Acanthobothrium usengozinius, Spuy & Smit & Schaeffner, 2022

Spuy, Linda Van Der, Smit, Nico J. & Schaeffner, Bjoern C., 2022, Threatened, host-specific affiliates of a red-listed host: Three new species of Acanthobothrium van Beneden, 1849 (Cestoda: Onchoproteocephalidea) from the endangered white skate, Rostroraja alba (Lac´ep`ede), International Journal for Parasitology: Parasites and Wildlife 17, pp. 114-126 : 120-121

Acanthobothrium usengozinius n. sp. is a category 2 species (sensu

Ghoshroy and Caira, 2001). Similar to the description of A. umbungus n. sp., hooks of A. usengozinius n. sp. are the most prominent feature, instantly distinguishing it from all but five (i.e. A. annapienkensis , A. brayi , A. domingae , A. guanghaiense and A. umbungus n. sp.) of the 52 representatives within category 2. The remaining category 2 species present much smaller hook measurements than those of the new species, as follows: lateral hooks: A <62 μm vs 62–73 μm, B <130 μm vs 135–151 μm, C <124 μm vs 129–141 μm, D <178 μm vs 190–216 μm, respectively; medial hooks: A ’ <64 μm vs 64–74 μm, B ’ <136 μm vs 139–162 μm, C ’ <122 μm vs 125–142 μm, D ’ <193 μm vs 193–228 μm, respectively. The only species with larger hooks than A. usengozinius n. sp. is A. annapienkensis (lateral hooks A> 73 μm vs 62–73 μm, B> 180 μm vs 139–162 μm, C> 160 μm vs 125–142 μm, D> 240 μm vs 193–228 μm, respectively). Apart from hook measurements, A. benedenii L¨onnberg, 1889,, A. bobconniorum , A. brachyacanthum , A. brayi , A. brevissime , A. campbelli , A. carolinae , A. chisholmae , A. dasi Ghoshroy et Caira, 2001 , A. domingae , A. dujardini , A. edwardsi , A. gloveri , A. lasti , A. lilium , A. mashnihae , A. michrohabentes , A. microtenuis , A. minus , A. mooreae , A. ocallaghani Campbell et Beveridge, 2002 , A. olseni , A. ppdeleoni , A. rajivi , A. sinaloansis , A. sphaera , A. stevensi , A. tasajerasi , A. tetabuanense , A. thomasae , A. tripartitum , A. quadripartitum , A. vargasi , A. walkeri and A. zapterycum can all be distinguished from A. usengozinius n. sp. by a much smaller body size (<6 mm vs 6.3–8.8 mm, respectively),

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whereas A. urotrygoni and A. woodsholei are significantly larger (> 12 mm vs 6.3–8.8 mm, respectively). Additionally, A. benedenii , A. bobconniorum , A. brachyacanthum , A. brevissime , A. campbelli , A. cimari , A. costaricense , A. crassus , A. dolichocollum , A. dujardini , A. edwardsi , A. hypanus , A. lasti , A. lilium , A. mashnihae , A. michrohabentes , A. microtenuis , A. minus , A. mooreae , A. ocallaghani , A. olseni , A. ppdeleoni , A. quadripartitum , A. semnovesiculum , A. sinaloansis , A. soniae , A. sphaera , A. stevensi , A. tasajerasi , A. tetabuanense , A. thomasae , A. umbungus n. sp., A. urotrygoni , A. vargasi , A. walkeri , and A. zapterycum show differences in the following features: scolex length (<540 μm vs 540–631 μm, respectively), bothridium width (<214 μm vs 215–245 μm, respectively), cephalic peduncle width (<115 μm vs 119–124 μm, respectively), and ovary width (<116 μm vs 143–180 μm, respectively). In comparison A. annapienkensis , A. bullardi and A. woodsholei all have a longer scolex (> 633 μm vs 540–631 μm, respectively). The poral ovarian lobe of A. bobconniorum , A. brachyacanthum , A. brayi , A. campbelli , A. carolinae , A. chisholmae , A. dasi , A. domingae , A. gloveri , A. guanghaiense , A. hypanus , A. lasti , A. mashnihae , A. michrohabentes , A. microtenuis , A. mooreae , A. ocallaghani , A. ppdeleoni , A. rajivi , A. sinaloansis , A. sphaera , A. stevensi , A. tasajerasi , A. tetabuanense , A. thomasae , A. urotrygoni , A. vargasi , and A. walkeri are shorter than that of A. usengozinius n. sp. (<525 μm vs 548–679 μm, respectively). The same applies for the aporal lobe (<565 μm vs 616–757 μm, respectively). The following species all have a wider cirrus-sac than that of A. usengozinius n. sp. (> 60 μm vs 43–57 μm): A. annapienkensis , A. bobconniorum , A. brachyacanthum , A. brayi , A. bullardi , A. costarricense , A. dolichocollum , A. domingae , A. mooreae , A. olseni , A. popi , A. ppdeleoni , A. rajivi , A. semnovesiculum , A. soniae , A. thomasae and A. urotrygoni . Acanthobothrium cimari , A. costarricense , A. crassus , A. dolichocollum , A. guanghaiense , A. hypanus , A. puntarenasense , A. semnovesiculum and A. soniae also differ from A. usengozinius n. sp. in a number of features such as: a narrower bothridium (<214 μm vs 215–245 μm, respectively), a shorter anterior loculus (<205 μm vs 235–257 μm, respectively), a shorter middle loculus (<90 μm vs 126–143 μm, respectively), a shorter posterior loculus (<91 μm vs 94–106 μm, respectively), and a narrower ovary (<120 μm vs 143–180 μm, respectively).

Acanthobothrium usengozinius n. sp. marks the fourth species described from the endangered host, R. alba , expanding the remarkable host specificity within the genus. This discovery therefore subsequently marks the importance of dedicating appropriate research to endangered elasmobranch species, as macrohabitats of numerous parasitic organisms new to science that are threatened by co-extinction. Acanthobothrium usengozinius n. sp. also marks the sixth species of this genus from the Eastern South Atlantic Ocean.