Petalophthalmus cristatus, Wittmann, 2020

Wittmann, Karl J., 2020, Lophogastrida and Mysida (Crustacea) of the “ DIVA- 1 ” deep-sea expedition to the Angola Basin (SE-Atlantic), European Journal of Taxonomy 628, pp. 1-43 : 7-14

Petalophthalmus cristatus sp. nov.

urn:lsid:zoobank.org:act:D4D691BD-4E1A-4D8B-B5A2-36979FBA2558

Figs 1–4

Diagnosis (based on adult female only)

Petalophthalmus with eyes elongate ovoid, dorsoventrally flattened by a factor of 1.4; no visual elements developed; stalk with short papilla on mesial margin. Inner margin of outer antennular flagellum subbasally with short, distally rounded, longitudinal crista. Antennal scale with distinct apical segment. Carapace with essentially transverse, centrally concave anterior margin, rostrum forms a proximally widening crista in dorsal view and an acute triangle in lateral view. Masticatory part of left mandible with well-developed lacinia mobilis, right mandible without. Mandibular palp powerful, (when stretched) anteriorly extending beyond antennular trunk; apical segment with 7 long, strong setae; apical segment half as long as median segment; basal segment with rounded lobe near disto-medial edge (dashed line in Fig. 2A ). Thoracopods 1–2 without exopods; thoracopods 3, 8 with exopods bearing a 17-segmented flagellum; exopods 4–7 with 18-segmented flagellum. Merus of thoracic endopod 2 with smooth setae along outer margin. Endopods 3–4 rudimentary, unsegmented, lobe-like. Endopod 5 fully developed, slender, elongate; carpus not fused with propodus; disto-medial edge of propodus with two proximally microserrated setae ( Fig. 3D ); dactylus with very short, stout, terminally bent claw serrated by strong teeth. Endopods 6–8 again more slender, longer than exopods; carpus fused with propodus; dactylus with small, slightly bent, smooth claw. Female pleopods uniramous, reduced to 3-segmented endopods, increasing in length caudally. Apical segment extremely miniaturized in pleopod 1 ( Fig. 3O ), well developed in pleopods 2–5. Exopod of uropod extends beyond endopod, the latter beyond telson; endopod without statocyst and spines. Exopod 2-segmented, basal segment with small, barbed seta and two spines on disto-lateral corner ( Fig. 4G ). Telson subquadrangular with rounded terminal edges; dense series of 23–24 spines only on distal 40% of lateral margins, proximal portions smooth. Telson almost truncate, mid-terminally emarginated by only 1% of its length. Terminal margin with short, bilaterally toothed, median spine, on each side flanked by three small teeth and again more laterally by five large, bilaterally toothed spines; the most lateral spine shorter than the sublateral one; spine length decreases from sublateral to innermost spines.

Etymology

The species name is a Latin adjective with masculine ending, referring to the longitudinal crista on the inner margin of the outer antennular flagellum and to the longitudinal median crista forming the rostrum.

Material examined

Holotype (by present designation)

ANGOLA BASIN • ♀ ad. (BL = 28.3 mm, brood pouch empty, dissected and mounted on 14 slides); SE-Atlantic, Angola Basin ; 20°0.733′ S, 3°2.230′ E to 20°6.409′ S, 3°7.197′ E; bottom depth 5487– 5497 m; 15 Jul. 2000; DIVA-1 exped., #327; Agassiz Trawl; ZMH 58247 .

Type locality

Station #327 ( Table 1 ) in the abyssal plain of the Angola Basin; 20°1′ S, 3°2′ E to 20°6′ S, 3°7′ E; bottom depth 5487–5497 m. Sample taken with Agassiz Trawl, therefore not definitely excluded that the material entered the gear during ascent.

Description

All features of the diagnosis. Body moderately slender, cephalothorax contributes 34% total length, pleon 46%, telson 20%, carapace 29%.

CARAPACE ( Fig. 1 A–C). Leaving ultimate 1.5 thoracic somites mid-dorsally exposed; antero-lateral edges rectangular, terminally rounded; small bulge behind rostrum; cervical sulcus weak but distinct. Posterior margin of carapace emarginated; emargination unapparent upon inspection in situ ( Fig. 1 A–B), but well visible in carapace detached and expanded on slide ( Fig. 1C ).

EYES ( Fig. 1 A–C). No external corneal structures visible. Definite ocular papilla on mesial margin visible in dorsal view ( Fig. 1 B–C) but not so in lateral view ( Fig. 1A ). Eyes 1⁄₅ carapace length; dorsoventrally weakly compressed with length ª⁄2 maximum width in dorsal view vs ̚⁄2 maximum height in lateral view. Eyes appear wider in Fig. 1C due to pressure exerted by cover glass.

ANTENNULA ( Fig. 1 A–B, D–E). Trunk long and slender, 1.1 times length of carapace. Three-segmented, whereby segments 1–3 are 46–48%, 35–37%, and 17% total trunk length, respectively. Basal segment with small spine in subterminal position. Terminal margin of distal segment dorsally produced in a triangular, setose lobe. Width at basis of outer flagellum is ¹⁄5 that of inner flagellum. Width of longitudinal crista near basis is ¼ width of outer flagellum, length is ¾ width of outer flagellum.

ANTENNA ( Fig. 1 A–B, F). Sympod on its mesial margin with small lobe bearing a minute spine at tip. Peduncle 3-segmented, whereby segments 1–3 contribute 9–11%, 40–44%, and 47–49% to total peduncle length. Mesial margin of basal segment with small lobe ending in a large spine. Flagellum tiny, short, 6-segmented. Antennal scale extends slightly beyond antennal peduncle, i.e., clearly beyond basal segment of antennular trunk. Scale 0.6 times length of carapace; scale length six times maximum width. Scale subdivided by a slightly oblique articulation; apical segment 4–5% total scale length.

LABRUM ( Fig. 1 G–H). Roughly trapezoidal in ventral view; caudal margin densely setose, with three bunches of slender spines facing the mandibles.

MANDIBLES ( Fig. 2 A–C). Palpus ³⁄2 length of carapace; segments 1–3 contribute 8–9%, 58–60%, and 32–33% to total length, respectively. Basal (first) segment laterally with spine on the tip of a triangular lobe. Analogous, smaller structure set subbasally on outer margin of median segment; apart from that, outer margin smooth all along; inner margin almost all along with numerous smooth, in part spine-like, long setae with shorter ones in between. Terminal segment reflexed, together with seven very long, strong setae rendering the palpus a large prehensile appendage. Left mandible with large processus incisivus ending in three blunt teeth; lacinia mobilis well developed with four, mostly less blunt teeth; pars centralis reduced to a single finger-like process; processus molaris with weakly sclerotized ridges and with ventral and dorsal ridges of stiff bristles. Right mandible with large processus incisivus bearing three rounded lobes representing surrogates of teeth; no lacinia mobilis developed; pars centralis reduced to a finger-like process; processus molaris trilobate.

LABIUM ( Fig. 2D ). Normal, bilobate. Inner face of the lobes all along densely setose, with dense series of stiff bristles (short spines) extending from half to ¾ length from basis.

MAXILLULA ( Fig. 1 I–J). Small, distal segment shorter than exopod of maxilla. This segment terminally with nine unilaterally serrated spines, namely four smaller ones on caudal face plus five large ones on rostral face. No pores visible. Endite subterminally with three setae barbed along their median to subterminal portions, basal third smooth. Terminal margin of endite with two additional setae showing longer barbs from their basal to subapical portions; additional two such setae subterminally on ventral margin.

MAXILLA ( Fig. 2E ). Sympod with striking, very long, barbed seta on inner face; this seta more densely barbed along its distal half; sympod with well-projecting endite, the latter setose on its distal half. Palp 2-segmented, with stout proximal and slender distal segment; the latter contributing 60% to total length, its length three times maximum width; distal segment densely setose along distal and inner margins, outer margin smooth; its most distal setae plumose, longer than distal segment. Basal segment of palp with densely setose, weakly projecting endite. Exopod slender, length four times maximum width; exopod reaches to mid of distal segment of palp; exopod densely setose all along outer margin and on distal half of inner margin; proximal quarter of inner margin with dense series of minute hairs.

FOREGUT ( Fig. 4 A–E). Object in Fig. 4A dorsally opened, laterally unfolded and expanded on slide; posterior half distorted. Gross morphology as described by Kobusch (1998) and De Jong-Moreau & Casanova (2001) for Petalophthalmus armiger . Gastric mill restricted to anterior half of the cardiac portion of the foregut. Anterior part of each laterale with 29–30 smooth spines ( Fig. 4C ) increasing in length posteriorly. Spines in ribbon-like arrangement on posterior half of this part of the lateralia. Posterior part of the right lateralia broken in this object; left ones intact, with linear series of throughout slender spines ( Fig. 4B ), the spines smooth except for tuft of acute spinules at tip. Dorso-lateral infoldings of the cardia each with antero-posterior series of setae, anteriorly starting with numerous long, smooth setae, continued by shorter setae with stiff bristles on apical half, and finally by 12–14 spine-like setae with continuous gradient from basally widened, oblong setae ( Fig. 4D ) all along with dense series of acute bristles (spinules) to basally smooth sheets ( Fig. 4E ) with oblique terminal margin densely occupied by such bristles. Pyloric portion of foregut with two slender, posteriorly directed, soft processes resembling spines (below drawing plane in Fig. 4A ). Foregut empty in this specimen.

THORACOPODS IN GENERAL ( Figs 2 F–G, 3A–I). Total length of exopods as well as their flagella increase from exopod 3 to 7, whereas that of exopod 8 ranges between nos 3 and 4. Basal plate of exopods slender, lateral margins parallel, disto-lateral edge rounded; length four times width in exopods 3–7, only three in exopod 8; basal plates 3–4, 8 with roughly equal length, plates 5–7 about 1.3 times longer. Flagella densely setose. Total length decreases from endopods 5 to 8. Dactylus 1–2, 5–8 not fused with claw (nail), endopods 3–4 without claw. Marsupium formed by seven pairs of oostegites emerging as setose epipods on thoracopods 2–8.

FIRST THORACOPOD (first maxilliped, Fig. 2F ). Epipod long, slender, smooth all around, scaphoceritelike, not contributing to the marsupium. Endopod strong, robust, densely setose on inner face from basis to dactylus; coxa with triangular endite (dashed line in Fig. 2F ) on rostral face (below drawing plane); merus with large, distally projecting endite; propodus swollen, length 1.5 times maximum width; dactylus elongate, with strong, curved, smooth claw.

SECOND THORACOPOD (second maxilliped; Figs 1A , 2G ). Epipod (if termed as such) represented by the first oostegite. Endopod robust, larger than that of the first thoracopod. Praeischium simple, smooth. Inner face of ischium with very large, broadly linguiform, subquadrangular endite with length about three times maximum width, endite distally projecting up to distal half of carpopropodus; mesial and terminal margins of endite all along with cuspidate setae; lateral margin with shorter such setae only on distal quarter, remainder smooth. Merus subquadrangular, distally widening, its length about three times maximum width; many smooth setae along inner margin, five such setae along outer margin. Carpopropodus swollen, length 1.9–2.1 times maximum width, three large and six small, smooth setae on outer margin, numerous smooth setae along inner margin, plus ten barbed setae on distal third of caudal face; dactylus elongate, with several setae and apically with strong, curved, smooth claw.

THIRD AND FOURTH THORACOPODS ( Fig. 3 A–B). Endopods unarmed, smooth, terminally well rounded, each only º⁄₅ length of basal plate of respective exopod.

FIFTH THORACOPOD ( Fig. 3 C–D). Endopod ̚⁄₅ length of exopod. Endopod with praeischium 0.3 (overlapping with ischium), ischium 0.6, carpus 0.3, propodus 0.6, and dactylus 0.04 times length of merus, each not subdivided (the same size relations reported by San Vicente et al. (2014), for ischium to dactylus in P. papilloculatus ). The here reported size relations take into account that praeischium and ischium are overlapping due to their oblique articulation. Setation of dactylus and of terminal margin of propodus together contributing to a strong brush of setae; short claw armed with eight strong teeth ( Fig. 3D ). Propodus with two modified setae at disto-medial edge ( Fig. 3D ).

SIXTH TO EIGHTH THORACOPODS ( Fig. 3 E–I). Endopods ^⁄₅ length of exopods. Merus 6–8 contribute 40– 46% to endopod length measured from praeischium to dactylus. Endopods with praeischium 0.13–0.21, ischium 0.3–0.4, carpopropodus 0.6–0.7, and dactylus 0.09–0.15 times length of merus, each element not subdivided.

PLEON ( Figs 1A , 3 J–P). Pleonites 1–5 measure 0.6, 0.5, 0.5, 0.5, and 0.6 times length of pleonite 6. Apical segment of pleopods 1–5 contributes 1%, 17%, 16%, 18%, 18% to total length; median segment 54%, 57%, 57%, 50%, 47%; basal segment 45%, 26%, 27%, 32%, 33%. Apical segment of pleopod 1 with a pair of minute spines on tip ( Fig. 3O ); pleopods 2–5 with such pair on caudo-terminal edge ( Fig. 3P ). Spines are 1.1–1.2% length of pleopod 1 or 0.7–0.8% of pleopods 2–5, respectively. Median segment of all pleopods with 15–19 papillae arranged in semicircle covering part of rostral and caudal faces ( Fig. 3 J–N). Pleopods 2–5 with separate pair of papillae in subterminal position on the anterior margin of median segment; other 2–5 papillae on terminal third of apical segment. Papillae much larger than spines and those setal bases present on apical segment ( Fig. 3P ).

UROPODS ( Fig. 4 F–G). Endopod slender, length six times maximum width; lateral margins straight, setose all around. Endopod as long as telson, nonetheless, due to its more caudal insertion shortly extending beyond telson ( Fig. 1A ). Exopod 1.15 times endopod or telson length. Exopod 2-segmented, total length five times maximum width, apical segment ¼ total length; basal segment 1.3 times broader than apical segment. Basal segment with smooth outer margin and densely setose inner margin; apical segment densely setose all around. The free latero-terminal portion of basal segment with small, smooth, blunt spine at disto-lateral corner, bordered by a threefold longer spine of that type in more mesial position, followed by an even longer, basally barbed seta, and finally a dense series of minute bristles close to insertion of apical segment ( Fig. 4G ).

TELSON ( Fig. 4 H–J). Length 2.3 times maximum width or 1.5 times length of pleonite 6. Distal 40% of each lateral margin with dense series of smooth spines except for the most distal 6–7 spines being unilaterally toothed. By contrast, all large spines of terminal margin bilaterally toothed. Terminal margin with two sets of three closely adjoining small teeth arranged in laterally increasing size, one set on each side of the bilaterally toothed, median spine ( Fig. 4J ).

Figures

Fig. 1. Petalophthalmus cristatus sp. nov., holotype, adult female with body length 28.3 mm (ZMH 58247). A. Habitus. B. Anterior body region, dorsal (most setae omitted). C. Carapace with attached frons, ocular symphysis and eyes, expanded on slide. D. Antennula, ventral. E. Detail of D, below drawing plane (showing basis of outer flagellum). F. Antenna, ventral (setae of scale omitted). G. Labrum. H. Detail of G, below drawing plane (showing spine bunch from posterior face). I. Maxillula. J. Detail of I, showing serrated spine.

Fig. 2.Petalophthalmus cristatussp.nov.,holotype,adult femalewith bodylength 28.3 mm(ZMH 58247). A. Right mandible with palpus. B. Detail of A, showing outer lobe ending in a spine. C. Masticatory parts of both mandibles. D. Labium. E. Maxilla. F. Thoracopod 1. G. Endopod of thoracopod 2.

Fig. 3. Petalophthalmus cristatus sp. nov., holotype, adult female with body length 28.3 mm (ZMH 58247). A. Endopod and exopod of thoracopod 3. B. Thoracopod 4. C. Endopod and exopod of thoracopod 5. D. Detail of C (non-modified setae omitted), showing dactylus and distal portion of propodus. E. Endopod and exopod of thoracopod 6. F. Detail of E, showing dactylus. G. Second order detail of E, showing distal portion of dactylus with nail. H. Endopod and exopod of thoracopod 8. I. Detail of H, showing distal portion of dactylus with nail. J–N. Series of pleopods 1–5, rostral (J–K, M–N) or caudal (L) aspect. O. Tip of pleopod 1. P. Tip of pleopod 3.

Fig. 4. Petalophthalmus cristatus sp. nov., holotype, adult female with body length 28.3 mm (ZMH 58247). A. Foregut dorsally opened, laterally unfolded and expanded on slide, distorted. B–E. Details of A, showing spines of gastric mill. F. Uropods. G. Detail of F, showing disto-lateral corner of basal segment of exopod. H. Telson. I–J. Details of H, showing terminal margin and medioterminal spine, respectively.