Cantellius cornutergum, Achituv, 2020

Zweifler, Adi, Simon-Blecher, Noa, Pica, Daniela, Chan, Benny K. K., Roth, Jonathan & Achituv, Yair, 2020, A stranger among us: the occurrence of Cantellius (Balnoidea: Pyrgomatidae) an epibiont of scleractinias in stylasterids (Hydrozoa), Zoological Journal of the Linnean Society 190, pp. 1077-1094 : 1087-1090

CANTELLIUS CORNUTERGUM ACHITUV SP. NOV.

( FIG. 10)

u r n: l s i d: z o o b a n k. o r g: p u b: 9 6 9 5 4 D 1 7 - 1 3 6 F - 4D68-9D59-64C5EAFB6053

Holotype: MNHN-IU-5872, host Distichopora violacea MNHN-IK-2015-660, 11°34.6 ′ S, 45°05.2 ′ E, 12 April 1977.

Paratype: MNHN-IU-5869, host Distichopora violacea MNHN-IK-2015-660, same data as holotype.

Diagnosis: Pyromatid with four shell plates. Scutum triangular, with occludent margin longer than basal margin. Small crests for the depressor muscle in the scutum. External median furrow along tergum with external median furrow. Carinal margin of tergum strongly curved.

Description: Shell conical, four plated (rostrum, carina and paired latera), externally covered by the hydroid skeleton and tissue ( Fig. 10A). Orifice central, rhomboid. Scutum and tergum separated, white. Scutum triangular; basal margin straight, curving at the basitergal angle; four to five parallel small pits for the scutal depressor muscle at basioccludent angle; four parallel small pits for the lateral depressor muscle at basitergal angle ( Fig. 10B). Occludent margin length approximately equal to tergal margin length. Occludent margin and tergal margin straight. Deep, round pit for a d d u c t o r m u s c l e. A d d u c t o r r i d g e p r o m i n e n t; articular ridge occupies about four-fifths of tergal margins. Externally, growth ridges parallel to basal margin outline, forming teeth on occludent margin. Tergum elongated; carinal margin about half of scutal margin, with blunt rounded spur; scutal margins strongly curved, forming prominent beak at the apex; basal margins slightly concave;

1090 A. ZWEIFLER ET AL.

external surface with growth ridges parallel to basal margins; shallow median furrow from apex to spur base. Internally, shallow crests for depressor muscle.

Etymology: From Latin cornu, horn, indicating the presence of prominent beak at the apex of the tergum, meaning ‘back’ or ‘rear’.

Remarks: The opercular valves of this species are different from all known species of Cantellius . The noticeable features are the small crests for the two depressor muscles. The shape of the scutum is most similar to that of Cantellius tredecimus ( Kolosvary, 1947) , which has neither adductor ridges nor adductor pits. The tergum may resemble that of C. arcuatus ; the lower part toward the basis is straight, whereasa in C. arcuatus the upper part next to the carinal margin is strongly curved. In the original description of C. arcuatus, Hiro (1938) does not mention the presence of an external median furrow and internal crests for the depressor muscle of the tergum. On the basis of these differences, we think this is a new species.