Laetmatophilus triceratops, Hughes, 2013

Hughes, L. E., 2013, Podoceridae of Tropical Australia (Peracarida: Amphipoda), Records of the Australian Museum 65 (1), pp. 1-37 : 3-7

Laetmatophilus triceratops sp. nov.

Figs 2–5

Type material. Holotype male, 4.3 mm, SEM pin mount and 2 slide, AM P. 87032, Area C Centre, Arafura Sea (9°22'52"S 133°39'53"E), 112 m, muddy sand, Smith McIntyre grab, 13 May 2005, coll. G. D. F. Wilson, Southern Surveyor Arafura Sea Cruise (SS05/2005/027/GR047); paratype female, 3.8 mm, dissected, 1 slide, AM P.87609, Area C Centre, Arafura Sea (9°22'52"S 133°39'53"E), 112 m, muddy sand, Smith McIntyre grab, 13 May 2005, coll. G. D. F. Wilson, Southern Surveyor Arafura Sea Cruise (SS05/2005/027/GR047); paratypes 2 juvenile specimens, AM P.79146, Area C Centre, Arafura Sea (9°22'52"S 133°39'53"E), 112 m, muddy sand, Smith McIntyre grab, 13 May 2005, coll. G. D. F. Wilson, Southern Surveyor Arafura Sea Cruise (SS05/2005/027/ GR047).

Additional material examined. Male (immature), 2.8 mm, dissected, AM P.87610, Carnarvon shelf (23°52'55"S 113°27'33"E), 37 m, 5 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group ( SOL097 GR02); female, 3.5 mm, dissected, AM P.87611, Carnarvon shelf (23°52'55"S 113°27'33"E), 37 m, 5 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group ( SOL097 GR02); male, SEM pin mount (poor condition), AM P.85674, Carnarvon shelf (23°52'55"S 113°27'33"E), 37 m, Smith McIntyre grab, 5 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group ( SOL097 GR02); 5 specimen (various growth stages 2 gravid females and 3 juveniles), AM P.84678, Carnarvon shelf (23°52'55"S 113°27'33"E), 37 m, Smith McIntyre grab, 5 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group ( SOL097 GR02); female specimen, AM P.84677, Carnarvon shelf (23°46'17"S 113°20'36"E), 44 m, Smith McIntyre grab, 7 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group ( SOL105 GR02); female gravid specimen (no carina), AM P.84679, Carnarvon shelf (23°46'18"S 113°20'37"E), 44 m, Smith McIntyre grab, 7 August 2008, coll. Geosciences Australia: Marine and Coastal Environment Group 2008 ( SOL105 GR02) .

Type locality. Arafura Sea (9°22'52"S 133°39'53"E).

Etymology. Named for the three carinae on the top of the head.

Diagnosis. Head with 3 carinae, projecting anteriorly, apically acute in triangle formation; rostrum well developed, elongate, about half the length of the head; eyes greatly bulging. Pereonite 1 with single broad dorsal carina, produced dorsally, with pair of lateral and ventral projections. Gnathopod 1 carpus rectolinear, 2.5 times as long as broad; propodus subovate, corner of palm with 4 robust setae. Pereonite 2 dorsal carina broad, produced evenly, subtriangular, apically rounded. Gnathopod 2 propodus medial surface with dense cluster of plumose setae, palm ⅓ the length of the propodus. Pereonite 3 dorsal carina broad, produced evenly, subtriangular, apically rounded, with ventral projections. Pereonite 4 dorsal carina broad, produced evenly, with ventral projections. Pereonites 5–7 fused. Pereonites 5–6 dorsal carina broad, evenly rounded. Pereonite 7 dorsal carina broad, produced posteriorly, apically subacute. Pleonite 1 dorsal carina narrow, produced anteriorly, subtriangular, apically subacute. Pleonite 2 dorsal carina narrow, produced evenly, subtriangular, apically subacute.

Description. Based on holotype male, AM P.87032, 4.3 mm. Body cuticle with dorsal projections. Head with 3 carinae, projecting anteriorly, apically acute in triangle formation; rostrum well developed, elongate, about half the length of the head; eyes greatly bulging; lateral cephalic lobe produced acute; anteroventral corner produced acute, posterior ventral corner produced acute. Mandible accessory setal row with 3 setae. Maxilla 1 palp distal margin with 4 robust setae

Pereonite 1 with single broad dorsal carina, produced dorsally, with pair of lateral and ventral projections. Gnathopod 1 coxa subequal to coxa 2, broader than long, anteroventral corner not produced, apically rounded; basis 3.5 times as long as broad, without anterodistal setae; carpus rectolinear, 2.5 times as long as broad; propodus subovate, anterior margin with sparse slender setae, palm margin minutely crenulate, corner of palm with 4 robust setae; dactylus posterior margin with slender setae. Pereonite 2 dorsal carina broad, produced evenly, extending the entire length of the pereonite, subtriangular, apically rounded. Gnathopod 2 basis 2.8 times as long as broad, with medial acute projection, anterodistal corner with acute produced lobes, corner without setae; merus posterior margin narrow with produced lobe, lobe as long as broad, apically acute, without short robust setae; carpus free, distinct from propodus; propodus elongate subovoid, length twice width, anterior margin with1 slender seta, medial surface with dense cluster of plumose setae, palm subacute, ⅓ the length of the propodus, with broad distal shelf, shelf margin strongly crenulate, palm with 2 proximal rounded teeth, palm defined by corner, without setae; dactylus eXtending beyond palm. Pereonite 3 dorsal carina broad, produced evenly, subtriangular, apically rounded, with ventral projections. Pereonite 4 dorsal carina broad, produced evenly, with ventral projections. Pereonites 5–7 fused. Pereonites 5–6 dorsal carina broad, evenly rounded. Pereonite 7 dorsal carina broad, produced posteriorly, apically subacute. Pleonite 1 dorsal carina narrow, produced anteriorly, subtriangular, apically subacute. Pleonite 2 dorsal carina narrow, produced evenly, subtriangular, apically subacute. Epimera 1−3 posteroventral corner rounded. Urosome with 2 pairs of uropods. Urosomite 1 length 1.5 times as long as broad. Uropod 1 peduncle 2.5 times as long as broad, ventromedial spine absent; inner ramus 1.9 times peduncule length; outer ramus about half the length of inner ramus. Uropod 2 absent. Uropod 3 uniramus; rami with row of slender setae. Telson dorsal lobe absent, apically rounded with single robust seta.

Female (sexually dimorphic characters) based on paratype female, 3.8 mm. AM P.87609.

Gnathopod 1 basis 4.5 times as long as broad, with anterodistal robust seta; propodus subtriangular, produced distally, anterior margin with clusters of long slender setae, palm with 6 robust setae near corner. Gnathopod 2 basis 4.4 times as long as broad; merus anterior margin with 2 robust setae; propodus subovate, length 1.6 times width, anterior margin with a few robust setae, posterior margin lined with robust setae, palm convex, 0.4 times length of the propodus, without distal shelf or teeth, palm defined by 2 robust setae; dactylus closing along palm.

Variation. Juveniles (c. 2.8 mm) have a smooth dorsum that develops into broad evenly rounded carina with acute carinae on the head and pleonites. The carination on the dorsal surface of the head transitions from a smooth hump in juveniles to three anterior projecting carinae in adults. The first acute body processes to develop are the head lateral cephalic lobes and anteroventral corner, and carinae on pleonites 1 and 2. In penultimate gravid females the carina on the head are apically rounded and appear cleaved, while the final adult female has acute carinae.

Remarks. In Laetmatophilus triceratops sp. nov., the body form develops from a smooth dorsum to having posterior carinae between juvenile and adult growth stage. A similar growth pattern has also been noted for L. hala J. L. Barnard, 1970 . The shape of the dorsal carinae separates adult L. triceratops sp. nov., and L. hala from L. acuticephalus Ledoyer, 1978 ; L. armatus ( Norman, 1869) ; L. hystrix Haswell, 1880 ; L. ledoyeri Ruffo, 1987 ; L. leptocheir K. H. Barnard, 1937 and L. tuburculatus Bruzelius, 1859 , which have dorsal, lateral and/or ventral projections along the body cuticle. A smooth body form distinguishes L. dabberi Barnard & Drummond, 1981 ; L. durbanensis K. H. Barnard, 1916 ; L. intermedius Ledoyer, 1979a ; L. paradurbanensis Bano & Kazmi, 2004 ; L. purus Stebbing, 1888 and L. tridens K. H. Barnard, 1916 .

The adult male gnathopod 2 in Laetmatophilus triceratops sp. nov. and L. hala , along with L. dabberi all have a distinct sickle-shape propodus with mainly distal setae. Laetmatophilus triceratops sp. nov. can be distinguished from L. hala by the formation of carinae on the head (3 acute carinae in triangle formation) and the absence of lateral ridging on the body.

Laetmatophilus triceratops sp. nov. juvenile specimens that have not developed dorsal carinae are very similar to L. dabberi known from southern Australia. However L. triceratops sp. nov. juveniles have a more developed head bump in comparison to the smooth form of L. dabberi . The adult specimens of L. triceratops sp. nov. have well developed carina, gnathopod 1 carpus and propodus more elongate, propodus palm with many robust setae and the male gnathopod 2 basis with acute medial processes, which are not present in L. dabberi .

Distribution. Australia. Western Australia: Arafura Sea; Carnarvon Shelf (current study).

Figures

Figure 2. Laetmatophilus triceratops sp. nov., holotype male, 4.3 mm, AM P. 87032, Arafura Sea. SEM photographs: (A) whole animal lateral view (scale 200 µm); (B) whole animal dorsal view (scale 200 µm); (C) head lateral view (scale 100 µm); (D) head dorsal view (scale 100 µm) and (E) gnathopod 2 propodus palm plumose setae (scale 20 µm).

Figure 3. Laetmatophilus triceratops sp. nov., holotype male, 4.3 mm, AM P.87032, and paratype female, 3.8 mm, AM P.87609, Arafura Sea (scale 0.1 mm).

Figure 4.Laetmatophilus triceratops sp. nov., juvenile male, 2.8 mm,AM P.87610, and juvenile female, 3.5 mm,AM P.87611, Carnarvon Shelf, Western Australia (scale 0.1 mm).

Figure 5.Laetmatophilus triceratops sp. nov., juvenile male, 2.8 mm,AM P.87610, Carnarvon Shelf, Western Australia (scale 0.1 mm).