Caprellid, "Ghost" or "Skeleton" shrimps, so called for their skeletal appearance. Amphipod crustaceans, easily distinguished by the elongate stick-like body form and reduction of the abdominal appendages. Head is generally fused with pereonite 1. Pereopods on first 2 segments (pereonites) are most flexible and called gnathopods; gnathopods 2 being the largest, used in defense, feeding and substrate attachment. In many species pereopods 3 and 4 may also be reduced or absent. Gills on pereonites 3 + 4, rarely on pereonite 2. Pereopods 5 - 7 much smaller than 1 + 2, used for clinging to the substratum. In females, brood plates (öostegites) develop on pereonites 3 + 4. Much remains to be learnt about their biology, ecology and in many cases changing distributions.
“Protella trilobata new species
Distribution. Type locality: 51°58'S, 56°38'W, 646-845 meters.
Diagnosis. Pereopods 3 and 4 terminally constricted, length less than :-Y1 length of gill, peduncular article 3 of antenna 1 much shorter than article 2.
Material examined.
Eltanin, cruise 8: Sta. 558, 51°58'S, 56°38W, March 14, 1963, 646-845 meters, 1 ♂ holotype USNM 123750, 8 ♂♂, 11 ♀♀ paratypes USNM 123751.
Description. Male holotype: Body smooth except for anterolateral processes on pereonites 2-4. Length 9.2 mm. Antenna 1 shorter than body length, article 3 much shorter than article 2. Antenna 2 approximately equal in length to the peduncle of antenna 1. Setal formula for terminal article of mandibular palp 1-13-1. Left mandible with 5-toothed incisor, 6- toothed lacinia mobilis serrate, setal row of 2 serrate spines, molar with flake. Palp of maxilla I with 4 terminal spines and 2 subterminal setae, outer lobe with 6 serrate spines. Inner and outer lobes of maxilla 2 with 6 terminal setae. Outer lobe of maxilliped not serrate with 5 or 6 marginal setae; inner lobe with 1 plumose and 2 nonplumose setae; penultimate article of palp produced distally with distal fringe of setae on medial margin, ultimate article dactyliform and rounded terminally. Propodus of gnathopod 1 subtriangular without distinct grasping spines, proximal portion of grasping margin minutely serrate; grasping margin of dactylus not distinctly serrate. Propodus of gnathopod 2 with proximal tooth and notch at midlength, dactylus minutely serrate. Gills elliptical to club-shaped. Pereopods 3 and 4 1-segmented, distal end constricted but not segmented. Pereopod 5 6-segmented, penultimate article with weakly developed grasping margin, ultimate article toothed lacinia mobilis, setal row of 3 serrate spines, dactyliform. Pereopods 6 and 7 usually with well-molar with flake. Right mandible with 6- developed propodus. Abdomen with pair of distally visor, appendages and pair of lobes.
Remarks. The largest male in our collection measured 11.9 mm, and the largest female 9.3 mm. The setal formula for the terminal article of the mandibular palp varied from 1-13-1 to 1-18-1. No other significant variation was noted
Protella trilobata differs from the other species of Protella, P. gracilis Dana, 1853, and P. similis Mayer, 1903, in that peduncular article 3 of antenna 1 is much shorter than article 2 in P. trilobata, whereas in the other species the third article is as long or longer than the second article. Pereopods 3 and 4 of P. trilobata are less than ¾ of the length of the gills, whereas in the other species these pereopods are longer than ¾ of the gill length. In both P. gracilis and P. similis pereopods 3 and 4 are somewhat rod-shaped and lack the terminal constriction found in those pereopods of P. trilobata.
The specific name refers to the 3-lobed appearance of the terminal portion of the male abdominal appendage.”
(McCain & Gray, 1971: 128-131)
