobe is lined with two rows of setae, the inner row long, straight, and plumose, the outer row short and curved outwards ( Fig. 11G ).

Female pleopods ( Fig. 12A–E ) 2-articulate, increasing in length towards posterior pairs, uniramous in all but the largest specimen where the pleopod develops a small exopod on the distal end of the first article ( Fig. 12F ); numerous long, articulated, pappose setae (not shown) adorning pronounced receptacles. Adult male pleopods biramous ( Fig. 12G–K ); first pleopod smallest, endopod short with 2 broad articles, exopod first article longest, 17-articulate; second pleopod largest, endopod first article longest and broadest, 14-articulate, exopod with one long, broad article with 3 long, flattened, distal setae, 15-articulate. These 3 long, flattened setae increase in size with maturity as do the sympods of all pleopods. Third to fifth pleopods similar in size and structure with exopod slightly longer than endopod; exopods 18–19-articulate, endopods 9–12-articulate. Juvenile male pleopods ( Fig. 12 L–P ). Sympod short, narrow; endopod of first pleopod smallest, second to fourth endopods subequal, fifth endopod longest, similar in shape to female pleopods; exopods 1–5 small unarticulated lobes, similar sized.

Uropod endopod ( Fig. 13 ) narrow, lanceolate, setose along entire margin, slightly longer than telson. Exopod longer and broader than endopod, 2-articulate, distal article 0.25 × length of the proximal article, narrower, fully setose, lateral margin of proximal article without setae, armed on the distal corner with 3 cuspidate seta increasing in size from outer to inner, a longer, inner, slender plumose seta.

Telson ( Fig. 13 ) rectangular, 2.5 × as long as broad, 1.2 × as long as sixth pleonite. Lateral margins armed with 25–28 cuspidate setae along the posterior 0.6 of telson length. Posterior margin straight, armed with one small median serrate seta with two very small cuspidate setae and 3 long serrate setae on either side, outer pair longest.

Distribution. Known from the Challenger Plateau, Chatham Rise, and eastern waters off the lower North Island and upper South Island with a depth range of 600–2200 m ( Fig. 1 ).

Remarks. The diagnostic features of the genus Petalophthalmus include: antennal scale setose all around; eyes not miniaturized, nonetheless cornea reduced, without or with some scattered visual elements, together not forming a compound sensory organ; anterior margin of carapace without pair of distinct submedian processes, rostrum present or absent; lacinia mobilis absent in one mandible, developed in the other one; pars centralis absent or reduced to one spine (tooth, digitus); thoracic endopods 3–4 reduced to 1–2 short segments; thoracic endopods 5–8 slender, with more than five segments; flagellum of thoracic exopods 3–8 with 13–21 segments; pleopods biramous in males, biramous or uniramous in females; telson large, subquadrangular, terminal margin truncate with or without slight emargination, terminal margin without or with two submedian groups of small teeth, in any case with 7–13 large, toothed spines, without setae Wittmann (2020). The description of Petalophthalmus lobatus sp. nov. we report herein fits all of the characters of this diagnosis and should therefore be placed within this genus.Females of Petalophthalmus lobatus sp. nov. can easily be distinguished from its congeners by the presence of enlarged ventilation lobes on the seventh oostegites which are lined distally with two different sets of setae, the inner set long, straight, and plumose, the outer set shorter and curved outwards. The laterally flattened eyes differ to previous descriptions of this genus, variously described as, leaf like for P. armiger and P. papilloculatus , dorsoventrally flattened for P. cristata , and globular for P. papuaensis . The combination of an acute rostrum and armature of the telson (<30 lateral setae on the distal 0.6 portion of the telson length and 7 terminal setae) can also be used. Of the known species of Petalophthalmus , the following characters also differ: P. cristatus carapace is longer, leaving 1.5 thoracic somites exposed (two in P. lobatus sp. nov.), anteroventral and posteroventral corners are more rectangular, and posterior margin much less rounded; antenna equal in length to scale (shorter in P. lobatus sp. nov.); P. armiger differs in having seven serrate setae on the outer lobe of the maxillule (nine-serrate in P. lobatus sp. nov.), a basal lobe present on the first thoracopod (absent in P. lobatus sp. nov.); P. papilloculatus differs in the truncate anterior and posterior margins of the carapace and lack of a rostrum, and seven serrate setae on the outer lobe of the maxillule compared to nine; P. papuaensis differs in the eyes being globular, with distinct retinular cells, carapace without rostrum and anterior margin truncate.

Figures

FIGURE 1. Distribution map of Ipirophthalmus crusulus sp. nov. (white circles) and Petalophthalmus lobatus sp. nov. (black triangles) off New Zealand. Isobaths are at 500 and 1000 m.

FIGURE 8. Petalophthalmus lobatus sp. nov., holotype female NIWA 135622.A, habitus, lateral view. B, anterior body, dorsal view. C, anterior part of carapace. D, left antennula, lateral view. E, left eye, mesial view. F, antenna and scale, ventral view.

FIGURE 9. Petalophthalmus lobatus sp. nov., paratype female NIWA 147401. A, mandibular palp, lateral view. B, right mandible, ventral view. C, left mandible, ventral view. D, labrum. E, maxilla. F, maxillule.

FIGURE 10. Petalophthalmus lobatus sp. nov., paratype female NIWA 147401. A, first thoracopod, outer view. B, second thoracopod and oostegite, outer view. C, second thoracopod, inner view. D, third and fourth thoracopod (in situ).

FIGURE 11. Petalophthalmus lobatus sp. nov., A–D, G, paratype female NIWA 147401, E, F, allotype male NIWA 147408. A, fifth thoracopod (exopod not drawn). B, sixth thoracopod. C, seventh thoracopod. D, eighth thoracopod. E, third thoracopod. F, eight thoracopod and penis. G, ventilation lobe of seventh oostegite.

FIGURE 12. Petalophthalmus lobatus sp. nov., A–E, paratype female NIWA 147401. F, adult female NIWA 147403. G–K, allotype male NIWA 147408. L–P, juvenile male NIWA 135623.A, F, G, L, first pleopod. B, H, M, second pleopod. C, I, N, third pleopod. D, J, O, fourth pleopod. E, K, P, fifth pleopod.

FIGURE 13. Petalophthalmus lobatus sp. nov., holotype female NIWA 135622. Telson and uropod, dorsal view.

FIGURE 14. Ipirophthalmus crusulus sp. nov., holotype female NIWA 135618 (4.9 mm CL, preserved in ethanol), top. Petalophthalmus lobatus sp. nov., adult female NIWA 10754 (7.2 mm CL, preserved in formalin), bottom.