Ingolfiella maldivensis, Vonk, Ronald & Jaume, Damia, 2014

Vonk, Ronald & Jaume, Damia, 2014, Ingolfiellamaldivensis sp. n. (Crustacea, Amphipoda, Ingolfiellidae) from coral reef sand off Magoodhoo island, Maldives, ZooKeys 449, pp. 69-79 : 71-75

Taxon classification Animalia Amphipoda Ingolfiellidae

Ingolfiella maldivensis sp. n. Figs 1, 2, 3, 4

Material examined.

One specimen, RMNH.CRUS.P.264, female paratype 1.85 mm, at station 'Blu Cove’, 6 May 2014, depth 15 m, N3°05'37.8", E72°57'59.4". Five specimens: RMNH.CRUS.P.265, undissected female holotype 1.80 mm (Fig. 1); RMNH.CRUS.P.266, female paratype 1.55 mm; RMNH.CRUS.A.5054, female paratypes, at Dharamboodhoo reef, 11 May 2014, depth 20 m., N3°03'30.5", E72°55'29.6". All collected by R. Vonk. Specimens are stored in the Crustacea collection of Naturalis Biodiversity Center, Leiden.

Diagnosis.

Lateral lobes on frontal margin of the head present. Dactyls of gnathopods armed with four javelin lancet shaped bladelike spines along posterior margin. Palm of G2 angle robust seta bifid; posteromedial surface of carpus lacking broad triangular spine. Medial surface of protopod of U2 with three denticle combs. Unguis of P3-P4 with four denticles; that of P5-P7 bifid. PL1-PL3 present and of similar form. Oostegites on P3-P4.

Etymology.

The new species is named after the group of islands where it was found, in the Republic of the Maldives.

Description.

Body elongate, cylindrical, without coloration, transparent to milky white (Fig. 1). Head with frontal margin nearly straight, no sinus visible, cephalic lobe placed a little backwards from the frontal margin (Fig. 2A).

Antennule (Fig. 2B), peduncle article 1 robust, slightly inflated, articles 2 and 3 of equal length. Flagellum 4-articulate, longer than peduncle articles 2-3 combined; proximal article unarmed and short, other three articles of equal length; articles 2-4 each provided with aesthetasc, aesthetascs progressively shorter towards distal. Accessory flagellum 3-articulate, shorter than two proximal articles of main flagellum combined.

Antenna (Fig. 2C) slightly shorter than antennule; gland cone short, hardly protruding dorsomedially; protopodal articles 3-5 inflated, especially the third one, fourth segment with two long setae on posterior margin; Flagellum 5-articulate, shorter than protopodal articles 4-5 combined.

Labrum (Fig. 2D) and paragnaths (not figured) ordinary, latter lacking inner lobes.

Mandibles with molar process non-triturative, spiniform and not serrated. Right mandible (Fig. 2E) with 6-denticulate incisor; spine row with three short, stubby, finely serrated elements. Left mandible (not figured) with spine row comprising two blunt finely ribbed elements.

Maxillule (Fig. 2F) coxal endite [= inner lobe] with two simple setae; basal endite [= outer lobe] with six robust setae of which two bicuspidate, one 3-cuspidate, one long and 5-cuspidate, one short, broad and 3-cuspidate, and one - the innermost - crooked and 4-cuspidate; endopod (=palp) 2-segmented, distal segment with two long slender setae.

Maxilla (Fig. 2G) with short, subequal blunt figs, outer one with five distal setae, inner one with four distal setae; two out of five setae on outer fig sparsely setulose.

Maxilliped (Fig. 2H) basal endite rudimentary, with one simple seta; merus with one simple seta on outer margin; propodus with two single simple seta on opposite margins; dactylus slender, with two distal setae, and long unguis.

Coxal gills (Fig. 1) present on P3-P5, rounded to ovoid. Oostegites (Figs 1, 3 B’) on P3-P4, short, subrectangular and shorter than corresponding coxal gill, each with one long slender seta.

Gnathopod 1 (Fig. 2I) carpo-subchelate, carpus almost 3 times as long as broad and exceptionally slender and elongated toward the tip, with three short, bifid flagellate robust setae along lateral side of palm margin, one robust seta on palm angle, and one short stout simple seta and broad triangular spine on medial surface of segment as figured; palm margin slightly convex and smooth; dactylus with four slender stalked-lanceolate bladelike denticles along posterior margin.

Gnathopod 2 (Fig. 2J) carpo-subchelate, carpus massive, shorter and broader than carpus of G1; palm margin strongly convex, clearly serrated, lined up with three short, bifid flagellate robust setae along lateral side; palm angle marked by stout, slightly curved bifid robust seta; medial surface of segment with short, simple robust seta that varies between individuals in width, however it is not a broad, strong triangular spine; posteromedial surface of carpus with excavation apparently to accommodate distal portion of unguis; dactylus with four lanceolate bladelike denticles along posterior margin.

Pereiopods 3-4 (Fig. 3A, B) subequal except for slightly longer propodus in P4; dactylus elongate, with two simple setae at the base of the unguis; unguis slender and with four fine denticles on tip.

Pereiopods 5-7 (Fig. 3 C–E) progressively longer towards posterior; basis of P5-P6 broad, that of P7 slender. P7 with one of distal armature elements on distolateral angle of carpus modified into a crooked comb-like seta. Dactylus of P5-P6 short, that of P7 longer. Unguis of P5 bifid but not so outspoken as in P6-P7. Gill present on P5.

Pleopods 1-3 (Fig. 3F) subtriangular.

Uropod 1 (Fig. 4A) protopod subrectangular; exopod much shorter than endopod, acuminate, with short robust seta terminally and tiny simple seta placed subdistally; endopod with short terminal spine plus row of three stout triangular robust setae subdistally; nine simple setae disposed on segment as figured.

Uropod 2 (Fig. 4B) protopod bearing three oblique combs of mostly bifid spines on medial surface; two most proximal combs including one long seta; rami tapering, each with strong terminal simple seta clearly articulating at base, exopod stouter and slightly shorter than endopod.

Uropod 3 (Fig. 4C) small and uniramous, protopod triangular, with two setae flanking the short exopod; exopod with long apical seta.

Telson (Fig. 4C) entire and thick, fleshy, with one plumose seta distomarginally at each side.

Remarks.

Previous knowledge on the ingolfiellids from the Maldives was restricted to specimens collected during the Xarifa Expedition 1957-1958. These came from washings of the coral Favites sp. ( Ruffo 1966). They were described as Ingolfiella xarifae Ruffo, 1966 and came from Rasdu atoll, some 130 kilometers north of the Faafu atoll where specimens of the present species were found. Ingolfiella xarifae differs from the rest of Ingolfiella species by having three denticles on the posterior margin of the dactylus of the first gnathopod, and four on the second (see Vonk and Jaume 2014). They also have a trifid unguis on the third and fourth pereiopod, and a broad triangular spine on the posteromedial surface of the carpus in the second gnathopod. These features set them clearly apart from Ingolfiella maldivensis sp. n. which has four denticles on both gnathopod dactyli, multidenticulate claws and no triangular spine on the carpus of the second gnathopod.

A comparison of fourteen easy to distinguish characters between members of the genus Ingolfiella (45 species) was done by Vonk and Jaume (2014). The new species ranks next to a Caribbean species from comparable shallow sublittoral habitats off the coast of Curaçao, namely Ingolfiella quadridentata Stock, 1979. Character states overlap entirely for the eight non-male-specific features of Vonk & Jaume’s matrix, but other features differ. Thus, the basal endite of the maxilliped is small and barely developed in Ingolfiella maldivensis , but separate and as long as the ischium in Ingolfiella quadridentata ; the triangular spine on the posteromedial surface of carpus of the first gnathopod is lacking in Ingolfiella quadridentata ; the oostegites are crowned with one long seta in Ingolfiella maldivensis , but have a 3-pronged distal margin in Ingolfiella quadridentata ; and the claw of the fourth pereiopod is 4-denticulate in Ingolfiella maldivensis but 7-denticulate in Ingolfiella quadridentata .

Other species bordering the Indian Ocean include: Ingolfiella kapuri Coineau & Rao, 1973, from the Andaman and Nicobar Islands in intertidal shell debris; Ingolfiella arganoi Iannilli & Vonk, 2013 from Abd-al-Kuri Island, Socotra Archipelago in an anchialine pool; Ingolfiella quokka Gallego-Martínez & Poore, 2003, from an intertidal sandy beach environment from the City of York Bay, Western Australia. All of these species differ sharply from Ingolfiella maldivensis (see Vonk and Jaume 2014: table 1).

The recently described Ingolfiella botoi Vonk & Jaume, 2014, from beach groundwater in the Gura Ici Islands, Molucca Sea, Indonesia ( Vonk and Jaume 2014), shares more features with Ingolfiella maldivensis than with the rest of the Indian Ocean species mentioned above. It can be remarked that the Maldives, forming the western rim, and the Moluccas, positioned in the middle, are both still part of one large Indo-Polynesian marine biogeographic province ( Briggs and Bowen 2012).