Phylladiorhynchus erebus, Schnabel & Ahyong, 2019

Schnabel, Kareen E. & Ahyong, Shane T., 2019, The squat lobster genus Phylladiorhynchus Baba, 1969 in New Zealand and eastern Australia, with description of six new species, Zootaxa 4688 (3), pp. 301-347 : 311-315

Phylladiorhynchus erebus n. sp.

( Fig. 4 , 5 )

Type material. HOLOTYPE: NIWA 135617 , male (3.3 mm) West Norfolk Ridge , NZOI Stn. P 10, 32.667°S, 167.473°E, 378 m, 25 Jan 1977 . PARATYPES: AWMM MA73597 (ex NIWA 123247 ), 1 male (3.1 mm), off L’Esperance Rock , Kermadec Islands, Stn. TAN 1612/108, 31.373–31.376 °S, 178.732– 178.733°W, 506– 502 m, 01 Nov 2016 . NIWA 21269 , 2 males (2.8, 3.1), station details as for holotype .

Other material. NIWA 21201 , 1 male (2.3 mm), 1 female (2.1 mm), Norfolk Island , NZOI Stn. I 85, 29.132°S, 168.25°E, 290 m, 22 Jul 1975 . NIWA 23099 , 1 male (2.6 mm), Norfolk Ridge , NZOI Stn. I 94, 29.337°S, 168.180°E, 308 m, 24 Jul 1975 .

Diagnosis. Carapace with transverse row of 5 epigastric spines (median and 2 on either side of midline); metagastric ridge medially interrupted; anterior branchial margin with 3 spines. Maxilliped 3 merus with 2 prominent spines on flexor margin. Thoracic sternite 3 anterior margin sinuous, with shallow median concavity. Antennular article 1 with 5 or 6 distal spines: distomesial spine distinctly shorter than upper distolateral spine; first lateral spine about as long as upper distolateral spine, followed laterally by 1 or 2 small spines similar to distomesial spine. Antennal article 1 mesial process distally falling well short of second lateral antennular spine; article 2 distolateral and distomesial spines subequal; article 3 with small to distinct mesial spine, laterally unarmed. P2–4 dactylus extensor margin without upright spines at bases of movable spines.

De s cription. Carapace: As long as wide; transverse ridges with dense short setae, and few scattered longer setae. Gastric region with 3 interrupted anterior transverse ridges: epigastric ridge indistinct, with 5 spines (1 median and 2 pairs of spines laterally); anterior protogastric ridge with small median gap or continuous, nearly extending laterally to carapace margin; anterior mesogastric ridge minutely interrupted or continuous, broken laterally by cervical groove, laterally continuing uninterrupted to first branchial spine; metagastric ridge medially broken; sometimes with short scales scattered between ridges. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove, followed by 2 complete, uninterrupted or minutely interrupted ridges, interspersed with 3 short lateral ridges and few short, scattered scales. Lateral margins weakly convex, with 7 or 8 spines: 2 spines (anterolateral, hepatic) in front of, and 5 or 6 spines (3 anterior branchial spines, 2 or 3 posterior branchial spines) behind distinct anterior cervical groove. Anterolateral spine well-developed, reaching or nearly reaching anteriorly to level of lateral orbital spine, subequal in size. Hepatic spine small, set slightly dorsomesially from lateral margin.Anterior branchial spines subequal in size. Posterior branchial spines progressively smaller posteriorly, first spine subequal to anterior branchial spines. Rostrum 0.5 × pcl, length-width ratio 1.5–1.8, distance between basal rostral spines about 0.3 × carapace width; dorsal surface very slightly concave; lateral margins straight, sub-apical spines obsolescent. Pterygostomian flap without anterior spine; surface unarmed, with series of short striae.

Thoracic sternum: Sternal plastron about as wide as long, lateral margins of posterior half slightly divergent. Sternite 3 width 2–3 × length; anterior margin with small median notch; lateral margins rounded.

Abdomen: Tergite 2 with anterior and posterior transverse ridges; tergites 3 and 4 with anterior transverse ridge, posterior transverse ridge absent; tergites 5–6 smooth, without elevated ridges.

Eye: Eye length 1.4–1.6 × width, peduncle distally setose, not distinctly expanded proximally, with few short transverse striae on lateral surfaces; cornea not dilated.

Antennule: Article 1 with [5]–6 well-developed distal spines: distomesial spine small, pair of distolateral spines present; proximal lateral spine small, always present. Short striae covering mesial surfaces.

Antenna: Article 1 with prominent mesial process, distally falling well short of lateral antennular spine. Article 2 with distinct distal spines laterally and mesially. Article 3 with small to distinct mesial spine, laterally unarmed. Article 4 unarmed.

Maxilliped 3 (Mxp3): Ischium with distinct distal spines on both flexor and extensor margins; crista dentata with regular row of spines along entire margin. Merus 0.7–0.8 × length of ischium at midline, with small distal spines on extensor margin and 2 much larger spines at flexor margin, otherwise unarmed.

Cheliped: Length about 3–4 × pcl in both sexes; subcylindrical, spiny and with scattered long setae. Ischiomerus 1.2–1.7 × pcl, slightly exceeding twice carpus length; with rows of spines, mesial spines strongest. Carpus with rows of spines on all surfaces, row of mesial spines most prominent. Palm 1.0–1.3 × carpus length, length-width ratio 1.5–2.4, with parallel rows of spines (2 closely running parallel along mesial, 1 at about dorsal surface midline, 1 close to lateral margin). Dactylus and pollex subequal in length to palm; surface with short setiferous striae; distally with row of spines along curved margin; tip excavated. Pollex lateral margin with 1 or 2 spines reaching onto proximal portion; occlusal margin with 2 proximal processes, distinct in massive chela. Dactylus with 1 small to distinct external spine at its base; occlusal margin with basal process, well developed if chela massive. Central portion of gape evenly concave.

Walking legs (P2–4): Slender, subcylindrical, moderately setose and spinose. Merus successively shorter posteriorly (P2 merus 1.1 × length of P3 merus, P3 merus 1.1 × length of P4 merus). P2 merus 0.8 × pcl, 1.2 × P2 propodus length; length 5–6 × width. P3 merus 1.2 × P3 propodus length; length about 5 × width. P4 merus as long as P4 propodus; length 5–6 × width. Extensor margin of P2 and P3 with regular row of spines, proximally diminishing, with prominent distal spine; P4 extensor margin irregular but unarmed other than distal spine; flexor margins of all legs irregular and with distal spine; P4 lateral surface with median row of 3 or 4 small spines, absent on P2 and P3. Carpus with 3 or 4 spines on extensor margin on P2–3, unarmed on P4; distal spine prominent on P2–3, minute on P4; row of small spines below extensor margin on lateral surface of P2–3, unarmed on P4; flexor margin unarmed. P2–4 propodus length 6–7 × height; extensor margin irregular, typically unarmed; flexor margin with 2–4 slender movable spines in addition to distal pair. Dactylus 0.6–0.7 × length of propodus, ending in incurved, strong, sharp spine; flexor margin with 6–9 movable spines, otherwise unarmed.

Size. Male pcl 2.3–3.3 mm; female pcl 2.1 mm.

Colour in life. Unknown.

Genetic data. A COI sequence was generated from a Kermadec Islands sample (AWMM MA73597, Table 1 ).

Etymology. From Erebus, of Greek mythology, a primordial deity personifying deep darkness and shadows, alluding to the deep-water occurrence of the new species. Used as a noun in apposition.

Di s tribution. Norfolk and Kermadec Ridges; 290–506 m.

Remarks. Phylladiorhynchus erebus n. sp. belongs to the ‘ ikedai / bengalensis’ group that share the five epigastric spines and the maxilliped 3 merus with two prominent spines along the flexor margin. This now also includes P. kermadecensis n. sp., which differs in the presence of two instead of three anterior branchial spines along the lateral carapace margin (see comments under that species below). Ongoing studies by Rodríguez-Flores and colleagues indicate at least three further species will be added to this complex.

Phylladiorhynchus erebus differs from P. ikedai ( Miyake & Baba, 1965) in the presence of 5–6 distal spines of the basal antennular article, the distolateral double spine is always present, and an additional third lateral spine may also be present; P. ikedai lacks the distolaterally split double spine. All the specimens examined here for P. erebus also show a medially broken metagastric ridge of the carapace, which appears continuous in P. ikedai s.s.

Some variation in the material examined here is observed in the posterior transverse ridge of abdominal tergite 3 (present or absent), the distomesial spine on antennal article 3 being small or obsolescent and the form of the protogastric and mesogastric ridges (continuous to variably interrupted). These characters can be diagnostic in other species of Phylladiorhynchus indicating that the New Zealand material for P. erebus might still represent more than one species.

Baba’s (1991) records of P. ikedai from New Caledonia and the Loyalty Islands might be referable to either of the new New Zealand species; records should be reviewed.

Figures

FIGURE 4. Phylladiorhynchus erebus n. sp., holotype male, 3.3 mm (NIWA 21269): A, carapace and abdomen, dorsal view. B, sternal plastron. C, telson. D, right antennal peduncle, ventral view. E, left cephalic region, showing antennular and antennal peduncles, ventral view. F, right Mxp3, lateral view. G, H, left and right cheliped, dorsal view. I, J, left P2–3, lateral view. K, right P4, lateral view. L, distal portion of propodus and dactylus of left P2. Scale bars: 2 mm.

FIGURE 5. Distribution records for Phylladiorhynchus erebus n. sp. (white circles) and P. kermadecensis n. sp. (crossed circle). Lines demarcating the EEZ for both Australia and NZ shown.