Acutiramus iwasakii, Harris, 2014

Harris, Vernon A., 2014, Porcellidiidae of Australia (Harpacticoida, Copepoda). II. The Importance of the Male Antennule in Taxonomy, Records of the Australian Museum 66 (2), pp. 111-166 : 149-151

publication ID	https://doi.org/ 10.3853/j.2201-4349.66.2014.1595
persistent identifier	https://treatment.plazi.org/id/03E56619-FFF4-3234-F5B7-7E2750254A9F
treatment provided by	Carolina
scientific name	Acutiramus iwasakii
status	sp. nov.

Treatment

Acutiramus iwasakii sp. nov.

Figs 26 View Figure 26 , 28 View Figure 28 , 29 View Figure 29

Type material. HOLOTYPE adult male, length 0.54 mm, mounted on slide [1360], P88555; ALLOTYPE adult female without egg mass, length 0.70 mm, mounted on slide [939], P88556 deposited at AM, Sydney; additional PARATYPES deposited at NHM, London.All collected from inside Turbo torquatus shells inhabited by hermit crabs of the species Pagurus sinuatus, O’Hara Head, Kioloa, NSW (25°34' S 150°25' E, estimated), V. A. Harris, 1976.

Diagnosis. Female rostrum unique, anterior edge with three curves giving an undulating appearance ( Fig. 26D View Figure 26 ), hyaline border present; male rostrum with anterior point, not obscured by cephalosome above; setae on male antennule sensory lobe and dactylus extremely long (> than length of antennule); female caudal ramus rhomboid with pinnate T4 at posterior apex, setules down length of medial edge, gap between γ and T2 equals gap between T3 and T4, α and β setae close (1/6 of ramus length apart); seta T1 on male caudal ramus very small; female genital double-somite with short cleft between anterior and posterior lobes; P3 endopod without seta on segment 1 (0:2:1, 3, 1); P4 endopod without seta on segment 1 (0:1:1, 2, 1).

Biometric data. Females (N = 6): maximum length (Lmax) mean 0.72 mm, length to posterior of genital double-somite (Lurs) mean 0.66 mm; width of cephalosome (W) 0.50 mm; rostrum width (R) 0.10 mm; genital double-somite length 0.13 mm, width 0.22 mm, arch 0.09 mm; caudal ramus length 0.08 mm, width 0.04 mm.

Ratios: Lmax / W 1.45, Lurs / W 1.35; cephalosome W/ R 5.0; genital double-somite width 44% of cephalosome width, w/l 1.7, arch/l 0.7; caudal ramus l/ w 2.0, ramus as % of Lmax 13%, Hicks’ index for α 83%, β 67%, α–β17 %.

Males (N = 4): maximum length 0.54 mm; cephalosome width 0.40 mm; antennule 0.126 mm; angle of P5 apex 45°.

Ratios: Caudal ramus l/ w 0.78, Hicks’ index for α 60%, β 50%, α–β 11%; antennule 23% of Lmax, segment 3+4 43%, dactylus 16% of antennule length.

Description. Adult females ( Fig. 26A View Figure 26 ): colourless, transparent.Anterior of cephalosome semicircular, no bulge above rostrum. Rostrum prominent, with characteristic undulating anterior border ( Fig. 26D View Figure 26 ). Dorsal pits small (3–4 µm), hyaline border 8 µm, dorsal surface without hair-like sensilla. Genital double-somite narrow, pointed posteriorly with a distinct cleft separating anterior and posterior lobes, border setules present, arch encloses about 1/2 of caudal ramus ( Fig. 26F View Figure 26 ). Caudal ramus ( Fig. 26E View Figure 26 ) rhomboid with pinnate T4 at apex, medial edge with setules, α and β setae not very close, T1 very small at lateral end of bevelled posterior edge, T2 and T3 close, equally spaced between γ and T4, setules along bevelled edge. No setules on labrum. Structure and setation of mouthparts and ambulatory limbs are typical of family. Geniculate setae on segment 2 of antenna endopod with plain terminal segment, terminal claw not comb-like, as long as first geniculate seta ( Fig. 29A View Figure 29 ). Maxillule ( Fig. 29C View Figure 29 ), P3 does not have internal seta on segment 1 of endopod (0:2:1,3,1). The serrate spinous terminal seta on P3 endopod is slender and not much longer than the endopod (1.2:1). No internal seta on segment 1 of P4 (0:1:1,2,1), ( Fig. 26C View Figure 26 ). P5 is broad and partly covers the genital double-somite, it is rounded posteriorly with an apical seta and one subterminal dorsal seta ( Fig. 26G View Figure 26 ). Mature females carry four or five large eggs.

Adult males ( Fig. 26B View Figure 26 ) colourless. Anterior of cephalosome only slightly truncated, shoulders rounded bearing two rows of dorsal pits arranged along a ridge ( Fig. 29D View Figure 29 ). The rostrum has a prominent anterior point that is not obscured dorsally. The rostrum and antennule sockets are recessed in a medial anterior concavity of the cephalosome ( Fig. 26H View Figure 26 ). Dorsal pits and hyaline border as for female. Caudal ramus sub-quadrate (l/w = 0.8), α and β setae close together (1/10 of ramus length), terminal setae appear to be plain, T1 is very short, recessed, T2 and T3 close, gap between T3 and T4 is 1/3–1/2 width of ramus ( Fig. 28B View Figure 28 ). Antennule is unique for the length of its setae ( Fig. 28G View Figure 28 ). Both the terminal seta on dactylus and σ seta on sensory lobe are as long, or longer, than length of extended antennule, δ seta 2/3 length of antennule, annulate seta associated with the distal denticle is equal to segment 3+ 4 in length. No denticle on segment 3, two denticles on segment 4 ( Fig. 28F View Figure 28 ). Structure and setation of mouthparts and ambulatory limbs as for female, but P2 has two terminal setae on segment 3 of the endopod, P5 acute trapezoid ( Fig. 28D View Figure 28 ), no rows of setules at base of each terminal seta.

Etymology. The species has been named after Dr Nozomu Iwasaki in recognition of his studies on Dactylopusoides species that burrow into brown algae.

Remarks. Nearly all animals in the present study are heavily burdened with protozoan organisms (large thecate and small naked suctoria as well as other thecate protozoa) which obscure detail of important organs such as the caudal rami and male antennules (see Fig. 27A View Figure 27 ). For this reason it was necessary to base identification and description on three newly metamorphosed specimens that had not been colonized by protozoa.

Animals were found living inside the shells occupied by the hermit crab Pagurus sinuatus , but not on empty shells or those occupied by the mollusc, thus the relationship appears to be commensal.