Galatheites aiola, ROBINS ET AL., 2016

GALATHEITES AIOLA ROBINS ET AL., 2016

( FIG. 8A–C)

Galatheites aiola Robins et al., 2016: 108 , fig. 12.5, 12.6, 12.8.

Diagnosis: Carapace moderately convex transversely, weakly so longitudinally; widens slightly posteriorly; longer than wide with rostrum excluded. Rostrum somewhat downturned, sulcate, with medial keel; terminates in at least three-pronged tip. Cervical groove well defined; axial portion fairly straight before arcing convex forwardly as groove approaches lateral margin. Gastric region contains distinct groove perpendicular to lateral margin with row of tubercles immediately posterior to it. Carapace, including rostrum, ornamented with slightly squamous tubercles; tubercles more elongated on posterior part of carapace.

Specimens studied: Holotype: NHMW 1990 View Materials /0041/3272 (= 2007z0149/0437, as described by Robins et al., 2016); paratypes: NHMW 1990 View Materials /0041/0584 (= 2007z0149/0440), 1990/0041/0700 (= 2007z0149/0441); additional material: NHMW 1990 View Materials /0041/0121, 1990/0041/0284, 1990/0041/0539, 1990/0041/0574 (= 2007z0149/0408), 1990/0041/0576a, 1990/0041/0578, 1990/0041/0958, 1990/0041/2594, 1990/0041/3128 (= 2007z0149/0443), 1990/0041/3256 (= 2007z0149/0442), 1990/0041/5181.

Measurements: See Robins et al. (2016: table 6) for 2007z0149/0408, 2007z0149/0437, 2007z0149/0440– 2007z0149/0443. Additionally: 1990/0041/0284 (largest specimen): maximal length excluding rostrum = 8.9 mm, maximal width = 7.2 mm.

Type locality: Ernstbrunn Quarries , Ernstbrunn, Austria .

Type stratum: Ernstbrunn Limestones , Tithonian, Upper Jurassic .

Description: Carapace moderately convex transversely, weakly so longitudinally; widens slightly posteriorly; longer than wide with rostrum excluded (length/ width = ~1.2). Rostrum somewhat downturned, sulcate, with medial keel; rostral shape broadly triangular, narrows anteriorly; terminates in at least three-pronged tip. Cervical groove well defined; axial portion fairly straight before arcing convex forwardly as groove approaches lateral margin. Deep groove branching off cervical groove defines base of epibranchial region. Epigastric region well defined anteriorly by groove at base of rostrum. Gastric region contains distinct groove perpendicular to lateral margin, with row of tubercles immediately posterior to it. Mesogastric region pyriform, least defined in mid-part; base may show posterior gastric muscle scars. Uro-/metagastric and cardiac regions defined by weak grooves or indentations. Posterior margin rimmed. Carapace, including rostrum, ornamented with slightly squamous tubercles on internal mould and cuticle; tubercles more elongated on posterior part of carapace. Ventral surface and appendages not preserved.

Discussion: Upon re-examination of the specimens reported by Robins et al. (2016) and discovery of many new specimens in the Ernstbrunn collection reminiscent of Galatheites aiola , we conclude that a portion of the specimens is best accommodated in a new species, described below as Galatheites britmelanarum . The axial part of the cervical groove is straighter in G. aiola and, as opposed to the new species, G. aiola exhibits a transverse groove adjacent to the tip of the mesogastric region marked posteriorly by a row of tubercles.

The number of spines at the tip of the rostrum cannot yet be confirmed, because none of the specimens has this part fully preserved. At least three spines can be confirmed. There appears to be limited intraspecific and ontogenetic variation in this species as currently defined.

GALATHEITES BRITMELANARUM ROBINS &