Amphipoda (Crustacea) from Palau, Micronesia: Families Ampeliscidae, Ampithoidae, Aoridae, Colomastigidae and Cyproideidae

Abstract 12 species of amphipod in 5 families, collected from shallow reefs in Palau by S. DeGrave during 2002, are reported here. Of these, five species are new to science and Microdeutopus tridens Schellenberg (1938) is redescribed and transferred to the genus Bemlos Shoemaker (1925). The collection included several additional species in the genera Amphilochus Bate, 1862, Ampithoe Leach (1814), Bemlos, Byblis Boeck (1871), Colomastix Grube (1861) and Notopoma Lowry & Berents (1996), that were either incomplete or juvenile and could therefore not adequately be described. In addition, two new species of Plumithoe Barnard & Karaman (1991) are erected from the literature. Other families collected in Palau will be considered in later contributions.


Introduction
During the 2002 Oxford University Museum Expedition to Palau, amphipods were collected and kindly made available to the author for study by Dr Sammy De Grave. The collection consisted of almost 50 species in 20 families. This first contribu-with large discrete lobe. Pereopod 7 basis posterodistal lobe not reaching beyond ischium; propodus inflated, sub-ovoid, dactylus basally expanded.
Pleon. Epimera 1-2 rounded. Epimeron 3 with well developed posterodistal spine. Uropod 3 rami broadly lanceolate, inner margins serrate and with long fine setae. Telson a little less than twice as long as broad, cleft to four fifths its length bearing rows of mid-dorsal setae on each side and with distal margins bearing stout setae. Female. Unknown. Remarks. Ampelisca malakalensis sp. n. resembles A. melanesiensis Myers from Fiji, but that species has a short antenna 1 the flagellum of which does not reach the end of peduncular article 5 of antenna 2. In having antenna 1 flagellum reaching the end of peduncular article 5 of antenna 2, this species is very close to A. jiigurru King from the Great Barrier Reef, but differs from that species in the much more elongated pedun- cular articles 4 and 5 of antenna 2, the basally swollen mandible palp, the discretely lobed posterior margin of the basis of pereopod 5, the elongate and slender dactylus of pereopod 7, and in the scalloped distal margin of the telsonic lobes.
Habitat. On soft sediment with Halimeda. Distribution. Known only from the type locality. Head. Head less than one and a half times as long as deep, anteroventral margin oblique. Eyes, two pairs each with a cuticular lens; lenses with strong brown pigment patches around or near them. Antenna 1 about half body length; peduncular article 2 more than twice times length of article 1; flagellum with 17 articles, reaching well beyond end of peduncular article 5 of antenna 2. Antenna 2 equal to body length, peduncular article 4 a little longer than article 5, flagellum with 24 articles.
Pleon. Epimera 1-3 rounded. Uropod 3 rami broadly lanceolate, inner margins proximally excavate and serrate. Telson one and a half times as long as broad, cleft to two fifths its length, distal margins broadly rounded Male. Unknown Remarks. Species of Byblis are only occasionally reported from shallow water, being characteristically found in depths of 20-300 metres. Byblis species are rather uniform in design, with character states being found in myriad combinations. This makes it difficult to assign Byblis species to groups and therefore difficult to compare a new species with existing species, since each species shares a different suite of characters with different species. The antennal length, distally rounded coxa 1-3, pereopod 7 basis shape and position and number of robust setae on the carpus and propodus, the rather short uropod 2, the slender, elongate uropod 3 rami, and the telson lacking dis-tal setae, when taken in combination distinguish B. levis sp. n. from all other described species. The possibility cannot be excluded that the material examined my not be fully mature. This could explain the scarcity of setae in the material.
Habitat. Sand flats in shallow water. Distribution. Known only from the type locality.
Distribution. Australia (New South Wales, Queensland); Palau. Remarks. As pointed out by Myers (1985), Ampithoe ramondi represents a species complex that has yet to be elucidated. Present material agrees very well with material described from Fiji by Myers (1985) under the name A. ramondi. It shows some Figure 6. Ampithoe cf ramondi Audouin male similarity with A. katae Peart (2007b), from the Great Barrier Reef, but it differs from that species in the more strongly produced posterodistal corner of the male gnathopod 2 merus and carpus and in the more elongate mandible palp article 3. In the latter character state it resembles A. cookana Peart, also from the Great Barrier Reef, but that species has a relatively weakly setiferous propodus anterior margin on the male gnathopod 2. For the moment this material, as well as material described from Fiji by Myers (1985), is simply referred to the A. ramondi complex.

Genus Plumithoe Barnard & Karaman (1991)
This genus currently contains three designated species (Poore and Lowry 1997). These are: P. hirsuta (Ledoyer, 1978), P. plumicornis (Ledoyer, 1979) and P. quadrimana (Haswell, 1879). A fourth species P. lata sp. n. is described here, and two described materials previously allocated to P. hirsuta (Ledoyer), are raised to species status.  Description. Based on male holotype 2.2 mm. Head. Head lateral lobes rounded, anterodistal margin scarcely excavate; eyes medium size. Antenna 1 a little over half length of body; peduncular articles short; article 3 about half length of article 1; accessory flagellum absent; flagellum more than two times length of peduncle, with 14 articles. Antenna 2 about two thirds length of antenna 1; peduncle short; articles 4 and 5 subequal; articles 3-5 bearing tufts of long setae on the posterior margin; flagellum with 10 articles. Mandible palp articles in the ratios (basi-distal) 2:3:3.
Remarks. Plumithoe lata sp. n. differs from P. hirsuta Ledoyer, from Mauritius and P. madagascarienis sp. n. from Madagascar, in the shape of the male gnathopod 1 coxa, Figure 10. Plumithoe lata sp. n., male, female which is expanded both anterodistally and anteroproximally in P. lata sp. n. but only anterodistally in Madagascan material. It also differs from P. hirsuta Ledoyer in the straight robust spine on the propodus of the male gnathopod 2 (slender and curved in P. hirsuta). P. lata sp. n. also resembles P. acuticoxa sp. n. from Fiji, but Fijian material differs in having a slender basis (as in A. pollex var hirsutus from Mauritius) fringed with long setae in the male gnathopod 2 (a unique feature of Fijian material).
Habitat Etymology. Named after the shape of the coxa of the male gnathopod 1. (1985). P. acuticoxa sp. n. differs from all other described species of Plumithoe by its male gnathopod 2 basis fringed with long setae on the anterior margin. In its acute coxa 1, it differs from all described Plumithoe species except P. quadrimana (Haswell), but that species lacks a spine on the propodus of the male gnathopod 2. It differs from all other Plumithoe species except P. hirsuta Ledoyer in its very short article 3 of the mandible palp but differs from that species in the male coxa 1 and gnathopod 2 basis as described above.

Remarks. A full description and figures of this species are provided by Myers
Distribution  Ledoyer (1982). P. madagascariensis sp. n. differs from P. hirsuta Ledoyer in its long mandible palp arti-cle 3, the more shortened and expanded basis and straight propodal spine of the male gnathopod 2. It differs from P. lata sp. n. in the shape of the male coxa 1 which lacks posterior expansion and has a subtriangular anterodistal projection, in the presence of numerous robust setae on the propdous of pereopod 5 and in the more slender spine on the male gnathopod 2 propodus, It differs from P. acuticoxa sp. n. in its non-acute male coxa 1, in the more robust basis of the male gnathopod 2 that lacks long setae on its anterior margin, and in the long palp article 3 of the mandible palp.

Aoridae Stebbing, 1899
Bemlos tridens ( Remarks. This material agrees very closely with the original description of Schellenberg (1938). The ratios of the mandible palp articles are slightly different at 4:7:11 (Schellenberg gives 2:3:4). Since Schellenberg's (1938) figures are extremely minimal and somewhat sketchy, and the species has never been reported since, additional figures are presented here.
Habitat. Coral rubble. Distribution. Gilbert Islands (Schellenberg, 1938): Palau.  Etymology. Named for Sara LeCroy for her extensive and invaluable work on this genus of amphipods.
Pleon. Uropod 1 rami subequal, about two thirds length of peduncle; inner ramus with modified weakly hooked tip. Uropod 2 rami subequal with each other and with peduncle; inner ramus with weakly curved, acute tip. Uropod 3 rami lanceolate; inner ramus a little shorter than outer ramus and shorter than peduncle. Telson narrowly subtriangular, more than twice as long as broad, distally excavate, and with ventral proximal protrusion. Remarks. In the shape of the male gnathopod 2 this species resembles C. truncatipes Ledoyer from Madagascar, but in that species the basis of that appendage has an evenly rounded anterodistal margin, whereas in C. lecroyae sp. n. the margin is complexly scalloped. C. truncatipes also has very unequal rami on uropod 3, whereas they are almost subequal in C. lecroyae sp. n. The single male Colomastix sp. described by Ledoyer from New Caledonia is 1.9 mm in total length and appears to be immature. It may be synonymous with C. lecroyae sp. n. but has a peculiar character in its bilobed inner lobe of the maxilliped.
Distribution. Known only from the type locality.
Habitat. In Halimeda Remarks. Colomastix excavata sp. n. appears to be closest to C. serratipalma Schellenberg (1938) from New Caledonia, but in that species, on gnathopod 2, the spine on the postero-distal margin of the carpus is very slender throughout its length (broad based in C. excavata sp. n.) and the palm is evenly convex. Cyproidea excavata sp. n. differs from both C. liodactyla Hirayama (1978) and C. cobia Azman (2009) in gnathopod 1 which in those species has a serrated palm and spines on the posterior margin of the dactylus. It differs from C. ornata Haswell (1880) in the more slender propodus of gnathopod 1, the excavate palm of gnathopod 2, and the subequal rami of uropod 3.
Distribution. Known only from the type locality.