Ipirophthalmus crusulus, 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 : 453-461

Ipirophthalmus crusulus sp. nov.

( Figs. 2–7 , 14 )

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

Material examined. Type material. Holotype. NIWA 135618 , adult female (4.9 mm CL, 24.4 mm TL), Chatham Rise, RV Tangaroa, TAN 0705/251, -42.996, 178.996, 24/04/2007, 520– 530 m, hyperbenthic sled . Allotype. NIWA 135620 , adult male (4.3 mm CL, 22.3 mm TL), Chatham Rise, FV Arrow, stn Z18647, -44.692, -176.633, 26/11/1986, 890– 912 m, plankton net . Paratypes. NIWA 135619 , adult female, dissected (4.6 mm CL, 22.1 mm TL), Chatham Rise, TAN0705/251, -42.996, 178.996, 24/04/2007, 520– 530 m, hyperbenthic sled . NIWA 157310 , juvenile male, (4.5 mm CL, 20.9 mm TL), Chatham Rise, TAN0705/251, -42.996, 178.996, 24/04/2007, 520– 530 m, hyperbenthic sled .

Additional material. NIWA 78906 , 2 adult females (5.2 mm CL, 24.8 mm TL, damaged), juvenile female (4.5 mm CL, 20.4 mm TL), TAN1116/96, lot 1275, -42.859, 177.922, 14/11/2011, 570– 575 m, beam trawl . NIWA 78994 , 4 juvenile males (2.7 mm CL, 13.1 mm TL, 3.8 mm CL, 18.3 mm TL 4.2 mm CL, 20.6 mm TL, 4.4 mm CL, 19.4 mm TL), 2 juvenile females (2.7 mm CL, 13.1 mm TL 4.0 mm CL, 21.3 mm TL), TAN1116/105, lot 1395, -42.897, 177.835, 15/11/2011, 420– 423 m, top net, hyperbenthic sled . NIWA 141483 , 5 adult females (5.0 mm CL, 25.4 mm TL, 4.3 mm CL, 21.1 mm TL, 4.8 mm CL, 22.3 mm TL, 4.9 mm CL, 23.3 mm TL, 5.0 mm CL, 24.9 mm TL), TAN0705/251, lot 3591, -42.996, 178. 996, 24/04/2007, 520– 530 m, hyperbenthic sled . NIWA 141484 , juvenile female (2.9 mm CL, 11.0 mm TL), TAN0707/29, lot 341, -38.618, 168.943, 29/05/2007, 480– 482 m, hyperbenthic sled . NIWA 141807 , 3 adult females, 12 juvenile females, 14 juvenile males, (not measured), TAN0705/285, lot 4061, -43.797, 175.316, 27/04/2007, 418– 422 m, top net elutriate, hyperbenthic sled . NIWA 147409 , two adult females (4.8 mm CL, no TL, 5.3 mm CL, no TL), stn Z18641, -44.180, 176.745, 4/11/1986, 673–673, plankton net . NIWA 147410 , adult female (4.7 mm CL, 20.0 mm TL), adult male (5.3 mm CL, 22.0, mm TL), stn Z18645, -44.327, 178.528, 23/11/1986, 700– 702 m, plankton net . NIWA 147411 , adult male (4.3 mm CL, 19.5 mm TL), stn Z18651, -39.793, 178.388, 6/10/1990, 700– 800 m, plankton net . NIWA 147412 , 3 adult females (4.9 mm CL, 22.5 mm TL, 5.0 mm CL, 22.5 mm TL, 5.0 mm CL, 23.0 mm TL), adult male (4.6 mm CL, no TL), stn Z18650, -43.392, 173.926, 26/09/1990, 676– 669 m, plankton net . NIWA 147413 , adult female (4.9 mm CL, 23.2 mm TL), stn Z18640, -43. 900, 177.900, 02/11/1986, 630– 657 m, plankton net . NIWA 147414 , adult female, (5.8 mm CL, 26.1 mm TL), stn Z18638, -43.995, 178.677, 01/11/1986, 746– 806 m, plankton net . NIWA 147415 , 3 adult females, (4.9 mm CL, 22.4 TL, 4.9 mm CL, 22.5 mm TL, too damaged to measure), stn Z18469, -42.974, 174.128, 25/09/1990, 1090– 1116 m, plankton net . NIWA 147416 , juvenile female (4.5 mm CL, 21.0 mm TL) stn Z18638, -43.995, 178.6767, 1/11/1986, 746– 806 m, plankton net . NIWA 147417 , 3 adult females (4.4 mm CL, 21.3 mm TL, 4.9 mm CL, 23.2 mm TL, 5.0 mm CL, 22.3 mm TL, CL 5.3 mm CL, 23.9 mm TL), 5 juvenile females (4.5 mm CL, 21.1 mm TL, 4,5 mm CL, 20.5 mm TL, 4.5 mm CL, 20.6 mm TL, 4.6 mm CL, 20.9 mm TL, 4.7 mm CL, 23.0 mm TL), 3 adult males (3.9 mm CL, 18.8 mm TL, 4.7 mm CL, 21.2 mm TL, 4.8 mm CL, 22.4 mm TL), 2 juvenile males (4.2 mm CL, 17.8 mm TL, 4.3 mm CL, 17.9 mm TL), stn Z18647, -44.692, 176.633, 26/11/1986, 890– 912 m, plankton net . NIWA 147418 , 15 specimens, not measured (damaged), stn Z18646, -44.308, -178.240, 23/11/1986, 633– 637 m, plankton net . NIWA 147419 , juvenile female (4.3 mm CL, 17,2 mm TL), stn Z18652, - 39.662, 178.413, 6/10/1990, 685– 800 m, plankton net . NIWA 147420 , 4 adult females (3.9 mm CL, 18.8 mm TL, 5.2 mm CL, 23.6 mm TL, 5.4 mm CL, 21.4 mm TL, 5.5 mm CL, 23.7 mm TL), 2 juveniles (damaged), stn Z18654, -40.650, 176.953, 2/10/1990, 646– 702 m, plankton net . NIWA 147421 , juvenile male (4.0 CL, 19.2 mm TL), stn V387 , -43.827, 176.997, 16/09/ 1989, 498 m, Agassiz trawl . NIWA 148017 , 2 juvenile females (3.0 mm CL, 13.2 mm TL, 2.4 mm CL, 9.6 mm TL), juvenile male (3.1 mm CL, 15.0 mm TL), TAN1116/105, -42.897, 177.835, 15/11/2011, 420– 423 m, hyperbenthic sled . NIWA 148018 , 2 juvenile females (2.6 mm CL, 11.5 mm TL, 2.7 mm CL, 11.7 mm TL), TAN0705/255, -43.530, 178.505, 24/04/2007, 346– 346 m, top net elutriate, hyperbenthic sled . NIWA 148019 , juvenile female (3.4 mm CL, 16.5 mm TL), TAN0705/41, lot 641, -43.836, 176.709, 05/04/2007, 478– 479 m, hyperbenthic sled . NIWA 148020 , juvenile male (3.4 mm CL, 14.5 mm TL), TAN0705/160, -42.782, - 176.715, 16/04/2007, 1023– 1026 m, top net elutriate, hyperbenthic sled . NIWA 148021 , four juveniles (1.1 mm CL, 5.1 mm TL, 1.2 mm CL, 5.2 mm TL, 1.4 mm CL, 5.5 mm TL, 1.5 mm CL, 5.8 mm TL), TAN0707/119, -40.880, 170.856, 6/06/2007, 529– 534 m, top net elutriate, hyperbenthic sled . NIWA 148022 , juvenile male (4.5 mm CL, 19.4 mm TL), TAN0707/119, -40.880, 170.856, 6/06/2007, 529– 534 m, top net, hyperbenthic sled .

Etymology. Derived as a diminutive form (-ulus) of the Latin word for leg (crūs), referring to the very small sixth to eighth thoracic endopods.

Diagnosis. Rostrum short, raised, and acute. Eyes stalked, cornea pigmented, small ocular papilla present on mesial margin. Carapace short, thin, semi-transparent, last 3 thoracic somites exposed dorsally. First thoracopods without exopod and basal lobe, with epipod. Second thoracopods without exopod, basal lobe, or epipod, ischium lobe not overreaching merus. Third and fourth thoracopods absent in females, rudimentary in males. Sixth to eighth thoracic endopods greatly reduced. Female pleopods uniramous, male pleopods biramous. Lateral margins of telson armed with 19–21 cuspidate setae along the distal 0.6 portion, apex slightly emarginate and armed with 10 robust serrate setae and 4 long plumose setae.

Description. Body slender, cephalothorax 0.41 × TL, pleon 0.47 × TL, telson 0.12 × TL, carapace 0.19 × TL. Pleonite long and thin, able to flex upwards and downwards. Pleonites 1–3 subequal in length, 0.12 × TPL, pleonites 4–5 subequal, 0.18 × TPL, pleonite 6 longest, 0.27 × TPL ( Fig. 2A , 14 ).

Carapace ( Fig. 2A ) short, thin, semi-transparent, anterior margin concave, cervical sulcus weak; rostrum triangular in lateral view, short, sharp, and raised, just overreaching the anterior margin of carapace; dorsomedial tubercle lies directly behind the base of the rostrum; border between the rostrum and the rounded anterolateral corner concave, armed in the middle with a small, raised, triangular tooth, lateral border extends to the basis of second thoracic limb then gradually rises upwards to the posterior-lateral corner exposing the ventral half of the sixth thoracic somite, posterior margin concave, exposing the last three thoracic somites.

Eyes pyriform, well developed, 1.6 × as long as broad; cornea pigmented, broader than stalk, occupying distal 0.5 of eye stalk; small ocular papilla on proximal third of mesial margin of eye stalk ( Fig. 2B ).

Antennule peduncle ( Fig. 2B, D ) very long, slender, 3-articulate; first article longest, armed with 4 setae at dorsal mid-point, 1 cuspidate seta near the dorsodistal margin, several long setae surround the distal margin, 1.4 × longer than second, 2.7 × longer than third; distal margin of second article surrounded by long simple setae; third article with 3 long setae on dorsodistal lobe, outer flagellum is thinner and shorter than inner, first article with longitudinal crista ( Fig. 2E ). Males’ outer flagellum wider and shorter than inner; in mature males outer flagellum swollen at base, densely covered in fine setae when fully mature.

Antenna peduncle ( Fig. 2C ) 3-articulate, subequal in length to scale; first article short with 1 acute and 1 obtuse process on the inner margin; second article slender and long with 2 long setae on distal margin; third article slightly longer than second with 6 long setae on distal margin, flagellum short and thin. Antennal scale lanceolate, slender, 9 × longer than wide, subequal in length to second article of antennular peduncle, covered with seta except for a small portion (0.1) of posterior lateral margin.

Mandibular palps ( Fig. 3A ) very long and prehensile, 3-articulate; first article very small; second article long and robust, 7 strong setae along ventral margin, 9 smaller setae on ventromesial margin, dorsoproximal lobe with small cuspidate seta; third article long and narrow, 0.6 × as long as the second, armed with 9 very long, curved, spine-like setae, 4 mesial, 2 ventral, 3 terminal. In very mature males, long setae with 2 densely lined rows of short, blade-like setules, develop along the ventral margin of the third article ( Fig. 3B ). Right mandible ( Fig. 3C ) with incisor process comprised of 4 spines and chitinous ridge, molar process (not shown) with 2 non-chitinous ridges. Left mandible ( Fig. 3D ) incisor process with 2 proximally close-set spines, chitinous ridge, and small distal spine, lacinia mobilis chitinous with three small spines, molar process (not shown) with 2 non-chitinous ridges, outer ridge with parallel outer row of setae.

Labrum ( Fig. 3E ) symmetrical with lobes on anterolateral margins, tuft of short setae on posterior margin.

Maxilla ( Fig. 3F ) 3-articulate. First article with elongate exopod, outer margin and half of the inner margin with long pappose setae, inner margin with one naked endite; second article with four short lobes with pappose setae; third article long and narrow, 3 × as long as broad, densely setose on outer and distal margin, single median pappose seta on the inner margin.

Maxillule ( Fig. 3G ) upper lobe armed distally with 10 strong cuspidate serrate setae arranged in a combination of 2 singles, 3 pairs, and 2 singles, each seta armed with 3–4 serrations, lower lobe armed distally with 3 simple setae.

First thoracopod ( Fig. 4A ) with long narrow epipod, without exopod; basis without lobe; preischium small, inner margin of ischium produced into conical lobe with 1 strong terminal setae; merus slightly larger than ischium; carpopropodus swollen, almost twice the length of merus; dactylus long terminating with 1 long, curved nail.

Second thoracopod ( Fig. 4B ) elongate and slender, longer than first thoracopod, without exopod and epipod. Basis lobe absent; ischium lobe long and rectangular, reaching three-quarter length of merus, armed with short cuspidate setae along ventral margin and long and short cuspidate setae interspersed along distal margin; merus long and robust, ventral margin proximal half armed with 3 long cuspidate setae, distal half with 3 pairs of closely set long and short cuspidate setae, dorsomedial margin armed with 5 downward and anteriorly pointing cuspidate setae, distal setae much longer than proximal; carpopropodus oval, robust, shorter than merus, dorsal margin armed with 3 short cuspidate setae, inner subdorsal margin armed proximally with 3 long downward and anteriorly pointing cuspidate setae, ventral margin armed with a row of long and short cuspidate setae and 3 distal simple setae; dactylus fused with nail to form a long, curved claw with long simple setae on the proximal inner and outer margin.

Third and fourth thoracic endopods absent in females ( Fig. 4C–D ). Male endopods rudimentary, 3-articulate; first article of exopod greatly enlarged ( Fig. 4E ).

Fifth thoracopod ( Fig. 5A ) long and slender, terminating in a dense tuft of setae. Preischium shorter than ischium; ischium 0.3 of merus; merus subequal to carpopropodus.

Sixth to eighth thoracopods ( Fig 5B–D ) very short and slender, 4-articulate with 2 terminal setae on fourth article.

Thoracic exopods similar in size, 14–16-articulate.

Marsupium composed of seven pairs of oostegites, first pair rudimentary, seventh pair with small ventilation lobe ( Fig. 4C, D , 5A–D ).

Pleopods uniramous in females ( Fig. 6A–E ), increasing in length towards posterior pairs. First pleopod 1- articulate. Second to fifth pleopods 2-articulate, long fragile pappose setae adorning distal end (not shown). Male pleopods biramous ( Fig. 6F–J ). First pleopod endopod 2-articulate, articles short, exopod first article long, followed by 15 short setose articles. Second pleopod endopod first article broad, followed by 13 short setose articles, exopod with first and second article long, followed by 13 short setose articles, second article with three long, flattened pappose setae, setae increasing in length with maturity. Third pleopod endopod first article broad, followed by 13 short setose articles, exopod with 18 articles. Fourth pleopod endopod first article broad, second article elongated, followed by eight short setose articles, exopod first article long, followed by 14 short setose articles. Fifth pleopod endopod with 14 articles, exopod with 17 articles. Juvenile male pleopods ( Fig. 6K–O ) sympod short, narrow; endopods increasing in length towards posterior pairs, similar in shape to female pleopods; exopods 1–5 of similar size.

Telson ( Fig. 7 ) rectangular, 3 × as long as broad; lateral margins armed with 19–21 spines along posterior 0.6 of telson length; posterior margin slightly emarginated, armed with one median serrate seta, 3 shorter serrate setae on each side from which 4 long plumose setae arise, and 3 longer serrate setae on apical lobes.

Uropod endopod ( Fig. 7 ) narrow, lanceolate, setose along entire margin, without spines, longer than telson. Exopod longer than endopod, 2-articulate, 8 × as long as wide, distal article 0.25 length of proximal article, narrower than proximal article, fully setose, lateral margin of proximal article without setae, armed on distal corner with one small cuspidate seta and a longer, stouter cuspidate seta, and then a longer, slender plumose seta.

Distribution. Known from the Challenger Plateau, Chatham Rise, and eastern waters of the lower North Island. Depth range: 346–1348 m ( Fig. 1 ).

Remarks. The diagnostic features of the genus Ipirophthalmus are: antennal scale setose all around; eyes with well-developed, pigmented cornea; anterior margin of carapace with rostrum flanked by a pair of processes; thoracic endopods 5–8 slender, each with more than three segments; flagellum of thoracic exopods 3–8 with 10–14 segments; male pleopods biramous, female pleopods uniramous or biramous; telson large, subquadrangular, terminal margin truncate without or with distinct mid-terminal emargination, terminal margin with two submedian groups of small teeth, with 7–8 large, toothed spines and 1–2 pairs of long setae, these setae arising from the emargination, if present, otherwise from homologous submedian position ( Wittmann 2020). Ipirophthalmus crusulus sp. nov. shares these diagnostic characters and is placed in this genus.

Ipirophthalmus crusulus sp. nov. can easily be distinguished from its four congeners by the rudimentary endopods of the sixth to eight thoracopods. This appears to be similar to Parapetalophthalmus suluensis that shares rudimentary endopods of the sixth to eight thoracopods. However, our new species does not share the diagnostic characters of the genus Parapetalophthalmus . In the latter the rostrum is absent, the endopods of the third and fourth thoracopods are well-developed, the proximal two-thirds of the outer margin of the antennal scale is naked, the female pleopods are biramous, and the eyes are elongated and without papillae. Within the genus Ipirophthalmus only I. oculatus has modified endopods in that they lack a dactylus and are reduced (thought by Pillai (1968) to be a result of regeneration); however, in I. crusulus sp. nov. they are still much shorter and smaller. Ipirophthalmus oculatus also differs in the distinct “long and slender pedicel” ( Pillai 1968: 284) that the eyes are connected to. Compared to I. liui , differences include the ischium lobe of the second thoracopod which is longer than the merus (shorter than merus in I. crusulus sp. nov.), scale longer than antenna (shorter than antenna in I. crusulus sp. nov.), third article of mandibular palp less than half the length of second article (0.6 in I. crusulus sp. nov.), and uropodal endopod similar in length to the exopod (exopod longer in I. crusulus ). Ipirophthalmus caribbeanus differs in the carapace, which is anteriorly truncate (concave in I. crusulus sp. nov.), the long and slender third and fourth thoracopods (absent in female I. crusulus sp. nov. and rudimentary in males), and the biramous female pleopods (uniramous in I. crusulus sp. nov.). Ipirophthalmus macrops differs with its larger eyes, third article of mandibular palp less than half the length of second article (vs. 0.6 times as long).

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 2. Ipirophthalmus crusulus sp. nov., holotype female NIWA 135618. A, habitus. B, anterior body in dorsal view. C, antenna and scale, ventral view. D, left antennula lateral view. E, first article of outer flagellum.

FIGURE 3. Ipirophthalmus crusulus sp. nov., A, C–G, paratype female NIWA 135619. B, allotype male NIWA 135620. A, left mandibular palp in lateral view. B, third article of left mandibular palp, arrows indicating rows of setae, lateral view. C, right mandible, ventral view. D, left mandible, ventral view. E, labrum. F, maxilla. G, maxillule.

FIGURE 4. Ipirophthalmus crusulus sp. nov., A–D paratype female NIWA 135619. E, male allotype NIWA 135620. A, first thoracopod. B, second thoracopod. C, third thoracopod. D, fourth thoracopod. E, third thoracopod.

FIGURE 5. Ipirophthalmus crusulus sp. nov., paratype female NIWA 135619. A, fifth thoracopod. B, sixth thoracopod. C, seventh thoracopod. D, eighth thoracopod.

FIGURE 6. Ipirophthalmus crusulus sp. nov., A–E, paratype female NIWA 135619; F–J, allotype male NIWA 135620. K–O, paratype juvenile male NIWA 157310. A, F, K, first pleopod. B, G, L, second pleopod. C, H, M, third pleopod. D, I, N, fourth pleopod. E, J, O, fifth pleopod.

FIGURE 7. Ipirophthalmus crusulus sp. nov., holotype female NIWA 135618. 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.