Leucothoe eltoni, Thomas, James Darwin, 2015

Thomas, James Darwin, 2015, Leucothoeeltoni sp. n., a new species of commensal leucothoid amphipod from coral reefs in Raja Ampat, Indonesia (Crustacea, Amphipoda), ZooKeys 518, pp. 51-66 : 54-62

Taxon classification Animalia Amphipoda Leucothoidae

Leucothoe eltoni sp. n. Figures 1, 2, 3, 4, 5, 6, 7, 8, 9

Paraleucothoe flindersi Stebbing, 1888, Muir 1997, pp 51-52

Type locality.

Reef slope, Yenweres Bay, Raja Ampat, Indonesia, 00° 29.216'S; 130° 40.394'E, coral reef slope, 20m.

Type material.

Holotype. Male A, 8.10mm; MZB Cru Amp 003, 10 December 2007, Yenweres Bay, Raja Ampat, Indonesia, 00°29.216'S; 130°40.394'E, JDT-RajAM-46, 20m, collected in-situ from branchial baskets of Herdmania sp. tunicates, James Thomas, collector.

Paratypes. Female B, 7.35mm; male C, 7.40mm; and six additional specimens. RMNH.Crus.A.5055, 10 December 2007, Station number JDT-RajAM-46, 20m, collected in-situ from branchial baskets of Herdmania sp. tunicates, James Thomas, collector.

Additional material examined.

Male and female specimens, RMNH.Crus.A.5056, 4 December 2004, Bunaken, Sulawesi, Indonesia, 1°37.063' N; 124°46.966' E. Station Indo04-01c, 8.5 m, from Herdmania sp. tunicates, reef wall in front of Living Colors Dive Resort. J. Thomas, K. White collectors. BPBM S11292-293, Pearl Harbor, Oahu, Hawaii, Station 6, 16 April 1996, from the sponge Mycale grandis , USN drydock “Machinist”. CASIZ 204559, Philippines, Batangas Province, Maricaban Island, Cemetery Beach, 13° 41.063N; 120° 49.813E, coral rubble, 5 m., from Polycarpa tunicate, J. Thomas, collector.

Etymology.

The specific epithet, eltoni, in honor of the rock musician Sir Elton John. Specifically, in reference to the large shoe-like first gnathopod of this species and the oversize boots Elton John wore as the local pinball champion in the movie “Tommy” (1975).

Diagnosis.

Male holotype A. Antenna 1 and 2 short, less than 0.10 body length; maxilliped, inner margin of outer plate crenulate, palp 2-articulate; gnathopod 1, carpus and propodus greatly enlarged; carpus setose posteriorly; distal margin of propodus tumid, inflated; gnathopod 2, palm oblique with 3 concavities separated by truncate projections; pereopods 5-7, article 4 extending beyond 0.5 × of article 5.

Description of male holotype A.

Ratios of antenna 1 and 2, 0.10 and 0.09 body length; relative lengths of antenna 1 and 2, 1.00:0.89, flagellae 8 and 6-segmented. Anterior margin of head broadly truncate; mid-ventral keel produced, anterior margin produced dorsally as small knob, tapering posteriorly, ventral margin straight.

Coxae. Coxae 1-4 width ratios, 1.00:1.87:1.37:1.40, coxa 4 posterior margin widest mid posteriorly, tapering proximally, coxa 5-6 bilobed; coxa 7 reduced, ovate.

Upper lip. Asymmetrically lobate, anterior margin setose.

Mandibles. Both lacking molars; palp 3-articulate, ratio of articles 1-3 1.00:2.50:2.60; incisors moderately dentate. Left mandible, palp articles 2-3 with 2 anterior and 2 apical setae; lacinia mobilis large, strongly toothed; 13 raker spines, two distal raker spines enlarged and modified. Right mandible, palp articles 2-3 with 13 anterior and 2 apical setae; lacinia mobilis an elongated flake; 15 raker spines.

Maxillae. 1, palp 2-articulate with four apical setae, and two rows nine and eleven facial setae; outer plate with seven apical setae and nine facial setae; inner plate small, ovate, with single apical seta. Maxilla 2: inner plate, distal margin with 6 apical setae and 6 submarginal setae, 20+ facial setae; outer plate with 5 marginal medial setae and 19 facial setae.

Maxilliped. Inner and outer plates reduced; inner plates fused, with three stout apical setae and numerous fine facial setae; outer plate, anterior one third of medi al margin tuberculate; palp article 1 with several apicodistal setae on medial dorsal margin and numerous marginal setae on ventral margin; article 4 with dense row of oblique and marginal setae on both dorsal and ventral margins; article 3 apical margin and dactyl with dense covering of pubescent setae.

Gnathopod 1. Coxa lobate, LW 1.25; basis linear, LW 3.66, anterior margin serrate with 22 long setae and single posterodistal apical seta; carpus expanded, basally stout, recurved distally with sharp apex; posterior margin with approximately 49 long recurved setae along 0.18-0.94 of carpal margin and 12 short, submarginal mediofacial setae; propodus, anterior margin greatly inflated, circular, LW 1.50, posterior margin expanded, with approximately 10 short posterior setae; dactyl reduced, straight, closing medially in groove on propodus.

Gnathopod 2. Coxa oval, expanded distally, distal margin smooth, LW 0.87; article 2 linear, LW 4.00, with tuft of six long posterodistal setae; carpal lobe slender, reaching 0.32 along propodus, distal margin expanded and subtruncate, lateral margin serrate, anterior margin oblique, with 15 rows of 6-15 medial setae; propodus, palm oblique, LW 4.25 with three major and two minor projections and two major and two minor concavities, primary mediofacial setal row extending 0.76 of propodus, secondary setal row extending along posterior margin, thicker proximally; dactyl smooth, gently curved, reaching 0.70 of propodus.

Pereopods 3-4. Pereopod 3, coxa elongate ventrally, LW 1.47; basis elongate, anterodistal margin slightly produced, posterior margin with 6 submarginal setae, LW measured at midpoint 6.61; Pereopod 4, coxa distal margin rounded, ventral and posterior margins slightly excavate, posterior margin serrate with 9 small submarginal setae, LW 1.13.

Pereopods 5-7. Coxae of 5-6 bilobed; coxa 7 small, ventrally convex; pereopods 5-7 bases moderately expanded, LW 1.42:1.20:1.09, posterior margin 5-6 smooth, 7 serrate; pereopods 5-7 article four with extended posteroventral lobe reaching 0.92:0.75:0.66 of article 4.

Epimera 1-3. Ventral setae 8:4:3, posterior margins round.

Uropods 1-3. Relative uropod lengths, 1.00: 0.75: 0.77; relative lengths of peduncles 1-3, 1.00:0.84: 0.85; uropod 1, peduncle 1.07 rami length, with 11 medial and 4 lateral setae; outer ramus subequal to inner ramus, with 12 lateral and 0 medial setae, margins minutely crenulate; inner ramus with 4 medial and 5 lateral setae, margins of rami minutely crenulate; uropod 2 peduncle 0.81 rami, with 0 medial and 2 lateral setae; outer ramus 1.30 inner ramus, with 0 medial and 4 lateral marginal setae; outer ramus with 2 medial and 4 lateral marginal setae; margins of rami minutely crenulate; uropod 3, peduncle 0.93 rami, with 1 lateral apical and 5 medial setae; outer ramus 1.34 inner ramus; with 2 medial and 3 lateral marginal setae; outer ramus with 0 medial and 4 lateral marginal setae, margins of rami minutely crenulate.

Telson. LW 1.95, apical margin minutely tridentate, with 2 apical and two pairs of 2 facial setae.

Description of female paratype B

, 7.35 mm. Similar to males except for gnathopods 1 and 2. Gnathopod 1, carpus and propodus not greatly inflated, propodus slightly swollen distally. Gnathopod 2, palm of propodus lacking distinct tuberculation and concavities found in males.

Relationships.

Leucothoe eltoni sp. n. most closely resembles Leucothoe tumida of Myers (2013) in the inflated carpus and propodus of gnathopod 1; in the short stubby antennae; pereopods 5-7 with article 4 extending more than 50 percent along posterior margin of article 5; and a 2-segmented maxilliped palp. Leucothoe tumida differs from Leucothoe eltoni in having a large excavation in the palm of gnathopod 2; and in having a smooth inner margin of the maxilliped outer plate. Both species differ in host preferences with Leucothoe tumida found in the mantle cavity of the winged pearl oyster Pteria penguin while Leucothoe eltoni prefers branchial chambers of large solitary ascidians, especially Herdmania and Polycarpa species.

Both Leucothoe tumida and Leucothoe eltoni superficially resemble members of the genus Paraleucothoe in the large inflated gnathopod 1 of terminal males. However, Paraleucothoe differs from all species of Leucothoe in having the outer plate of the maxilliped extended distally beyond palp article 1. Paraleucothoe novaehollandiae (Haswell, 1879) also has a uniarticulate maxilla 1 palp but this feature is no longer unique to the genus as a number of recently described Leucothoe species have this feature. Paraleucothoe novaehollandiae is reported from the branchial chambers of the stalked tunicates Pyura spinifera and Pyura praeputialis (formerly Pyura stolonifera ) in southern Australia waters ( Lowry et al 2000) and other large solitary tunicates such as Herdmania sp. The exact placement of Paraleucothoe flindersi described by Stebbing (1888) from the Torres Straits remains problematic as it lacks the extended apical lobe of maxilliped outer plate typical of Leucothoe novaehollandiae , but has a uniarticulate palp and gnathopod 1 reminiscent of Leucothoe eltoni females and juvenile males. Further resolution awaits examination of material from the type locality.

Ecology.

Coral reefs, coral rubble, found primarily in branchial baskets of solitary tunicates such as Herdmania and Polycarpa sp., rarely in bivalve mollusks (winged pearl oyster Pteria penguin ), and branched yellow rope sponges Callyspongia (species undetermined).

Distribution.

Indonesia: Celebes Sea, Sulawesi, Kri Island, Halmera Sea, Raja Ampat Islands. Philippines: Cape Verde Passage, Mabini Tingloy. Hawaiian Islands (invasive): Ohau to Molokai, 2-20m.

Discussion.

While the native range of Leucothoe eltoni sp. n. encompasses shallow coral reef habitats in Indonesian and the Philippines, it is also an established invasive in Hawaiian waters ( Coles et al. 1999). The most likely vector for introduction was a dry dock, USS Machinist , transported to Pearl Harbor from Subic Bay, Philippines in 1992. Prior extensive treatment of Hawaiian amphipods by J.L. Barnard (1970, 1971) and ongoing monitoring by the Bishop Museum did not document any leucothoid resembling Leucothoe eltoni sp. n. prior to 1992. Ongoing sampling of marine flora and fauna by the Bishop Museum first reported this species in 1997 as Paraleucothoe flindersi . Muir (1997) speculated it was most likely an introduced species. Such rafting on floating metal objects is a possible means of transportation for benthic marine organism ( Cairns 2000; Creed and de Paula 2007, Hoeksema et al. 2012). Since first reported from Pearl Harbor in 1997 (as Paraleucothoe flindersi ) Leucothoe eltoni sp. n. has spread throughout Oahu and other islands including Molokai. The author has collected Leucothoe eltoni sp. n. from sponges in Kaneohe Bay, Ohau. The effects, if any, of this species on endemic leucothoid commensals and its spread in Hawaii is unknown at this time.