Little is known about the sponge fauna from Kosrae, one of four Federated States of Micronesia (FSM). The sponge fauna of FSM are summarized by Kelly-Borges and Valentine (1995), based upon the work of de Laubenfels (1954) and Bergquist (1965). De Laubenfels (1954) report one species, Agelas mauritiana from the Marshall Islands. No species of Agelas were recorded from Truk and Ponpei Island, located near Kosrae. Studies of the genus Agelas in tropical regions were made by Duchassaing De Fonbressin and Michelotti (1864), Carter (1883), Wilson (1902), Wiedenmayer (1977), Thomas (198019811998), Pulitzer-Finali (1982 1986 1996), Alcolado (1984), Hoshino (1985), Zea (1987), Van Soest and Stentoft (1988), Lehnert and Van Soest (1996 1998) and Mothes et al. (2007). Assmann et al. (2001) reported the new species A. cerebrum and recorded other Agelas species from the Carribbean. De Voogd et al. (2008) reported one new species, A. linnaei from Indonesia and compared it with all other Agelas species occurring in the Indo-west Pacific.

Sponge collections were made from the region of Kosrae, the most eastern of the Caroline Islands. The island is located approximately 370 miles (600 km) north of the equator (5°19′ N, 162°59′E) between Guam and the Hawaiian Islands. They were taken from depths of 10-50 m using scuba diving, 23- 30 Jan 2011, 8-15 Jan 2012, 18-28 Oct 2012 and 20-24 Nov 2013. The GPS coordinates of each site were recorded (Table 1, Fig. 1). Collected specimens were frozen and some preserved in 95% ethyl alcohol and were identified based on their morphological characters. The external feature of sponges was observed with a stereo microscope (Stemi SV 6, Carl Zeiss, Jana, Germany). The skeletal arrangements and spicules were studied under a light microscope (Axioscope II, Carl Zeiss) and SEM (HITACHI S-3500; Hitachi, Tokyo, Japan).

Order Agelasida Hartman, 1980 Family Agelasidae Verrill, 1907 Genus Agelas Duchassaing ＆ Michelotti, 1864

1*Agelas fragum n. sp. (Fig. 2)

Type specimen. Holotype (MABIK IV00151590), Molsron Tukunsru Village, Kosrae, Micronesia, 22 Oct 2012, Rho HS, by scuba, depth 10 m, deposited in the MABIK, Seocheon, Korea.

Description. Thin encrusting small pieces, size up to 9×6×0.1-0.3 cm, more or less tuberculated on the surface, attached tightly to the broad rocky substratum. Microscopically the tubercles are rugose with openings and with spicule clusters that protrude from the surface. Surface of many round projecting conules (1-2 mm height) with oscules. Texture hard at surface, soft at bottom. Color dark red.

Skeleton. Primary fibres cored and echinated, 65-78-232 μm in diameter, the end of primary fibres have densely echinated spicules. Secondary fibres 35 μm in diameter. Secondary fibres make large meshes, less echinated at the sponge base. The top of the surface, tubercle has many echinated brush-like bundles of spicules, mixed with thin smooth Acanthostyles. Tertiary fibres 20-30 μm in diameter, no echinating spicules.

Spicules. Acanthostyles 110-200×10-15 μm, number of spine whorls 11-17.

Etymology. This species named after the strawberry-like surface characteristics of the specimen.

Remarks. This sponge is similar to Agelas nakamurari Hoshino, 1985 from the Ryukyu Islands, Japan, thickly encrusting with orange to red color. The surface of A. nakamurari is smooth with uneven and irregularly meandering surface grooves whereas our specimen is rough with tubercules. Sizes of spicules are larger than those of our new species.

2*Agelas kosrae n. sp. (Fig. 3)

Type specimen. Holotype (MABIK IV00151591), Molsron Tukunsru Village, Kosrae, Micronesia, 22 Oct 2012, Rho HS, by scuba depth 15 m, deposited in the MABIK, Seocheon, Korea.

Description. Irregular elongated repent sponge with several branches, size up to 20×6×1.5-2 cm thick. Some wide parts of sponge attached tightly to the substrate. Surface smooth. Texture firm, compressible and hard to tear. Oscules sparse on the surface. Color live, purple on the surface and beige in the choanosome.

Skeleton. Primary fibres rarely cored and rarely echinated, 100-200 μm in diameter. Secondary fibres echinated, 30-60 μm in diameter. Secondary fibres meshes 83-163-232 μm in diameter. Tertiary fibres 10-20 μm in diameter are very rarely echinated.

Spicules. Acanthostyles 110-140×6-8 μm, number of spine whorls 19-22. Acanthoxeas 150-170×6-8 μm, number of spine whorls 18-22.

Etymology. This species is named after the type locality, Kosrae, Micronesia.

Remarks. This new sponge is similar to Agelas cervicornis (Schmidt, 1879) in branching type but different in skeletal structure, and no tertiary fibers.

3*Agelas purpurea n. sp. (Fig. 4)

Type specimen. Holotype (MABIK IV00151592), Molsron Tukunsru Village, Kosrae, Micronesia, 22 Oct 2012, Rho HS, by scuba, depth 15 m, deposited in the MABIK, Seocheon, Korea.

Description. Subcylindrical, irregular branched, size up to 13×2×1.8 cm, attached to the sponge Agelas kosrae. Two specimens not fused to each other as they grow separately but adherent. Surface rough with small tubes, and numerous elevated oscules 2-5 mm in diameter. Texture soft and compressible. Color dark purple in life. This sponge is less dense than A. kosrae.

Skeleton. Primary fibres, 50-100 μm in diameter, heavily cored; secondary fibres, 30-40 μm diameter, cored; tertiary fibres 10 μm in diameter, cored. All fibres rarely echinated; free spicules occur in the choanosome.

Spicules. Acanthoxeas 150-180×6 μm, number of spine whorls 20-21. Acanthostyles 150-220×5-8 μm, number of spine whorls 19-21.

Etymology. This species named after the live color purple.

Remarks. This new species is similar to A. kosrae but differs in the skeletal structure. The primary, secondary and tertiary fibres are all cored. Texture is softer than in A. kosrae.

1*Agelas bakusi n. sp. (Fig. 5)

Type specimen. Holotype (MABIK IV00151593), Foko Fukunsral, Kosrae, Micronesia, 19 Jan 2011, Rho HS, by scuba, depth 17 m, deposited in the MABIK, Seocheon, Korea.

Description. Thickly encrusting, size up to 22×20×2-3 cm. Surface smooth with many hole-like pits. Consistency firm. Color orange in life. Cavernous interior.

Skeleton. Ectosome consists of a thick membrane with free spicules (mostly acanthoxeas) and mixed fibres. Choanosome consists of a dense network of primary and secondary fibres, not distinct. Primary fibres 50-130 μm in diameter, lightly cored with spicules, echinated and reticulated. Secondary fibres 40-70 μm in diameter, rarely echinated; meshes 50- 230 μm in diameter. No tertiary fibres. Choanosome weak cavernous, many spicules.

Spicules. Acanthostyles 150-200×8-10 μm, acanthoxeas 140-250×6-8 μm. Number of spine whorls, acanthostyles 10-18, acanthoxeas 14.

Etymology. This species name bakusi is named after Dr. Gerald J. Bakus who is a professor in the department of Biological Sciences, University of Southern California, a marine ecologist and a sponge taxonomist.

Remarks. This species is similar to Agelas clathrodes (Schmidt, 1870) in morphology but it clearly differs in its fibres. Primary fibres of the new species are larger. The mesh in A. clathrodes is narrower than that of this new species and the spicules are longer. The new species has numerous acanthoxeas. Agelas clathrodes from a Caribbean specimen is strong cavernous in choanosome but this new species has very weak cavernous.

1*Agelas vansoesti n. sp. (Fig. 6)

Type specimen. Holotype (MABIK IV00151594), Foko Fukunsral, Kosrae, Micronesia, 19 Jan 2011, Rho HS, by scuba, depth 17 m, deposited in the MABIK, Seocheon, Korea.

Description. Flabellate, cup-shaped, size up to 23×10×1.5 cm. Surface very rough inside but outside smooth with slight protuberances. No oscules. Consistency firm and difficult to tear. Color yellowish brown in life.

Skeleton. Ectosome a thin membrane, very resilient with cored fibres and free spicules. Choanosome a irregular reticulation with loose primary fibres 150 μm in diameter, heavily cored and echinated, primary fibres form a simple fascicle; secondary fibres 60-70 μm in diameter, not cored and rarely echinated; tertiary fibres 20-30 μm in diameter, not cored and rarely echinated, The secondary fibre mesh is 30 -350 μm in diameter.

Spicules. Acanthostyles 180-200×8-10 μm, number of spine whorls, 24. Acanthostrongyles 160-200 μm, number of spine whorls 19-24. Acanthoxeas 200-220 μm, number of spine whorls 22-24 (very rare).

Etymology. This species name vansoesti is named after Dr. Rob W.M. van soest, Naturalis Biodiversity Center, Department of Marine Zoology, The Netherlands, a marine sponge taxonomist.

Remarks. The new species is similar to Agelas clathrodes in morphology, but differs in skeletal structure. The new species has primary, secondary and tertiary fibres. Spicules in the new species are longer than that of A. clathrodes. This new species has many acanthostrongyles.

1*Agelas incrustans n. sp (Fig. 7)

Type specimen. Holotype (MABIK IV00151595), Molsron Tukunsru Village, Kosrae, Micronesia, 22 Oct 2012, Rho HS by scuba, depth 17 m, deposited in the MABIK, Seocheon, Korea.

Description. Thick encrusting sponge, size up to 18×10×2 cm. Surface with many protuberances but smooth. Texture hard. Color light orange in life.

Skeleton regularly arranged, interior not cavernous; many fasciculate, primary fibres with numerous spicule; echinating spicules rare. Mesh variable. Primary fibres 140-150 μm in diameter and make a fascicle complex, spaced at intervals of 400 μm in diameter. Secondary fibres 30-40 μm. Mesh 31- 179-184-238 μm with rare echinating spicules.

Spicule. Acanthostyles 170-210×5-10 μm, number of spine whorls 21-23.

Etymology. This species named after the encrusting habit.

Remarks. This species is similar to Agelas clathrodes Schmidt, 1870 in external shape but the new species is distinguished from A. clathrodes by its encrusting habit and relatively solid interior.

The genus Agelas has only one spicule type and shows a very similar range of spicule sizes in all species. Lehnert and Van Soest (1998) stated that the spicule characters of Agelas species are not useful for species discrimination as they exhibit a large variation within each specimen. In most reported papers, there are few details on skeletal structure. Our study was focused on skeletal structure. And we divided the specimens into three group habitat; tuberculate surface with brush-like terminal, repent type and thick incrusting with smooth surface or funnel shape.

These three group show different spicule types. Rough surface with brushed spicules have very distinct verticilliate shape and thick diameter. In repent sponge, spicules have irregular spine of whorls and thinner than brush-like spicules. Thick encrusting or funnel shape sponge has also irregular spine of whorls but thicker than repent sponge.

Although Kosrae is geographically close to Truk, Kosrae has a high diversity of species of Agelas compared with Truk. The genus Agelas has resilient fibres like keratose sponges, but it is difficult to distinguish between primary and secondary fibres. Agelas is also difficult to tear, because it has tougher fibres than those in keratose sponges.

Thirteen species of Indo pacific Agelas (one species from Indonesia) are known but the majority is from the Caribbean (17 spp.) (De Voogde et al., 2008), thirteen species from the Caribbean. Kosrae shows the high diversity of Agelas species.