PHOTIDAE, Boeck, 1871

Vader, Wim & Krapp, Traudl, 2005, Crab-associated amphipods from the Falkland Islands (Crustacea, Peracarida), Journal of Natural History 39 (33), pp. 3075-3099 : 3082-3086

Family PHOTIDAE

Gammaropsis monodi ( Schellenberg, 1931)

( Figures 4–6 )

Eurystheus sp. Monod 1926 , p 60, Figure 57.

Eurystheus monodi Schellenberg 1931, p 238 , Figure 121.

Eurystheus eurypodii K. H. Barnard 1932, p 231 , Figure 145.

Eurystheus Monodi Ruffo 1949, p 56 .

Gammaropsis monodi Barnard and Karaman 1991, p 191 .

Material examined

Seven ovigerous females, 29 males and juveniles in alcohol, two slides deposited at TromsØ Museum ( Norway), reg. no. 13844. Two males and two females deposited at Museo Civico di Storia Naturale , Verona ( Italy), all collected East Falkland, Choiseul Sound, 30 m, from Paralomis granulosa and Eurypodius latreillei , caught in baited traps, 29 October 2003, A. and W. Vader leg.

Additional material

One specimen, Lively Sound, East Falkland, March 2003, A. Vader, from Paralomis ; 21 specimens, Choiseul Sound , East Falkland, 29 October 2003, A. and W. Vader, from crab bins ; seven specimens, Choiseul Sound , East Falkland, 29 October 2003, coll. A. and W. Vader, from Paralomis granulosa .

Diagnosis

A Gammaropsis species with accessory flagellum, moderately acute epistome, triangular head lobes, rounded Cx1, Gn2 dactylus less than half length of propodus, U3 rami subequal to peduncle length.

Description of Falkland material

Male. 4–5 mm. Head with cephalic lobes triangular, pointed, eyes roundish, drop-shaped, black. A1 a little shorter than A2, both with few but long setae. Antennae: A1 with peduncle article 1 subequal to 3, article 2 almost twice as long, flagellum four-articulate; accessory flagellum two- to three-articulate, last article very short. A2 with peduncle articles 4 and 5 subequal, long, flagellum eight-articulate.

Mouthparts: upper lip with acute epistome, longer than labrum, reaching along insertion of antennae. Mandible: palp with article 3 almost as long as article 2. Maxilla 1: inner plate triangular, with a row of setules along margin; outer plate with seven pectinate robust setae, palp two-articulate, article 2 smooth except for distal setae: four robust pectinate setae, and two simple setae. Maxilla 2 plates of equal breadth, inner plate setose also on inner margin. Maxilliped: in reasonable agreement with the figure provided by Monod: merus (first article of palp) triangular; carpus double length of propodus, dactylus three-quarters length of propodus; outer plate reaching half of carpus; inner plate reaching half of outer plate. Lower lip: with inner lobes.

Gnathopods: Gn1 coxa rectangular, distally rounded, carpus and propodus subequal in length, propodus oval, hind margin regularly rounded, palm scarcely defined and not delimited by spines, covering 75% of hind margin, dactyl long, narrow, falcate. Gn2 larger than Gn1, Cx2 similar to Cx1, but distally tongue-shaped, rounded, propodus 1.5× longer than carpus, broad and robust, palm almost transverse, with a right-angled to V-shaped indentation centrally, palmar angle not delimited by spines, but greatly and roundly expanded; dactyl broad and curved, shorter than palm.

Peraeopods: P4 coxa deep, rounded, covers ca two-thirds of basis; basis moderately expanded, merus with small distal lobe, with bunch of setae; propodus. carpus, dactyl falcate, ca two-thirds length of propodus. P5: basis greatly broadened, merus, carpus and propodus with stiff setae on posterior margin, propodus longer than carpus, dactyl falcate, 50–66% of propodus. P7: more slender than P3–6, basis moderately expanded, propodus twice length of carpus, dactyl falcate, ca two-thirds length of propodus.

Uropods moderately spinose. U1–2: peduncle shorter than outer ramus, with two marginal spines on distal half; interramal spine strong, about half length inner ramus; U3 peduncle as long as rami, rami subequal.

Telson entire, subquadrate, distally triangular, with one pair of long lateral setae.

Female. Ovigerous 3–3.7 mm. Basically as male, Gn1 similar to male, Gn2 with propodus less robust and more slender than in male, palm sinuously convex, palmar angle without the great rounded expansion.

Colour in life. The eyes are black. The colour pattern consists otherwise of many small brown dots, often vaguely arranged in stripes, over the entire body, including coxae and bases of the peraeopods. The colour persists some time in alcohol.

Distribution

Choiseul Sound ( Falkland Islands), picked from Eurypodius , Paralomis and unidentified spider crab. Magellan Straits, from Eurypodius ( Monod 1926; Barnard 1932), Beagle Channel ( Ruffo 1949).

Remarks

In spite of the scantiness of the earlier descriptions, there is no doubt that our material belongs to Gammaropsis monodi : the animals were collected from the same host in the same geographic area, and the form of the male gnathopods is very characteristic. The specimen reported by Ruffo (1949) had ‘‘one enormous egg filling the marsupium’’; this was probably a sphaeronellid copepod, as the species normally carries many small eggs.

The vast genus Gammaropsis is greatly in need of a revision. Several species in the genus associate regularly with large crustaceans, examples are Gammaropsis (Podoceropsis) nitida (Stimpson, 1853) in Europe on hermit crabs (cf. Vader 1971; Hoberg et al. 1982), G. (P.) chionoecetophila Conlan, 1983 on the Snow Crab Chionoecetes opilio in Canada ( Steele et al. 1986) and on the Alaska King Crab Paralithodes campschatica in Alaska ( Kuris et al. 1991), and various Gammaropsis s. str. on large hermit crabs off east Australia (W. Vader, unpublished data).

Figures

Figure 4. Gammaropsis monodi (Schellenberg): head female (×6, ×10); A25antenna 2 (×10); Md5mandible, UL5upper lip, LL5lower lip (×20); Md’5mandible detail, Mx1, Mx25maxilla 1, 2, Mxp5maxilliped (×40).

Figure 5. Gammaropsis monodi (Schellenberg): Gn15gnathopod 1 male (×20); Gn2 male (×10); Gn2’ male detail (×20); Gn1 female (×10); Gn2 female (×20).

Figure 6. Gammaropsis monodi (Schellenberg): Gn5gnathopod 2 female (×20); P5peraeopod 4, 5, 7 (×10); Us5urosomite (×10, ×20).