Psammoleptastacus arenaridus, PENNAK, 1942

Sak, Serdar, Huys, Rony & Karaytuğ, Süphan, 2008, Disentangling the subgeneric division of Arenopontia Kunz, 1937: resurrection of Psammoleptastacus Pennak, 1942, re-examination of Neoleptastacus spinicaudatus Nicholls, 1945, and proposal of two new genera and a new generic classification (Copepoda, Harpacticoida, Arenopontiidae), Zoological Journal of the Linnean Society 152, pp. 409-458 : 423-426

PSAMMOLEPTASTACUS ARENARIDUS PENNAK, 1942 A

Psammoleptastacus arenardius Pennak, 1942a : Coull (1977) (lapsus calami)

Arenopontia arenarida ( Pennak, 1942a) Noodt (1955a)

Arenopontia (Arenopontia) arenarida ( Pennak, 1942a) : Wells (1967)

Arenopontia arenardia ( Pennak, 1942a) : Coull (1971, 1977) (lapsus calami)

Arenopontia stygia Noodt (1955b) sensu Coull (1971) and Lindgren (1976)

Original description: Pennak (1942a): pp. 275–278; plate I, figures 1–11.

Type locality: USA, Massachusetts, Woods Hole. Pennak (1942a) collected material from both Nobska and north Cape Cod beaches, but did not specify the type locality; sand washings in vicinity of high tide mark .

Material examined: NMNH: one ♂ syntype mounted in toto on slide, and partly remounted by one of us ( RH) ; erroneously labelled ‘ Paraleptastacus arenaridus n.g. n. sp.’; Cat. no. 81982; leg. R. W. Pennak, September 1939 .

Partial redescription

Male: Total body length from tip of rostrum to posterior margin of caudal rami: 325 M m. Body: slender and cylindrical, without clear distinction between prosome and urosome. Hyaline frills of thoracic somites weakly developed and crenulated ( Fig. 6A, B); those of abdominal somites strongly developed and consisting of rectangular digitate lappets ( Fig. 6A).

Caudal rami ( Fig. 6A, C): approximately 2.8 times longer than basal width, tapering posteriorly; with one pore dorsally, one pore near ventral proximal margin, and two pores laterally near outer spinules; outer distal corner produced into posteriorly directed recurved spinous process, accompanied by ventral spinular row at base; dorsomedial surface with posteriorly directed spinous process. Armature consisting of seven setae: seta I, small; setae II and III, long and naked; seta IV, short, sparsely pinnate, located between seta V and distal spinous process; seta V, long and with fracture plane; seta VI, small, naked, and fused at base to seta V; seta VII, weakly foliaceous and triarticulate at base.

Rostrum ( Fig. 6D): small, broadly subtriangular, tapering distally, with two delicate sensillae and subapical pore.

Antennule ( Fig. 7A): nine-segmented, haplocer; geniculation between segments 7 and 8. Segment 2 longest; segment 4 an incomplete sclerite with one modified (fused at base) and one tiny element; segment 5 with long aesthetasc fused basally to seta; segments 6–8 with one seta and one basally fused spiniform element. Setal formula: 1-[1], 2-[7 + 1 plumose], 3-[4 + 1 pinnate spine], 4-[1 + 1 modified], 5-[2 + (1 + ae)], 6-[1 + 1 modified], 7-[1 + 1 modified], 8-[1 + 1 modified], 9-[7 + acrothek]. Acrothek consisting of short aesthetasc fused basally to two slender setae.

P1 ( Fig. 7B): coxa without ornamentation. Basis: with spinular row near bases of endopod and exopod; anterior surface with inner naked seta. Exopod: three-segmented; about 1.3 times the length of endopod; all segments with spinules along outer margin; exp-1 longest, with long unipinnate outer spine; exp-2 without outer element; exp-3 with two unipinnate spines and two geniculate setae of different lengths. Endopod: two-segmented, not prehensile; enp-1 slightly longer than exp-1, with a serrate seta at about halfway along the length of the inner margin, and with two subdistal spinules along outer margin; enp-2 about half the size of enp-1, with two geniculate setae and a few spinules.

P2 endopod ( Fig. 7C): two-segmented; enp-1 with few spinules along outer margin; enp-2 short, with a long, apically serrate, backwardly directed seta near proximal inner corner, and a long bipinnate inner seta and a short bare outer spine around distal margin.

P3 endopod ( Fig. 7D): two-segmented; enp-1 with few strong spinules along outer margin; enp-2 minute, with strong spinule at outer distal corner, short thin seta arising from inner distal corner (homologous with long inner distal seta of female), and naked curved apical spine, fused at base (homologous with outer distal spine of female).

P4 endopod ( Fig. 7E): two-segmented; enp-1 with five strong spinules along outer margin; distal margin of enp-2 with long, basally fused, serrate seta and long, unipinnate outer seta.

P2–P4: spine and seta formula as for the genus.

P5 ( Fig. 6B): forming subrectangular plate; outer basal seta sparsely plumose. Free distal margin: with three short bipinnate spines and one long bipinnate outer seta; inner spine longer than the other two.

Sixth legs ( Fig. 6B): asymmetrical, with smallest P6 closing off functional gonopore; each with a short inner and a long plumose outer seta.

Remarks: Pennak’s (1942a) illustrations of the male are restricted to the antennule, and no reference was made to the sexual dimorphism on the P3 endopod. His erroneous description of the caudal ramus, showing a basally swollen seta V and a triangular process at the distal outer corner, has no doubt been a source of confusion for subsequent identifications. Re-examination of a male paratype proved: (1) caudal ramus seta V to be normally developed, and the terminal spinous process to be much longer and more sharply pointed; and (2) P1 endopod to be markedly shorter than the exopod. Both aspects contradict Pennak’s (1942a) description, but agree with Lindgren’s (1976) observations based on North Carolina specimens. Lindgren also found that the proximal third of seta V was modified in approximately 60% of the population; individuals with unmodified setae were provisionally identified as A. stygia . Given this intraspecific variability, in conjunction with both ‘populations’ having the same distribution within the beach, we attribute all North Carolina records of A. stygia to P. arenaridus . These include Lindgren’s (1976) intertidal record from west of the Iron Steamer Pier near Morehead City, and, although provisionally, Coull’s (1971) subtidal record north of Cape Hatteras (at a depth of 100 m!). Psammoleptastacus arenaridus appears to be restricted to the north-eastern Atlantic seaboard of the USA, from the Woods Hole area in the north ( Pennak, 1942a, b, 1952; Lindgren, 1976) to at least North Inlet, South Carolina ( Coull & Dudley, 1985) in the south. Pennak (1942b) provides data on the horizontal distribution and relative abundance.