Cerapus chiltoni, Berents, 2023

Berents, Penelope B., 2023, New Species of Cerapus from Australian Waters (Amphipoda: Senticaudata: Ischyroceridae), Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 381-403 : 386-389

Cerapus chiltoni sp. nov.

urn:lsid:zoobank.org:act:395F0B53-201A-48D1-8309-147C5F42DDAB

Figs 4–8

Cerapus flindersi .— Chilton, 1892: 1 – 6, pl. 1.

Holotype: Male, 4.1 mm, AM P.106341, Port Jackson , New South Wales, Australia, 33°51'S 151°16'E, R. Helms, pre-1892. Paratypes: Female, 3.3 mm, AM P.106345; male, 4.1 mm, AM P.106343; male 2.8 mm, AM P.106344; male, 5.5 mm, AM P.106342; male, 3.3 mm, AM P.106345; data as for holotype. Male, 4.6 mm, AM P.27296, Fly Point, Port Stephens, New South Wales, Australia, 32°43'S 152°9'E, on orange hydroid, 20 m, N. Coleman, 27 November 1977.

Additional material examined. 5 specimens, AM P.106355, north-west end of South Solitary Island, New South Wales, Australia, 30°12'07"S 153°15'59"E, coral rubble, hand collected on scuba, 14.5 m, NSW 2813, K. B. Atwood, 1 May 2005;>1000 specimens, AM P.106354, Port Jackson, New South Wales, Australia, 33°51'S 151°16'E, K. Sheard.

Type locality. Port Jackson, New South Wales, Australia, 33°51'S 151°16'E.

Etymology. Named for Professor Charles Chilton who first examined Australian Museum specimens of this species from Port Jackson and attributed them to Cerapus flindersi Stebbing, 1888 .

Description. Male (based on holotype, 4.1 mm, AM P.106341).

Head. Rostrum short, length 0.1 × head, evenly tapered, apically subacute; lateral cephalic lobe with ventral corner rounded, subocular margin deeply recessed, reaching beyond eye, anteroventral corner subquadrate, ventral margin horizontal, posterior margin vertical. Antenna 1 long, length 0.6 × body length; peduncle without scales; peduncular article 1 shorter than article 3, length 0.8 × peduncular article 3, not produced anterodistally and anteromedially, slightly swollen along posterior margin, posterodistal corner not produced; peduncular article 2 anterodistal corner without distal projection; flagellum 7-articulate; article 1 long. Antenna 2 length equal to antenna 1; flagellum 9-articulate.

Pereon. Pereonite 1 with lateral keel, without sternal keel. Pereonite 2 with sternal keel. Pereonite 3 without sternal keel. Pereonite 5 length 1.9 × depth.

Gnathopod 1 coxa not fused to pereonite 1, length 1.5 × depth, without anteroventral lobe; basis length 2.2 × depth; carpus broad, length 1.6 × depth with setose posterior lobe; propodus palm extremely acute, robust setae absent. Gnathopod 2 carpochelate; coxa not fused to pereonite 2, length 1.9 × depth, with strongly produced anteroventral lobe or cusp; basis short, broad, length twice breadth, without anteroproximal group of long slender setae; carpus very long, length 1.9 × breadth, slender, posterior margin without teeth, palm deeply excavate, anterodistal tooth extremely produced, located near articulation with propodus, posterodistal tooth well defined, long, length 2.2 × width; propodus slender, strongly curved, length 5.3 × width, without tooth on posterior margin, posterodistal corner smooth, without teeth; dactylus, length 0.5 × propodus.

Pereopod 3 coxa with narrow anteroventral lobe, not fused to pereonite 3, length 1.7 × depth; basis, length 1.6 × breadth, with proximal rounded anterodorsal corner, with simple setae along anterior margin, without denticles along anterior margin; ischium long, length 1.6 × breadth; merus length 1.2 × breadth; short; without ridges. Pereopod 4 coxa not fused to pereonite 4, with anterior lobe separated from an anteroventral lobe; basis length 1.5 × breadth, with simple setal group midway along anterior margin; ischium long, length 2.3 × breadth; merus long, length 1.3 × breadth. Pereopod 5 coxa length 1.8 × depth, without patches of small setae, with setae along ventral margin few or absent; merus with anterior lobe not extending beyond anterior margin of carpus, posterior lobe with 1 plumose seta; propodus with 1 seta along posterior margin; dactylus short, uncinate with 1 accessory hook. Pereopod 6 coxa with setal fringe ventrally, without patches of small setae near margins; basis without patch of small setae near anterior margin; merus, length 1.9 × breadth; dactylus short, uncinate, with 1 accessory hook. Pereopod 7 coxa without posterodorsal lobe; merus length 2.3 × breadth; dactylus short, uncinate, with 1 accessory hook.

Pleon. Pleopods 1–3 biramous, decreasing in size. Pleopod 1 inner ramus 7-articulate; outer ramus 3-articulate article 1 evenly swollen. Pleopod 2 inner ramus reduced, 1-articulate; outer ramus, broad, 1-articulate. Pleopod 3 inner ramus reduced, 1-articulate; outer ramus broad, 1-articulate. Uropod 1 biramous; peduncle, length 1.3 × outer ramus; rami with distoventral fan of robust setae; outer ramus with lateral row of denticles, without medial setae, with 3 lateral setae, with large apical robust seta, without smaller slender setae; inner ramus, length 0.6 × outer ramus, without medial and 1 lateral seta, with large apical robust seta. Uropod 2 uniramous, peduncle, length 2.1× breadth, 5 × length of ramus; ramus small with 2 denticles and 1 slender apical seta. Uropod 3 uniramous, peduncle length 1.7 × breadth; ramus with 2 curved hooks. Telson as broad as long, length 1.0 × breadth, cleft to base, each lobe with 7–8 anteriorly directed recurved spines in 2 rows.

Female (sexually dimorphic characters). Based on paratype female, 3.3 mm, AM P.106345. Antenna 1 peduncle without scales; flagellum 7-articulate. Antenna 2 flagellum 9-articulate. Pereonite 1 without lateral keel. Pereonites 2–3 without sternal keel. Pereonite 5 length 1.9 × depth. Gnathopod 1, coxa length 1.2 × depth; basis length 1.5 × depth; carpus, length equal to depth with setose posterior lobe. Gnathopod 2 subchelate; coxa length 2.7 × depth; basis length 1.7 × depth without medial line of setae; palm extremely acute. Pereopod 5 coxa, length 1.9 × depth. Oostegites from gnathopod 2 to pereopod 5.

Tube. Composed of fine-grained grey sediment, flared at one end.

Habitat. Marine, 14.5 – 20 m depth.

Remarks. The Port Jackson material of C. chiltoni sp. nov. was collected by Richard Helms and deposited in the collections of the Australian Museum. Helms was a collector for the Australian Museum from 1888 but the precise locality and date of these collections is unknown. Specimens collected by Helms were sent to Professor Charles Chilton who published a description of amphipod specimens that were collected in Port Jackson ( Chilton, 1892). Chilton illustrated and described the specimens, attributing the material to Cerapus flindersi Stebbing, 1888 . Specimens in ethanol and seven microscope slides prepared by Chilton are held in the Australian Museum collections (4 slides of parts of large male, 1 slide of parts of smaller male, 2 slides of whole females) and are considered to be the slides used for the description and illustrations by Chilton (1892). Labels on the slides confirm that the Chilton’s material was collected by Helms.

Berents & Lowry (2018) assigned Cerapus flindersi Stebbing, 1888 to the new genus Kapalana and considered Chilton’s specimens to be an undescribed species of Cerapus . The material examined by Chilton is attributed to the new species described herein as Cerapus chiltoni .

The shape of the male gnathopod 2 changes with body size. The carpus and the propodus become more elongate as the male grows. The length to breadth ratio of the carpus changes from 1.3:1 in small males (up to 3.3 mm) to 1.9:1 in large males (greater than 4.0 mm).The palm changes from shallowly excavate in males less than 3.0 mm to deeply excavate in males larger than 4.0 mm. The posterodistal tooth becomes more elongate and chisel-like in large males (> 4.0 mm). The chisel-like posterodistal tooth is unique to C. chiltoni .

Distribution. New South Wales: Port Jackson to South Solitary Island.