Petalophthalmus papilloculatus, Vicente, Carlos San, Frutos, Inmaculada & Cartes, Joan E., 2014

Vicente, Carlos San, Frutos, Inmaculada & Cartes, Joan E., 2014, Petalophthalmus papilloculatus sp. nov. (Crustacea: Mysida: Petalophthalmidae), a new bathyal suprabenthic mysid from the Galicia Bank (NE Atlantic Ocean), Zootaxa 3765 (1), pp. 77-91 : 78-88

publication ID	https://doi.org/ 10.11646/zootaxa.3765.1.5
publication LSID	lsid:zoobank.org:pub:9672C31D-6D1D-4CAF-A69E-BE45AE9AB635
DOI	https://doi.org/10.5281/zenodo.6131819
persistent identifier	https://treatment.plazi.org/id/174687DE-4D20-637F-62F0-E15AFD1A2782
treatment provided by	Plazi
scientific name	Petalophthalmus papilloculatus
status	sp. nov.

Treatment

Petalophthalmus papilloculatus sp. nov.

( Figs. 2–7 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

Material examined. Holotype. 1 brooding (empty marsupium) female (43.6 mm TL), MNCN 20.04/9201, Galicia Bank, RV “Miguel Oliver”, INDEMARES BANGAL0711 cruise, 8 August 2011, GOC73 bottom trawl, haul G10, 42º42.99’N 11º25.62’W, 1808 m depth, very fine sand bottom, temperature: 6.36ºC, salinity: 35.38; dissected, one vial.

Allotype. 1 mature male (34.0 mm TL), MNCN 20.04/9202, Galicia Bank, RV “Miguel Oliver”, INDEMARES BANGAL0711 cruise, 6 August 2011, beam trawl, haul V8, 42 º38.48’N 11º29.68’W, 1565 m depth, fine sand bottom, temperature: 6.36ºC, salinity: 35.38; dissected, one vial.

Paratypes. 1 immature female (29.3 mm TL), MNCN 20.04/9203, partially dissected, one vial. 1 immature female (41.3 mm TL), MNCN 20.04/9204, not dissected, one vial. Both from holotype locality. 2 immature females (5.8 mm CL, 33.7 mm TL), MNCN 20.04/9205, Galicia Bank, RV “Miguel Oliver”, INDEMARES BANGAL0711 cruise, 8 August 2011, beam trawl, haul V10, 42 º41.88’N 11º26.71’W, 1720 m depth, very fine sand bottom, temperature: 6.36ºC, salinity: 35.38; not dissected, one vial. 2 immature females (27.7 mm TL, 28.7 mm) TL; MNCN 20.04/9206, not dissected, one vial. 1 brooding female (empty marsupium) (5.5 mm CL), MNCN 20.04/9207, not dissected, one vial. 1 mature male (29.3 mm TL), MNCN 20.04/9208, not dissected one vial; from allotype locality. 1 juvenile (14.6 mm TL), MNCN 20.04/9209, Galicia Bank, RV “Miguel Oliver”, INDEMARES BANGAL0711 cruise, 7 August 2011, suprabenthic sled, haul TS9, 42º57.55’N 11º59.39’W, 1669 m depth, 0–65 cm near-bottom water layer, fine sand bottom, temperature 5.65ºC, salinity: 35.27; not dissected, one vial. 1 juvenile (10.4 mm TL), MNCN 20.04/9210, Galicia Bank, RV “Miguel Oliver”, INDEMARES BANGAL0711 cruise, 29 July 2011, suprabenthic sled, haul TS2, 42º57.97’N 12º00.52’W, 1726 m depth, 65–90 cm near-bottom water layer, fine sand bottom, temperature: 5.65ºC, salinity: 35.27; not dissected, one vial.

Etymology. This species is named for the peculiar papilla located on the inner dorsomedial surface of the eyes.

Diagnosis. Anterior margin of the carapace almost truncate without rostrum. Eyes flattened and leaf-like with an ocular papilla on the dorsomedial inner surface. Antennal scale with an apical lobe. First article of mandibular palp with a small lobe on the inner distal margin. Distal outer margin of the basal segment of the uropod exopod with three cuspidate setae that increase in length from outer to inner one. Lateral margin of telson with 20–36 cuspidate setae. Telson apex armed with 3–4 pairs of serrate setae decreasing in length form the outer to the inner ones, and 3–8 pairs of ventral small spines.

Description. The morphological characteristic refers to both sexes, unless otherwise stated.

Carapace short and membranous, leaving the last three or four thoracic somites uncovered dorsally ( Fig. 2 View FIGURE 2 A); anterior margin rectilinear and without rostral projection, lateral corners anteriorly rounded; one median acute tooth anterior to cervical sulcus; posterior margin not emarginated dorsally and without posterolateral lobes ( Fig. 2 View FIGURE 2 A).

Eyes flattened and leaf-like ( Figs 2 View FIGURE 2 A, B), without functional visual element, with a definite ocular papilla on mesial margin ( Fig. 2 View FIGURE 2 B).

Antennule peduncle very long and slender, longer than carapace. First article almost as long as the remaining two combined, armed on distal dorsal margin with one cuspidate seta and 2–4 pappose setae, rounded lobe on the outer proximal margin armed with two pappose setae; second article armed with 2–3 simple setae and one cuspidate seta on distal outer margin; third article shorter than second, armed with two–three dorsal pappose setae on distal margin ( Fig. 2 View FIGURE 2 B–C). Outer flagellum thinner than inner in females, basal portion of outer flagellum considerably thickened than inner in males.

Antenna peduncle 3-articulate, extending to 4/5 scale length ( Fig. 2 View FIGURE 2 D–E); first article short, as long as broad, inner margin produced medially into triangular lobe; second article five times as long as broad, distal margin armed with 2–3 simple setae; third article longer than second, distal margin armed with 4 simple setae; flagellum 5- articulate in females, with more than 60 articles and longer than peduncle in males, most articles short and scarcely as long as broad. Antennal scale about 6–7 times as long as maximum width, extending slightly beyond first article of antennular peduncle; margins setose all round; apical lobe short, nearly 1/15 scale length.

Labrum more or less symmetrical, distal margin with short irregularly distributed thin simple setae ( Fig. 3 View FIGURE 3 A).

Mandibles with elongated and 3-articulate palp ( Figs 3 View FIGURE 3 E, H); first article very small, armed with one cuspidate seta (with supracuticular pocket) on distal outer margin ( Fig. 3 View FIGURE 3 F) and a small lobe on the inner distal margin; second article about twice as long as third with 8–9 strong simple setae and about 11 pappose short setae on inner distal margin; third article armed on inner margin with five strong simple setae on inner margin and three large conspicuous simple setae on distal margin. Right mandible with incisor process composed of a single chitinous ridge with one broad terminal tooth and a smaller one behind it; lacinia mobilis reduced, setal row reduced to single spine, molar process with one chitinous ridge ( Fig. 3 View FIGURE 3 I). Left mandible with incisor process composed of two chitinous ridges with rounded distal end; lacinia mobilis and setal row absent, molar process similar to that of right mandible ( Fig. 3 View FIGURE 3 G).

Maxillule comparatively small ( Fig. 3 View FIGURE 3 B), outer lobe distally armed with seven strong cuspidate-serrate setae, each one with one row of denticles ( Fig. 3 View FIGURE 3 C); inner lobe with seven pappose setae.

Maxilla with elongate and narrow exopod, extending to half length of endopod distal article, outer margin armed with long pappose setae, inner margin with seven distal pappose setae ( Fig. 3 View FIGURE 3 D). Endopod with the distal article long and narrow, about 2.6 times as long as broad, densely setose on inner margin. Two coxal endites armed with pappose setae on inner margins, basal endite with proximal longer pappose seta.

Thoracopods classified into four different shape groups: first and second thoracopods represented as robust appendages (maxillipeds), third and fourth with peculiar endopods, fifth with apically setose endopod and sixth to eighth with clawed dactylus.

First thoracopod with long narrow epipodite, without exopod ( Fig. 4 View FIGURE 4 A). Endopod powerful and robust; basis without lobe; preischium very short; ischium produced into inner triangular lobe, tipped with four simple long seta; carpopropodus about twice as long as its greatest width, tapering somewhat distally; dactylus fused with nail to form a long curved claw armed with a few simple setae.

Second thoracopod longer and broader than first thoracopod, without epipodite and exopodite ( Fig. 4 View FIGURE 4 B). Endopod with preischium unarmed; ischium inner margin produced into a large quadrangular lobe overreaching merus distal margin, about 4 times as long as broad and bearing short cuspidate setae on inner and outer margins and five long simple setae on apex; merus longest, 3.4 times as long as broad, inner margin armed with row of simple long and short cuspidate setae; carpopropodus twice as long as greatest width, tapering somewhat distally, outer margin armed with two cuspidate setae and one long subdistal simple seta, inner margin armed with an irregularly row of simple long setae, short cuspidate setae and apical pappose setae; dactylus fused with nail to form long curved claw, armed with one long and robust simple seta on inner proximal margin and one simple seta on middle inner margin.

Third and fourth thoracopods ( Figs 4 View FIGURE 4 C–E). Endopod reduced to 1 or 2-articulate naked articles. Exopod 19/20- articulate.

Fifth thoracopod slender ( Fig. 5 View FIGURE 5 A). Endopod with only distal setae; ischium, merus and carpus subequal in length; propodus divided in 2 segments, the distal one about twice as long as the proximal one and armed on its inner distal margin with two rows of simple setae; dactylus very small and densely setose, armed with two proximal serrate setae and one distal hook-like serrate seta ( Fig. 5 View FIGURE 5 B). Exopod shorter than endopod, 18-articulate.

Sixth to eighth thoracopods ( Figs 5 View FIGURE 5 C, E–F). Endopod bearing a few plumose setae; preischium slightly shorter than ischium, merus about twice as long as carpopropodus, carpopropodus undivided; dactylus short, terminating in one simple seta, dactylus apparently fused to distal curved nail ( Figs 5 View FIGURE 5 D, G). Exopod longer than endopod, 17- articulate. Penis elongate, cylindrical, ending in hemispherical apex, without setae ( Fig. 5 View FIGURE 5 F). In females, marsupium composed of seven pairs of oostegites.

Pleopods uniramous in female, increasing in length towards posterior pairs; first pleopod 2-articulate, remaining pleopods 3-articulate ( Figs 6 View FIGURE 6 A–E). Male pleopods biramous. First pair with endopod 2-articulate ( Fig. 6 View FIGURE 6 F), distal article finger-like shaped, ending in two small simple setae ( Fig. 6 View FIGURE 6 G); exopod 16-articulate. Second to fifth pleopods with exopod slightly longer than endopod; exopods 18/19-articulate, endopods 11-articulate ( Figs 6 View FIGURE 6 H, J–L). Exopod basal article of second pleopod bearing rounded distal lobe armed with two strong simple setae ( Fig. 6 View FIGURE 6 I).

Uropod endopod slender, without statocyst, not extending beyond telson apex, fully setose, distal inner margin concave ( Fig. 7 View FIGURE 7 D). Uropod exopod 2-articulate, longer and broader than endopod, extending slightly beyond telson apex; distal article about one third of the basal article length; outer margin of the basal article entire, ending with three cuspidate setae lengthening from outer to inner one.

Telson quadrangular, 2.8 times as long as broad, nearly as long as the sixth abdominal somite; 2/3 of posterior lateral margins armed with 25–37 cuspidate setae increasing distally in size ( Figs 7 View FIGURE 7 A, E). In females, apex with four pairs of serrate setae decreasing in length towards medial point and three pairs of ventral small teeth ( Figs 7 View FIGURE 7 B, C). In males, apex with three pairs of serrate setae decreasing in length towards medial point, one medial serrate seta, and 7–8 pairs of ventral small teeth ( Figs 7 View FIGURE 7 F, G).

Distribution. The known distributional area of the new Petalophthalmus species is at the moment limited to the Galicia Bank (NE Atlantic), between 1536 and 1809 m depths.

Remarks. According to Tattersall (1968), the main diagnostic features of the genus Petalophthalmus are: the long and slender antennular peduncle; the powerful, long and prehensile mandibular palp; the prominent lobe on the ischium of thoracopods 1–2; the 2-articulated uropodal exopod with outer proximal margin entire, ending with 3 cuspidate setae at distal angle; the quadrangular shape of the telson with slightly emarginate apex and armed with serrate setae. The specimens herein described share all these diagnostic features and are therefore ascribed to genus Petalophthalmus .

P. papilloculatus sp. nov. is the sixth species to be discovered in genus Petalophthalmus . It can be easily distinguished from P. oculatus , P. caribbeanus , P. macrops and P. l i u i by the structure of its eyes, leaf-like and without visual elements (versus eyes being more or less globular in shape, with functional visual elements).

P. papilloculatus sp. nov. shows some similarity to P. armiger Willemoes-Suhm, 1875 View in CoL but can be distinguished by the main following features:

(1) Anterior margin of the carapace truncate, without rostrum (versus an acute triangular rostrum in P. armiger View in CoL ).

(2) An ocular papilla (versus without papilla in P. armiger View in CoL ).

(3) Antennal scale relatively longer and with an apical lobe that is not described in P. armiger View in CoL .

(4) Molar process of mandible with only one chitinous ridge (versus three ridges separated by deep grooves in P. armiger View in CoL . First article of mandibular palp with a small lobe on its inner distal margin (versus absent in P. armiger View in CoL ).

(5) Male second pleopod with a rounded distal lobe on exopod first article, bearing two strong simple setae (versus lobe and setae absent in P. armiger View in CoL ).

(6) Basal article of uropodal exopod with three distal cuspidate setae on outer distal corner, lengthening from outer to inner one (versus two or three cuspidate setae, lengthening from inner to outer in P. armiger View in CoL ).

(7) Telson of mature specimens with 25–37 setae along lateral margins (versus 40–50 setae in P. armiger View in CoL ).

(8) Telson apex armed with 3–4 pairs of serrate setae decreasing in length towards the medial point and 3–8 pairs of small ventral teeth (versus 5 pairs of serrate setae, a single median serrate seta and 5 pair of small ventral teeth in P. armiger View in CoL ).

The endopod of the third and fourth thoracopods of P. papilloculatus sp. nov. shows a rudimentary structure, reduced to 1–2 articles. Such a peculiarity was observed in all the specimens herein examined and was previously mentioned for P. macrops ( Tchindonova and Vereshchaka 1991) View in CoL and for P. liui ( Wang 1998) View in CoL . On the contrary, these thoracopod endopods are not rudimentary in P. caribbeanus View in CoL , as shown by Tattersall (1968) and were not described in the case of P. armiger View in CoL (see Willemoes-Suhm 1875; Sars 1885; Tatttersall and Tattersall 1951; broken appendages) and P. oculatus View in CoL (see Pillai 1968; the figured ‘fourth thoracopod 4’ is in fact the fifth one, as demonstrated by the habitus of this species).