Acaenosquilla keablei Ahyong 2022, sp. nov.
Creators: name: Ahyong, Shane T.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Stomatopoda
Tetrasquillidae
Acaenosquilla
Acaenosquilla keablei

description: Acaenosquilla keablei sp. nov.
(Fig. 1)
Type material. AM P100914, male holotype (TL 42 mm), Old Settlement Beach, Lord Howe Island, 31.51969°S, 159.05719°E, intertidal sand burrow, yabby pump, LHI 2017Mar29 _059, coll. S. Keable & E. Kupriyanova, 29 March 2017.
Diagnosis. Cornea mesial lobe rounded. Rostral plate with ventral spine near base of median spine. Raptorial claw dactylus with 9 teeth on occlusal margin (including terminal tooth). Telson submedian and intermediate carinae well-defined; without longitudinal carinae on surface between median boss and submedian carina.
Description of holotype. Eye not extending beyond antennular peduncle article 2 (Fig. 1A); cornea broadened, inclined laterally on stalk (Fig. 1C), not concealed by rostral plate, mesial lobe rounded. Ophthalmic somite anterior margin faintly convex. Ocular scales small, rounded, separate (Fig. 1A).
Antennular peduncle 0.61CL. Antennular somite dorsal processes with acute apices, spiniform, directed almost anteriorly (Fig. 1A). Antennal protopod dorsally unarmed; with small ventrodistal tooth and 1 ventral papilla (Fig. 1D). Antennal scale length 3.17× width, 0.41CL.
Rostral plate cordiform, about as wide long, widest basally, with slender anterior spine; anterior lateral margins sinuous; dorsum smooth, weakly elevated in midline; with slender ventral spine at base of median anterior spine (Fig. 1A, B). Carapace anterolateral angles broadly rounded.
Raptorial claw (Fig. 1E) dactylus occlusal margin with 9 teeth (including terminal tooth), outer margin broadly curved, with shallow proximal notch. Propodus occlusal margin fully pectinate, with 4 proximal movable spines. Carpus dorsal margin terminating in short spine tooth, directed ventrally. Merus inferodistal angle blunt, rounded, approximating right angle; length shorter than carapace, PI 103. Ischium about one-third merus length.
Mandibular palp of 3-articles. Maxillipeds 1–5 each with epipod. Maxilliped 5 basal article without ventrally directed spine.
Pereopods 1–3 (Fig. 1G–I) first article each with posterior spine on outer margin; inner margin unarmed. Pereopod 1 endopod distal article subcircular. Pereopod 2 endopod distal article ovate. Pereopod 3 endopod distal article slender, elongate.
Male pleopod 1 endopod with distinct lateral lobe on distal ‘endite’. Hook process short, squat, distinctly shorter than tube process (Fig. 1O).
Thoracic somite 5 lateral process obsolete, lacking ventrally directed spine. Thoracic somites 6–8 lateral process subtruncate to broadly rounded (Fig. 1F). Thoracic sternite 8 keel bluntly angular (Fig. 1N).
Abdominal somites 1–5 smooth; posterior margin unarmed; posterolateral corners bluntly angular, unarmed (Fig. 1L). Abdominal somite 6 smooth, lacking carinae; posterolateral spine prominent, elongated (Fig. 1J); with short spine and blunt, obtuse projection anterior to uropodal articulation (Fig. 1M); sternum posterior margin unarmed, slightly concave.
Telson thick, about twice as wide as long, with three pairs of primary marginal teeth (submedian, intermediate, lateral) (Fig. 1J); submedian teeth slender, movable, slightly upcurved; with 10 spiniform submedian denticles in transverse row either side of midline; with 4 acute ‘intermediate’ denticles, second and fourth from midline slightly longer and more slender than first and third; lateral denticle spiniform. Intermediate and lateral teeth slender, subequal. Mid-dorsal surface with broad, posteriorly trispinous median elevation, flanked by single spine, and 2 cristate, posteriorly armed carinae (submedian and intermediate). Median elevation flat, margins converging posteriorly; median spine slightly overreaching posterior margin of telson, almost twice length of lateral spines. Minute spine present (right) or absent (left) between intermediate and lateral carina. Post-anal spine prominent, reaching posteriorly beyond midpoint between anal pore and posterior margin of telson (Fig. 1K).
Uropodal protopod terminal spines slender, dorsally flattened, ventrally carinate, outer spine shorter than inner spine; with slender ventral spine anterior to endopod articulation (Fig. 1M). Exopod (Fig. 1F) proximal article inner margin straight, unarmed; small distoventral spine; outer margin with 7 movable spines, distalmost spine reaching distal quarter of distal article. Exopod distal article longer than proximal article. Endopod length 3.19× width, dorsal surface with weak proximal fold.
Colour in preservative. Largely faded. Carapace, thorax and abdomen with diffuse transverse bands.Abdominal somite 5 with dark, narrow posterolateral bar. Telson median elevation with pair of longitudinal, elongate, black bars. Ocular peduncle with dark proximodorsal spot. Antennules, antennae, raptorial claw, pereopods and uropods with scattered brown chromatophores. Uropodal exopod distal article dark on inner half; endopod distolateral quarter dark.
Etymology. Named for my colleague, Steve Keable, for his longstanding contributions to isopod research and decades of dedication to the marine invertebrate collections at the Australian Museum.
Measurements. TL 42 mm, CL 7.90 mm, cornea width 2.15 mm, antennular peduncle 4.84 mm, antennal scale 3.27 mm, raptorial claw propodus length 7.68 mm, abdominal somite 5 width 8.15 mm.
Remarks. Acaenosquilla currently includes two species: the type species, A. latifrons (de Haan, 1844), from Japan and Korea (Hwang et al. 2019), and A. brazieri (Miers, 1880) from coastal eastern Australia and New Caledonia (Ahyong 2001). Acaenosquilla keablei sp. nov., the third known species of the genus, is the first lysiosquilloid to be recorded from Lord Howe Island.
Acaenosquilla keablei differs from both A. latifrons and A. brazieri in having nine instead of six or seven (usually six) teeth on the dactylus of the raptorial claw. The new species further differs from A. brazieri in having a rounded rather than conical mesial lobe of the cornea and in lacking carinae between the median elevation and submedian carina of the telson. Acaenosquilla keablei is further distinguished from A. latifrons by the presence of the ventral spine on the rostral plate (absent in A. latifrons), sharply defined submedian and intermediate carinae on the telson (versus indistinct) in which the submedian carina is flanked mesially by a small spine (absent in A. latifrons). Acaenosquilla keablei is ecologically unusual in the genus in occurring intertidally. Both other species of Acaenosquilla are currently known only from sublittoral depths: 36–59 m for A. brazieri (see Ahyong 2001), and shallower than 20 m in A. latifrons (see Hwang et al. 2019).
Acaenosquilla is closely related to three other Indo-West Pacific tetrasquillid genera sharing five or more teeth on the dactylus of the raptorial claw and a postanal spine on the telson: Heterosquillopsis Moosa, 1991 (type species: H. danielae Moosa, 1991, New Caledonia), Kasim Manning, 1995 (type species: K. philippinensis (Moosa, 1986), South China Sea; K. insuetus (Manning, 1970), southwestern Australia; K. karubar Ahyong, 2002, Indonesia), and Pariliacantha Ahyong, 2012 (type species: P. georgeorum Ahyong, 2012, New Zealand) (Ahyong & Harling 2000; Ahyong 2012). Of these, Acaenosquilla is closest to the monotypic Pariliacantha Ahyong, 2012 from New Zealand, differing chiefly in the armature of the ischium and dactylus of the raptorial claw (ischium unarmed versus with prominent distoventral spine; dactylus with 6–9 versus 12–17 teeth) (Ahyong 2012). Along eastern Australia, A. brazieri is a largely warm-temperate water species ranging from southern Queensland south to Sydney (Ahyong 2001; Hutchings et al., 2013), corresponding the Peronian marine region (Ebach et al. 2013). Discovery of Acaenosquilla on the southern Lord Howe Rise, at an intermediate locality between eastern Australia and northern New Zealand, is biogeographically parsimonious.
Distribution. Presently known only from Lord Howe Island; intertidal.
description: Published as part of Ahyong, Shane T., 2022, Stomatopod Crustacea of Lord Howe Island, pp. 144-150 in Zootaxa 5194 (1) on pages 146-147, DOI: 10.11646/zootaxa.5194.1.9, http://zenodo.org/record/7142133