Gastroptychus, CAULLERY, 1896

Schnabel, Kareen E., 2009, A review of the New Zealand Chirostylidae (Anomura: Galatheoidea) with description of six new species from the Kermadec Islands, Zoological Journal of the Linnean Society 155 (3), pp. 542-582 : 544-546

GENUS GASTROPTYCHUS CAULLERY, 1896

Ptychogaster A. Milne Edwards, 1880: 63 . – Henderson, 1888: 170.

Gastroptychus Caullery, 1896: 390 [replacement name for Ptychogaster A. Milne Edwards, 1880 , junior homonym of Ptychogaster Pomel, 1847 : fossil Reptilia Chelonia]. – Miyake & Baba, 1968: 379. – Baba, 2005: 19. – Poore, 2004: 220.

GASTROPTYCHUS NOVAEZELANDIAE BABA, 1974

( FIG. 2 )

Gastroptychus novaezelandiae Baba, 1974: 381 , figs 1 and 2. – Baba, 2005: 212 (key), 214 (list).

Type material: HOLOTYPE: ♂ (11.5 mm), Chatham Rise, 43° 14.5′S, 174° 43.0′E, 440 m, 13.vii.1968, FV Kaiyo Maru Stn 28, coll. K. Baba ( ZLKU 15123 ).

Other material examined: Northland Plateau: 1 ♂ (6.8 mm), 35° 35.90′S, 175° 12.80′E, 308 m, 4.v.1975, stn I11 ( NIWA 14565 ) . 4 ♀ ovig. (10.8–15.3 mm), 1 ♀ (10.8 mm), 2 ♂ (10.7, 16.8 mm) from five stations. 1 ♀ (8.6 mm), 38° 40.00′S, 169° 25.99′E, 550 m, 16.iv.1970, NZOI stn J30 ( NMNZ Cr.012072) . 2 ♀ (10.0, 11.3 mm), 39° 33.90′S, 169° 14.70′E, 604 m, 18.x.1982, stn U227 ( NIWA 14581 ) on Challenger Plateau. 1 ♀ ovig. (19.2 mm), 37° 20.19′S, 176° 22.40′E, 297 m, 19.i.1998, stn Z8994 ( NIWA 14568 ) . 1 ♀ (13.3 mm), 1 ♂ (13.0 mm), 37° 32.56′S, 177° 7.57′E, 339-360 m, 20.ii.2000, stn Z10021 ( NIWA 14572 ) 2 ♀ ovig. (14.7, 15.7 mm), 5 ♀ (14.5–15.3 mm), 1 ♂ (14.4 mm) from six stations in the Bay of Plenty . 20 ♀ ovig. (9.2–15.0 mm), 16 ♀ (7.7–15.8 mm), 17 ♂ (6.6– 17.5 mm) from 35 stations on the Chatham Rise . 8 ♀ ovig (10.0–13.0 mm) 6 ♀ (7.5–9.2 mm), 10 ♂ (8.4– 13.1 mm), from three stations on the Otago shelf . 1 ♂ (11.7 mm), Puysegur Bank , 46° 20.29S, 166° 19.00E, 23.x.1967, 461- 466 m, NZOI stn E818 . 3 ♀ ovig. (12.3, 12.7, 13.7 mm), 4 ♀ (10.3–14.7 mm), 6 ♂ (11.2– 15.8 mm) from four stations on the Bounty Plateau. Auckland Islands : 1 ♀ ovig. (12.3 mm), 50° 58.00′S, 165° 45.00′E, 549 m, 7.v.1963, stn D39 ( NIWA 11620 ) . 1 ♂ (8.1 mm), 50° 58.00S, 165° 45.00E, 7.v.1963, 549- 465 m, NZOI stn D39 ( NMNZ Cr.012073) . 1 ♀ (11.7 mm), Campbell Plateau , 53° 15.90′S, 172° 46.10′E, 501 m, 22.ix.1978, stn S51 ( NIWA 14580 ) . 2 ♀ (17.5, 17.9 mm) from two stations with no location information.

Diagnosis: Carapace 1.7–1.8 times as long as wide (including rostrum), covered with spinules and spines (paired spines in epigastric region and just anterior of posterior margin, one median spine in metagastric, and two spines along midline of cardiac region and four or five strong spines along lateral branchial region, decreasing in size posteriorly). Rostrum with large, curved dorsal spine. Anterior margin of sternite 3 concave with row of six to eight spines. Sternite 4 with one pair of large lateral spines; surface with scattered small spines and granules only. Abdomen covered with spines; pair of large submedian spines on anterior portions of segments 1–6 each; telson anterior portion covered with denticles. Antennal scale small and triangular, barely reaching midpoint of penultimate article, rudimentary or absent; ultimate article with distal spine; penultimate article unarmed. Maxillipeds 3 widely separated; propodus with two to five spines along extensor margin; ischium with 33 teeth on mesial ridge (including two to three strong teeth on basis). Pereopod 1 (cheliped) slender, palm 2.4–3.0 times as long as dactyli. Pereopods 2–4 carpi seven to eight times longer than propodi.

Variation: Baba (1974) gave only one measurement of the carapace length (11.5 mm). The material presented here includes a further 115 specimens with carapace lengths between 6.6 ( NIWA 14565 ) and 19.2 mm ( NIWA 14568 ). Within this size range, the morphometric proportions of the carapace, telson, sternum, and pereopods correspond well with that of the holotype examined. The only significant difference appears to be in the height–width ratio of the cheliped palm with the male holotype palm being nearly 12 times as high as wide. In both small males and females, the palm is more slender (15.5 and 16.3 times as high than wide, respectively) .

Body sizes of males and females were not significantly different; ovigerous females were generally the largest specimens (range: 9.2–19.2, mean: 12.8, median: 12.8 mm, N = 42), followed by males (range: 6.6–17.5, mean: 12.0, median: 11.9 mm, N = 40). Nonovigerous females were the smallest on average (range: 7.5–15.8, mean: 11.2, median 10.8 mm, N = 34).

The size of the ovum ranged from 1.6–2.2 mm in diameter.

The large series of specimens examined showed considerable variation in the presence, absence, and size of the antennal scale. Of 58 specimens examined for this character, only six (10%) bore a scale as shown in Baba (1974). Most specimens (70%) showed a rudimentary scale and in 20% of the specimens, the scale appeared to be absent. This character varied even from left to right on the same specimen ( Fig. 2 ), from specimens collected from one station, and no sex or geographical correlation was obvious.

The basis of maxilliped 3 usually bears three strong spines (proximal smallest), the holotype lacks the smaller proximal spine.

Small differences are noted amongst major spines on the dorsal surfaces of the carapace and abdomen, usually with an additional spine to the characteristic spines noted by Baba (1974). The only exception are two specimens from the NMNZ collection that, unfortunately, lack location information; both females lack the dorsal spine on the carapace but otherwise match the diagnostic characters of G. novaezelandiae .

A curious deformation of the rostrum was noted on male NIWA 14572 that had a sagittal split along most of the length of the rostrum (appearing like two parallel rostra and lacking a dorsal spine). Otherwise, the specimen matched the species description well.

Remarks: Gastroptychus novaezelandiae Baba, 1974 is a New Zealand endemic and the most common chirostylid in New Zealand waters. It belongs to the group with a concave anterior margin of sternite 3, maxillipeds 3 widely separated, and the P2–4 propodi very short (carpus more than seven times longer than propodus). It is most similar to Gastroptychus brachyteres Baba, 2005 (from the Kei Islands, Indonesia) and Gastroptychus brevipropodus Baba, 1991 (from around New Caledonia) but it can be readily distinguished from both these species by the dorsal spine on the rostrum, the pronounced paired submedian spines on the abdominal tergites 1–6, at least two spines on the extensor margin of the propodus of the third maxilliped, and the lack of prominent submedian spines on the sternal plastron (only scattered granules and very small spines along sternite 4).

Distribution: Margins of the New Zealand continental shelf at depths of 264–732 m and from about 34°S (north-east of the North Island) to 53°S (sub- Antarctic slope) ( Fig. 3 ).

Ecological and biological remarks: Baba (1974) noted that the holotype of G. novaezelandiae was taken from a dorsal groove of the pennatulacean Balticina willemoesii (Kölliker) . The NIWA station register provides notes for occasional collection of pennatulaceans and other cnidarians in the same haul containing G. novaezelandiae and recent benthic imagery taken on the Chatham Rise revealed this species perched on small hydrozoans and gorgonian corals as well as two occasions with specimens walking on the soft sediment (unpubl. data).

The female specimen NIWA 14574 carried a sacculinid rhizocephalan parasite under the abdomen. Additionally, some pereopods of the female NIWA 14580, the southernmost record, are thickly covered with solitary hydroids.

Figures

Figure 2. Gastroptychus novaezelandiae Baba, 1974, holotype, ♂, ZLKU 15123: A, carapace and abdomen, lateral; B, antenna, right, ventral; C, antenna, left, ventral; D, mesial ridge, left, dorsal; E, telson, most setae omitted; Scale bars = 2 mm.

Figure 3. Records of Gastroptychus novaezelandiae Baba, 1974 around New Zealand. Solid circles indicate the type records. 250, 1000, and 2500 m bathymetric contours are shown.