Eubrachiella sublobulata Barnard 1955

Eubrachiella sublobulata (Barnard, 1955)

(Figs 8–13)

Syn. Parabrachiella sublobulata (Piasecki et al. 2010) Neobrachiella sublobulata (Ho & Takeuch 1996)

Material examined. 8 females (1 dissected) and two detached males (S.A.M A7611) from the gill filaments of the smooth horse fish Congiopodus torvus (Gronow) off Table Bay deposited in the Iziko South African Museum.

Description of adult female. Body length, excluding egg sacs about 2.1 mm (Fig. 3 A) and 2.5 mm (Fig. 3 B). Cephalothorax (1.0 mm and 1.1 mm, respectively), cylindrical, about as long as trunk (0.8 mm and 0.9 mm, respectively); anterior part slightly expanded to form head, inclined almost at right angle to long axis of posterior part, dorsally covered by well developed, dorsal shield (Figs 3 A, B). Trunk cylindrical, about as wide as long with conical protuberances anterolaterally and anterodorsally, posteriorly with numerous, unequally sized protuberances (vestiges of posterior processes (see Ho & Takeuch 1996)). Genital process not observed. Egg sacs (Figs 3 A, B) about 0.8mm and 1.6mm respectively, with multiseriate egg arrangements.

Antennule (Fig. 3 C) 3-segmented; segments 1 and 2 unarmed; distal segment short, armed with five unequal elements; digitiform seta 4 elongate, tubercles 1 and 2 short, slender seta 6 elongate, seta 5 and tubercle 3 not observed (see Kabata 1979). Antenna (Fig. 3 D) biramous, bulbous exopod with numerous, short denticles and 2 prominent spines distomedially; endopod 2-segmented, segment 1 short, unarmed; distal segment with prominent hook 1, slender seta 2 and denticulated process 4; conical processes 3 and 5 not observed (see Kabata 1979). Mandible (Fig. 3 E) with dental formula P1, S1, P1, S1, P1, S1, B4. Maxillule (Fig. 3 F) bilobed; palp (outer lobe) small, tipped with 2 short setae; endite (inner lobe) larger, terminally armed with 2 papillae tipped with setae and 1 shorter seta near base of papillae. Maxillae (Fig. 3 A) (0.4µm) about half length of cephalothorax, united only at bulla; latter (Figs 3 G, H) with short manubrium and circular anchor. Maxilliped (Fig. 3 I) with broad corpus, myxal area with two denticulated swellings and 1 short seta in the middle; subchela elongate, armed with 1 short seta proximally, distomedially with sparsely denticulated margin; barb slender, about half length of claw; latter tapering, slightly curved with rounded tip, with short auxiliary tooth near base.

Description of adult male. Body (Figs 4 A, B) (1.4mm) divided into anterior cephalothorax (0.6mm) and posterior genito-abdominal complex (0.6 mm). Latter, obtusely flexed with long axis of cephalothorax, with distinctive furrow separating it from cephalothorax. Cephalothorax covered with dorsal carapace. Caudal rami short, tipped with 2 apical setae. Antennule (Fig. 4 C) 3-segmented; segment 1 with elongate whip reaching base of distal segment; segment 2 unarmed; distal segment armed with 3 setae of varying lengths and 2 short tubercles. Antenna (Fig. 4 D) biramous; 2-segmented endopod larger than exopod; latter armed with 2 prominent spines; endopod segment 1 with patch of short denticles, segment 2 with well-developed dorsal hook 1, slender seta 2 elongate and process 4 armed with short spines (tubercle 3 and process 5 not observed) (see Kabata 1979). Mandible not observed. Maxillule (Fig. 4 E) similar to that of female. Maxilla (Fig. 4 F) with bulbous corpus, myxal area raised to receive tip of claw; subchela short, with bent claw not clearly delimited from subchela. Maxilliped (Fig. 4 G) with strong corpus, myxal area armed with conical outgrowth edged with rows of short denticles; subchela short, with curved claw bearing auxiliary tooth near base.

Remarks. Eubrachiella sublobulata was originally described from specimens collected from the gill filaments of C. torvus off Table Bay. However, due to incomplete information about the structure and armature of the appendages it was tentatively transferred to the genus Neobrachiella (Ho & Takeuch 1996). Piasecki et al. (2010) transferred all Neobrachiella species to Parabrachiella and thus N. sublobulata became Parabrachiella sublobulata. A thorough re-examination of the original material revealed that even though the majority of morphological characteristics of the appendages of both males and females are almost identical to species of the genus Parabrachiella, they differed from Parabrachiella species by the presence of numerous, unequal protuberances (vestiges of posterior processes) present posteriorly on the female trunk instead of well-developed posterior processes as in Parabrachiella. Additionally, the transverse constriction separating the male posterior genito-abdominal complex from the cephalothorax and the anteriorly flexed posterior extremity that points forward is also different from those in Parabrachiella species. Thus, this species should remain a member of the genus Eubrachiella.

Currently there are two valid species, namely E. gaini and E. antarctica both reported from teleosts of Antarctic waters (Ho & Takeuch 1996). Eubrachiella sublobulata can be distinguished from these species by the cylindrical trunk of the adult female which is about as wide as long, with short distinct protuberances anterolaterally and anterodorsally as well as a posterior margin edged with numerous, unequal protuberances (vestiges of posterior processes). The female E. antarctica has a quadrangular trunk which is about as wide as long with the posterior margin bearing a short genital process with no traces of posterior processes and E. gaini female has a wider than long trunk bearing a broad, dorsal tubercle on the posterior margin and 2 similar tubercles on the posterolateral margin (Ho & Takeuch 1996). Kabata (1967) suggested that the short protuberances present anterolaterally and anterodorsally on the trunk in Eubrachiella species could indicate variation within the genus. Thus, although the protuberances are absent in E. antarctica, there are few short, non-prominent protuberances along the lateral and dorsal margins of the trunk of E. gaini compared to the numerous, well-developed protuberances anterodorsally and anterolaterally on the trunk of E. sublobulata (Figs. 3 A, B). Eubrachiella sublobulata thus represents a different geographical location and host record for Eubrachiella species which were previously only reported from Chaenocephalus aceratus (Lönnberg), Champsocephalus gunnari Lönnberg, Chionodraco hamatus (Lönnberg), Gobionotothen gibberrifrons (Lönnberg), Prionodraco evansii Regan, Pseudochaenichthys georgianus Norman, Dissotichus mawsoni Norman, Chionodraco hamatus (Lönnberg), Trematomus hansoni Boulenger, Trematomus scotti (Boulenger), Trematomus bernacchii Boulenger and Channichthys rhinoceratus Richardson, in Antarctic waters (Ho & Takeuch 1996).