Arenallianassa katrinae, Schnabel & Rowden & Poore, 2023

Schnabel, Kareen E., Rowden, Ashley A. & Poore, Gary C. B., 2023, A new species of Arenallianassa (Decapoda: Axiidea: Callianassidae) from hydrothermal vents with notes on its ecology and a redescription of Arenallianassa arenosa (Poore, 1975), Memoirs of Museum Victoria (Mem. Mus. Vic.) 82, pp. 55-69 : 61-66

Arenallianassa katrinae sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:A8C9C6CA-DF84- 4F0F-A939-D0E95002FB53

Figures 4–7

Material examined. Holotype. New Zealand, Bay of Plenty, Calypso Vent Field , 37.6125° S, 177.1018° E, 181 m, 27 April 2007, TV grab, RV Sonne stn SO192-2/4, NIWA 157709 (male, cl 17.6 mm) . Paratypes. Collected with holotype, GenBank: OP178649 (16S), NIWA 157710 (female, cl 16.6 mm); NIWA 157715 (1 female, cl 19.0 mm, mouthparts figured); GenBank: OP178651 (16S), OP174574 (CO1), BOLD: DECNZ389-22 (CO1), NIWA 157716 (1 male, cl 23.3 mm) .

Additional material. Tongan Volcanic Arc, Volcano 1, 21.143° S, 175.759° W, 111 m, 12 May 2007, TV grab, RV Sonne stn SO192-2/63, GenBank : OP178650 (16S), OP174573 (CO1), BOLD: DECNZ388-22 (CO1), NIWA 32198 (1 female, cl 7.2 mm). New Zealand, Bay of Plenty, Calypso Vent Field , 37.612° S, 177.1025° E, 179 m, 07 Oct 1998, TV grab, RV Sonne stn SO135/81, NIWA 157435 (1 female, cl 16.7 mm). Calypso Vent Field , same locality as holotype, NIWA 32141 (6 females, cl 5.8–20.8 mm; 5 males, cl 11.5–22.0 mm); NIWA 45911 (4 females, cl 7.6–20.8 mm) .

Diagnosis. Male major cheliped merus lower margin with prominent oval tooth directed obliquely, followed by prominent denticulate blade near midpoint, squared off distally. Minor cheliped merus lower margin without spine at midpoint. Pereopod 3 propodus subrectangular, proximally distinctly expanded, with evenly concave lower margin. Telson with convex parallel lateral margins.

Description. Male. Carapace 0.2–0.3 [0.24] of total length; with distinct linea thalassinica, with defined dorsal oval marked posteriorly by shallow transverse cervical groove (at 0.7 cl) extending anteroventrally to each side above linea thalassinica as shallow groove; frontal margin broadly convex, anterolateral lobe obsolete. Rostrum level with anterior carapace, broadly triangular, acute in dorsal view, reaching about halfway to cornea; orbital margin concave; anterolateral lobe flat, round in dorsal and lateral views; subanterolateral margin oblique, concave; anterior margin of branchiostegite strongly produced.

Pleonites 1 and 2 together as long as carapace; ratio of lengths of pleonites 2–6: 1: 0.7–1.0[0.8]: 0.6–[0.7]: [0.8]–0.9: 0.9.

Eyestalks extending almost to end of antennular peduncle article 1, with distinct mesiodistal lobe; pigmented area covered by large, thinly pigmented, circular dome.

Antennular peduncle about half carapace length; article 1 about as wide as eyestalk; article 3 2.4–[2.6] times as long as article 2, unarmed, with ventrolateral row of long setae. Antennal peduncle as long as antennular peduncle; article 5 0.8–[0.9] times as long as article 4; scaphocerite semicircular in lateral view.

Mandibular molar process with serrate margin, incisor process toothed. Maxillule, maxilla, maxillipeds 1 and 2 as in fig. 6. Maxilliped 3 ischium 1.2–[1.3] as wide as long at meral suture, dilating distally; crista dentata curved, consisting of 14 or 15 small spines, not overlapping ischium-merus suture; merus semicircular, 1.6–[1.7] times as wide as long, 0.8 as long as ischium, distal margin curved beyond base of carpus; propodus [1.4]–1.5 times as long as wide, widest proximally, flexor margin almost straight; dactylus truncate, 0.6 as wide as long, 0.9 times as long as propodus, with convex extensor margin, flexor margin with dense setal brush over distal two-thirds.

Pereopods 1 (chelipeds) unequal, dissimilar, sexually dimorphic. Male major cheliped massive, heterochelous (split even right: left major chela), carpus-palm length (fingers of chelae not included) 1.3–1.4 times carapace length; ischium slender, outer margin concave, lower (flexor) margin with 5–6 proximal spines; ratio of dorsal lengths—merus: carpus: propodus—1:1.0–1.1:1.0–1.3; merus upper margin smooth, lower margin with prominent oval tooth (meral hook) directed obliquely, followed by prominent denticulate blade near midpoint, squared off distally, lateral face with deep, welldefined excavation at base of tooth; carpus slightly wider than long, upper and lower margins carinate, proximal margin convex, overreaching mero-carpal articulation, lower margin serrate in larger individuals; palm 1.0–1.1 times as long as greatest width, lower margin carinate, distolateral margin lobate with tooth at base of fixed finger, strongly excavate between tooth and fixed finger; fixed finger 0.4 length of lower margin, almost conical, cutting edge smooth; dactylus nearly as long as upper margin of palm, cutting edge with blunt tooth in proximal third, second tooth near midpoint, third subdistal. Minor cheliped carpus–palm about as long as carapace; palm 0.35 times width of that of major; ischium narrow, unarmed, subequal to or shorter than meral length; merus twice as long as wide, margins smooth; carpus [1.3]–1.5 times as long as merus, 2.8– [2.9] times as long as wide, parallel-sided over distal half; palm upper margin 0.5 times as long as carpus, [1.2]–1.3 times as long as wide; fixed finger evenly tapering, 0.8 length of lower margin of palm, cutting edge smooth, unarmed; dactylus weakly curved, cutting edge unarmed.

Pereopod 2 chelate; carpus 1.7 times as long as wide; palm twice as wide as upper margin. Pereopod 3 propodus elongate, subrectangular, proximally distinctly expanded, with evenly concave lower margin, 1.9 times as long as wide at midlength; spiniform seta on flexor margin, near distal end, buried among finer setae. Pereopod 4 simple, propodus densely setose laterally. Pereopod 5 chelate, propodus and dactylus densely setose.

Male pleopod 1 consisting of 2 simple articles, subequal in length. Male pleopod 2 absent. Pleopod 3–5 endopods with small, ovoid appendices internae, embedded at proximal third of mesial margin.

Uropodal endopod anterior margin straight, slightly longer than wide at midlength; distal margin falls away acutely, indistinguishable from posterior margin; margins setose; with variable scattered spiniform setae (usually a cluster of 3–4 distal setae with 2–3 scattered proximally) near anterodistal margin; exopod about as wide as anterior margin, anterior margin almost straight, posterodistal margin evenly curved, dorsal plate extending more than half width of exopod, slightly differentiated from distal margin, setose.

Telson trapezoid, [1.1]–1.2 times as wide as long, distinctly wider proximally, tapering to rounded posterolateral corners, posterior margin shallowly convex; dorsal surface with cluster of long, fine setae near midpoint.

Female. Major cheliped carpus–palm 1.4–1.7 times carapace length; ischium, merus and carpus essentially as in male; palm upper margin 1.2–1.3 as long as carpus, 1.0–1.2 times as long as greatest width, lower margin carinate, distolateral margin projected, with truncate lobe above base of fixed finger, with small notch between lobe and fixed finger; fixed finger 0.4 length of lower margin, almost conical, cutting edge denticulate; dactylus about as long as upper margin of palm, cutting edge straight, denticulate, with acute reflexed tip.

Pleopod 1 uniramous, 2-articulate, first article strongly curved in larger females, with clusters of long setae, indistinct in smaller females (cl less than ~ 10 mm); second article slightly expanded medially and curved distally (slightly curved in small females, fully folded in large females). Pleopod 2 biramous, exopod narrow, curved, longer than 2-articulate endopod.

Colour. Dorsal oval of the carapace, chelipeds and pereopods pale, rest of carapace, pleon and tailfan darker, peach to reddish-brown (fig. 7 inset).

Etymology. Named for benthic ecologist Katrin Berkenbusch, in acknowledgment of her research on ghost shrimp ecology in Aotearoa/ New Zealand.

Distribution. Kermadec and Tonga Volcanic Arc systems, from Bay of Plenty, New Zealand, to Tonga, collected around active venting (Calypso Vent Field and Volcano 1 off Tonga); 111–181 m (fig. 7).

Remarks. The molecular and morphological evidence shows that A. katrinae sp. nov. is clearly aligned with A. arenosa from south-eastern Australia, which occurs at a shallower depth of usually <25 m depth and is the only other member of the genus.

Diagnostic differences between the two species are small variations in the proportions of the carapace, namely that the transverse cervical groove is at 0.7 cl in A. katrinae (0.8 cl in A. arenosa ); the maxilliped 3 with the ischium wider at ischiomeral suture than long in A. katrinae (longer than wide in A. arenosa ); the maxilliped 3 merus is 0.8 times as long as the ischium in A. katrinae (0.6 in A. arenosa ); the major chelipeds in both males and females share the pronounced serrated meral hook but in A. katrinae a serrate semi-circular lobate carina is placed distally, more pronounced than apparent in A. arenosa and irrespective of size of the specimen; the palm of the female major cheliped is proportionally longer in A. katrinae (longer than the carpus; shorter in A. arenosa ); the minor cheliped ischium is subequal in length to the merus in A. katrinae (longer in A. arenosa ) and the carpus is narrower (2.8–2.9 times as long as wide in A. katrinae , 2.3 times in A. arenosa ), most notably, the lower margin of the merus is smooth in A. katrinae (with a spine at midlength in A. arenosa ); pereopod 3 propodus is subquadrate and longer, 1.9 times as long as wide in A. katrinae with a slightly concave lower margin (1.4 times as long as wide and convex lower margin in A. arenosa ); the telson is distinctly trapezoid in A. katrinae (subquadrate in A. arenosa ).

Both species share short spiniform setae towards the distal end of the uropodal endopod upper face; A. katrinae usually bears a short transverse row of 3–7 setae, and usually 2–3 further single setae or pairs scattered across the posterolateral face (figs 4a, 5h, i, j).

A single female ( NIWA 32198) was collected from Volcano 1 off Tonga that matches the description of the new species. However, DNA sequence information indicates some significant divergence (see remarks above) that need to be resolved, pending the collection of further material.

Figures

Figure 4. Arenallianassa katrinae sp. nov. NIWA 157709 (holotype male, cl 17.6 mm): a, eyestalks, carapace, pleon, left uropod, telson, dorsal view; b, c anterior carapace, eyestalk, antennule, antenna, dorsal view (b), lateral view (c); d, thoracic sternites 4–7, pereopodal coxae 1–4, ventral view; e, maxilliped 3, lateral face; f, pereopod 2; g, pereopod 3 (lateral view, mesial view of propodus and dactylus); h, pleopod 1, right, lateral view. Scale bars = 5 mm.

Figure 5. Arenallianassa katrinae sp. nov. NIWA 157709 (holotype, male, cl 17.6 mm), lateral view unless stated otherwise: a, major cheliped; b, minor cheliped, right.NIWA 157710 (paratype female, cl 16.6 mm): c, maxilliped 3, left; d, major cheliped, left; e, pereopod 3; f, pleopod 1; g, pleopod 2; h, i, left and right uropodal endopods showing distribution of robust setae. NIWA 32141 (paratype female, cl 9.5 mm); j, major cheliped; k, minor cheliped; l, pleopod 1; m, pleopod 2. Top 3 scale bars = 5 mm; bottom scale bar = 2 mm.

Figure 6. Arenallianassa katrinae sp. nov. NIWA 157715 (paratype female, cl 19.0 mm), lateral view unless stated otherwise: a, mandible, left, inside view; b, maxillule; c, maxilla; d, maxilliped 1; e, maxilliped 2; f, pleopod 1, lateral view. Scale bar = 5 mm.

Figure 7. Sample locations of Arenallianassa katrinae sp. nov. (white stars). Known hydrothermal vent locations along the Kermadec-Tonga Volcanic Arc are shown in triangles with shallow (≤200 m) vents in grey and deep (>200 m) vents in white. Locations where invertebrate specimens were collected at depths ≤200 m are indicated by white circles. The 200 m bathymetric line is shown. Lower insert shows close-up of Bay of Plenty (BOP) including locations of geothermal ‘bubble zones’ reported by Sarano et al. (1989). Upper insert shows colour of an undetermined specimen from type locality (RV Sonne stn SO192-2/4). Camera symbols indicate locations of 2010 camera tows.