Schistobrachia kabata Dippenaar, 2016, sp. nov.

Schistobrachia kabata sp. nov.

(Figs. 1–4)

Schistobrachia ramosa (Krøyer, 1863) sensu Kensley & Grindley (1973: 114).

Type material. Originally identified as Charopinus ramosus and deposited in the Iziko South African Museum by M.L. Pritchard. Holotype ♀ (ovigerous) (SAM A74035) with 1 ♂ attached (allotype SAM A74036) from R. straeleni caught off the west coast during January 2008. Paratypes include 3 ovigerous ♀♀ (1 dissected) (A 13015) and 2 ovigerous ♀♀ from R. alba (SAM A74037) caught off the south coast during April 2007; 1 ♀ (nonovigerous) (SAM A74038) from R. straeleni caught off the west coast during January 2008.

Other material examined. 3 ♀♀ from one R. alba and 8 ♀♀ from four R. straeleni caught off the south coast during April 2007; 11 ♀♀ and 2 ♂♂ from six R. straeleni caught off the west coast during January 2008; and 1 ♀ from one R. alba, 7 ♀♀ from four R. straeleni and 1 ♀ from one L. wallacei caught off the south coast during April 2008.

Description of adult female. Body length of adult female from tip of cephalothorax to tip of abdomen (excluding posterior processes) varying, 5.7–9.7 mm. Tip of cephalothorax, including maxillipeds, ventrally inclined to trunk (Figs. 1 A, 2A, F, G, I), with proximal portions of maxillae at an almost 90º angle to trunk, conforming to Kabata’s (1979) “ Type A” structural plan. Distance between maxillipeds and origin of maxillae approximately 8–15% of body length. Dorsal shield of cephalothorax indistinct, region between maxillipeds and base of maxillae cylindrical, expanding slightly posteriorly to form cylindrically shaped trunk. Small abdomen situated posteriorly on trunk (Figs. 1 B, 2B). Posterior processes oblong with slightly pointed tips (Figs. 1 A, B, 2A, B, F, G, I), 0.9–3.2 mm (approximately 16–33% of body length). Egg sacs (Figs. 1 A, 2F, G) multiseriate.

Antennule (Figs. 1 C, 2C) 3-segmented. Basal segment with lateral whip; second segment with solus; apical segment with three short and three long elements, conforming to Kabata’s (1979) Type A antennule structure, but with element nr 5 not observed in one specimen. Antenna (Fig. 1 D) biramous, rami almost equal in length; exopod 1-segmented, covered mostly by denticles, with two short, naked setae near tip; endopod 2-segmented, first segment with medial denticles, second segment (Figs. 1 E, 3D) with flexed hook (1), naked seta (2), denticulated process (4) and truncated seta (5), element 3 not observed (element notation according to Kabata (1979)). Mouth cone (Fig. 3 C) similar to other lernaeopodids with labrum and labium fringed with setules; mandible (Figs. 1 F, 2D) with dental formula P1, S1, P1, S1, P1, S1, B4. Maxillule (Figs. 1 G, 3E) biramous; exopod/palp with two apical naked setae; endopod/endite proximally with lateral denticulated patch, apically bearing three terminal papillae with apical setae. Maxillae (Figs. 1 A, 2A, F, G) approximately 60% of body length and mostly equal in diameter, distally inflated, united only at vestigial bulla (Fig. 2 E). Tip of each maxilla leading to two processes of holdfast organ (Figs. 1 A, H, I, 2A, F, G, I), processes of mostly equal length and width, especially in young female (Fig. 2 I); adult females with ventral processes sometimes slightly thinner (Fig. 2 F). One of the ventral processes of a specimen collected from R. alba with bifurcating tip (Fig. 2 H). Maxilliped (Fig. 1 J) robust, consisting of long narrow corpus and long subchela; myxal area (Figs. 1 K, 3A) inflated with a short, slender seta on inflated base and additional digitiform process; small denticulated process surrounded by tiny denticles (Figs. 1 L, 3F) distomedially on corpus; subchela (Figs. 1 J, M, 3B) with small seta on proximal half, inner distal margin with few small denticles, small protruding papilla at base of small naked seta next to claw; claw (Figs. 1 M, 3B) curved, tapering with small secondary tooth on proximal half of inner margin.

Description of adult male. Cephalothorax (Fig. 4 A) more than half body length, comprising two indistinctly separated parts; anterior part ventrally inclined towards posterior part and trunk, anteriorly with large mouth tube, antennules, antennae and buccal appendages; posteriorly with prominent maxillae and maxillipeds on bifid mediative process. Trunk (Fig. 4 B) more slender than cephalothorax, indistinctly 3-segmented with 1 pair of vestigial legs laterally on first segment, posterior part with caudal rami.

Antennule (Fig. 4 C) similar to female with solus not observed but all six elements of apical segment present. Antenna (Fig. 4 D), mandible (Fig. 4 E) and maxillule (Fig. 4 F) resembling those of female. Maxillae (Fig. 4 G) subchelate, broad and stout, bigger than maxillipeds, linked by tympanum; corpus broad, myxal area with prominent tubercle with rounded protrusions on distal margin; subchela tapering into strongly curved claw with small secondary tooth proximally on inner margin. Maxillipeds (Fig. 4 H) subchelate, linked, robust, squat, situated on mediative process (Fig. 4 I); corpus broad, myxa elevated to receive tip of claw; subchela (Fig. 4 J) short, indistinctly delimitated from claw, one seta midway on lateral margin and one distomedially; claw short, tapered, curved. Vestigial leg (Fig. 4 K) papilliform armed with single naked seta. Caudal ramus (Fig. 4 L) setiform, with three short setae on lateral margin (one caudal ramus deformed (Fig. 4 B)).

Attachment site. On gill filaments with holdfast organ inserted in host tissue.

Etymology. This species is named in honour of the late Dr Zbigniew Kabata for his extraordinary contribution to the taxonomy and systematics of symbiotic copepods. The species name is a noun in apposition.

Remarks. Comparison of these specimens with the re-description of S. ramosa given by Kabata (1979) reveals many differences. The general habitus of the South African females (Figs. 1 A, 2A, F, G) differs from that of North Atlantic S. ramosa in the shape of the trunk, the length and diameter of the maxillae compared to the length of the trunk, and most notably the length of the posterior processes which are twice as long in the current species compared to S. ramosa (cf. Markewitch 1956). The antennae (Figs. 1 E, 3D) differ in the absence of element 3 on the endopod, but also in the structure of element 4 and the size of the denticles on it (cf. Kabata 1979; Fig. 1602). The maxillae of our specimens (Figs. 1 A, 2A, F, G) equal about 60% of the body length while those of S. ramosa are about 90% of the body length (cf. Markewitch 1956). The diameter of the maxillae seems to be larger in S. kabata sp. nov. compared to the body length than that of S. ramosa (cf. Figs. 1 A, 2A, F, G and Kabata 1979: Fig. 1598), but the structure of the holdfast organ is similar. The maxillipeds of S. kabata sp. nov. (Fig. 1 J) differ from those of S. ramosa (cf. Kabata 1979: Fig. 1606) in the structure of the myxal area (cf. Kabata 1979: Fig. 1607) displaying a digitiform process in the new species (Figs. 1 K, 3A) rather than a small distally pointing conical process as in S. ramosa. In addition, the protruding papilla at the base of the naked seta on the inner side of the claw and the naked seta (Figs. 1 M, 3B) are both shorter compared to the length of the claw than those of S. ramosa (cf. Kabata 1979; Fig. 1608).

Schistobrachia kabata sp. nov. is thus different from S. ramosa in a number of features including the general habitus and the morphology of several appendages. Comparing it with the other known congeners, it differs in general appearance from S. tertia but also in the size of the posterior processes that are about 50% of the body length in S. tertia (Kabata 1970) compared to only about 16–33% of the body length in S. kabata sp. nov. There are also clear differences in the structure of the holdfast organ which has three pairs of “tines” at the tips of the maxillae in S. tertia (Kabata 1970: Fig. 5) compared to the two pairs of much longer branches in S. kabata sp. nov. (Figs. 1 H, I, 2A, F, G). The myxal area of the maxillipeds of S. tertia (Kabata 1970: Fig. 15) is without the digitiform processes clearly visible in S. kabata sp. nov. (Figs. 1 K, 3A). The general appearance of the new species is also completely different from that of S. jordaanae, with additional differences observed in the structure of the appendages (Dippenaar et al. 2004). The same is true when comparing S. kabata sp. nov. with S. pilgrimi (Kabata 1988) and S. chimaerae (Yamaguti 1939). Even though the holdfast organs appear to be mostly similar in structure, the general habitus (see Kabata 1988: Fig. 1 and Yamaguti 1939: Fig. 122) with the position of the maxillae on the cephalothorax (very close to maxillipeds) and the length of the maxillae compared to the body length (equal or longer) as well as the length of the posterior processes (very short) are clearly different. In addition there are also obvious differences in the structure of the appendages. The fact that one of the specimens of S. kabata sp. nov. has one of the four processes of the holdfast organ bifurcating (Fig. 2 H) raises the question whether this may have happened during the development of the process when it could have been opposed by the gill arch.

Kabata (1979) provided a very short description of the male of S. ramosa with no illustrations of the appendages and stated that antennae and buccal appendages are similar to those of the female while the maxillae and maxillipeds resemble those of the male of Charopinus dubius T. Scott, 1901. Differences in the structure of the appendages between S. kabata sp. nov. and S. ramosa females have been highlighted above; in addition there are clear differences in the structure of most of the appendages (except antennule and maxillule) between the males of S. kabata sp. nov. and those of C. dubius (see Kabata 1979: Figs 1587–1597).