Phylladiorhynchus triginta, 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 : 339-343

Phylladiorhynchus triginta n. sp.

( Figs. 12 , 14 )

Phylladiorhynchus integrirostris .— Ahyong, 2007: 42 , fig. 21.

Type material. HOLOTYPE AM P103671 (ex NIWA 28066 ), female (2.3 mm), NORFANZ Station TAN0308 /67, Lord Howe Island, Australia, 31.874–31.878°S, 159.240–159.258°E, 72–82 m, 23 May 2003.

Other material. Australia: AM P38013, 1 male (2.2 mm), Middleton Reef ; outer slope; near “Runic” wreck, 29.457°S, 159.062°E, 15 m, 5 Dec 1987 . AM P38014, 1 male (2.2 mm), Middleton Reef; N face of outer reef slope, 29.453°S, 159.113°E, 10 m, 4 Dec 1987 . NIWA 21153 , 1 male (2.5 mm), NZOI Stn. P 82, Lord Howe Island, 31.830°S, 159.328°E, 78–84 m, 28 May 1977. NIWA 135605 , 1 female ov. (1.8 mm), NZOI Stn. P 29, N of Norfolk

Island, 28.908°S, 167.963°E, 37 m, 28 Jan 1977.

Diagnosis. Rostrum lateral margins distinctly convex; subapical spines present. Carapace with 2 epigastric spines; metagastric ridge between third branchial marginal spines interrupted medially; anterior branchial margin with 3 spines; hepatic spine present. Thoracic sternite 3 anterior margin biconcave, with obtuse median projection. Antennular article 1 with 5 spines: distomesial spine large, overreaching end of lower distolateral spine, overreached by upper distolateral and first lateral spines; second lateral spine long, slender. Antennal article 1 mesial process falling well short of second lateral antennular spine; article 2 distolateral and distomesial spines well developed, subequal in length; article 3 with small to minute distomesial spine, distolaterally unarmed. Maxilliped 3 merus with 1 prominent spine on flexor margin. P2–4 dactylus extensor margin without upright spines at bases of movable spines.

De s cription. Carapace: Length [0.9]–1.0 × width; transverse ridges with dense short setae, and few scattered longer setae. Gastric region with 4 interrupted anterior transverse ridges: epigastric ridge distinct, with 2 submedian spines; anterior protogastric ridge continuous, nearly extending laterally to carapace margin; anterior mesogastric ridge continuous, interrupted laterally by cervical groove, laterally continuing uninterrupted to first branchial spine; metagastric ridge interrupted medially and by cervical groove forming 4 arcuate striae, outermost stria continuing laterally to third branchial spine; median stria on posterior metagastric ridge usually distinct; few short scales sometimes scattered between ridges. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove, followed by 2 complete, uninterrupted ridges, interspersed with short lateral ridges. Lateral margins distinctly convex, with 7 spines: 2 spines in front of (anterolateral, hepatic) and 5 spines (3 anterior branchial spines, 2 posterior branchial spines) behind distinct anterior cervical groove. Anterolateral spine well-developed, nearly reaching lateral orbital spine, subequal in size. Hepatic spine distinct, set slightly mesially from lateral margin. Anterior branchial spines subequal in size. Posterior branchial spines with first spine subequal to anterior branchial spines, second spine smaller. Rostrum length [0.5]–0.6 × pcl, length-width ratio 1.6, distance between basal pair of rostral spines about 0.3 × carapace width; dorsal surface concave; lateral margins distinctly convex, sub-apical spines distinct. Pterygostomian flap anteriorly with sharp anterior spine; surface unarmed, with series of short striae.

Thoracic sternum: Sternal plastron slightly wider than long, length-width ratio 0.8, lateral margins slightly divergent posteriorly. Sternite 3 width 1.8–[2.0] × length; anterior margin biconcave, median process obtusely triangular; lateral margins rounded.

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

Eye: Eye length about 1.3 × width, peduncle distally setose, very slightly expanded at midlength; with few short transverse striae on lateral surfaces; cornea not dilated.

Antennule: Article 1 with 5 well-developed distal spines: distomesial spine large, overreaching end of lower distolateral spine; paired distolateral spines present; proximal lateral spine long and slender. Short striae covering mesial surfaces.

Antenna: Article 1 with prominent mesial process, distally falling well short of lateral spine of antennule. Article 2 with distinct distal spines laterally and mesially. Article 3 with small to minute 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 slightly shorter than ischium at midline, with prominent distal spine on extensor margin, subequal to prominent spine at midlength of flexor margin; otherwise unarmed.

Cheliped: Stout, length [2.9]–3.4 × pcl (males 3.2–3.4); subcylindrical, very spiny and setose. Ischiomerus [1.2]–1.3 × pcl, [2.1]–2.2 × carpus length; with rows of spines, mesial spines strongest. Carpus with rows of spines on all surfaces, 1 or 2 mesial spines most prominent. Palm [1.2]–1.4 × carpus length, length-width ratio [1.8]–2.0, with 5 parallel rows of spines (2 mesial, 2 at about dorsal midline, 1 irregular row close to lateral margin). Fingers 0.8 × palm length; surface with short setiferous striae, distally excavated, occasionally slightly gaping. Pollex outer margin unarmed, occlusal margin with 1 prominent process near midlength. Dactylus with distinct proximal spine, 3 or 4 well-developed spines along or just below outer margin; occlusal margin with prominent basal process, distally with row of spines along curved margin; tip excavated.

Walking legs (P2–4): Relatively stout, subcylindrical, moderately setose and spinose. Merus successively shorter posteriorly (P2 merus 1.1 × P3 merus length, P3 merus 1.1 × P4 merus length). P2 merus length 0.6 × pcl, [1.2]–1.3 × P2 propodus length, length about 4 × width. P3 merus length 1.1 × P3 propodus length; length 3–[4] × width. P4 merus length [0.9]–1.0 × P4 propodus length; length 3.5–4.0 × width. Extensor margin of P2 and P3 with regular row of spines, proximally diminishing, with prominent distal spine; P4 extensor margin irregular but unarmed, distal spine absent; flexor margins of all legs irregular with rows of projecting scales and prominent distal spine; P4 lateral surface with median row of 2 or 3 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 distinct spines below extensor margin on lateral surface of P2–3, unarmed on P4; flexor margin unarmed. P2–4 propodus length 4–5 × height; extensor margins with 2–4 proximal, fixed spines; flexor margin with 1–4 movable spines in addition to distal pair. Dactylus 0.6 × propodus length, ending in incurved, strong, sharp spine; flexor margin with 6 or 7 movable spines, otherwise unarmed.

Size. Male pcl 2.2–2.5 mm, female pcl 1.8–2.3 mm, ovigerous female pcl 1.8 mm.

Colour in life. Not known.

Genetic data. The holotype (AM P103671) was successfully sequenced for the COI fragment ( Table 1 ).

Etymology. Trīgintā, Latin for the number 30, used to signify the narrow known latitudinal range of this species. Specimens have been collected between latitude 28.9– 31.8°S from the southwestern Pacific ridges, around the Lord Howe and Norfolk Islands. Used as a noun in apposition.

Di s tribution. Tasman Sea, from Lord Howe Island, Middleton Reef and Norfolk Island; 10–84 m.

Remarks. Phylladiorhynchus triginta n. sp. belongs to the ‘ integrirostris’ group with a single pair of epigastric spines; differences from both P. integrirostris and P. spinosus n. sp. are discussed under the former above. Considering the variability of the epigastric spines observed, particularly in small specimens of P. pusillus , these two species can be difficult to separate. Diagnostic differences, apart from the number of epigastric spines (two pairs in P. pusillus ; one pair in P. triginta ), are in the condition of the mesial spine on antennal article 2 (distinct in P. pusillus ; indistinct in P. triginta ), the shape of the anterior margin of thoracic sternite 3 (distinctly convex in P. pusillus ; biconcave and medially produced in P. triginta ), and the spination of the base of the cheliped dactylus (one proximal spine in P. pusillus ; more than one spine in P. triginta ).

Figures

FIGURE 12. Distribution records for Phylladiorhynchus pusillus (white circles), P. spinosus n. sp. (crossed circles) and P. triginta n. sp. (black circles). Lines demarcating the EEZ for both Australia and NZ shown.

FIGURE 14. Phylladiorhynchus triginta n. sp., holotype female, 2.3 mm (AM P103671): A, carapace and abdomen, dorsal view. B, sternal plastron. C, left cephalic region, showing antennular and antennal peduncles, ventral view. D, right antennal peduncle, ventral view. E, right Mxp3 and anterior portion of pterygostomian flap, lateral view. F, left cheliped, dorsal view. G–I, P2–4, lateral view. Scale bars: 2 mm.

Tables

TABLE 1. Pairwise percentage genetic distances (below diagonal) and genetic similarity (above diagonal) for the partial COI gene between specimens of Phylladi- orhynchus. Cells highlighted in grey indicate intraspecific levels of divergence. The sequence of P. integrirostris from Hawaii was kindly provided as a reference by P. Rodríguez-Flores (National Museum of Natural Sciences, Madrid).

Species (% identity)			n. sp.
	. integrirostris	. erebus n. sp.	. kermadecensis	. triginta n. sp.	. pusillus	. australis n. sp.	. nui n. sp.
P. integrirostris (Hawaii)			20.36	23.56	20.82 26.14	26.29 26.14 21.43 21.12	21.43 21.12 21.43 20.82	21.12	20.97	21.28
P. erebus (AWMM MA73597)		79.64		17.02	19.76 22.95	23.10 22.95 17.17 17.17	16.98 17.02 17.17 15.96	15.81	16.26	15.81
P. kermadecensis (NIWA 118955, paratype)		76.44	82.98		22.19 28.72	29.33 28.72 19.91 20.06	19.68 19.76 19.91 19.60	19.91	19.60	19.76
P. triginta (AM P103672, holotype)		79.18	80.24	77.81	24.16	24.47 24.16 20.97 20.67	20.32 20.82 20.97 20.82	20.36	20.52	20.97
P. pusillus (NIWA 135601)		73.86	77.05	71.28	75.84	0.91 0.00 25.08 24.92	25.08 24.92 25.08 25.08	25.38	25.23	24.92
P. pusillus (NIWA 57503)		73.71	76.90	70.67	75.53 99.09	0.91 25.53 25.38	25.56 25.38 25.53 25.53	25.84	25.68	25.68
P. pusillus (NIWA 135602)		73.86	77.05	71.28	75.84 100	99.09 25.08 24.92	25.08 24.92 25.08 25.08	25.38	25.23	24.92
P. australis (NIWA 92587, holotype)		78.57	82.83	80.09	79.03 74.92	74.47 74.92 0.46	0.16 0.30 0.00 8.05	8.51	8.05	8.51
P. australis (NIWA 33656, paratype)		78.88	82.83	79.94	79.33 75.08	74.62 75.08 99.54	0.32 0.46 0.46 8.21	8.66	8.21	8.66
P. australis (NIWA 108588, paratype)		78.57	83.02	80.32	79.68 74.92	74.44 74.92 99.84 99.68	0.00 0.16 7.78	8.25	7.78	8.25
P. australis (NIWA 56530, paratype)		78.88	82.98	80.24	79.18 75.08	74.62 75.08 99.70 99.54	100 0.30 7.90	8.36	7.90	8.36
P. australis (NIWA 122226, paratype)		78.57	82.83	80.09	79.03 74.92	74.47 74.92 100 99.54	99.84 99.70 8.05	8.51	8.05	8.51
P. nui (NIWA 33682, paratype)		79.18	84.04	80.40	79.18 74.92	74.47 74.92 91.95 91.79	92.22 92.10 91.95	1.37	0.61	0.46
P. nui (NIWA 33657, holotype)		78.88	84.19	80.09	79.64 74.62	74.16 74.62 91.49 91.34	91.75 91.64 91.49 98.63		1.37	1.22
P. nui (NIWA 33658, paratype)		79.03	83.74	80.40	79.48 74.77	74.32 74.77 91.95 91.79	92.22 92.10 91.95 99.39	98.63		0.76
P. nui (NIWA 42691, paratype)		78.72	84.19	80.24	79.03 75.08	74.32 75.08 91.49 91.34	91.75 91.64 91.49 99.54	98.78	99.24