Acutiramus cumulus, 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 : 151-154

publication ID	https://doi.org/ 10.3853/j.2201-4349.66.2014.1595
persistent identifier	https://treatment.plazi.org/id/03E56619-FFFA-3231-F5B5-7D8155344B84
treatment provided by	Carolina
scientific name	Acutiramus cumulus
status	sp. nov.

Treatment

Acutiramus cumulus sp. nov.

Figs 27–29 View Figure 27 View Figure 28 View Figure 29

Type material. HOLOTYPE adult male, length 0.55 mm, dissected, P89051, and ALLOTYPE, adult female not carrying eggs, length 0.78 mm, both mounted on a slide [1651], P89052, 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. Male rostrum without anterior point, anterior border of cephalosome convex in midline obscuring rostrum, slightly concave on each side with angular shoulders; T1 on male caudal ramus large, pinnate, α and β setae not close together (1/4 length of ramus apart); anterior border of female rostrum straight, cephalosome bulged above rostrum; female caudal ramus rhomboid with conspicuous network of ridges; terminal setae T2, T3 and T4 pinnate, equal in size and bunched up together at posterior apex; no internal seta on segment 1 of P3 endopod (0:2:1,3,1); P4 has plain internal seta on segment 1 of endopod (1:1:1,2,1); setae on male antennule not longer than antennule (<1/2 antennule length).

Biometric data. Females (N = 8): maximum length (Lmax) mean 0.78 mm, length to posterior of genital double-somite (Lurs) mean 0.72 mm; width of cephalosome (W) 0.51 mm; rostrum width (R) 0.12 mm; genital double-somite length 0.16 mm, width 0.26 mm, arch 0.09 mm; caudal ramus length 0.10 mm, width 0.03 mm.

Ratios: Lmax / W 1.5, Lurs / W 1.4; cephalosome W/ R 4.2 ; genital double- somite width 50% of cephalosome width, w/l 1.65, arch/l 0.55; caudal ramus l/ w 3.1, ramus as % of Lurs 14%, Hicks’ ratios α 88%, β 61%, α–β 27 %.

Males (N = 2): maximum length 0.58 mm; cephalosome width 0.42 mm.

Ratios: Caudal ramus l/ w 1.0, Hicks’ index for α = 70%, β 42%, α–β 28%.

Description. Adult females ( Fig. 27A View Figure 27 ): colourless, anterior of cephalosome semicircular with a distinct bulge above the rostrum. Rostrum prominent with slightly convex anterior border ( Fig. 27G View Figure 27 ). Dorsal surface without hair-like sensilla, dorsal pits large (6–9 µm) conspicuous over all parts of the body except the caudal rami. Genital double-somite posterior lobe pointed, separated from anterior lobe by a distinct cleft ( Fig. 27B View Figure 27 ). Caudal ramus ( Fig. 27F View Figure 27 ) rhomboid, long (length 21/2 times width) with conspicuous dorsal network of ridges, α and β setae not close (> 1/4 length of ramus). The arrangement of terminal setae is unique, T2, T3 and T4 are clustered together at the posterior apex of the ramus ( Fig. 27F View Figure 27 ), T1 is small at the lateral end of the bevelled posterior edge and there is a gap between γ and T2. A terminal fringe of setules could not be seen on specimens available. Labrum without setules. Structure and setation of mouthparts and ambulatory limbs typical of family except for P3 which lacks internal seta on segment 1 of endopod. Serrated spinous seta on segment 3 of P3 much longer than endopod (1.6:1). P4 endopod ( Fig. 27C View Figure 27 ) has plain internal seta on segment 1, P5 broad, rounded posteriorly with apical seta and one sub-terminal seta ( Fig. 27D View Figure 27 ). Mature females carry four or five large eggs.

Adult males ( Fig. 27E View Figure 27 ) colourless. Anterior of cephalosome truncated, convex in midline above the rostrum and slightly concave on either side with pointed shoulders. Rostrum not pointed, obscured from above by cephalosome ( Fig. 28A View Figure 28 ). Dorsal pits as for female. Caudal ramus ( Fig. 28E View Figure 28 ) quadrate, lateral edge convex, dorsal surface with rows of conspicuous pits, α and β setae not close (1/4 length of ramus apart). Terminal seta T1 pinnate, recessed at lateral corner, T2 and T3 pinnate close together in middle of posterior border, T4 small set in from rounded medial corner. Antennule ( Fig. 29B View Figure 29 ) sensory lobe on segment 4 does not have a blade-like (acuminate) process, all setae less than length of antennule. (No fully extended antennule available for measurement and study of denticles). Structure and setation of mouthparts and ambulatory limbs as for female. P2 has two terminal setae on segment 3 of the endopod, P5 is trapezoidal with apical angle 47° ( Fig. 28C View Figure 28 ) no rows of setules at base of terminal setae.

Remarks. The trivial name refers to the way in which terminal setae T2, T3 and T4 on the female caudal ramus are heaped together at the apex (L. cumulus = a heap or pile), this feature has not been found on any other member of the family.

Specimens of A. cumulus and A. iwasakii were found living together in the same shells inhabited by hermit crabs. Both species are heavily burdened with suctorian protozoans round their perimeter (compare with Fig, 28A).

Porcellidium tapui described by Hicks & Webber, 1983 does not fit the diagnosis for Porcellidium , but fits the diagnosis for Acutiramus and should be moved to that genus as A. tapui (Hicks & Webber, 1983) . A. tapui displays a degree of variability in morphology and measurements that is unknown among algal living species, Hicks & Webber (1983). The question arises whether A. cumulus may be just an extreme form of A. tapui . There are some similarities between the two animals, but there are also significant differences as shown in Table 2.