Alicellidae

Broyer, De, 2008, Alicellidae and Valettiopsidae, two new callynophorate families (Crustacea: Amphipoda), Zootaxa 1843, pp. 57-66 : 59-63

Alicellidae new family

Type genus. Alicella Chevreux, 1899 .

Description. Head exposed; deeper than long; anteroventral margin concave or rounded, weakly or moderately recessed or not recessed, moderately excavate or not excavate; anteroventral corner rounded, subquadrate or absent; rostrum vestigial or absent; eyes present or absent, if present then small, oval. Body laterally compressed.

Antenna 1 shorter than or subequal in length to antenna 2; peduncle 3-articulate, with sparse slender setae; peduncular article 1 longer than article 2; article 2 longer than article 3; peduncular articles not geniculate; accessory flagellum short; callynophore present; calceoli present ( Lincoln & Hurley 1981). Antenna 2 short or medium length; peduncle with sparse slender setae, without brush setae; without hook-like process; flagellum longer than peduncle, 5 or more articulate.

Mouthparts well developed, forming a subquadrate bundle. Mandible incisors asymmetrical, straight or slightly curved, smooth to minutely dentate anteriorly, posterodistal part of incisor becoming strongly dentate; lacinia mobilis present on both mandibles (left broader than deep with serrate margin, occasionally narrow or vestigial; right reduced or vestigial, occasionally broadened with serrate margin); molar present, non-triturative or with tiny triturating patch; palp present. Maxilla 1 inner plate setose along medial margin; outer plate with 8/3 setal-tooth formula; palp symmetrical, 2-articulate. Maxilla 2 inner plate at least 3/4 length of outer plate; inner plate with oblique setal row. Maxilliped inner plates well developed, separate; outer plate longer than palp article 1, not longer than palp article 2; palp 4-articulate.

Pereon. Pereonites 1–7 separate; complete; pleurae absent. Coxae 1–7 well developed, none fused with pereonites, overlapping, none acute ventrally. Coxae 1–3 well developed, none hidden or vestigial and hidden by other coxae. Coxae 2–4, none extensively broadened.

Gnathopod 1 similar in males and females; smaller (or weaker) than or similar in size to gnathopod 2; similar in form to gnathopod 2; simple or subchelate; coxa smaller than or subequal to coxa 2, not produced anteroventrally; ischium elongate, about 2 x as long as broad; merus and carpus not rotated; carpus shorter than, subequal to, or longer than propodus; dactylus large. Gnathopod 2 similar in males and females (not sexually dimorphic); subchelate to minutely subchelate; coxa subequal to but not hidden by coxa 3; ischium long; carpus/propodus elongate, rectolinear; carpus long, not produced along posterior margin of propodus; propodus without complex setae along posterodistal margin; dactylus small.

Pereopods, none prehensile, 3–7 without hooded dactyli. Pereopod 3 coxa longer than broad or as long as broad; carpus shorter than or subequal to propodus, not produced; dactylus well developed. Pereopod 4 coxa subequal to or larger than coxa 3, not ventrally acute, with small to large posteroventral lobe; carpus shorter than or subequal to propodus, not produced; dactylus well developed. Pereopods 5–7 with few robust or slen- der setae. Pereopod 5 shorter than or subequal in length to pereopod 6; coxa smaller than or subequal to coxa 4, coxa equilobate; basis expanded, subquadrate, without posteroventral lobe; carpus linear; dactylus with setae absent. Pereopod 6 subequal in length to or longer than pereopod 7; basis expanded; dactylus without setae. Pereopod 7 longer than pereopod 5, similar in structure to pereopod 6; basis expanded, without dense slender setae; dactylus minute (less than 1/8 length of propodus), short (between 1/8 and1/4 length of propodus) or medium length (1/4 to 1/2 length of propodus).

Pleon. Pleonites 1–3 without transverse dorsal serrations, pleonite 3 with or without dorsal spines, without lateral teeth or ridging, without dorsal carina. Epimeron 1 well developed. Epimeron 2 setose.

Urosome not dorsoventrally flattened; urosomites 1–3 free; urosomite 1 carinate or not. Urosomite 3 not fused with telson. Uropods 1–2 apices of rami without robust setae or setae embedded. Uropod 1 peduncle without long plumose setae; biramous. Uropod 2 well developed; without dorsal flange; inner ramus subequal in length to or longer than outer ramus. Uropod 3 not sexually dimorphic; without medial process; biramous; outer ramus longer than peduncle; inner ramus subequal to outer ramus. Telson longer than broad; deeply cleft; dorsal or lateral robust setae present; apical slender setae absent; apical robust setae present.

Included genera. The Alicellidae includes 6 genera: Alicella Chevreux, 1899 ; Apotectonia Barnard & Ingram, 1990 ; Diatectonia Barnard & Ingram, 1990 ; Paralicella Chevreux, 1908 ; Tectovalopsis Barnard & Ingram, 1990 ; Transtectonia Barnard & Ingram, 1990 .

Remarks. Alicellids are distinguished from other callynophorate amphipod families by the following combination of characters: both mandibles with lacinia mobilis; gnathopod 2 with elongate ischium, elongate, rectolinear carpus and propodus and small to medium dactylus; uropods 1–2 without apical robust setae; telson deeply cleft. De Broyer & Thurston (1987) reported type 1 calceoli in Alicella . This is unexpected because type 1 calceoli usually occur only in gammaroid amphipods.

Alicellids are callynophorate amphipods. Although they are similar to lysianassoid amphipods they differ from lysianassoids by the presence of a right lacinia mobilis and the non-mitten-shaped second gnathopod. Alicellids and amaryllidids have similarities. In both families the left lacinia mobilis is broad with a serrate distal margin, the first gnathopod has a reduced coxa, the second gnathopod has an elongate ischium, a rectolinear carpus and propodus with a small dactylus, but amaryllidids have type 3 calceoli, they do not have a right lacinia mobilis, maxilla 1 inner plate is apically setose and the outer plate has a 6/5 seta-tooth formula, and the telson is ventrally swollen proximally and never deeply cleft. Amaryllidids may occasionally turn up in a baited trap, but they are not scavengers. Vijayines are free-living usually deep-sea amphipods and amaryllidines are often associated with bryozoans or soft corals and it is possible they feed on the polyps.

Among the Cebocaris group Cyclocaris Stebbing, 1888 , is a deep-sea scavenger, which is similar to the alicellids, particularly gnathopod 2 with its elongate ischium, rectolinear carpus and propodus and small dactylus, but Cyclocaris has a hugely expanded incisor on the right mandible, the left lacinia mobilis is a vestigial peg, longer than broad, the right lacinia mobilis is absent, the inner plate of maxilla 2 has no oblique setal row and is half the length of the outer plate, both coxae 1 and 2 are vestigial and the posteroventral lobe on coxa 4 is well developed.

Further outside the lysianassoid group alicellids show affinities to the Miramarassidae Lowry, 2006 . Both have uropods 1 and 2 lack apical robust setae, deeply cleft telsons, elongate ischia on gnathopod 2 with rectolinear carpi and propodi and a lacinia mobilis on both mandibles. But among other differences, the miramarassids have apparent symmetrical dentate incisors and the lacinia mobiles are well developed and symmetrical.

Alicellids might be similar to some scopelocheirids such as Paracallisoma Chevreux, 1903 and Scopelocheiropsis Schellenberg, 1926 , which have rectolinear second gnathopods, although not as well developed.

Members of the Alicellidae are all deep-sea scavengers and the highly modified mandibles appear to be an important modification to this mode of life. Alicellids may be associated with thermal vents ( Barnard & Ingram 1990) or living on the deep abyssal and hadal plains where species such as Alicella gigantea are among the deepest living and largest amphipods known ( Chevreux 1899; Barnard & Ingram 1986; De Broyer & Thurston 1987).

Distribution. Probably cosmopolitan in the deep-sea, 706–8480 m.