Dilatatiocauda medialis, Harris, 2002

Harris, V. A., 2002, A New Genus Belonging to the Family Porcellidiidae (Crustacea: Copepoda: Harpacticoida) With Three New Species from Australia, Records of the Australian Museum 54, pp. 1-24 : 11-12

Dilatatiocauda medialis n.sp.

Figs. 3, 6–8

Type material. HOLOTYPE adult female without egg mass, length 0.88 mm, AM P58794. ALLOTYPE adult male, length 0.65 mm, AM P58795. PARATYPES, BMNH 2000.1251– 1252, 1♀, 13. Type material pooled from Sargassum sp. , (7) and Dictyopteris sp. , (9), infralittoral fringe, rock headland Cronulla, Sydney (34°03'S 151°11'E), Australia, 17.2.77, V.A. Harris.

Material collected from Shelly Beach rocks, Cronulla, Sydney, New South Wales by V.A. Harris, 7.2.74; Dilophus marginatus 13; Sargassum sp. , 1♀, 13, 21.8.75; Dictyopteris sp. , 1♀, 17.2.77; Dictyopteris sp. , 2♀♀; stones with coralline incrustation 1♀; Ecklonia radiata 2♀♀; Dictyopteris sp. , 4♀♀, 13; coralline weed 1♀, 13; Sargassum sp. with other weeds 4♀♀, 13, 18.2.77.

Diagnosis. Adult female: conspicuous dorsal fold parallel to anterior edge of cephalosome; comb plates on labrum with numerous ridges (>8); sternal plate of metasome segment 4 fimbriate, not ridged; caudal rami elongate, rectangular (L/W = 3), widen posteriorly, dorsal surface with network of ridges, seta inserted ½ way down ramus; terminal seta T3 slender, plain, seta T4 set in from medial corner; longest geniculate seta of antenna not longer than length of endopod segment 2; area of denticulate pegs on P1 endopod small (<½ endopod width), no medial peg area; segments 2 & 3 of P4 endopod not fused; no chitinous striations along anterolateral border of P5, posterior extremity of P5 notched. Adult male: antennule coupling denticles not conspicuous or denticulate; P2 endopod with two plumose terminal setae; P5 with ventral setule row to first seta, no setule rows at base of other terminal setae.

Dimensions. Females: mean length 0.92 mm (N = 6) range 0.88–0.93 mm, cephalosome width 0.64 mm, body length to width ratio 1.4. Rostrum 0.18 mm, body width to rostrum ratio 3.55. Urosome width to length ratio 1.25. Caudal ramus length to width ratio 3.0; dilation index 15. Males: mean length 0.7 mm (N = 5) range 0.67–0.72 mm, cephalosome width 0.58 mm, body length to width ratio 1.2.

Description. Adult female ( Fig. 7A) pale yellow or colourless. Anterior outline of cephalosome rounded, slightly truncated, body outline ellipsoidal. Rostrum broad, prominent with hyaline edge, projects 1 3 of its width. Dorsal surface of body ornamented with pits (c. 3 µm), conspicuous dorsal fold parallel to anterior edge of cephalosome ( Fig. 7B,C and Plate 1C), conspicuous reticulate ridges on dorsal surface of caudal rami ( Fig. 6B and Plate 1D). Hyaline border 13 µm wide, granular in appearance. Comb plates on labrum ( Fig. 8F) with numerous ridges (>8). Sternal plate of metasomal segment 4 not ridged, posterior border with fine hair-like setules. Urosome broad ( Fig. 7I), no cleft, small notch and scar mark boundary between anterior and posterior lobe. Anterior lobe without marginal setules, posterior lobe with strong marginal setules, two sensory setae on posterior border, medial corner square. Caudal arch very deep (66% of urosome length). Caudal rami elongate, lateral edge slightly convex, widen posteriorly ( Fig. 6B).Alpha seta near middle of ramus (Hicks’ index 55%).Alpha and beta setae close (L/[] = 18). Terminal seta T1 short, thick, pinnate ( Fig. 7J), setae T2 and T4 longer, pinnate, seta T3 plain, slender, very close to T2, T4 set in from medial corner (¼ ramus width), terminal fringe of fine setules present between T2 and medial corner.

Limbs typical of family. Exopod of antenna with five plumulose setae and one spinous seta. Segment 1 of endopod without seta or marginal setules, longest geniculate seta not longer than segment 2, terminal part straight finely serrulate, claw long with fine comb-like edge ( Fig. 7F). Coxal lobe of maxillipeds reduced, widely separated from opposite side, not fimbriate; basis quadrate, not fimbriate, fimbriate process absent ( Fig. 7G). First segment of P1 exopod with denticulate ridge parallel to edge ( Fig. 3C), lateral denticulate peg area on endopod of P1 small (<½ width of endopod), no denticulate pegs along medial edge, striated band parallel to fimbriate crescent V-shaped. Spinous seta on P3 endopod segment 2 slender, serrulate, almost as long as endopod (0.9:1), sickle shaped serrate spinous seta on segment 3 longer than endopod (1.5:1), long straight spinous terminal seta on segment 3 serrulate ( Fig. 8C). External spinous seta on segment 1 of P3 and P4 exopod very long (= segment 1), segments 2 and 3 of P4 endopod not fused ( Fig. 8A). P5 exopod ovo-lanceolate, expanded dorsal part does not reach back as far as posterior apex and leaves a conspicuous notch close to the four terminal dorsal setae near apex ( Fig. 8B), marginal setules strong, anterolateral chitinous striations absent.

Adult male ( Fig. 7H). Pale yellow or colourless. Shoulder rounded with two dorsal folds parallel to anterior edge of cephalosome and ending in a small epaulet laterally ( Fig. 7D,E), hyaline border passes round shoulder, lateral angle of antennule socket not prominent. Rostrum broad (0.07 mm), cephalosome width to rostrum ratio 8. Caudal rami quadrate (L/W = 1), dorsal surface with reticulate ridges, setation similar to female ( Fig. 8D). Coupling denticles on antennule elongate, tooth-like, not denticulate, associated seta plumose ( Figs. 8G,I), seta projects anteriorly, ventral process (blade) with finely ridged surface ( Fig. 8H), aesthetasc without bulbous base, dactylus with large basal expansion. P2 endopod terminates in two plumose setae. First terminal seta of P5 with long row of ventral setules, remaining setae without row of setules at their base ( Fig. 8E).

Remarks. Dilatatiocauda medialis is characterised by the position of the seta which is inserted about the middle of the caudal ramus. The specific name refers to this feature (L. medius = middle). Other distinctive features are the broad oval body (L/W = 1.4) and the conspicuous reticulate ridges on the caudal rami.

Distribution and abundance. No large population of this species has been found. The pooled type material has been separated from populations of the more abundant D. multidenticulata with which it is associated. Animals in small numbers have been found on Sargassum sp. , and Dictyopteris sp. , at Cronulla, Sydney, New South Wales.