Description

Remarks. The original description of Rhinebothrium tetralobatum was based on six specimens and did not include information on tegumental structures (i. e., microtriches). In addition, we also detected some discrepancies between the original description and re-examination of the type series. Brooks (1977) reported R. tetralobatum as being 15 – 30 mm in length, with a genital pore position between 44 and 48 % from anterior end of proglottid and an ovary measuring 198 – 300 in length. These accounts differ from our measurements of the type series (i. e., 5.4 – 9.7 mm, 23 – 33 %, and 86 – 159, respectively). Furthermore, the examination of additional material shows that R. tetralobatum ranges from 4.1 to 19.0 mm in length, possesses genital pores that are located 18 to 33 % from the anterior end, and that the ovary is 68 – 348 in length (Table 1). Also, Brooks (1977) reported the presence of a cephalic peduncle, which was not seen in either the newly collected specimens, or the type series, and described the worms as apolytic rather than euapolytic (sensu Caira et al. 1999). Among 41 valid species of Rhinebothrium, R. tetralobatum shares the presence of two testes per proglottid with five other members of the genus. This group includes the freshwater species R. fulbrighti Reyda & Marques, 2011 ex Potamotrygon orbignyi Castelnau from the Bay of Marajó, Brazil; the marine Atlantic R. biorchidum Huber & Schmidt, 1985 ex Urobatis jamaicensis Cuvier from Jamaica; R. spinicephalum Campbell, 1970 ex Hypanus americanus (Hildebrand & Schroeder) from the coast of Virginia, U. S. A.; the eastern Pacific R. ditesticulum Appy & Dailey, 1977 ex Urobatis halleri Cooper from California, U. S. A.; and R. rhinobati Dailey & Carvajal, 1976 ex Rhinobatos planiceps Garman from the coast Antofagasta, Chile. Biogeographical distribution aside, R. biorchidum, R. rhinobati, and R. spinicephalum differ from R. tetralobatum by having fewer segments (15 – 26, 18 – 33, 36 – 49 vs. 80 – 206, respectively) and a smaller number of bothridial loculi (22 – 30, 22, 32 – 34 vs. 47 – 69, respectively). In addition, R. biorchidum and R. rhinobati can be further distinguished from R. tetralobatum by their smaller size (1.2 – 2.5, 1.8 – 2.8 mm vs. 4.1 – 19.0 mm, respectively). Rhinebothrium ditesticulum and R. fulbrighti most closely resemble R. tetralobatum in their total length (9.6 – 28.7 and 3.1 – 18.0 mm vs. 4.1 – 19.0, respectively) and the number of proglottids (160 – 276 and 40 – 168 vs. 80 – 206, respectively). Besides the slightly overlap, R. fulbrighti possesses fewer bothridial loculi in comparison to R. tetralobatum (43 – 53 vs. 47 – 69, respectively). In addition to that, the former has been described as having only two ovarian lobes whereas the latter has four. Rhinebothrium ditesticulum can be distinguished from R. tetralobatum by the morphology of the bothridia. It has a single posterior-most loculus on the bothridia and the anterior and posterior bothridial surfaces are completely separated, whereas, R. tetralobatum possess two posterior-most loculi and the anterior and posterior bothridial surfaces are not completely separated, but have a constriction at the center.

Common Names

Taxonomic Hierarchy

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Cestoda

Order: Rhinebothriidea

Family: Rhinebothriidae

Genus: Rhinebothrium

Species: Rhinebothrium tetralobatum Brooks, 1977