Phylladiorhynchus kermadecensis, 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 : 318-320

Phylladiorhynchus kermadecensis n. sp.

( Fig. 5 , 7 )

Type material. HOLOTYPE: NIWA 135616 , male (2.9 mm), Macauley Island , Kermadec Ridge, 30.223–30.219° S, 178.354–178.353° W, 195–287 m, 30 Oct 2016, NIWA Kermadec-Rangitahua Stn. TAN 1612/90 . PARATYPES: AWMM MA73590 , 1 male (2.6 mm), station details as for holotype. NIWA 118955 , 1 female (2.4 mm), station details as for holotype .

Diagnosis. Rostrum without subapical spines; lateral margins slightly concave. Carapace with transverse row of 5 epigastric spines (1 median and 2 on either side of midline); anterior branchial margin with 2 spines. Thoracic sternite 3 anterior margin sinuous, with shallow median concavity. Antennular article 1 with 5 well-developed spines: distomesial spine small, similar to lower distolateral spine, shorter than upper distolateral spine, well overreached by first lateral spine; second (proximal) lateral spine smallest but distinct. Antennal article 1 mesial process distally falling well short of second lateral antennular spine; article 2 distomesial spine longer than distolateral; article 3 with [small] to distinct distomesial spine. Maxilliped 3 merus with 2 prominent spines on flexor margin. 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 epigastric ridge indistinct, with 5 spines: 1 median and 2 pairs of spines lateral, followed by 3, usually interrupted transverse ridges: anterior protogastric ridge [continuous] or with small medial gap, falling short laterally of carapace margin; anterior mesogastric ridge with small medial gap, interrupted laterally by cervical groove, laterally following cervical groove, then continuing uninterrupted to first anterior branchial spine; 1 medially interrupted metagastric ridge, laterally interrupted by cervical groove. Mid-transverse ridge uninterrupted, extending laterally to posterior branchial spine, followed by 2 uninterrupted ridges, intervened by 1 short lateral ridge, otherwise smooth. Lateral margins weakly convex, with 5 spines: 2 spines (anterolateral, hepatic) in front of, and 3 spines (2 anterior branchial, 1 posterior branchial) behind distinct anterior cervical groove. Anterolateral spine well-developed, nearly reaching lateral orbital spine, size about equal. Hepatic spine small, set slightly mesially from lateral margin. Anterior branchial spines largest, size diminishing posteriorly. Rostrum length nearly 0.5 × pcl, length-width ratio 1.4, distance between basal pair of rostral spines about 0.3 × carapace width; dorsal surface very slightly concave; lateral margins slightly concave, sub-apical spines absent. Pterygostomian flap anteriorly rounded, without spine; surface with series of short striae, unarmed.

Thoracic sternum: Sternal plastron as wide as long, lateral margins slightly divergent posteriorly. Sternite 3 width about 3 × length; anteriorly biconvex with shallow median notch; laterally rounded.

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

Eye: Eye length about 1.2 × width, peduncle distally setose, slightly expanded proximally, with few short transverse striae on lateral surface; cornea not dilated.

Antennule:Article 1 with 5 well-developed distal spines, distomesial spine small, shorter than distolateral spines; paired distolateral spines present; proximal lateral spine distinct. Short striae covering mesial parts of surface.

Antenna: Article 1 with prominent mesial process, distally falling well short of second (proximal) lateral antennular spine. Article 2 with distinct distal spines laterally and mesially, mesial spine larger. Article 3 with [small] to distinct distomesial spine. Article 4 unarmed.

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

Cheliped: Total length 3.5–4.4 [4.2 and 4.4] × pcl (probably female); subcylindrical, spiny, with scattered long setae. Ischiomerus 1.4–1.8 [1.6 and 1.8] × pcl, just over twice length of carpus; with rows of spines, mesial spines strongest. Carpus with rows of spines around entire article, 1 or 2 mesial spines most prominent. Palm 1.0–[1.3] × carpus length, length-width ratio [1.5]–2.3, with 4 parallel rows of spines (2 mesial, 1 at about dorsal midline, 1 close to lateral margin); fingers gaping; outer base of dactylus with sharp spine. Pollex outer proximal margin with spine; occlusal margin with 1 proximal process and distinct triangular process distally when a gape is present (process absent when not gaping). Dactylus subequal in length to palm; outer proximal margin with spine; occlusal margin with 2 processes, distally with row of spines along curved margin; tip excavated; surface with short setiferous striae.

Walking legs (P2–4): Slender, subcylindrical, moderately setose and spinose. P2–4 meri subequal in length; length 5–7 × width; P4 merus slightly shorter (0.8–[0.9] ×P2 merus length). P2 merus [0.8]–1.0 × pcl, length [5.9] × width, [1.2] × longer than propodus. P3 merus 1.2 × P3 propodus length. P4 merus 0.9–[1.0] × P4 propodus length. Extensor margin of P2 and P3 with regular row of spines, proximally diminishing, with prominent distal spine; P4 extensor margin unarmed other than distal spine; ventral margins of all legs irregular and with strong distal spine; P4 lateral surface with median row of small spines, absent on P2 and P3. Carpus with 3 or 4 spines on extensor margin on P2–3 (very small in smaller specimens), irregular but unarmed on P4; distal spine prominent on all legs; 1–4 minute spines along row below extensor margin on lateral surface on all legs; flexor margin unarmed. P2–4 propodus length about 7–8 × height; extensor margin typically with 2 proximal spines on P2–3, unarmed on P4; flexor margin with 3 or 4 slender movable spines in addition to distal pair. Dactylus 0.5–0.6 × propodus length, ending in incurved, strong, sharp spine; flexor margin with 10 or 11 movable spines, otherwise unarmed.

Size. Male pcl 2.6–2.9 mm, female pcl 2.4 mm.

Colour in life. Unknown.

Genetic data. DNA extracted from two detached walking legs derived from the paratypes (NIWA 123247 and AWMM MA73590). COI sequence divergence between P. kermadecensis n. sp. and P. erebus n. sp. (MA125788) is 17%, supporting interspecific levels of divergence ( Table 1 ).

Etymology. Named after its only known area of occurrence, the Kermadec Islands.

Distribution. Known from the Kermadec Ridge, off Macauley Island, 195– 287 m.

Remarks. Phylladiorhynchus kermadecensis n. sp. belongs to the ‘ ikedai / bengalensis group’ of species with five epigastric spines on the carapace and two spines on the flexor margin of the Mxp3 merus. Significant genetic divergence from congeners, however, supports P. kermadecensis as a distinct species. Diagnostic characters are subtle but the presence of two anterior branchial carapace spines (rather than three as in both P. ikedai and P. erebus n. sp.) and a single spine along the posterior branchial margin (instead of two or three spines in P. ikedai and P. erebus n. sp.) are constant in the material examined. Additionally, the lateral margin of the rostrum is concave in all specimens of P. kermadecensis n. sp. examined, rather than straight as in P. ikedai and P. erebus n. sp. The presence of a distinct distal process on the occlusal margin of the cheliped pollex in the male holotype is absent in the single loose cheliped that remains, which is presumably from the small paratype female, indicating sexual dimorphism. This process, however, is absent from the chelipeds of P. ikedai of similar size indicating that this feature might be diagnostic.

Figures

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.

FIGURE 7. Phylladiorhynchus kermadecensis n. sp., holotype male, 2.9 mm (NIWA 135616): A, carapace and abdomen, dorsal view. B, sternal plastron. C, telson. D, left cephalic region, showing antennular and antennal peduncles, ventral view. E, left Mxp3, lateral view. F, left cheliped, dorsal view. G–I, left P2–4, lateral view. Scale bars: 2 mm.